- Email: [email protected]
Photochromic properties of stimuli-responsive cellulosic papers modified by spiropyran-acrylic copolymer in reusable pH-sensors
Carbohydrate Polymers 200 (2018) 583–594
Contents lists available at ScienceDirect
Carbohydrate Polymers journal homepage: www.elsevier.com/locate/carbpol
Photochromic properties of stimuli-responsive cellulosic papers modified by spiropyran-acrylic copolymer in reusable pH-sensors Amin Abdollahi, Alireza Mouraki, Mohammad Hossain Sharifian, Ali Reza Mahdavian
T
⁎
Polymer Science Department, Iran Polymer & Petrochemical Institute, P.O. Box: 14965/115, Tehran, Iran
A R T I C LE I N FO
A B S T R A C T
Keywords: Spiropyran Photochromic pH-sensor Cellulose Acrylic copolymer
Photochromic chemosensors based on spiropyran have attracted great attentions in recent years. Here, stimuliresponsive papers were prepared by chemical attachment of epoxy functionalized latex particles containing spiropyran moieties on the cellulose fibers by a new strategy for design and preparation of an acrylic copolymer pH-sensor. pH-Responsivity, photo-switchablity, photofatigue resistant and kinetic of photoisomerization were investigated by soaking of the papers in water with different pHs and they were analyzed by solid-phase UV–vis spectroscopy. Photoisomerization rate constants were measured for the wet papers in acidic and basic media (kc = 0.11–0.14 s−1) and they were much faster than in the dry state (kc = 0.08 s−1). Remarkable photochromic properties with no negative photochromism were observed here and also not influenced by hydrogen bondings and dipolar interactions. SEM images and contact angle measurements revealed high resistance of such papers against their surrounding environment. Moreover, the immediate response to pH changes was accompanied with different distinct colors.
1. Introduction Stimuli-responsive materials based on photochromic compounds have found much interests nowadays as a result of their unique properties such as responsivity toward light irradiation (Bertrand & Gohy, 2017; Crano & Guglielmetti, 2002a, 2002b; Wang & Li, 2018), induced stress or mechanical force (Li, Zhang, Zhou, & Zhu, 2018; Metzler et al., 2015; Peterson, Larsen, Ganter, Storti, & Boydston, 2015; Wan et al., 2016; Zhang et al., 2014), polarity (Abdollahi, Mahdavian, & SalehiMobarakeh, 2015; Abdollahi, Rad, & Mahdavian, 2016; Abdollahi, Alinejad, & Mahdavian, 2017; Florea, McKeon, Diamond, & BenitoLopez, 2013), pH changes (Chen et al., 2016; Jiang, Chen, Cao, & Wang, 2016; Su et al., 2017) and also photodetection of the metal or non-metal ions in different media (Avella-Oliver, Morais, Puchades, & Maquieira, 2016; Fries, Samanta, Orski, & Locklin, 2008; Huang et al., 2015; Qin, Huang, Li, & Song, 2015; Sahoo & Kumar, 2016; Zheng et al., 2018; Zhou, Zhang, & Luo, 2014).Therefore, several researchers have focused on incorporation of these chromophores into different matrices (Hu & Liu, 2010; Klajn, 2014; Kumar, Kumar, & Paik, 2013; Mura, Nicolas, & Couvreur, 2013; Theato, Sumerlin, O’Reilly, & Epps, 2013) and especially polymeric ones. Among different types of organic photochromic compounds, spiropyran is of the most interest, because of its intense and facile response when exposed to versatile analytes and media under UV irradiation. Spiropyran (SP) derivatives can be converted to ⁎
merocyanine (MC) form with zwitterionic character upon triggering. For example, MC could be protonated in acidic and protic media to give the protonated MC (MCH) with different absorption bands in UV–vis region (Genovese, Athanassiou, & Fragouli, 2015, 2017; Vallet, Micheau, & Coudret, 2016; Wojtyk et al., 2007). On the other hand, it may change to the quinoidal MC (MCQ) form in less polar media such as aprotic solvents (Khakzad, Mahdavian, Salehi-Mobarakeh, Rezaee Shirin-Abadi, & Cunningham, 2016; Wang, 2016). Additionally, MC can be chelated to different cationic and anionic ions to form ion-bonded MC (MCI) structure and display ionochromism with different colors and spectroscopic characteristics (Deshpande, Jachak, Khopkar, & Shankarling, 2018; Shao, Wang, Gao, Yang, & Chan, 2010; Xie, Mistlberger, & Bakker, 2012). Stabilization of the colored isomers (MC, MCH, MCQ and MCI) will thus cause to prevent facile SP ⇌ MC and observe irreversible negative photochromism, which is considered as an undesired phenomenon (Abdollahi et al., 2017, 2015, 2016). This is a challenge and weak point for such stimuli-responsive systems (Wang, 2016; Shao et al., 2010; Xie et al., 2012; Deshpande et al., 2018; Keyvan Rad & Mahdavian, 2016). Hence, review of the recent studies by Mahdavian’s group illustrates that using of the polymeric carriers for introducing spiropyran into high-polar media could significantly reduce negative photochromism and also protect spiropyran moieties from environmental degradations (Abdollahi et al., 2017, 2015, 2016; Keyvan Rad & Mahdavian, 2016; Khakzad et al., 2016). This had been
Corresponding author. E-mail address: [email protected] (A.R. Mahdavian).
https://doi.org/10.1016/j.carbpol.2018.08.042 Received 21 April 2018; Received in revised form 21 July 2018; Accepted 10 August 2018 Available online 12 August 2018 0144-8617/ © 2018 Elsevier Ltd. All rights reserved.
Carbohydrate Polymers 200 (2018) 583–594
A. Abdollahi et al.
Fig. 1. Schematic representation for preparation of the functionalized photochromic latex nanoparticles and the corresponding stimuli-responsive paper.
Fig. 2. The possible isomers from spiropyran groups upon UV irradiation (365 nm) in different media.
584
Carbohydrate Polymers 200 (2018) 583–594
A. Abdollahi et al.
Fig. 3. Solid-state UV–Vis analysis of the wet stimuli-responsive papers containing spiropyran groups in different pHs before (…….) and after ( at 365 nm.
) UV irradiation
necessary factors in preparation of efficient photochromic sensors (Francis, Dunne, Delaney, Florea, & Diamond, 2017; Yu et al., 2017; Zheng et al., 2018). However, lack of the chemical linkages between polymer matrix and photoactive compound (simple doping by mixing or impregnation) is the main reason that will consequate in negative photochromism and low photofatigue resistance (Sun et al., 2013; Sun,
proposed as an influential resolution to tackle the above mentioned issue. Actually, hydrophobic polymeric cavities from copolymerization of spiropyran derivatives protect them against establishment of strong dipolar interactions with the surrounding and demonstrate their usual expected role. Using of polymer carriers and chemically attachment of a photochromophore to the polymer backbone are two important and 585
Carbohydrate Polymers 200 (2018) 583–594
A. Abdollahi et al.
functionalized photochromic latex particles (EPLPs) and photochromic cellulosic papers (Abdollahi et al., 2015, 2016; Keyvan Rad & Mahdavian, 2016), some critical properties like acidochromism, pHresponsivity, photostability and kinetic of photoisomerization on the prepared cellulosic papers are investigated in a wide range of pH (1–14) here. This is the first comprehensive report on such systems that shows their susceptibility for being employed as reusable photo-responsive pH-sensors. For this reason, morphological studies and surface properties together with UV–vis spectra of the samples have been recorded in this pH domain. Interestingly, no sign of negative photochromism as a week point in the polar or cellulosic media was observed even in the extreme line of pHs, i.e. 1 and 14.
Table 1 Extracted data from UV–Vis spectra of the stimuli-responsive papers in different pHsa .
Stimuli-responsive cellulosic paper
pH
λmax (nm)
Rmax (%)
1 2 3 4 5 6 7 8 9 10 11 12 13 14
447 and 586 581 581 577 579 582 582 583 577 581 577 577 578 444 and 587
46 and 53 66 65 94 71 68 70 65 98 66 82 78 76 53 and 90
2. Experimental 2.1. Materials 2,3,3-Trimethylindolenin,which was used for the synthesis of spiropyran derivative, glycidyl methacrylate (GMA) and sodium dodecyl sulfate (SDS) were purchased from Sigma-Aldrich. Other materials that were used in the current study, including 2-hydroxy-5-nitrobenzaldehyde, methyl methacrylate (MMA), potassium persulfate (KPS), sodium hydrogencarbonate (NaHCO3), triethylamine, potassium hydroxide (KOH), hydrochloric acid (HCl), Triton X-100, 2-bromoethanol and acryloyl chloride (AC) were supplied by Merck Chemical Co. All chemicals were used without further purification. High quality filter paper (MUNKTELL-Grade: 391, Lot No: 09-158, Bärenstein, Germany) was used for preparation of stimuli-responsive papers. Deionized (DI) water was employed in all recipes.
a λmax shows the wavelength at maximum reflective index and Rmax is the maximum reflective index at λmax.
Hou, He, Liu, & Ni, 2014; Tian & Tian, 2014; Vallet, Micheau, & Coudret, 2016). Several investigations have been conducted to study the responsivity of spiropyran derivatives that are induced by versatile triggers, except UV irradiation recently. These can be performed by the changes in polarity (Abdollahi et al., 2017; Grogan et al., 2016; Shi et al., 2015), pH (2015, Genovese et al., 2017; Zheng et al., 2018), ions concentration or type (Baldrighi, Locatelli, Desper, Aakeröy, & Giordani, 2016; Benito-Lopez et al., 2009; Tao et al., 2016) and mechanical stress (Caruso et al., 2009; Di Credico, Griffini, Levi, & Turri, 2013; O’Bryan, Wong, & McElhanon, 2010). The photochromic behavior will be of great importance as this nominates such materials for exploitation in chemosensors or mechanosensors. Hence, photodetection of pH in different media (by using of spiropyran as the sensing material) has vastly been investigated (Genovese et al., 2017, 2015; Wan, Zheng, Shen, Yang, & Yin, 2014; Zheng et al., 2018). For instance, Genovese and coworkers prepared photochromic elastomeric composite films by doping of spiropyran into poly(dimethylsiloxane) matrix for photodetection of vapor of hydrochloric, trifluoroacetic, formic and acetic acids by means of protonation of MC phenolate ions and the corresponding acidochromic response (Genovese et al., 2015). Recently, this group has reported the fabrication of spiropyran-doped poly (vinylidenefluoride-co-hexafluoropropylene) electrospun fibers for photosensing of similar acid vapors under UV irradiation (Genovese et al., 2017). Physically attachment of spiropyran to polymer matrices by doping could be considered as the main disadvantage in such investigations, because of the decrease of photofatigue resistance with time as a result of the spiropyran leakage. Zheng et al prepared spiropyran-appended polysiloxane for design of a chemosensor for photodetection of ions and pH in the solution phase (Zheng et al., 2018). Generally, such sensors are not reusable after sensing process, because the polymeric sensor should be dissolved in a solvent which may lead to its degradation and decrease in sensitivity. Therefore, chemically attachment of spiropyran to the sensor substrate and reusability are two important factors that should essentially be considered in development of photochromic chemosensors. Cellulose is one of the most important substrates for grafting of different polymeric materials in fabrication of chemosensors and advanced devices, because of its easy accessibility and low price. Such composites have extensively been studied in the recent years, specifically in order to improve mechanical and physical properties of cellulose fibers (Poyraz et al., 2018; Poyraz, Tozluoglu, Candan, & Demir, 2017; Poyraz, Tozluoglu, Candan, Demir, & Yavuz, 2017; Sarwar, Niazi, Jahan, Ahmad, & Hussain, 2018; Tozluoglu, Poyraz, Candan, Yavuz, & Arslan, 2017). In continuum to our previous studies on preparation of epoxy-
2.2. Synthesis of epoxy functionalized latex particles containing spiropyran 1-(2-acryloxyethyl)-3,3-dimethyl-6-nitrospiro-(2H-1-benzopyran2,2-indoline) (SPEA) were synthesized according to the described procedure in our previous study (Abdollahi et al., 2015). EPLPs containing MMA, GMA and SPEA were prepared through semi-continuous emulsion polymerization as reported before (Abdollahi et al., 2015). Typically, sodium hydrogen carbonate as the buffer (NaHCO3, 0.030 g), SDS (0.045 g), and Triton X-100 (0.012 g) as emulsifiers were dissolved in 27 mL DI water under stirring and the solution was transferred into the reactor under continuous flow of nitrogen gas. After addition of KPS (0.030 g) as the initiator at 75 °C, a solution of SPEA (0.100 g) in 3 mL DI water and 2.3 g MMA were added separately and simultaneously into the reactor dropwise within 10 min and the polymerization continued for 45 min after completion of addition. Then, a mixture of GMA (0.400 g) and MMA (0.750 g) was added to the above latex within 10 min and the polymerization continued for 20 min. The final conversion was above 95% (from gravimetric method) and the amount of coagulation at the end of polymerization was below 1 wt%. 2.3. Preparation of the stimuli-responsive papers Firstly, the paper pulp precursor was prepared by mechanical stirring (1000 rpm) of the scraps of a high-quality filter paper in water at room temperature to yield a 10 wt% paper-in-water dispersion. In order to improve the dispersion and uniformity of the pulp paper, ultrasound waves were also applied to the above mixture for 20 min at 75% amplitude by the probe-sonication with a titanium microtip probe. Then, 70 mL of the paper pulp (7 g cellulose) and 30 mL of the previously prepared photochromic latex (3 g neat EPLPs) were mixed by mechanical stirring (1200 rpm) at 25 °C for 5 h. Then, the obtained mixture was casted into a petri-dish and dried at 80 °C to give modified and untreated paper. Finally, their photochromic properties, color changes, photo-switchablity, pH-responsivity and photofatigue resistance were investigated under UV (365 nm) and visible light irradiations, either primarily or those immersed in the aqueous solutions with different pHs 586
Carbohydrate Polymers 200 (2018) 583–594
A. Abdollahi et al.
Fig. 4. Real-time solid state UV–vis spectra with different UV irradiation time (365 nm) for the untreated and treated (in various pHs) papers.
EPLPs and cellulose. Scanning electron microscopy (SEM) was taken by a Vega Tescan II (Czeck Republic). Prior to scanning, a piece of the prepared stimuli-responsive paper was placed on the sample holder after washing with DI water and dried at room temperature. Then, a layer of gold was deposited by using EMITECH K450x sputter-coater (England) under vacuum and flushing with argon. Photochromic properties of the papers were investigated by solid-phase UV–vis analysis and by using high performance double beam scanning spectrophotometer T90+ (PG Instrument, England). The excitation was done by a UV lamp (365 nm), model Camag 12VDC/VAC (50/60 HZ, 14VA, SER 1206, Switzerland). The source for visible light was a common LED lamp with white light. According to the existing reports (Grogan et al.,
(from 1 to 14) and then dried for UV–vis analysis. The latter is called modified and treated paper. 2.4. Characterization To prepare paper pulp, SONOPULS ultrasonic homogenizer (20 kHz, HFeGM 2200, GmbH & Co. Germany) was used with a titanium microtip KE-76 probe (D: 6 mm), while set for 75% amplitude in all of the steps. Fourier transform infrared (FTIR) spectra were recorded on KBr pellets of the samples by using a BRUKER-IFS48 (Germany) spectrometer with a frequency range from 4000 to 400 cm−1 and resolution of 2 cm−1 at 25 °C to endorse the reaction between functional groups of 587
Carbohydrate Polymers 200 (2018) 583–594
A. Abdollahi et al.
Fig. 5. Normalized reflective index at the corresponding λmax for the untreated paper and the treated ones in different pHs.
polyacrylic matrix through chemical bonding. The progress of chemical reaction between facial epoxy groups in EPLPs and cellulosic substrate had been reported before (Abdollahi et al., 2016; Keyvan Rad & Mahdavian, 2016). Fig. 1 shows a schematic illustration for preparation such stimuli-responsive papers by chemical modification with the aforementioned latex nanoparticles, including 70 wt%. of neat cellulosic fiber and 30 wt%. of the acrylic photochromic polymer. Solidphase UV–vis characteristics of the prepared photochromic papers will be studied in this work comprehensively together with morphological and surface properties to assess their potentiality for being used as chemo- or pH-sensors.
Table 2 Coloration rate equation and kinetic parameters for the prepared stimuli-responsive papers under UV irradiation at 365 nm in different conditions. Condition
Equation
R2
kc (s−1)
T1/2 (s)a
Untreated paper Treated pH = 1 Paper pH = 4 pH = 7 pH = 10 pH = 14
0.02-exp(−0.08 t) 0.01595-exp(−0.11 t) 0.016608-exp(−0.13 t) 0.018428-exp(−0.14 t) 0.019434-exp(−0.13 t) 0.0208-exp(−0.13 t)
0.987 0.986 0.987 0.974 0.995 0.998
0.08 0.11 0.13 0.14 0.13 0.13
40 31 26 23 25 25
a Time required to reach to half of the final reflective index for the coloration.
3.1. Solid-phase UV–vis analysis on the stimuli-responsive papers 2016; Khakzad et al., 2016; Moo, Presolski, & Pumera, 2016), white LED light is a most efficient tool for induction of MC to SP isomerization as a powerful source of visible light. In all investigations, UV and visible irradiation time were set 5 min for the samples. The contact angle of water on the surface of stimuli-responsive papers was measured using a KRUSS G10 (Germany) at room temperature and 25% relative humidity. Thicknesses of the neat cellulosic paper and the prepared stimuli-responsive paper were measured by a digital caliper and were 0.12 mm and 0.53 mm, respectively. A double distilled water (DDW) droplet (5 μL) was placed on the surface of the as-prepared papers. Minimum of three measurements were carried out for each sample and then averaged and reported.
3.1.1. Dependency of photochromic behavior on pH Spiropyran groups undergo isomerization to MC form upon UV irradiation and the newly formed MC may change to MCH, MCQ or MCI, depending on acidity (Genovese et al., 2017; Khakzad et al., 2016) or polarity (Abdollahi et al., 2017; Grogan et al., 2016) of the surrounding environment and also type of the dissolved ions (Baldrighi, Locatelli, Desper, Aakeröy, & Giordani, 2016; Zheng et al., 2018) in the media. The observed different colors for MC in acidic, basic or ion-containing systems are due to its probable stabilized form as MC, MCH and MCI by protonation or coordination (Fig. 2). Each of the existing isomers display different λmax in UV–vis region after UV irradiation at 365 nm. MC and MCH derivatives have two distinct λmax at 500–600 nm and 400–500 nm, respectively, as a result of acidochromism phenomenon (Genovese et al., 2017, 2015; Vallet et al., 2016b). On the other hand, various λmax would be observable for MCQ (in nonpolar media) and MCI (in ionic solutions) forms (Khakzad et al., 2016; Klajn, 2014; Qin et al., 2015). MCI is also favored in acidic or basic media due to the chelation of anions or cations to MC isomer. Here, photochromic properties of the prepared stimuli-responsive papers in different pHs were investigated by their soaking in acidic (pH = 1–6), neutral (pH = 7) and basic (pH = 8–14) aqueous solutions under UV irradiation (365 nm). Then, their UV–vis spectra were recorded in solid state before and after exposure to UV irradiation at 365 nm for 5 min (Fig. 3) and their spectroscopic characteristics (i.e. wavelength at maximum reflective index (λmax) and maximum reflective index at λmax (Rmax)) have been summarized in Table 1. UV–vis
3. Results and discussion It has been quite understood that chromophores (e.g. spiropyran) have to be embedded in a polymeric matrix for being protected against environmental issues that may cause their decomposition and decrease in life time. This is more critical if you are exploiting them in harsh conditions like at very low or high pHs. In continuum to our previous studies in development of chemosensors based on cellulosic paper and spiropyran (Abdollahi et al., 2017, 2016; Keyvan Rad & Mahdavian, 2016), we have developed such sensors with fast photo-switchability and pH-responsivity in a reversible manner; and also improved their photofatigue resistance even at extreme line of pHs, i.e. 1 and 14 here. This could be achieved by the linkage of photoactive groups to the 588
Carbohydrate Polymers 200 (2018) 583–594
A. Abdollahi et al.
Fig. 6. Photofatigue resistance of the prepared stimuli-responsive papers at different pHs upon alternating UV (365 nm for 5 min) and visible (5 min) irradiations.
conditions increased by irradiation time according to the increase in their populations. Similar photochromic behavior was observed for the soaked paper in solutions with weaker acidity (pH = 4) and basicity (pH = 10) as well as neutral (pH = 7) and untreated ones. These observations display that the photochromism of spiropyran moieties in stimuli-responsive paper was not under the influence of negative photochromism too. This is attributed to the affecting role of the polymer carrier in the protection of spiropyran molecules and perverting them from establishment of undesired interactions with the cellulosic substrate and making SP to MC isomerization irreversible. The effect of pH on the isomerization rate of SP to MC was investigated for the prepared stimuli-responsive untreated and treated (in different pHs) papers. This was carried out by measuring of the reflective index intensities at specific λmax and different time intervals of UV irradiation at 365 nm. Opposite to usual UV–vis analysis, less reflective index in solid state UV–vis analysis displays more absorption of UV light and larger photochromic intensity as a result of formation of more MC isomers. Therefore, primary measured reflective index values were converted to the normalized ones (with respect to the reflective index of each sample before UV irradiation) and plotted versus irradiation time (Fig. 5). The obtained results show an exponential dependency of the isomerization rate (SP to MC) to irradiation time in all conditions. Actually, variation of normalized reflective index demonstrates a steep slope for all the samples at early stage of irradiation and before reaching to a plateau. Hence, the kinetic of photo-switching of SP to MC form on the surface of stimuli-responsive papers could be well-described by Eq. (1), extracted from Fig. 5.
spectra in strong acidic (pH = 1–3) and basic (pH = 13, 14) conditions displayed two peaks in the range of 400–700 nm. The intense peak in 500–700 nm was attributed to MC isomers and the weak one, in the range of 400–500 nm, was related to MCH or MCI isomers. Intensity of the peak in 400–500 nm increases gradually with reaching to the extreme lines of pH (i.e. pH < 4 and pH > 12) and is explicitly observed in pH = 1 and 14. This could be attributed to the elevation in population of newly formed MCH and MCI isomers and these are in good agreement with the previous reports on pH-responsivity of the prepared stimuli-responsive papers (Genovese et al., 2015; Zheng et al., 2018). However, MC isomer is the main established form in the middle pHs according to the existing strong absorption in 500–700 nm, because of its stabilization by the surrounding polymer chains. Actually, PMMA as the substrate for spiropyran protects MC groups by dipolar interactions and does not allow them to be influenced by pH changes in the middle points. It is notable that the negative photochromism and irreversibility were not observed in any of the prepared samples. This illustrates that the presence of such polymeric matrix is essential for designing and development of these photoactive systems as chemosensors for photodetection of pH and polarity of the environment. 3.1.2. Real-time photo-isomerization and its kinetic studies upon pH changes To investigate the effect of interactions on photo-isomerization and responsivity rate of the spiropyran molecules, the untreated paper and also the treated ones with acidic (pH = 1 and 4), neutral (pH = 7) and basic (pH = 10 and 14) aqueous solutions were analyzed by solid-state UV–vis spectroscopy before and after illumination with UV light (365 nm) in different time intervals (Fig. 4).Obviously, there is a direct relationship between the reflecting intensity and UV irradiation time according to the generation of MC, MCH and MCI isomers with the increase in exposure time. Comparison between the spectra of untreated and treated samples display a slight promotion in SP to MC isomerization extent as a result of contamination in different pHs. This is due to the role of hydrogen bondings or dipolar interactions for stabilization of MC forms in polar media and reduction of its energy level relative to the SP forms. On the other hand, the intensity of MCH and MCI reflective peaks in high acidic (pH = 1) and high basic (pH = 14)
Normalized reflactive index (t ) = A − exp (−kct ) Normalized reflactive index ( ∞ )
(1)
A is a constant and kc represents the rate constant of SP to MC isomerization upon UV irradiation. The normalized reflective indexes at time t and ∞ were extracted from Fig. 5. It is noteworthy that kc could be a good indication of susceptibility or responsivity of the stimuli-responsive paper toward UV irradiation during photo-isomerization. This parameter also denotes the photo-switchablity and pH-responsivity of the system. Extracted kinetic equations and the corresponding parameters such as R2 (regression), kc and T1/2 (time required to reach to 589
Carbohydrate Polymers 200 (2018) 583–594
A. Abdollahi et al.
Fig. 7. SEM micrographs with different magnifications from the surface of primary cellulosic paper (a, aʹ, aʺ), and stimuli-responsive paper in untreated state (b, bʹ, bʺ), after soaking in water with pH of 1 (c, cʹ, cʺ) and 14 (d, dʹ, dʺ) for 10 days at room temperature.
half of the final reflective index for coloration) have been presented in Table 2. R2 values reveal that the kinetic of SP to MC isomerization conforms with Eq. (1) well. According to the obtained parameters for different conditions,
maximum responsivity (kc = 0.14) and minimum T1/2 (24 s) were observed at pH = 7. In turn, minimum responsivity (kc = 0.08) and maximum T1/2 (40 s) were found for the untreated paper as a result of difficult isomerization process and less stability of MC form in this 590
Carbohydrate Polymers 200 (2018) 583–594
A. Abdollahi et al.
Fig. 8. Contact angle measurement of a water droplet on the surface of primary cellulosic paper (a), untreated paper (b), and those treated in pH = 1 (c), pH = 7 (d) and pH = 14 (e) aqueous solutions for 10 days and ambient condition.
Fig. 9. Color changes of the prepared stimuli-responsive paper in various pHs under UV irradiation at 365 nm.
conditions by converting to MCH and MCI, respectively (Fig. 4). Therefore, the population of MC is expected to be maximum at pH of 7 because of two reasons: i) high stability of MC isomers by dipolar interactions in the treated state compared to the untreated one; ii) less
condition relative to the treated ones. Calculated kc and T1/2 for the prepared stimuli-responsive paper in acidic and basic media displayed a slight decrease in isomerization rate and increment in T1/2. This can be attributed to the decrease in MC population for both acidic and basic 591
Carbohydrate Polymers 200 (2018) 583–594
A. Abdollahi et al.
2017) ones with polymers. Hence, hydrolysis of the acrylic ester groups (COOR) to carboxylic (COOH) or carboxylate (COO−) one will leads to the increase in surface hydrophilicity and this can be followed by measurement of the contact angle of water droplet on the prepared paper surface. This could be in complementary with the observed morphology changes from SEM micrographs. Hence, some pieces of the stimuli-responsive papers were floated in solutions with different pHs (1, 7 and 14) for 10 days and similar to those conditions for SEM analysis. Afterward, contact angles of the primary cellulosic paper, untreated and treated stimuli-responsive papers were measured after soaking (Fig. 8). These reveal that contact angle on the cellulosic papers changed from 0° for the primary one (Fig. 8a) to 67° for the modified ones (Fig. 8b) as a result of chemical attachment of the hydrophobic photochromic acrylic copolymer on the surface of cellulose fibers. This is in agreement with those reported by Malmstrom group for the changes in contact angle via grafting of different polymers on the cellulosic materials (Carlmark & Malmstrom, 2002; Lonnberg et al., 2006; Nystrom et al., 2006). Fig. 8c and d demonstrate that the measured contact angles for the untreated and soaked papers in pH 1 and 7 are almost identical (θ = 66-67°). This means that the induced treatments have not influenced on the hydrophobicity of the stimuli-responsive papers through hydrolytic degradation. As expected, surface hydrophobicity of the base-treated stimuli-responsive paper (pH 14) has decreased (θ = 54°). This could be attributed to few hydrolysis of the esteric groups in the basic media and is in accordance with the SEM results. These indicate that the prepared stimuli-responsive paper has a remarkable stability toward environmental degradations in high acidic and high basic media for a long term and they could be an appropriate nominee for reusable pH-sensors based on photochromic polymers.
stability of MCH and MCI forms in the inert media compared to the high acidic or basic conditions. Finally, these kinetic studies demonstrate the capability of such prepared stimuli-responsive photochromic papers to pH changes in a proper manner. 3.1.3. Photofatigue resistant and photo-switchability Among different photochromic properties of the stimuli-responsive materials, photofatigue resistance and photo-switchability are the most important ones for developing optical sensors. Recent studies show that polymeric carriers containing spiropyran, for incorporation into the high polar matrices such as cellulose, can lead to significant improvement in photostability, photo-switchability and also reversibility (Li, Trosien, Schenderlein, Graf, & Biesalski, 2016; Sun et al., 2014; Xue et al., 2015). Here, the effect of surrounding pH on photostability and optical reversibility of the prepared stimuli-responsive paper was studied by measurement of its reflective index in different pHs and also in the untreated state (Fig. 6). For this propose, some pieces of the paper were soaked in acidic and basic solutions (pH of 1, 4, 7, 10 and 14) and were subsequently exposed to UV irradiation (365 nm, 5 min) and then visible light (5 min) at ambient condition for 15 cycles. The corresponding reflective index was measured immediately after each irradiation within a 5 min interval between each cycle. This could be attributed to the facile SP ⇄ MC isomerization in the polar and wet media. However, Fig. 5 implies that high polar interactions in acidic and basic media have not influenced on photo-switchability, reversibility and photofatigue resistance of SP and MC groups in the modified papers. Actually, the employed acrylic polymer carrier has achieved to protect them against environmental degradation, even in very low or high pHs and under alternating UV and visible irradiations. On the other hand, the surrounding polarity and pH have not affected on the performance of such prepared pH sensors, illustrating their reusability for the desired applications.
3.3. Visual pH sensing by the prepared stimuli-responsive paper In the our previous studies (Abdollahi et al., 2017, 2016; Keyvan Rad & Mahdavian, 2016), stimuli-responsive copolymers and the corresponding modified papers based on spiropyran were developed as optical sensors for facile and fast photo-sensing of polarity in different protic and aprotic media. Here and in continuum, we have examined the prepared stimuli-responsive paper as a chemosensor for photodetection of pH even in wide range of pHs. Fig. 9 reveals different color changes under UV irradiation, while floated in water at different pHs. It is worth mentioning that exploitation of the photochromic copolymers instead of doped polymers with photochromic molecules will lead to remarkable improvement in photostability, photo-switchability and photofatigue resistance of spiropyran chromophore in polar media. SP groups convert to MC isomer under UV irradiation at 365 nm and could be stabilized in MCH (acidic media) and MCI (basic media) with different colors (Fig. 9). This reveals the potentiality of such a paper for photodetection with evident and various color changes, depending on the surrounding pH.
3.2. Morphology of the prepared stimuli-responsive paper It is generally believed that an acrylic-based copolymer can undergo a degradation process by probable hydrolysis in high acidic or high basic environment. On the other hand, we tried to protect photoactive spiropyran groups in the prepared stimuli-responsive paper from environmental degradations by inclusion in the acrylic polymer matrix. Therefore, it is essential to ensure about the stability of such papers in the performance conditions for being employed in reusable sensors. Beside photofatigue resistance and photo-switchability, morphological studies will be helpful to confirm the capability of these papers for pH sensing. For this reason, some pieces of the prepared papers were soaked in different pHs (1 and 14) for 10 days and then, SEM images of their surfaces were taken together with the primary and untreated papers (Fig. 7). Microscopic images for the primary cellulosic paper (a, aʹ, aʺ) and untreated one (b, bʹ, bʺ) displayed obvious morphology changes of cellulose fibers as a result of penetration and chemical attachment of the prepared photochromic copolymer into the cellulose substrate. However, surface morphology of the stimuli-responsive paper, after soaking in high acidic solution (pH = 1, 6c, cʹ, cʺ) was not changed significantly. Slight roughness could be attributed to the removal of salts and surfactants through its treatment with the acidic solution. As can be seen in Fig. 7d, dʹ, dʺ, surface of the cellulose fibers is not smooth and a more roughness is observable. This shows that the basic media has probably facilitated the hydrolysis of acrylic copolymer and its degradation. Although, this has not influenced on the photochromic properties and its photo-responsivity remarkably. Modification of cellulosic materials with hydrophobic compounds can decrease their surface hydrophilicity and it can be identified by changes in contact angle for chemically modified (Carlmark & Malmstrom, 2002; Lonnberg et al., 2006; Nystrom, Lindqvist, Ostmark, Hult, & Malmstrom, 2006; Roy, Semsarilar, Guthrie, & Perrier, 2009) and also for physically modified (Aarne et al., 2013; Kontturi et al.,
4. Conclusion Herein, we have introduced a new stimuli-responsive cellulosic paper modified with MMA-SPEA copolymer as a reusable pH-sensor. Such chemosensors were prepared by chemical attachment of epoxy functionalized latex particles bearing spiropyran moieties on the surface of a cellulosic paper. The obtained results from solid-state UV–vis analysis displayed a remarkable photostability, reversibility, photofatigue resistant and also good pH-responsivity for the immersed stimuli-responsive papers in solutions with different pHs in the range of 114. Investigations on the SP to MC isomerization kinetic by solid-phase UV–vis analysis illustrated that the interactions between spiropyran groups and acidic or basic solutions in the treated paper can accelerate MC formation (kc = 0.11–0.14s−1) compared with the untreated one (kc = 0.08 s−1). SEM images and the measured contact angles from the surface of floated papers in pH 1 and 14 for 10 days showed high 592
Carbohydrate Polymers 200 (2018) 583–594
A. Abdollahi et al.
stability and resistance toward hydrolytic environmental degradations of the coated polymer on cellulosic fibers without specific loss in photochromic properties. This is essential for employment in reusable pHsensors. The prepared smart paper revealed different colors when triggered by various pHs under UV irradiation at 365 nm as a result of establishment of MC, MCH and MCI forms in such media and consequent acidochromism and basochromism. It was concluded that the obtained papers containing spiropyran moieties can be exploited in reusable optical pH-sensors because of its unique properties such as photo-switchability, photofatigue, fast and reversible pH-responsivity and enhanced stability toward hydrolytic degradation. These are vital properties to be considered for development of optical pH-sensors. Facile accessibility and low price of the cellulose materials are two significant advantages for the industrial development of stimuli-responsive papers based on such spiropyran copolymers as reusable chemosensors in near future.
1016/j.snb.2017.11.138. Di Credico, B., Griffini, G., Levi, M., & Turri, S. (2013). Microencapsulation of a UVresponsive photochromic dye by means of novel UV-screening polyurea-based shells for smart coating applications. ACS Applied Materials & Interfaces, 5(14), 6628–6634. https://doi.org/10.1021/am401328f. Florea, L., McKeon, A., Diamond, D., & Benito-Lopez, F. (2013). Spiropyran polymeric microcapillary coatings for photodetection of solvent polarity. Langmuir, 29(8), 2790–2797. https://doi.org/10.1021/la304985p. Francis, W., Dunne, A., Delaney, C., Florea, L., & Diamond, D. (2017). Spiropyran based hydrogels actuators—Walking in the light. Sensors and Actuators B: Chemical, 250, 608–616. https://doi.org/10.1016/j.snb.2017.05.005. Fries, K., Samanta, S., Orski, S., & Locklin, J. (2008). Reversible colorimetric ion sensors based on surface initiated polymerization of photochromic polymers. Chemical Communications, 47, 6288. https://doi.org/10.1039/b818042c. Genovese, M. E., Athanassiou, A., & Fragouli, D. (2015). Photoactivated acidochromic elastomeric films for on demand acidic vapor sensing. Journal of Materials Chemistry A, 3(44), 22441–22447. https://doi.org/10.1039/C5TA06118K. Genovese, M. E., Colusso, E., Colombo, M., Martucci, A., Athanassiou, A., & Fragouli, D. (2017). Acidochromic fibrous polymer composites for rapid gas detection. Journal of Materials Chemistry A, 5(1), 339–348. https://doi.org/10.1039/C6TA08793K. Grogan, C., Florea, L., Koprivica, S., Scarmagnani, S., O’Neill, L., Lyng, F., ... Raiteri, R. (2016). Microcantilever arrays functionalised with spiropyran photoactive moieties as systems to measure photo-induced surface stress changes. Sensors and Actuators B: Chemical, 237, 479–486. https://doi.org/10.1016/j.snb.2016.06.108. Hu, J., & Liu, S. (2010). Responsive polymers for detection and sensing applications: Current status and future developments. Macromolecules, 43(20), 8315–8330. https://doi.org/10.1021/ma1005815. Huang, Y., Li, F., Ye, C., Qin, M., Ran, W., & Song, Y. (2015). A photochromic sensor microchip for high-performance multiplex metal ions detection. Scientific Reports, 5(1), 9724. https://doi.org/10.1038/srep09724. Jiang, F., Chen, S., Cao, Z., & Wang, G. (2016). A photo, temperature, and pH responsive spiropyran-functionalized polymer: Synthesis, self-assembly and controlled release. Polymer, 83, 85–91. https://doi.org/10.1016/j.polymer.2015.12.027. Keyvan Rad, J., & Mahdavian, A. R. (2016). Preparation of fast photoresponsive cellulose and kinetic study of photoisomerization. The Journal of Physical Chemistry C, 120(18), 9985–9991. https://doi.org/10.1021/acs.jpcc.6b02594. Khakzad, F., Mahdavian, A. R., Salehi-Mobarakeh, H., Rezaee Shirin-Abadi, A., & Cunningham, M. (2016). Redispersible PMMA latex nanoparticles containing spiropyran with photo-, pH- and CO2- responsivity. Polymer (United Kingdom), 101, 274–283. https://doi.org/10.1016/j.polymer.2016.08.073. Klajn, R. (2014). Spiropyran-based dynamic materials. Chemical Society Reviews, 43(1), 148–184. https://doi.org/10.1039/c3cs60181a. Kontturi, K. S., Biegaj, K., Mautner, A., Woodward, R. T., Wilson, B. P., Johansson, L.-S., ... Kontturi, E. (2017). noncovalent surface modification of cellulose nanopapers by adsorption of polymers from aprotic solvents. Langmuir, 33(23), 5707–5712. https:// doi.org/10.1021/acs.langmuir.7b01236. Kumar, K. S., Kumar, V. B., & Paik, P. (2013). Recent advancement in functional coreshell nanoparticles of polymers: Synthesis, physical properties, and applications in medical biotechnology. Journal of Nanoparticles, 2013, 1–24. https://doi.org/10. 1155/2013/672059. Li, M., Zhang, Q., Zhou, Y. N., & Zhu, S. (2018). Let spiropyran help polymers feel force!. Progress in Polymer Science, 79, 26–39. https://doi.org/10.1016/j.progpolymsci.2017. 11.001. Li, W., Trosien, S., Schenderlein, H., Graf, M., & Biesalski, M. (2016). Preparation of photochromic paper, using fibre-attached spiropyran polymer networks. RSC Advances, 6(111), 109514–109518. https://doi.org/10.1039/C6RA23673A. Lonnberg, H., Zhou, Q., Brumer, H., Teeri, T. T., Malmstrom, E., & Hult, A. (2006). Grafting of cellulose fibers with poly(ε-caprolactone) and poly(lactic acid) via ringopening polymerization. Biomacromolecules, 7(7), 2178–2185. https://doi.org/10. 1021/bm060178z. Metzler, L., Reichenbach, T., Brügner, O., Komber, H., Lombeck, F., Müllers, S., ... Sommer, M. (2015). High molecular weight mechanochromic spiropyran main chain copolymers via reproducible microwave-assisted Suzuki polycondensation. Polymer Chemistry, 6(19), 3694–3707. https://doi.org/10.1039/c5py00141b. Moo, J. G. S., Presolski, S., & Pumera, M. (2016). Photochromic spatiotemporal control of bubble-propelled micromotors by a spiropyran molecular switch. ACS Nano, 10(3), 3543–3552. https://doi.org/10.1021/acsnano.5b07847. Mura, S., Nicolas, J., & Couvreur, P. (2013). Stimuli-responsive nanocarriers for drug delivery. Nature Materials, 12(11), 991–1003. https://doi.org/10.1038/NMAT3776. Nystrom, D., Lindqvist, J., Ostmark, E., Hult, A., & Malmstrom, E. (2006). Superhydrophobic bio-fibre surfaces via tailored grafting architecture. Chemical Communications, 34, 3594–3596. https://doi.org/10.1039/B607411A. O’Bryan, G., Wong, B. M., & McElhanon, J. R. (2010). Stress sensing in polycaprolactone films via an embedded photochromic compound. ACS Applied Materials & Interfaces, 2(6), 1594–1600. https://doi.org/10.1021/am100050v. Peterson, G. I., Larsen, M. B., Ganter, M. A., Storti, D. W., & Boydston, A. J. (2015). 3Dprinted mechanochromic materials. ACS Applied Materials & Interfaces, 7(1), 577–583. https://doi.org/10.1021/am506745m. Poyraz, B., Tozluoglu, A., Candan, Z., Demir, A., Yavuz, M., Buyuksarı, U., ... Saka, R. C. (2018). TEMPO-treated CNF composites: Pulp and matrix effect. Fibers and Polymers, 19(1), 195–204. https://doi.org/10.1007/s12221-018-7673-y. Poyraz, B., Tozluoglu, A., Candan, Z., & Demir, A. (2017). Matrix impact on the mechanical, thermal and electrical properties of microfluidized nanofibrillated cellulose composites. Journal of Polymer Engineering, 37(9), https://doi.org/10.1515/polyeng2017-0022. Poyraz, B., Tozluoglu, A., Candan, Z., Demir, A., & Yavuz, M. (2017). Influence of PVA
Acknowledgment We wish to express our gratitude to Iran Polymer and Petrochemical Institute (IPPI) for financial support of this work (Grant No. 24761176). References Aarne, N., Laine, J., Hänninen, T., Rantanen, V., Seitsonen, J., Ruokolainen, J., ... Kontturi, E. (2013). Controlled hydrophobic functionalization of natural fibers through self-assembly of amphiphilic diblock copolymer micelles. ChemSusChem, 6(7), 1203–1208. https://doi.org/10.1002/cssc.201300218. Abdollahi, A., Alinejad, Z., & Mahdavian, A. R. (2017). Facile and fast photosensing of polarity by stimuli-responsive materials based on spiropyran for reusable sensors: A physico-chemical study on the interactions. Journal of Materials Chemistry C, 5(26), 6588–6600. https://doi.org/10.1039/c7tc02232h. Abdollahi, A., Mahdavian, A. R. A. R., & Salehi-Mobarakeh, H. (2015). Preparation of stimuli-responsive functionalized latex nanoparticles: the effect of spiropyran concentration on size and photochromic properties. Langmuir, 31(39), 10672–10682. https://doi.org/10.1021/acs.langmuir.5b02612. Abdollahi, A., Rad, J. K., & Mahdavian, A. R. (2016). Stimuli-responsive cellulose modified by epoxy-functionalized polymer nanoparticles with photochromic and solvatochromic properties. Carbohydrate Polymers, 150(18), 131–138. https://doi.org/10. 1016/j.carbpol.2016.05.009. Avella-Oliver, M., Morais, S., Puchades, R., & Maquieira, Á. (2016). Towards photochromic and thermochromic biosensing. TrAC Trends in Analytical Chemistry, 79, 37–45. https://doi.org/10.1016/j.trac.2015.11.021. Baldrighi, M., Locatelli, G., Desper, J., Aakeröy, C. B., & Giordani, S. (2016a). Probing metal ion complexation of ligands with multiple metal binding sites: The Case of Spiropyrans. Chemistry–A European Journal, 22(39), 13976–13984. https://doi.org/ 10.1002/chem.201602608. Baldrighi, M., Locatelli, G., Desper, J., Aakeröy, C. B., & Giordani, S. (2016b). Probing metal ion complexation of ligands with multiple metal binding sites: the case of spiropyrans. Chemistry- A European Journal, 22(39), 13976–13984. https://doi.org/ 10.1002/chem.201602608. Benito-Lopez, F., Scarmagnani, S., Walsh, Z., Paull, B., Macka, M., & Diamond, D. (2009). Spiropyran modified micro-fluidic chip channels as photonically controlled self-indicating system for metal ion accumulation and release. Sensors and Actuators B: Chemical, 140(1), 295–303. https://doi.org/10.1016/j.snb.2009.03.080. Bertrand, O., & Gohy, J.-F. (2017). Photo-responsive polymers: Synthesis and applications. Polymer Chemistry, 8(1), 52–73. https://doi.org/10.1039/C6PY01082B. Carlmark, A., & Malmstrom, E. (2002). Atom transfer radical polymerization from cellulose fibers at ambient temperature. Journal of the American Chemical Society, 124(6), 900–901. https://doi.org/10.1021/ja016582h. Caruso, M. M., Davis, D. A., Shen, Q., Odom, S. A., Sottos, N. R., White, S. R., ... Moore, J. S. (2009). Mechanically-induced chemical changes in polymeric materials. Chemical Reviews, 109(11), 5755–5798. https://doi.org/10.1021/cr9001353. Chen, S., Gao, Y., Cao, Z., Wu, B., Wang, L., Wang, H., ... Wang, G. (2016). Nanocomposites of spiropyran-functionalized polymers and upconversion nanoparticles for controlled release stimulated by near-infrared light and pH. Macromolecules, 49(19), 7490–7496. https://doi.org/10.1021/acs.macromol. 6b01760. Crano, J. C., & Guglielmetti, R. J. (2002a). Organic photochromic and thermochromic compounds. Main photochromic families, Vol. 1Boston: Springer US: Kluwer Academic Publishershttps://doi.org/10.1007/b114211. Crano, J. C., & Guglielmetti, R. J. (2002b). Organic photochromic and thermochromic compounds. Physicochemical studies, biological applications, and thermochromism, Vol. 2Boston: Springer US: Kluwer Academic Publishershttps://doi.org/10.1007/ b115590. Deshpande, S. S., Jachak, M. A., Khopkar, S. S., & Shankarling, G. S. (2018). A simple substituted spiropyran acting as a photo reversible switch for the detection of lead (Pb2+) ions. Sensors and Actuators B: Chemical, 258, 648–656. https://doi.org/10.
593
Carbohydrate Polymers 200 (2018) 583–594
A. Abdollahi et al.
Vallet, J., Micheau, J.-C., & Coudret, C. (2016a). Switching a pH indicator by a reversible photoacid: A quantitative analysis of a new two-component photochromic system. Dyes and Pigments, 125, 179–184. https://doi.org/10.1016/j.dyepig.2015.10.025. Vallet, J., Micheau, J. C., & Coudret, C. (2016b). Switching a pH indicator by a reversible photoacid: A quantitative analysis of a new two-component photochromic system. Dyes and Pigments, 125, 179–184. https://doi.org/10.1016/j.dyepig.2015.10.025. Wan, S., Ma, Z., Chen, C., Li, F., Wang, F., Jia, X., ... Yin, M. (2016). A supramoleculetriggered mechanochromic switch of cyclodextrin-jacketed rhodamine and spiropyran derivatives. Advanced Functional Materials, 26(3), 353–364. https://doi.org/ 10.1002/adfm.201504048. Wan, S., Zheng, Y., Shen, J., Yang, W., & Yin, M. (2014). On–off–on” switchable sensor: A fluorescent spiropyran responds to extreme pH conditions and its bioimaging applications. ACS Applied Materials & Interfaces, 6(22), 19515–19519. https://doi.org/10. 1021/am506641t. Wang, L.-F. (2016). Application of response surface methodology for exploring β-cyclodextrin effects on the decoloration of spiropyran complexes. Chemical Physics Letters, 662, 296–305. https://doi.org/10.1016/j.cplett.2016.09.068. Wang, L., & Li, Q. (2018). Photochromism into nanosystems: towards lighting up the future nanoworld. Chemical Society Reviews. https://doi.org/10.1039/C7CS00630F. Wojtyk, J. T. C., Wasey, A., Xiao, N. N., Kazmaier, P. M., Hoz, S., Yu, C., ... Buncel, E. (2007). Elucidating the mechanisms of acidochromic spiropyran-merocyanine interconversion. The Journal of Physical Chemistry A, 111(13), 2511–2516. https://doi. org/10.1021/jp068575r. Xie, X., Mistlberger, G., & Bakker, E. (2012). Reversible photodynamic chloride-selective sensor based on photochromic spiropyran. Journal of the American Chemical Society, 134(41), 16929–16932. https://doi.org/10.1021/ja307037z. Xue, Y., Tian, J., Tian, W., Gong, P., Dai, J., & Wang, X. (2015). Significant fluorescence enhancement of spiropyran in colloidal dispersion and its light-induced size tunability for release control. The Journal of Physical Chemistry C, 119(35), 20762–20772. https://doi.org/10.1021/acs.jpcc.5b06905. Yu, G., Cao, Y., Liu, H., Wu, Q., Hu, Q., Jiang, B., ... Yuan, Z. (2017). A spirobenzopyranbased multifunctional chemosensor for the chromogenic sensing of Cu 2+ and fluorescent sensing of hydrazine with practical applications. Sensors and Actuators B: Chemical, 245, 803–814. https://doi.org/10.1016/j.snb.2017.02.020. Zhang, H., Chen, Y., Lin, Y., Fang, X., Xu, Y., Ruan, Y., ... Weng, W. (2014). Spiropyran as a mechanochromic probe in dual cross-linked elastomers. Macromolecules, 47(19), 6783–6790. https://doi.org/10.1021/ma500760p. Zheng, T., Xu, Z., Zhao, Y., Li, H., Jian, R., & Lu, C. (2018). Multiresponsive polysiloxane bearing photochromic spirobenzopyran for sensing pH changes and Fe 3+ ions and sequential sensing of Ag + and Hg 2+ ions. Sensors and Actuators B: Chemical, 255, 3305–3315. https://doi.org/10.1016/j.snb.2017.09.158. Zhou, Y.-N., Zhang, Q., & Luo, Z.-H. (2014). A light and pH dual-stimuli-responsive block copolymer synthesized by copper(0)-mediated living radical polymerization: Solvatochromic, Isomerization, and “schizophrenic” behaviors. Langmuir, 30(6), 1489–1499. https://doi.org/10.1021/la402948s.
and silica on chemical, thermo-mechanical and electrical properties of celluclasttreated nanofibrillated cellulose composites. International Journal of Biological Macromolecules, 104, 384–392. https://doi.org/10.1016/j.ijbiomac.2017.06.018. Qin, M., Huang, Y., Li, F., & Song, Y. (2015). Photochromic sensors: A versatile approach for recognition and discrimination. Journal of Materials Chemistry C, 3(36), 9265–9275. https://doi.org/10.1039/C5TC01939G. Roy, D., Semsarilar, M., Guthrie, J. T., & Perrier, S. (2009). Cellulose modification by polymer grafting: A review. Chemical Society Reviews, 38(7), 2046. https://doi.org/ 10.1039/b808639g. Sahoo, P. R., & Kumar, S. (2016). Photochromic spirooxazine as highly sensitive and selective probe for optical detection of Fe3+ in aqueous solution. Sensors and Actuators B: Chemical, 226, 548–552. https://doi.org/10.1016/j.snb.2015.12.039. Sarwar, M. S., Niazi, M. B. K., Jahan, Z., Ahmad, T., & Hussain, A. (2018). Preparation and characterization of PVA/nanocellulose/Ag nanocomposite films for antimicrobial food packaging. Carbohydrate Polymers, 184, 453–464. https://doi.org/10.1016/j. carbpol.2017.12.068. Shao, N., Wang, H., Gao, X., Yang, R., & Chan, W. (2010). Spiropyran-based fluorescent anion probe and its application for urinary pyrophosphate detection. Analytical Chemistry, 82(11), 4628–4636. https://doi.org/10.1021/ac1008089. Shi, W., Xing, F., Bai, Y.-L., Hu, M., Zhao, Y., Li, M.-X., ... Zhu, S. (2015). High sensitivity viologen for a facile and versatile sensor of base and solvent polarity in solution and solid state in air atmosphere. ACS Applied Materials & Interfaces, 7(26), 14493–14500. https://doi.org/10.1021/acsami.5b03932. Su, T., Cheng, F. R., Cao, J., Yan, J. Q., Peng, X. Y., & He, B. (2017). Dynamic intracellular tracking nanoparticles via pH-evoked “off–on” fluorescence. Journal of Materials Chemistry B, 5(17), 3107–3110. https://doi.org/10.1039/C7TB00713B. Sun, B., He, Z., Hou, Q., Liu, Z., Cha, R., & Ni, Y. (2013). Interaction of a spirooxazine dye with latex and its photochromic efficiency on cellulosic paper. Carbohydrate Polymers, 95(1), 598–605. https://doi.org/10.1016/j.carbpol.2013.03.032. Sun, B., Hou, Q., He, Z., Liu, Z., & Ni, Y. (2014). Cellulose nanocrystals (CNC) as carriers for a spirooxazine dye and its effect on photochromic efficiency. Carbohydrate Polymers, 111, 419–424. https://doi.org/10.1016/j.carbpol.2014.03.051. Tao, J., Zhao, P., Li, Y., Zhao, W., Xiao, Y., & Yang, R. (2016). Fabrication of an electrochemical sensor based on spiropyran for sensitive and selective detection of fluoride ion. Analytica Chimica Acta, 918, 97–102. https://doi.org/10.1016/j.aca. 2016.03.025. Theato, P., Sumerlin, B. S., O’Reilly, R. K., & Epps, T. H., Jr. (2013). Stimuli responsive materials. Chemical Society Reviews, 42(17), 7055. https://doi.org/10.1039/ c3cs90057f. Tian, W. W., & Tian, J. (2014). Synergy of different fluorescent enhancement effects on spiropyran appended onto cellulose. Langmuir, 30(11), 3223–3227. https://doi.org/ 10.1021/la404628p. Tozluoglu, A., Poyraz, B., Candan, Z., Yavuz, M., & Arslan, R. (2017). Biofilms from micro/nanocellulose of NaBH4-modified kraft pulp. Bulletin of Materials Science, 40(4), 699–710. https://doi.org/10.1007/s12034-017-1416-y.
594
Contents lists available at ScienceDirect
Carbohydrate Polymers journal homepage: www.elsevier.com/locate/carbpol
Photochromic properties of stimuli-responsive cellulosic papers modified by spiropyran-acrylic copolymer in reusable pH-sensors Amin Abdollahi, Alireza Mouraki, Mohammad Hossain Sharifian, Ali Reza Mahdavian
T
⁎
Polymer Science Department, Iran Polymer & Petrochemical Institute, P.O. Box: 14965/115, Tehran, Iran
A R T I C LE I N FO
A B S T R A C T
Keywords: Spiropyran Photochromic pH-sensor Cellulose Acrylic copolymer
Photochromic chemosensors based on spiropyran have attracted great attentions in recent years. Here, stimuliresponsive papers were prepared by chemical attachment of epoxy functionalized latex particles containing spiropyran moieties on the cellulose fibers by a new strategy for design and preparation of an acrylic copolymer pH-sensor. pH-Responsivity, photo-switchablity, photofatigue resistant and kinetic of photoisomerization were investigated by soaking of the papers in water with different pHs and they were analyzed by solid-phase UV–vis spectroscopy. Photoisomerization rate constants were measured for the wet papers in acidic and basic media (kc = 0.11–0.14 s−1) and they were much faster than in the dry state (kc = 0.08 s−1). Remarkable photochromic properties with no negative photochromism were observed here and also not influenced by hydrogen bondings and dipolar interactions. SEM images and contact angle measurements revealed high resistance of such papers against their surrounding environment. Moreover, the immediate response to pH changes was accompanied with different distinct colors.
1. Introduction Stimuli-responsive materials based on photochromic compounds have found much interests nowadays as a result of their unique properties such as responsivity toward light irradiation (Bertrand & Gohy, 2017; Crano & Guglielmetti, 2002a, 2002b; Wang & Li, 2018), induced stress or mechanical force (Li, Zhang, Zhou, & Zhu, 2018; Metzler et al., 2015; Peterson, Larsen, Ganter, Storti, & Boydston, 2015; Wan et al., 2016; Zhang et al., 2014), polarity (Abdollahi, Mahdavian, & SalehiMobarakeh, 2015; Abdollahi, Rad, & Mahdavian, 2016; Abdollahi, Alinejad, & Mahdavian, 2017; Florea, McKeon, Diamond, & BenitoLopez, 2013), pH changes (Chen et al., 2016; Jiang, Chen, Cao, & Wang, 2016; Su et al., 2017) and also photodetection of the metal or non-metal ions in different media (Avella-Oliver, Morais, Puchades, & Maquieira, 2016; Fries, Samanta, Orski, & Locklin, 2008; Huang et al., 2015; Qin, Huang, Li, & Song, 2015; Sahoo & Kumar, 2016; Zheng et al., 2018; Zhou, Zhang, & Luo, 2014).Therefore, several researchers have focused on incorporation of these chromophores into different matrices (Hu & Liu, 2010; Klajn, 2014; Kumar, Kumar, & Paik, 2013; Mura, Nicolas, & Couvreur, 2013; Theato, Sumerlin, O’Reilly, & Epps, 2013) and especially polymeric ones. Among different types of organic photochromic compounds, spiropyran is of the most interest, because of its intense and facile response when exposed to versatile analytes and media under UV irradiation. Spiropyran (SP) derivatives can be converted to ⁎
merocyanine (MC) form with zwitterionic character upon triggering. For example, MC could be protonated in acidic and protic media to give the protonated MC (MCH) with different absorption bands in UV–vis region (Genovese, Athanassiou, & Fragouli, 2015, 2017; Vallet, Micheau, & Coudret, 2016; Wojtyk et al., 2007). On the other hand, it may change to the quinoidal MC (MCQ) form in less polar media such as aprotic solvents (Khakzad, Mahdavian, Salehi-Mobarakeh, Rezaee Shirin-Abadi, & Cunningham, 2016; Wang, 2016). Additionally, MC can be chelated to different cationic and anionic ions to form ion-bonded MC (MCI) structure and display ionochromism with different colors and spectroscopic characteristics (Deshpande, Jachak, Khopkar, & Shankarling, 2018; Shao, Wang, Gao, Yang, & Chan, 2010; Xie, Mistlberger, & Bakker, 2012). Stabilization of the colored isomers (MC, MCH, MCQ and MCI) will thus cause to prevent facile SP ⇌ MC and observe irreversible negative photochromism, which is considered as an undesired phenomenon (Abdollahi et al., 2017, 2015, 2016). This is a challenge and weak point for such stimuli-responsive systems (Wang, 2016; Shao et al., 2010; Xie et al., 2012; Deshpande et al., 2018; Keyvan Rad & Mahdavian, 2016). Hence, review of the recent studies by Mahdavian’s group illustrates that using of the polymeric carriers for introducing spiropyran into high-polar media could significantly reduce negative photochromism and also protect spiropyran moieties from environmental degradations (Abdollahi et al., 2017, 2015, 2016; Keyvan Rad & Mahdavian, 2016; Khakzad et al., 2016). This had been
Corresponding author. E-mail address: [email protected] (A.R. Mahdavian).
https://doi.org/10.1016/j.carbpol.2018.08.042 Received 21 April 2018; Received in revised form 21 July 2018; Accepted 10 August 2018 Available online 12 August 2018 0144-8617/ © 2018 Elsevier Ltd. All rights reserved.
Carbohydrate Polymers 200 (2018) 583–594
A. Abdollahi et al.
Fig. 1. Schematic representation for preparation of the functionalized photochromic latex nanoparticles and the corresponding stimuli-responsive paper.
Fig. 2. The possible isomers from spiropyran groups upon UV irradiation (365 nm) in different media.
584
Carbohydrate Polymers 200 (2018) 583–594
A. Abdollahi et al.
Fig. 3. Solid-state UV–Vis analysis of the wet stimuli-responsive papers containing spiropyran groups in different pHs before (…….) and after ( at 365 nm.
) UV irradiation
necessary factors in preparation of efficient photochromic sensors (Francis, Dunne, Delaney, Florea, & Diamond, 2017; Yu et al., 2017; Zheng et al., 2018). However, lack of the chemical linkages between polymer matrix and photoactive compound (simple doping by mixing or impregnation) is the main reason that will consequate in negative photochromism and low photofatigue resistance (Sun et al., 2013; Sun,
proposed as an influential resolution to tackle the above mentioned issue. Actually, hydrophobic polymeric cavities from copolymerization of spiropyran derivatives protect them against establishment of strong dipolar interactions with the surrounding and demonstrate their usual expected role. Using of polymer carriers and chemically attachment of a photochromophore to the polymer backbone are two important and 585
Carbohydrate Polymers 200 (2018) 583–594
A. Abdollahi et al.
functionalized photochromic latex particles (EPLPs) and photochromic cellulosic papers (Abdollahi et al., 2015, 2016; Keyvan Rad & Mahdavian, 2016), some critical properties like acidochromism, pHresponsivity, photostability and kinetic of photoisomerization on the prepared cellulosic papers are investigated in a wide range of pH (1–14) here. This is the first comprehensive report on such systems that shows their susceptibility for being employed as reusable photo-responsive pH-sensors. For this reason, morphological studies and surface properties together with UV–vis spectra of the samples have been recorded in this pH domain. Interestingly, no sign of negative photochromism as a week point in the polar or cellulosic media was observed even in the extreme line of pHs, i.e. 1 and 14.
Table 1 Extracted data from UV–Vis spectra of the stimuli-responsive papers in different pHsa .
Stimuli-responsive cellulosic paper
pH
λmax (nm)
Rmax (%)
1 2 3 4 5 6 7 8 9 10 11 12 13 14
447 and 586 581 581 577 579 582 582 583 577 581 577 577 578 444 and 587
46 and 53 66 65 94 71 68 70 65 98 66 82 78 76 53 and 90
2. Experimental 2.1. Materials 2,3,3-Trimethylindolenin,which was used for the synthesis of spiropyran derivative, glycidyl methacrylate (GMA) and sodium dodecyl sulfate (SDS) were purchased from Sigma-Aldrich. Other materials that were used in the current study, including 2-hydroxy-5-nitrobenzaldehyde, methyl methacrylate (MMA), potassium persulfate (KPS), sodium hydrogencarbonate (NaHCO3), triethylamine, potassium hydroxide (KOH), hydrochloric acid (HCl), Triton X-100, 2-bromoethanol and acryloyl chloride (AC) were supplied by Merck Chemical Co. All chemicals were used without further purification. High quality filter paper (MUNKTELL-Grade: 391, Lot No: 09-158, Bärenstein, Germany) was used for preparation of stimuli-responsive papers. Deionized (DI) water was employed in all recipes.
a λmax shows the wavelength at maximum reflective index and Rmax is the maximum reflective index at λmax.
Hou, He, Liu, & Ni, 2014; Tian & Tian, 2014; Vallet, Micheau, & Coudret, 2016). Several investigations have been conducted to study the responsivity of spiropyran derivatives that are induced by versatile triggers, except UV irradiation recently. These can be performed by the changes in polarity (Abdollahi et al., 2017; Grogan et al., 2016; Shi et al., 2015), pH (2015, Genovese et al., 2017; Zheng et al., 2018), ions concentration or type (Baldrighi, Locatelli, Desper, Aakeröy, & Giordani, 2016; Benito-Lopez et al., 2009; Tao et al., 2016) and mechanical stress (Caruso et al., 2009; Di Credico, Griffini, Levi, & Turri, 2013; O’Bryan, Wong, & McElhanon, 2010). The photochromic behavior will be of great importance as this nominates such materials for exploitation in chemosensors or mechanosensors. Hence, photodetection of pH in different media (by using of spiropyran as the sensing material) has vastly been investigated (Genovese et al., 2017, 2015; Wan, Zheng, Shen, Yang, & Yin, 2014; Zheng et al., 2018). For instance, Genovese and coworkers prepared photochromic elastomeric composite films by doping of spiropyran into poly(dimethylsiloxane) matrix for photodetection of vapor of hydrochloric, trifluoroacetic, formic and acetic acids by means of protonation of MC phenolate ions and the corresponding acidochromic response (Genovese et al., 2015). Recently, this group has reported the fabrication of spiropyran-doped poly (vinylidenefluoride-co-hexafluoropropylene) electrospun fibers for photosensing of similar acid vapors under UV irradiation (Genovese et al., 2017). Physically attachment of spiropyran to polymer matrices by doping could be considered as the main disadvantage in such investigations, because of the decrease of photofatigue resistance with time as a result of the spiropyran leakage. Zheng et al prepared spiropyran-appended polysiloxane for design of a chemosensor for photodetection of ions and pH in the solution phase (Zheng et al., 2018). Generally, such sensors are not reusable after sensing process, because the polymeric sensor should be dissolved in a solvent which may lead to its degradation and decrease in sensitivity. Therefore, chemically attachment of spiropyran to the sensor substrate and reusability are two important factors that should essentially be considered in development of photochromic chemosensors. Cellulose is one of the most important substrates for grafting of different polymeric materials in fabrication of chemosensors and advanced devices, because of its easy accessibility and low price. Such composites have extensively been studied in the recent years, specifically in order to improve mechanical and physical properties of cellulose fibers (Poyraz et al., 2018; Poyraz, Tozluoglu, Candan, & Demir, 2017; Poyraz, Tozluoglu, Candan, Demir, & Yavuz, 2017; Sarwar, Niazi, Jahan, Ahmad, & Hussain, 2018; Tozluoglu, Poyraz, Candan, Yavuz, & Arslan, 2017). In continuum to our previous studies on preparation of epoxy-
2.2. Synthesis of epoxy functionalized latex particles containing spiropyran 1-(2-acryloxyethyl)-3,3-dimethyl-6-nitrospiro-(2H-1-benzopyran2,2-indoline) (SPEA) were synthesized according to the described procedure in our previous study (Abdollahi et al., 2015). EPLPs containing MMA, GMA and SPEA were prepared through semi-continuous emulsion polymerization as reported before (Abdollahi et al., 2015). Typically, sodium hydrogen carbonate as the buffer (NaHCO3, 0.030 g), SDS (0.045 g), and Triton X-100 (0.012 g) as emulsifiers were dissolved in 27 mL DI water under stirring and the solution was transferred into the reactor under continuous flow of nitrogen gas. After addition of KPS (0.030 g) as the initiator at 75 °C, a solution of SPEA (0.100 g) in 3 mL DI water and 2.3 g MMA were added separately and simultaneously into the reactor dropwise within 10 min and the polymerization continued for 45 min after completion of addition. Then, a mixture of GMA (0.400 g) and MMA (0.750 g) was added to the above latex within 10 min and the polymerization continued for 20 min. The final conversion was above 95% (from gravimetric method) and the amount of coagulation at the end of polymerization was below 1 wt%. 2.3. Preparation of the stimuli-responsive papers Firstly, the paper pulp precursor was prepared by mechanical stirring (1000 rpm) of the scraps of a high-quality filter paper in water at room temperature to yield a 10 wt% paper-in-water dispersion. In order to improve the dispersion and uniformity of the pulp paper, ultrasound waves were also applied to the above mixture for 20 min at 75% amplitude by the probe-sonication with a titanium microtip probe. Then, 70 mL of the paper pulp (7 g cellulose) and 30 mL of the previously prepared photochromic latex (3 g neat EPLPs) were mixed by mechanical stirring (1200 rpm) at 25 °C for 5 h. Then, the obtained mixture was casted into a petri-dish and dried at 80 °C to give modified and untreated paper. Finally, their photochromic properties, color changes, photo-switchablity, pH-responsivity and photofatigue resistance were investigated under UV (365 nm) and visible light irradiations, either primarily or those immersed in the aqueous solutions with different pHs 586
Carbohydrate Polymers 200 (2018) 583–594
A. Abdollahi et al.
Fig. 4. Real-time solid state UV–vis spectra with different UV irradiation time (365 nm) for the untreated and treated (in various pHs) papers.
EPLPs and cellulose. Scanning electron microscopy (SEM) was taken by a Vega Tescan II (Czeck Republic). Prior to scanning, a piece of the prepared stimuli-responsive paper was placed on the sample holder after washing with DI water and dried at room temperature. Then, a layer of gold was deposited by using EMITECH K450x sputter-coater (England) under vacuum and flushing with argon. Photochromic properties of the papers were investigated by solid-phase UV–vis analysis and by using high performance double beam scanning spectrophotometer T90+ (PG Instrument, England). The excitation was done by a UV lamp (365 nm), model Camag 12VDC/VAC (50/60 HZ, 14VA, SER 1206, Switzerland). The source for visible light was a common LED lamp with white light. According to the existing reports (Grogan et al.,
(from 1 to 14) and then dried for UV–vis analysis. The latter is called modified and treated paper. 2.4. Characterization To prepare paper pulp, SONOPULS ultrasonic homogenizer (20 kHz, HFeGM 2200, GmbH & Co. Germany) was used with a titanium microtip KE-76 probe (D: 6 mm), while set for 75% amplitude in all of the steps. Fourier transform infrared (FTIR) spectra were recorded on KBr pellets of the samples by using a BRUKER-IFS48 (Germany) spectrometer with a frequency range from 4000 to 400 cm−1 and resolution of 2 cm−1 at 25 °C to endorse the reaction between functional groups of 587
Carbohydrate Polymers 200 (2018) 583–594
A. Abdollahi et al.
Fig. 5. Normalized reflective index at the corresponding λmax for the untreated paper and the treated ones in different pHs.
polyacrylic matrix through chemical bonding. The progress of chemical reaction between facial epoxy groups in EPLPs and cellulosic substrate had been reported before (Abdollahi et al., 2016; Keyvan Rad & Mahdavian, 2016). Fig. 1 shows a schematic illustration for preparation such stimuli-responsive papers by chemical modification with the aforementioned latex nanoparticles, including 70 wt%. of neat cellulosic fiber and 30 wt%. of the acrylic photochromic polymer. Solidphase UV–vis characteristics of the prepared photochromic papers will be studied in this work comprehensively together with morphological and surface properties to assess their potentiality for being used as chemo- or pH-sensors.
Table 2 Coloration rate equation and kinetic parameters for the prepared stimuli-responsive papers under UV irradiation at 365 nm in different conditions. Condition
Equation
R2
kc (s−1)
T1/2 (s)a
Untreated paper Treated pH = 1 Paper pH = 4 pH = 7 pH = 10 pH = 14
0.02-exp(−0.08 t) 0.01595-exp(−0.11 t) 0.016608-exp(−0.13 t) 0.018428-exp(−0.14 t) 0.019434-exp(−0.13 t) 0.0208-exp(−0.13 t)
0.987 0.986 0.987 0.974 0.995 0.998
0.08 0.11 0.13 0.14 0.13 0.13
40 31 26 23 25 25
a Time required to reach to half of the final reflective index for the coloration.
3.1. Solid-phase UV–vis analysis on the stimuli-responsive papers 2016; Khakzad et al., 2016; Moo, Presolski, & Pumera, 2016), white LED light is a most efficient tool for induction of MC to SP isomerization as a powerful source of visible light. In all investigations, UV and visible irradiation time were set 5 min for the samples. The contact angle of water on the surface of stimuli-responsive papers was measured using a KRUSS G10 (Germany) at room temperature and 25% relative humidity. Thicknesses of the neat cellulosic paper and the prepared stimuli-responsive paper were measured by a digital caliper and were 0.12 mm and 0.53 mm, respectively. A double distilled water (DDW) droplet (5 μL) was placed on the surface of the as-prepared papers. Minimum of three measurements were carried out for each sample and then averaged and reported.
3.1.1. Dependency of photochromic behavior on pH Spiropyran groups undergo isomerization to MC form upon UV irradiation and the newly formed MC may change to MCH, MCQ or MCI, depending on acidity (Genovese et al., 2017; Khakzad et al., 2016) or polarity (Abdollahi et al., 2017; Grogan et al., 2016) of the surrounding environment and also type of the dissolved ions (Baldrighi, Locatelli, Desper, Aakeröy, & Giordani, 2016; Zheng et al., 2018) in the media. The observed different colors for MC in acidic, basic or ion-containing systems are due to its probable stabilized form as MC, MCH and MCI by protonation or coordination (Fig. 2). Each of the existing isomers display different λmax in UV–vis region after UV irradiation at 365 nm. MC and MCH derivatives have two distinct λmax at 500–600 nm and 400–500 nm, respectively, as a result of acidochromism phenomenon (Genovese et al., 2017, 2015; Vallet et al., 2016b). On the other hand, various λmax would be observable for MCQ (in nonpolar media) and MCI (in ionic solutions) forms (Khakzad et al., 2016; Klajn, 2014; Qin et al., 2015). MCI is also favored in acidic or basic media due to the chelation of anions or cations to MC isomer. Here, photochromic properties of the prepared stimuli-responsive papers in different pHs were investigated by their soaking in acidic (pH = 1–6), neutral (pH = 7) and basic (pH = 8–14) aqueous solutions under UV irradiation (365 nm). Then, their UV–vis spectra were recorded in solid state before and after exposure to UV irradiation at 365 nm for 5 min (Fig. 3) and their spectroscopic characteristics (i.e. wavelength at maximum reflective index (λmax) and maximum reflective index at λmax (Rmax)) have been summarized in Table 1. UV–vis
3. Results and discussion It has been quite understood that chromophores (e.g. spiropyran) have to be embedded in a polymeric matrix for being protected against environmental issues that may cause their decomposition and decrease in life time. This is more critical if you are exploiting them in harsh conditions like at very low or high pHs. In continuum to our previous studies in development of chemosensors based on cellulosic paper and spiropyran (Abdollahi et al., 2017, 2016; Keyvan Rad & Mahdavian, 2016), we have developed such sensors with fast photo-switchability and pH-responsivity in a reversible manner; and also improved their photofatigue resistance even at extreme line of pHs, i.e. 1 and 14 here. This could be achieved by the linkage of photoactive groups to the 588
Carbohydrate Polymers 200 (2018) 583–594
A. Abdollahi et al.
Fig. 6. Photofatigue resistance of the prepared stimuli-responsive papers at different pHs upon alternating UV (365 nm for 5 min) and visible (5 min) irradiations.
conditions increased by irradiation time according to the increase in their populations. Similar photochromic behavior was observed for the soaked paper in solutions with weaker acidity (pH = 4) and basicity (pH = 10) as well as neutral (pH = 7) and untreated ones. These observations display that the photochromism of spiropyran moieties in stimuli-responsive paper was not under the influence of negative photochromism too. This is attributed to the affecting role of the polymer carrier in the protection of spiropyran molecules and perverting them from establishment of undesired interactions with the cellulosic substrate and making SP to MC isomerization irreversible. The effect of pH on the isomerization rate of SP to MC was investigated for the prepared stimuli-responsive untreated and treated (in different pHs) papers. This was carried out by measuring of the reflective index intensities at specific λmax and different time intervals of UV irradiation at 365 nm. Opposite to usual UV–vis analysis, less reflective index in solid state UV–vis analysis displays more absorption of UV light and larger photochromic intensity as a result of formation of more MC isomers. Therefore, primary measured reflective index values were converted to the normalized ones (with respect to the reflective index of each sample before UV irradiation) and plotted versus irradiation time (Fig. 5). The obtained results show an exponential dependency of the isomerization rate (SP to MC) to irradiation time in all conditions. Actually, variation of normalized reflective index demonstrates a steep slope for all the samples at early stage of irradiation and before reaching to a plateau. Hence, the kinetic of photo-switching of SP to MC form on the surface of stimuli-responsive papers could be well-described by Eq. (1), extracted from Fig. 5.
spectra in strong acidic (pH = 1–3) and basic (pH = 13, 14) conditions displayed two peaks in the range of 400–700 nm. The intense peak in 500–700 nm was attributed to MC isomers and the weak one, in the range of 400–500 nm, was related to MCH or MCI isomers. Intensity of the peak in 400–500 nm increases gradually with reaching to the extreme lines of pH (i.e. pH < 4 and pH > 12) and is explicitly observed in pH = 1 and 14. This could be attributed to the elevation in population of newly formed MCH and MCI isomers and these are in good agreement with the previous reports on pH-responsivity of the prepared stimuli-responsive papers (Genovese et al., 2015; Zheng et al., 2018). However, MC isomer is the main established form in the middle pHs according to the existing strong absorption in 500–700 nm, because of its stabilization by the surrounding polymer chains. Actually, PMMA as the substrate for spiropyran protects MC groups by dipolar interactions and does not allow them to be influenced by pH changes in the middle points. It is notable that the negative photochromism and irreversibility were not observed in any of the prepared samples. This illustrates that the presence of such polymeric matrix is essential for designing and development of these photoactive systems as chemosensors for photodetection of pH and polarity of the environment. 3.1.2. Real-time photo-isomerization and its kinetic studies upon pH changes To investigate the effect of interactions on photo-isomerization and responsivity rate of the spiropyran molecules, the untreated paper and also the treated ones with acidic (pH = 1 and 4), neutral (pH = 7) and basic (pH = 10 and 14) aqueous solutions were analyzed by solid-state UV–vis spectroscopy before and after illumination with UV light (365 nm) in different time intervals (Fig. 4).Obviously, there is a direct relationship between the reflecting intensity and UV irradiation time according to the generation of MC, MCH and MCI isomers with the increase in exposure time. Comparison between the spectra of untreated and treated samples display a slight promotion in SP to MC isomerization extent as a result of contamination in different pHs. This is due to the role of hydrogen bondings or dipolar interactions for stabilization of MC forms in polar media and reduction of its energy level relative to the SP forms. On the other hand, the intensity of MCH and MCI reflective peaks in high acidic (pH = 1) and high basic (pH = 14)
Normalized reflactive index (t ) = A − exp (−kct ) Normalized reflactive index ( ∞ )
(1)
A is a constant and kc represents the rate constant of SP to MC isomerization upon UV irradiation. The normalized reflective indexes at time t and ∞ were extracted from Fig. 5. It is noteworthy that kc could be a good indication of susceptibility or responsivity of the stimuli-responsive paper toward UV irradiation during photo-isomerization. This parameter also denotes the photo-switchablity and pH-responsivity of the system. Extracted kinetic equations and the corresponding parameters such as R2 (regression), kc and T1/2 (time required to reach to 589
Carbohydrate Polymers 200 (2018) 583–594
A. Abdollahi et al.
Fig. 7. SEM micrographs with different magnifications from the surface of primary cellulosic paper (a, aʹ, aʺ), and stimuli-responsive paper in untreated state (b, bʹ, bʺ), after soaking in water with pH of 1 (c, cʹ, cʺ) and 14 (d, dʹ, dʺ) for 10 days at room temperature.
half of the final reflective index for coloration) have been presented in Table 2. R2 values reveal that the kinetic of SP to MC isomerization conforms with Eq. (1) well. According to the obtained parameters for different conditions,
maximum responsivity (kc = 0.14) and minimum T1/2 (24 s) were observed at pH = 7. In turn, minimum responsivity (kc = 0.08) and maximum T1/2 (40 s) were found for the untreated paper as a result of difficult isomerization process and less stability of MC form in this 590
Carbohydrate Polymers 200 (2018) 583–594
A. Abdollahi et al.
Fig. 8. Contact angle measurement of a water droplet on the surface of primary cellulosic paper (a), untreated paper (b), and those treated in pH = 1 (c), pH = 7 (d) and pH = 14 (e) aqueous solutions for 10 days and ambient condition.
Fig. 9. Color changes of the prepared stimuli-responsive paper in various pHs under UV irradiation at 365 nm.
conditions by converting to MCH and MCI, respectively (Fig. 4). Therefore, the population of MC is expected to be maximum at pH of 7 because of two reasons: i) high stability of MC isomers by dipolar interactions in the treated state compared to the untreated one; ii) less
condition relative to the treated ones. Calculated kc and T1/2 for the prepared stimuli-responsive paper in acidic and basic media displayed a slight decrease in isomerization rate and increment in T1/2. This can be attributed to the decrease in MC population for both acidic and basic 591
Carbohydrate Polymers 200 (2018) 583–594
A. Abdollahi et al.
2017) ones with polymers. Hence, hydrolysis of the acrylic ester groups (COOR) to carboxylic (COOH) or carboxylate (COO−) one will leads to the increase in surface hydrophilicity and this can be followed by measurement of the contact angle of water droplet on the prepared paper surface. This could be in complementary with the observed morphology changes from SEM micrographs. Hence, some pieces of the stimuli-responsive papers were floated in solutions with different pHs (1, 7 and 14) for 10 days and similar to those conditions for SEM analysis. Afterward, contact angles of the primary cellulosic paper, untreated and treated stimuli-responsive papers were measured after soaking (Fig. 8). These reveal that contact angle on the cellulosic papers changed from 0° for the primary one (Fig. 8a) to 67° for the modified ones (Fig. 8b) as a result of chemical attachment of the hydrophobic photochromic acrylic copolymer on the surface of cellulose fibers. This is in agreement with those reported by Malmstrom group for the changes in contact angle via grafting of different polymers on the cellulosic materials (Carlmark & Malmstrom, 2002; Lonnberg et al., 2006; Nystrom et al., 2006). Fig. 8c and d demonstrate that the measured contact angles for the untreated and soaked papers in pH 1 and 7 are almost identical (θ = 66-67°). This means that the induced treatments have not influenced on the hydrophobicity of the stimuli-responsive papers through hydrolytic degradation. As expected, surface hydrophobicity of the base-treated stimuli-responsive paper (pH 14) has decreased (θ = 54°). This could be attributed to few hydrolysis of the esteric groups in the basic media and is in accordance with the SEM results. These indicate that the prepared stimuli-responsive paper has a remarkable stability toward environmental degradations in high acidic and high basic media for a long term and they could be an appropriate nominee for reusable pH-sensors based on photochromic polymers.
stability of MCH and MCI forms in the inert media compared to the high acidic or basic conditions. Finally, these kinetic studies demonstrate the capability of such prepared stimuli-responsive photochromic papers to pH changes in a proper manner. 3.1.3. Photofatigue resistant and photo-switchability Among different photochromic properties of the stimuli-responsive materials, photofatigue resistance and photo-switchability are the most important ones for developing optical sensors. Recent studies show that polymeric carriers containing spiropyran, for incorporation into the high polar matrices such as cellulose, can lead to significant improvement in photostability, photo-switchability and also reversibility (Li, Trosien, Schenderlein, Graf, & Biesalski, 2016; Sun et al., 2014; Xue et al., 2015). Here, the effect of surrounding pH on photostability and optical reversibility of the prepared stimuli-responsive paper was studied by measurement of its reflective index in different pHs and also in the untreated state (Fig. 6). For this propose, some pieces of the paper were soaked in acidic and basic solutions (pH of 1, 4, 7, 10 and 14) and were subsequently exposed to UV irradiation (365 nm, 5 min) and then visible light (5 min) at ambient condition for 15 cycles. The corresponding reflective index was measured immediately after each irradiation within a 5 min interval between each cycle. This could be attributed to the facile SP ⇄ MC isomerization in the polar and wet media. However, Fig. 5 implies that high polar interactions in acidic and basic media have not influenced on photo-switchability, reversibility and photofatigue resistance of SP and MC groups in the modified papers. Actually, the employed acrylic polymer carrier has achieved to protect them against environmental degradation, even in very low or high pHs and under alternating UV and visible irradiations. On the other hand, the surrounding polarity and pH have not affected on the performance of such prepared pH sensors, illustrating their reusability for the desired applications.
3.3. Visual pH sensing by the prepared stimuli-responsive paper In the our previous studies (Abdollahi et al., 2017, 2016; Keyvan Rad & Mahdavian, 2016), stimuli-responsive copolymers and the corresponding modified papers based on spiropyran were developed as optical sensors for facile and fast photo-sensing of polarity in different protic and aprotic media. Here and in continuum, we have examined the prepared stimuli-responsive paper as a chemosensor for photodetection of pH even in wide range of pHs. Fig. 9 reveals different color changes under UV irradiation, while floated in water at different pHs. It is worth mentioning that exploitation of the photochromic copolymers instead of doped polymers with photochromic molecules will lead to remarkable improvement in photostability, photo-switchability and photofatigue resistance of spiropyran chromophore in polar media. SP groups convert to MC isomer under UV irradiation at 365 nm and could be stabilized in MCH (acidic media) and MCI (basic media) with different colors (Fig. 9). This reveals the potentiality of such a paper for photodetection with evident and various color changes, depending on the surrounding pH.
3.2. Morphology of the prepared stimuli-responsive paper It is generally believed that an acrylic-based copolymer can undergo a degradation process by probable hydrolysis in high acidic or high basic environment. On the other hand, we tried to protect photoactive spiropyran groups in the prepared stimuli-responsive paper from environmental degradations by inclusion in the acrylic polymer matrix. Therefore, it is essential to ensure about the stability of such papers in the performance conditions for being employed in reusable sensors. Beside photofatigue resistance and photo-switchability, morphological studies will be helpful to confirm the capability of these papers for pH sensing. For this reason, some pieces of the prepared papers were soaked in different pHs (1 and 14) for 10 days and then, SEM images of their surfaces were taken together with the primary and untreated papers (Fig. 7). Microscopic images for the primary cellulosic paper (a, aʹ, aʺ) and untreated one (b, bʹ, bʺ) displayed obvious morphology changes of cellulose fibers as a result of penetration and chemical attachment of the prepared photochromic copolymer into the cellulose substrate. However, surface morphology of the stimuli-responsive paper, after soaking in high acidic solution (pH = 1, 6c, cʹ, cʺ) was not changed significantly. Slight roughness could be attributed to the removal of salts and surfactants through its treatment with the acidic solution. As can be seen in Fig. 7d, dʹ, dʺ, surface of the cellulose fibers is not smooth and a more roughness is observable. This shows that the basic media has probably facilitated the hydrolysis of acrylic copolymer and its degradation. Although, this has not influenced on the photochromic properties and its photo-responsivity remarkably. Modification of cellulosic materials with hydrophobic compounds can decrease their surface hydrophilicity and it can be identified by changes in contact angle for chemically modified (Carlmark & Malmstrom, 2002; Lonnberg et al., 2006; Nystrom, Lindqvist, Ostmark, Hult, & Malmstrom, 2006; Roy, Semsarilar, Guthrie, & Perrier, 2009) and also for physically modified (Aarne et al., 2013; Kontturi et al.,
4. Conclusion Herein, we have introduced a new stimuli-responsive cellulosic paper modified with MMA-SPEA copolymer as a reusable pH-sensor. Such chemosensors were prepared by chemical attachment of epoxy functionalized latex particles bearing spiropyran moieties on the surface of a cellulosic paper. The obtained results from solid-state UV–vis analysis displayed a remarkable photostability, reversibility, photofatigue resistant and also good pH-responsivity for the immersed stimuli-responsive papers in solutions with different pHs in the range of 114. Investigations on the SP to MC isomerization kinetic by solid-phase UV–vis analysis illustrated that the interactions between spiropyran groups and acidic or basic solutions in the treated paper can accelerate MC formation (kc = 0.11–0.14s−1) compared with the untreated one (kc = 0.08 s−1). SEM images and the measured contact angles from the surface of floated papers in pH 1 and 14 for 10 days showed high 592
Carbohydrate Polymers 200 (2018) 583–594
A. Abdollahi et al.
stability and resistance toward hydrolytic environmental degradations of the coated polymer on cellulosic fibers without specific loss in photochromic properties. This is essential for employment in reusable pHsensors. The prepared smart paper revealed different colors when triggered by various pHs under UV irradiation at 365 nm as a result of establishment of MC, MCH and MCI forms in such media and consequent acidochromism and basochromism. It was concluded that the obtained papers containing spiropyran moieties can be exploited in reusable optical pH-sensors because of its unique properties such as photo-switchability, photofatigue, fast and reversible pH-responsivity and enhanced stability toward hydrolytic degradation. These are vital properties to be considered for development of optical pH-sensors. Facile accessibility and low price of the cellulose materials are two significant advantages for the industrial development of stimuli-responsive papers based on such spiropyran copolymers as reusable chemosensors in near future.
1016/j.snb.2017.11.138. Di Credico, B., Griffini, G., Levi, M., & Turri, S. (2013). Microencapsulation of a UVresponsive photochromic dye by means of novel UV-screening polyurea-based shells for smart coating applications. ACS Applied Materials & Interfaces, 5(14), 6628–6634. https://doi.org/10.1021/am401328f. Florea, L., McKeon, A., Diamond, D., & Benito-Lopez, F. (2013). Spiropyran polymeric microcapillary coatings for photodetection of solvent polarity. Langmuir, 29(8), 2790–2797. https://doi.org/10.1021/la304985p. Francis, W., Dunne, A., Delaney, C., Florea, L., & Diamond, D. (2017). Spiropyran based hydrogels actuators—Walking in the light. Sensors and Actuators B: Chemical, 250, 608–616. https://doi.org/10.1016/j.snb.2017.05.005. Fries, K., Samanta, S., Orski, S., & Locklin, J. (2008). Reversible colorimetric ion sensors based on surface initiated polymerization of photochromic polymers. Chemical Communications, 47, 6288. https://doi.org/10.1039/b818042c. Genovese, M. E., Athanassiou, A., & Fragouli, D. (2015). Photoactivated acidochromic elastomeric films for on demand acidic vapor sensing. Journal of Materials Chemistry A, 3(44), 22441–22447. https://doi.org/10.1039/C5TA06118K. Genovese, M. E., Colusso, E., Colombo, M., Martucci, A., Athanassiou, A., & Fragouli, D. (2017). Acidochromic fibrous polymer composites for rapid gas detection. Journal of Materials Chemistry A, 5(1), 339–348. https://doi.org/10.1039/C6TA08793K. Grogan, C., Florea, L., Koprivica, S., Scarmagnani, S., O’Neill, L., Lyng, F., ... Raiteri, R. (2016). Microcantilever arrays functionalised with spiropyran photoactive moieties as systems to measure photo-induced surface stress changes. Sensors and Actuators B: Chemical, 237, 479–486. https://doi.org/10.1016/j.snb.2016.06.108. Hu, J., & Liu, S. (2010). Responsive polymers for detection and sensing applications: Current status and future developments. Macromolecules, 43(20), 8315–8330. https://doi.org/10.1021/ma1005815. Huang, Y., Li, F., Ye, C., Qin, M., Ran, W., & Song, Y. (2015). A photochromic sensor microchip for high-performance multiplex metal ions detection. Scientific Reports, 5(1), 9724. https://doi.org/10.1038/srep09724. Jiang, F., Chen, S., Cao, Z., & Wang, G. (2016). A photo, temperature, and pH responsive spiropyran-functionalized polymer: Synthesis, self-assembly and controlled release. Polymer, 83, 85–91. https://doi.org/10.1016/j.polymer.2015.12.027. Keyvan Rad, J., & Mahdavian, A. R. (2016). Preparation of fast photoresponsive cellulose and kinetic study of photoisomerization. The Journal of Physical Chemistry C, 120(18), 9985–9991. https://doi.org/10.1021/acs.jpcc.6b02594. Khakzad, F., Mahdavian, A. R., Salehi-Mobarakeh, H., Rezaee Shirin-Abadi, A., & Cunningham, M. (2016). Redispersible PMMA latex nanoparticles containing spiropyran with photo-, pH- and CO2- responsivity. Polymer (United Kingdom), 101, 274–283. https://doi.org/10.1016/j.polymer.2016.08.073. Klajn, R. (2014). Spiropyran-based dynamic materials. Chemical Society Reviews, 43(1), 148–184. https://doi.org/10.1039/c3cs60181a. Kontturi, K. S., Biegaj, K., Mautner, A., Woodward, R. T., Wilson, B. P., Johansson, L.-S., ... Kontturi, E. (2017). noncovalent surface modification of cellulose nanopapers by adsorption of polymers from aprotic solvents. Langmuir, 33(23), 5707–5712. https:// doi.org/10.1021/acs.langmuir.7b01236. Kumar, K. S., Kumar, V. B., & Paik, P. (2013). Recent advancement in functional coreshell nanoparticles of polymers: Synthesis, physical properties, and applications in medical biotechnology. Journal of Nanoparticles, 2013, 1–24. https://doi.org/10. 1155/2013/672059. Li, M., Zhang, Q., Zhou, Y. N., & Zhu, S. (2018). Let spiropyran help polymers feel force!. Progress in Polymer Science, 79, 26–39. https://doi.org/10.1016/j.progpolymsci.2017. 11.001. Li, W., Trosien, S., Schenderlein, H., Graf, M., & Biesalski, M. (2016). Preparation of photochromic paper, using fibre-attached spiropyran polymer networks. RSC Advances, 6(111), 109514–109518. https://doi.org/10.1039/C6RA23673A. Lonnberg, H., Zhou, Q., Brumer, H., Teeri, T. T., Malmstrom, E., & Hult, A. (2006). Grafting of cellulose fibers with poly(ε-caprolactone) and poly(lactic acid) via ringopening polymerization. Biomacromolecules, 7(7), 2178–2185. https://doi.org/10. 1021/bm060178z. Metzler, L., Reichenbach, T., Brügner, O., Komber, H., Lombeck, F., Müllers, S., ... Sommer, M. (2015). High molecular weight mechanochromic spiropyran main chain copolymers via reproducible microwave-assisted Suzuki polycondensation. Polymer Chemistry, 6(19), 3694–3707. https://doi.org/10.1039/c5py00141b. Moo, J. G. S., Presolski, S., & Pumera, M. (2016). Photochromic spatiotemporal control of bubble-propelled micromotors by a spiropyran molecular switch. ACS Nano, 10(3), 3543–3552. https://doi.org/10.1021/acsnano.5b07847. Mura, S., Nicolas, J., & Couvreur, P. (2013). Stimuli-responsive nanocarriers for drug delivery. Nature Materials, 12(11), 991–1003. https://doi.org/10.1038/NMAT3776. Nystrom, D., Lindqvist, J., Ostmark, E., Hult, A., & Malmstrom, E. (2006). Superhydrophobic bio-fibre surfaces via tailored grafting architecture. Chemical Communications, 34, 3594–3596. https://doi.org/10.1039/B607411A. O’Bryan, G., Wong, B. M., & McElhanon, J. R. (2010). Stress sensing in polycaprolactone films via an embedded photochromic compound. ACS Applied Materials & Interfaces, 2(6), 1594–1600. https://doi.org/10.1021/am100050v. Peterson, G. I., Larsen, M. B., Ganter, M. A., Storti, D. W., & Boydston, A. J. (2015). 3Dprinted mechanochromic materials. ACS Applied Materials & Interfaces, 7(1), 577–583. https://doi.org/10.1021/am506745m. Poyraz, B., Tozluoglu, A., Candan, Z., Demir, A., Yavuz, M., Buyuksarı, U., ... Saka, R. C. (2018). TEMPO-treated CNF composites: Pulp and matrix effect. Fibers and Polymers, 19(1), 195–204. https://doi.org/10.1007/s12221-018-7673-y. Poyraz, B., Tozluoglu, A., Candan, Z., & Demir, A. (2017). Matrix impact on the mechanical, thermal and electrical properties of microfluidized nanofibrillated cellulose composites. Journal of Polymer Engineering, 37(9), https://doi.org/10.1515/polyeng2017-0022. Poyraz, B., Tozluoglu, A., Candan, Z., Demir, A., & Yavuz, M. (2017). Influence of PVA
Acknowledgment We wish to express our gratitude to Iran Polymer and Petrochemical Institute (IPPI) for financial support of this work (Grant No. 24761176). References Aarne, N., Laine, J., Hänninen, T., Rantanen, V., Seitsonen, J., Ruokolainen, J., ... Kontturi, E. (2013). Controlled hydrophobic functionalization of natural fibers through self-assembly of amphiphilic diblock copolymer micelles. ChemSusChem, 6(7), 1203–1208. https://doi.org/10.1002/cssc.201300218. Abdollahi, A., Alinejad, Z., & Mahdavian, A. R. (2017). Facile and fast photosensing of polarity by stimuli-responsive materials based on spiropyran for reusable sensors: A physico-chemical study on the interactions. Journal of Materials Chemistry C, 5(26), 6588–6600. https://doi.org/10.1039/c7tc02232h. Abdollahi, A., Mahdavian, A. R. A. R., & Salehi-Mobarakeh, H. (2015). Preparation of stimuli-responsive functionalized latex nanoparticles: the effect of spiropyran concentration on size and photochromic properties. Langmuir, 31(39), 10672–10682. https://doi.org/10.1021/acs.langmuir.5b02612. Abdollahi, A., Rad, J. K., & Mahdavian, A. R. (2016). Stimuli-responsive cellulose modified by epoxy-functionalized polymer nanoparticles with photochromic and solvatochromic properties. Carbohydrate Polymers, 150(18), 131–138. https://doi.org/10. 1016/j.carbpol.2016.05.009. Avella-Oliver, M., Morais, S., Puchades, R., & Maquieira, Á. (2016). Towards photochromic and thermochromic biosensing. TrAC Trends in Analytical Chemistry, 79, 37–45. https://doi.org/10.1016/j.trac.2015.11.021. Baldrighi, M., Locatelli, G., Desper, J., Aakeröy, C. B., & Giordani, S. (2016a). Probing metal ion complexation of ligands with multiple metal binding sites: The Case of Spiropyrans. Chemistry–A European Journal, 22(39), 13976–13984. https://doi.org/ 10.1002/chem.201602608. Baldrighi, M., Locatelli, G., Desper, J., Aakeröy, C. B., & Giordani, S. (2016b). Probing metal ion complexation of ligands with multiple metal binding sites: the case of spiropyrans. Chemistry- A European Journal, 22(39), 13976–13984. https://doi.org/ 10.1002/chem.201602608. Benito-Lopez, F., Scarmagnani, S., Walsh, Z., Paull, B., Macka, M., & Diamond, D. (2009). Spiropyran modified micro-fluidic chip channels as photonically controlled self-indicating system for metal ion accumulation and release. Sensors and Actuators B: Chemical, 140(1), 295–303. https://doi.org/10.1016/j.snb.2009.03.080. Bertrand, O., & Gohy, J.-F. (2017). Photo-responsive polymers: Synthesis and applications. Polymer Chemistry, 8(1), 52–73. https://doi.org/10.1039/C6PY01082B. Carlmark, A., & Malmstrom, E. (2002). Atom transfer radical polymerization from cellulose fibers at ambient temperature. Journal of the American Chemical Society, 124(6), 900–901. https://doi.org/10.1021/ja016582h. Caruso, M. M., Davis, D. A., Shen, Q., Odom, S. A., Sottos, N. R., White, S. R., ... Moore, J. S. (2009). Mechanically-induced chemical changes in polymeric materials. Chemical Reviews, 109(11), 5755–5798. https://doi.org/10.1021/cr9001353. Chen, S., Gao, Y., Cao, Z., Wu, B., Wang, L., Wang, H., ... Wang, G. (2016). Nanocomposites of spiropyran-functionalized polymers and upconversion nanoparticles for controlled release stimulated by near-infrared light and pH. Macromolecules, 49(19), 7490–7496. https://doi.org/10.1021/acs.macromol. 6b01760. Crano, J. C., & Guglielmetti, R. J. (2002a). Organic photochromic and thermochromic compounds. Main photochromic families, Vol. 1Boston: Springer US: Kluwer Academic Publishershttps://doi.org/10.1007/b114211. Crano, J. C., & Guglielmetti, R. J. (2002b). Organic photochromic and thermochromic compounds. Physicochemical studies, biological applications, and thermochromism, Vol. 2Boston: Springer US: Kluwer Academic Publishershttps://doi.org/10.1007/ b115590. Deshpande, S. S., Jachak, M. A., Khopkar, S. S., & Shankarling, G. S. (2018). A simple substituted spiropyran acting as a photo reversible switch for the detection of lead (Pb2+) ions. Sensors and Actuators B: Chemical, 258, 648–656. https://doi.org/10.
593
Carbohydrate Polymers 200 (2018) 583–594
A. Abdollahi et al.
Vallet, J., Micheau, J.-C., & Coudret, C. (2016a). Switching a pH indicator by a reversible photoacid: A quantitative analysis of a new two-component photochromic system. Dyes and Pigments, 125, 179–184. https://doi.org/10.1016/j.dyepig.2015.10.025. Vallet, J., Micheau, J. C., & Coudret, C. (2016b). Switching a pH indicator by a reversible photoacid: A quantitative analysis of a new two-component photochromic system. Dyes and Pigments, 125, 179–184. https://doi.org/10.1016/j.dyepig.2015.10.025. Wan, S., Ma, Z., Chen, C., Li, F., Wang, F., Jia, X., ... Yin, M. (2016). A supramoleculetriggered mechanochromic switch of cyclodextrin-jacketed rhodamine and spiropyran derivatives. Advanced Functional Materials, 26(3), 353–364. https://doi.org/ 10.1002/adfm.201504048. Wan, S., Zheng, Y., Shen, J., Yang, W., & Yin, M. (2014). On–off–on” switchable sensor: A fluorescent spiropyran responds to extreme pH conditions and its bioimaging applications. ACS Applied Materials & Interfaces, 6(22), 19515–19519. https://doi.org/10. 1021/am506641t. Wang, L.-F. (2016). Application of response surface methodology for exploring β-cyclodextrin effects on the decoloration of spiropyran complexes. Chemical Physics Letters, 662, 296–305. https://doi.org/10.1016/j.cplett.2016.09.068. Wang, L., & Li, Q. (2018). Photochromism into nanosystems: towards lighting up the future nanoworld. Chemical Society Reviews. https://doi.org/10.1039/C7CS00630F. Wojtyk, J. T. C., Wasey, A., Xiao, N. N., Kazmaier, P. M., Hoz, S., Yu, C., ... Buncel, E. (2007). Elucidating the mechanisms of acidochromic spiropyran-merocyanine interconversion. The Journal of Physical Chemistry A, 111(13), 2511–2516. https://doi. org/10.1021/jp068575r. Xie, X., Mistlberger, G., & Bakker, E. (2012). Reversible photodynamic chloride-selective sensor based on photochromic spiropyran. Journal of the American Chemical Society, 134(41), 16929–16932. https://doi.org/10.1021/ja307037z. Xue, Y., Tian, J., Tian, W., Gong, P., Dai, J., & Wang, X. (2015). Significant fluorescence enhancement of spiropyran in colloidal dispersion and its light-induced size tunability for release control. The Journal of Physical Chemistry C, 119(35), 20762–20772. https://doi.org/10.1021/acs.jpcc.5b06905. Yu, G., Cao, Y., Liu, H., Wu, Q., Hu, Q., Jiang, B., ... Yuan, Z. (2017). A spirobenzopyranbased multifunctional chemosensor for the chromogenic sensing of Cu 2+ and fluorescent sensing of hydrazine with practical applications. Sensors and Actuators B: Chemical, 245, 803–814. https://doi.org/10.1016/j.snb.2017.02.020. Zhang, H., Chen, Y., Lin, Y., Fang, X., Xu, Y., Ruan, Y., ... Weng, W. (2014). Spiropyran as a mechanochromic probe in dual cross-linked elastomers. Macromolecules, 47(19), 6783–6790. https://doi.org/10.1021/ma500760p. Zheng, T., Xu, Z., Zhao, Y., Li, H., Jian, R., & Lu, C. (2018). Multiresponsive polysiloxane bearing photochromic spirobenzopyran for sensing pH changes and Fe 3+ ions and sequential sensing of Ag + and Hg 2+ ions. Sensors and Actuators B: Chemical, 255, 3305–3315. https://doi.org/10.1016/j.snb.2017.09.158. Zhou, Y.-N., Zhang, Q., & Luo, Z.-H. (2014). A light and pH dual-stimuli-responsive block copolymer synthesized by copper(0)-mediated living radical polymerization: Solvatochromic, Isomerization, and “schizophrenic” behaviors. Langmuir, 30(6), 1489–1499. https://doi.org/10.1021/la402948s.
and silica on chemical, thermo-mechanical and electrical properties of celluclasttreated nanofibrillated cellulose composites. International Journal of Biological Macromolecules, 104, 384–392. https://doi.org/10.1016/j.ijbiomac.2017.06.018. Qin, M., Huang, Y., Li, F., & Song, Y. (2015). Photochromic sensors: A versatile approach for recognition and discrimination. Journal of Materials Chemistry C, 3(36), 9265–9275. https://doi.org/10.1039/C5TC01939G. Roy, D., Semsarilar, M., Guthrie, J. T., & Perrier, S. (2009). Cellulose modification by polymer grafting: A review. Chemical Society Reviews, 38(7), 2046. https://doi.org/ 10.1039/b808639g. Sahoo, P. R., & Kumar, S. (2016). Photochromic spirooxazine as highly sensitive and selective probe for optical detection of Fe3+ in aqueous solution. Sensors and Actuators B: Chemical, 226, 548–552. https://doi.org/10.1016/j.snb.2015.12.039. Sarwar, M. S., Niazi, M. B. K., Jahan, Z., Ahmad, T., & Hussain, A. (2018). Preparation and characterization of PVA/nanocellulose/Ag nanocomposite films for antimicrobial food packaging. Carbohydrate Polymers, 184, 453–464. https://doi.org/10.1016/j. carbpol.2017.12.068. Shao, N., Wang, H., Gao, X., Yang, R., & Chan, W. (2010). Spiropyran-based fluorescent anion probe and its application for urinary pyrophosphate detection. Analytical Chemistry, 82(11), 4628–4636. https://doi.org/10.1021/ac1008089. Shi, W., Xing, F., Bai, Y.-L., Hu, M., Zhao, Y., Li, M.-X., ... Zhu, S. (2015). High sensitivity viologen for a facile and versatile sensor of base and solvent polarity in solution and solid state in air atmosphere. ACS Applied Materials & Interfaces, 7(26), 14493–14500. https://doi.org/10.1021/acsami.5b03932. Su, T., Cheng, F. R., Cao, J., Yan, J. Q., Peng, X. Y., & He, B. (2017). Dynamic intracellular tracking nanoparticles via pH-evoked “off–on” fluorescence. Journal of Materials Chemistry B, 5(17), 3107–3110. https://doi.org/10.1039/C7TB00713B. Sun, B., He, Z., Hou, Q., Liu, Z., Cha, R., & Ni, Y. (2013). Interaction of a spirooxazine dye with latex and its photochromic efficiency on cellulosic paper. Carbohydrate Polymers, 95(1), 598–605. https://doi.org/10.1016/j.carbpol.2013.03.032. Sun, B., Hou, Q., He, Z., Liu, Z., & Ni, Y. (2014). Cellulose nanocrystals (CNC) as carriers for a spirooxazine dye and its effect on photochromic efficiency. Carbohydrate Polymers, 111, 419–424. https://doi.org/10.1016/j.carbpol.2014.03.051. Tao, J., Zhao, P., Li, Y., Zhao, W., Xiao, Y., & Yang, R. (2016). Fabrication of an electrochemical sensor based on spiropyran for sensitive and selective detection of fluoride ion. Analytica Chimica Acta, 918, 97–102. https://doi.org/10.1016/j.aca. 2016.03.025. Theato, P., Sumerlin, B. S., O’Reilly, R. K., & Epps, T. H., Jr. (2013). Stimuli responsive materials. Chemical Society Reviews, 42(17), 7055. https://doi.org/10.1039/ c3cs90057f. Tian, W. W., & Tian, J. (2014). Synergy of different fluorescent enhancement effects on spiropyran appended onto cellulose. Langmuir, 30(11), 3223–3227. https://doi.org/ 10.1021/la404628p. Tozluoglu, A., Poyraz, B., Candan, Z., Yavuz, M., & Arslan, R. (2017). Biofilms from micro/nanocellulose of NaBH4-modified kraft pulp. Bulletin of Materials Science, 40(4), 699–710. https://doi.org/10.1007/s12034-017-1416-y.
594