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Fluorescence and conductivity studies on wool
Materials Chemistry and Physics 113 (2009) 480–484
Contents lists available at ScienceDirect
Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys
Fluorescence and conductivity studies on wool Akif Kaynak a,∗ , Richard C. Foitzik b , Frederick M. Pfeffer c a
Deakin University, School of Engineering & Information Technology, Pigdons Road, Geelong, Victoria 3217, Australia Medicinal Chemistry and Drug Action, Monash Institute of Pharmaceutical Sciences, Monash University, 381 Royal Parade, Parkville, Victoria 3052, Australia c Deakin University, School of Life and Environmental Science, Geelong, Victoria 3217, Australia b
a r t i c l e
i n f o
Article history: Received 15 February 2008 Received in revised form 14 July 2008 Accepted 17 July 2008 Keywords: Conducting polymers Conducting textiles Fluorescent polymers
a b s t r a c t An optimized synthetic method for the production of fluorescent conductive wool using pyrene, rhodamine B and fluorescein is reported. The application of fluorescent conductive polymers to wool was studied using solution and mist polymerization techniques. The effects of incorporating fluorescent dopants into the polymerization solution as well as the encapsulation of fluorescent dyes in a polypyrrole (PPy) micelle were also investigated. It was determined on the basis of both conductivity and fluorescence measurements that the encapsulation of dyes in PPy onto the surface of textiles gave the best results. © 2008 Elsevier B.V. All rights reserved.
1. Introduction Apart from sensor technologies, the combining of fluorescence dyes with conductive polymers has received little attention [1]. Indeed the fabrication of fluorescent conductive polymer-coated textiles, to the best of our knowledge has not been attempted. Fluorescent conductive textiles could be valuable in the apparel industry where one application would be the production of security clothing labels that exhibit both fluorescence and conductivity, thus allowing the easy detection of imitation items. Fluorescent dyes were first encapsulated in a polypyrrole (PPy) shell by Jang and Oh [2] The particle size was controlled by the reaction conditions and the work required low temperatures for the synthesis of an emulsion of fluorescent conductive nano-particles [2]. Additional research has been performed (and patented) by WellaTM , where fluorescent nano-particles were used to increase the brightness of hair dyes [3]. Recently, coloured conductive polymers were produced by polymerization in the presence of dyes [4–6]. Research published on coloured conductive polymers, involved covalent attachment of photo-chromic dyes to pyrrole [1,7–8]. Photo-chromic conductive polymers are of interest due to the polymer’s ability to exhibit light switching tendencies [9]. The majority of work on conductive photo-chromic polymers utilizes monomers other than pyrrole, such as polyaniline and poly(3,4-ethylenedioxythiophenes) [9–16].
Herein were report an optimized synthetic method for the production of fluorescent conductive wool. The fluorescent dyes used in this investigation were pyrene, rhodamine B and fluorescein. Several methods were studied including solution polymerization, mist polymerization, the use of fluorescent dopants and finally the encapsulation of fluorescent dyes in a PPy micelle. 2. Experimental 2.1. General experimental All solvents used were AR grade or higher. The pyrrole, iron(III) chloride and fluorescent dyes were purchased from Sigma–Aldrich and had a purity of 98% or greater. All textiles were tested for abrasion resistance using a Martindale abrasion tester. Each specimen was tested for 2000 abrasion cycles with a pressure of 9 kPa. Scanning electron microscope (SEM) images were generated by sputter coating a thin layer of gold (∼7–10 nm) onto the textile surface. Surface resistance was measured by a Fluke multimeter with a probe distance of 10.0 mm. All wool samples used were 40 mm × 40 mm of a woven material. The wool samples were cleaned and degreased prior to use by stirring for 3 h in 1 L of water at 60 ◦ C with decon 90 (2 mL). The pH of the solution was maintained around a value of 1 by the addition of hydrochloric acid (HCl). The wool substrates were then washed with water followed by rinsing with acetonitrile. A fine mist or vapour was sprayed directly onto the textile samples by using a solution of the monomer in ethanol with a commercially available Preval Sprayer® [17–19]. The fluorescence intensities of the textile samples were measured using a Cary Eclipse spectrofluorometer, or visually using a powerful poly-light. The excitation wavelength and emission of rhodamine B on the surface of wool were 356 nm and 600 nm respectively whereas for the pyrene-coated textile surface these excitation and emission values were 336 nm and 395 nm, respectively. 2.2. Preparation of fluorescent conductive textiles by pre-treatment of a textile sample followed by solution polymerization
∗ Corresponding author. E-mail address: [email protected] (A. Kaynak). 0254-0584/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2008.07.098
A fluorescent dyeing solution was prepared by dissolving dye (1 g of pyrene or rhodamine B) in acetone (20 mL). A woven textile was soaked in this solution
A. Kaynak et al. / Materials Chemistry and Physics 113 (2009) 480–484 for 15 min, then removed and dried, to produce a fluorescent textile. The textile was then submerged in water (100 mL) and held by a wire frame to fix its location. Pyrrole (0.50 g, 7.46 mmol) and FeCl3 (1.21 g, 7.46 mmol) were added in quick succession, and the reaction stirred for 3 h. The textile sample was washed with copious amounts of warm water (to remove excess polymer and FeCl3 ). The textile was rinsed with a dilute solution of HCl (pH ∼2) then again washed with water. The coated textile was dried under reduced pressure (∼0.1 mmHg) for 4 h before being tested for fluorescence, surface resistance, and surface abrasion durability.
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polymer and FeCl3 ). The textile was rinsed with a dilute solution of HCl (pH ∼2) then again washed with water. The coated textile was dried under reduced pressure (∼0.1 mmHg) for 4 h before being tested for fluorescence, surface resistance, and surface abrasion durability.
3. Results and discussion 3.1. Conductive fluorescent textiles by pre-dyeing the wool
2.3. Preparation of fluorescent conductive textiles by pre-treatment of a textile sample followed by mist polymerization A fluorescent dyeing solution was prepared by dissolving a dye (1 g of pyrene or rhodamine B) in acetone (20 mL). A woven textile was soaked in this solution for 15 min, then removed and dried, leaving a fluorescent textile. The textile sample was then sprayed with pyrrole in ethanol (1:2, w/w). The textile was slowly heated with a heat gun to induce polymerization. When the sample was completely dried the coating process was repeated two times, starting from the application of FeCl3 . The sample was then washed with copious amounts of warm water until the washings were clear. The sample was then washed in a solution of HCl in water with the pH maintained at ∼2 followed by washing with water. The coated textile was dried under reduced pressure (∼0.1 mmHg) for 4 h before being tested for fluorescence, surface resistance, and surface abrasion durability. 2.4. A one-pot preparation of fluorescent conductive textiles by solution polymerization A textile sample was submerged in water (100 mL) and held by a wire frame to fix its location. Pyrrole (0.50 g, 7.46 mmol) and a fluorescent dye (1–4 mol. equiv. pyrene, rhodamine B or fluorescein) in acetone (10 mL) were added and stirred for 5 min. Iron(III) chloride (1.21 g, 7.46 mmol) was added in one portion and the reaction stirred for 3 h. The resulting textile sample was washed with copious amounts of warm water (to remove excess polymer and FeCl3 ). The textile was rinsed with a dilute solution of HCl (pH ∼2) then washed with water. The coated textile was dried under reduced pressure (∼0.1 mmHg) for 4 h before being tested for fluorescence, surface resistance, and surface abrasion durability. 2.5. Encapsulation of fluorescent dyes in PPy for the preparation of fluorescent conductive textiles A textile sample was submerged in ice-cold water (100 mL) and held by a wire frame to fix its location. Pyrrole (0.50 g, 7.46 mmol), a surfactant (decon 90, 10 mL) and varying amounts of a fluorescent dye in acetone (1 g of pyrene or rhodamine B in 10 mL), were added and stirred for 15 min, where upon iron(III) chloride (1.21 g, 7.46 mmol) was added in one portion and the reaction vigorously stirred at 0 ◦ C for 5 h. The textile sample was washed with copious amounts of warm water (to remove excess polymer and FeCl3 ). The textile was rinsed with a dilute solution of HCl (pH ∼2) and again washed with water. The coated textile was dried under reduced pressure (∼0.1 mmHg) for 4 h before being tested for fluorescence, surface resistance, and surface abrasion durability. 2.6. Preparation of fluorescent conductive textiles using fluorescent dopants A textile sample was submerged in water (100 mL) and held by a wire frame to fix its location. Pyrrole (0.50 g, 7.46 mmol) and 1-pyrenesulfonic acid (1.05 g, 3.73 mmol) were added and stirred for 5 min. Iron(III) chloride (1.21 g, 7.46 mmol) was then added in one portion and the reaction stirred for 3 h. The textile sample was removed then washed with copious amounts of warm water (to remove excess
The first method employed for the production of fluorescent conductive textiles involved pre-dyeing the samples with fluorescent dyes, followed by the polymerization of pyrrole onto the textiles surface. The samples were pre-dyed by soaking in a solution containing fluorescent dyes. The dyes that worked efficiently for this method were pyrene and rhodamine B. The textile samples that were pre-dyed with a fluorescent dye were coated with PPy by either the solution or mist polymerization method. The solution polymerization of the pre-dyed textiles was done in water to avoid organic solvent leaching the dye out of the textiles. Mist polymerization was also employed to coat the predyed textiles with PPy. Both the solution and mist polymerization methods produced even polymer coatings on the textiles surface; however, fluorescent textiles coated by the mist polymerization method retained greater fluorescence intensity. Investigation utilizing SEM showed little change in the surface appearance of wool. Coating the textile samples by mist polymerization showed little dendritic PPy formation (Fig. 1). This was in line with our previous findings in relation to PPy coatings [17]. The coated textile surfaces were also investigated after administrating the sample to abrasion testing, these results appeared visually to have little or no change in the polymer coating thickness, thus it was concluded that the polymer was strongly attached to the wool surface (good fastness), again in line with previous findings [17]. 3.2. Preparation of the conductive fluorescent textiles by solution polymerization Fluorescent conductive textiles were also produced by modifications to the solution polymerization method. Addition of a fluorescent dye to a reaction mixture of FeCl3 and textile sample was followed by the addition of pyrrole. Once the pyrrole was added, polymerization occurred immediately on the textile surface. It was originally postulated that this method would have the same effect as the solution polymerization of a pre-dyed sample. Increasing the concentrations of the fluorescent dyes increased the fluorescence intensities of the resultant textile samples. It was found that the optimum fluorescence intensity was produced when a dye to pyrrole ratio of 4:1 was used. In general for every 2 g of
Fig. 1. Mist polymerization of pyrrole onto fluorescent pre-dyed woven wool.
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Fig. 2. Solution polymerization of pyrrole in the presence of a fluorescent dye and woven wool.
woven wool 1 g of pyrrole was added to the solution for polymerization onto the textiles surface. Polymerization in the presence of fluorescent dopants was also trialled however the resultant surface showed only isolated areas of fluorescence. Unlike the mist polymerization method the coating thickness of the solution polymerization method appeared thicker by SEM imaging (Fig. 2). There appeared to be a high level of dendritic PPy formation on the textiles surface, which is common with the solution polymerization technique [17]. The fastness and feel of the coatings of these textile samples was poor with rapid removal of excess PPy from the surface. 3.3. Preparation of the conductive fluorescent textiles by encapsulation The encapsulation of fluorescent dyes in PPy is achieved by the use of surfactants. Rapid stirring of a reaction mixture containing, a fluorescent dye, FeCl3 , pyrrole and a surfactant at low temperatures produced conductive fluorescent polymers. The fluorescent dyes become encapsulated in PPY due to the formation of micelles, which cause the organic dye and pyrrole monomer to cluster together. When the oxidizing agent is added, the fluorescent dyes become encapsulated or trapped in a PPy shell. The solvent has a crucial role in the nano-encapsulation process; some solvents inhibit the formation of micelles and also prevent the adherence of the polymer to the textiles surface. Indeed the fastness of the polymer coating was poor when organic solvents were used. When tetrahydrofuran was used the quality of the polymer coating on textile surface was very poor, whereas polymerization in water produced a homogeneous coating with good adherence to the wool surface. The temperature of the solution in which the encapsulated particles were produced had a large effect on the fluorescence intensity and conductivity of the resultant polymer coatings. Lower temperatures produced grey coatings with low conductivity and high fluorescence intensity after a polymerization time of 5 h, whereas at room temperature black-coated textiles were observed after 30 min, exhibiting high conductivity and low fluorescence intensities. The lower temperature polymerizations also resulted in textiles that had better handling properties due to the reduced deposits of bulk polymerized PPy (Fig. 3).
Fig. 3. Encapsulated rhodamine B in PPy on the surface of wool.
ization method. This is due to the clean textile sample being dyed before polymerization onto the surface was performed. The choice of solvent and dyes used was important, as many organic solvents dissolve the dyes, thereby removing them from the surface of the textiles. The properties of conductivity and fluorescence were inversely related, a coating that was highly conductive exhibited little fluorescence and vice versa. Increasing the thickness of the PPy coating on the textiles surface decreased or even blocked the fluorescence emission. Fig. 4 shows two textile samples, produced by solution polymerization of pyrrole in the presence of rhodamine B. The coated textile sample on the left had a very thin coating of PPy, allowing the fluorescent properties of the dye to be observed, how-
3.4. Fluorescence and conductivity testing of coated textiles Pre-dyeing of the textile samples with a florescent dye before the solution or mist polymerization of pyrrole onto the textiles surface, gave the same results as the standard solution polymer-
Fig. 4. Wool samples with a thin (left) and thick (right) coating of PPy. The textiles were pre-dyed with rhodamine B, coated with PPy by solution polymerization and exposed under a 505-m light and viewed using a green filter.
A. Kaynak et al. / Materials Chemistry and Physics 113 (2009) 480–484
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Fig. 7. Fluorescence intensity measurement by increasing the molar ratios of pyrene to 1 mol. equiv. pyrrole. Fig. 5. Fluorescent response of PPy-coated textiles with increasing rhodamine B concentrations.
ever the conductivity of this sample was very poor, with a surface resistance of around 15 M. On the other hand a thick coating of PPy on a textile sample is shown on the right in Fig. 4, which had no fluorescence response but a much lower surface resistance (0.8 k). Thus the pre-dyeing method has limitations, a compromise between conductivity and fluorescent must be made. Increasing the molar ratio of rhodamine B to pyrrole increased the intensity of the fluorescence response without altering the conductivity. The fluorescent intensity reached a maximum when a 4:1 ratio of rhodamine B to pyrrole was used (Fig. 5). Unfortunately, fluorescence was only observed if the PPy coating was thin enough to allow the excitation and emission process. Nano-encapsulation of fluorescent dyes in PPy gave the best results for the synthesis of fluorescent conductive textiles. A comparison of fluorescent textiles produced by the solution polymerization of pyrrole in the presence of pyrene and the nanoencapsulation of pyrene in PPy can be seen in Fig. 6. The same ratio of pyrrole to pyrene was used for both samples shown in Fig. 6, however the fluorescence response of the nano-encapsulated pyrene samples has a much higher intensity than that emitted from the sample formed from the solution polymerization method. The conductivity of the samples produced by these two methods is comparable (3–5 M). Increasing the molar ratio of pyrrole to pyrene had a considerable effect on the fluorescent intensities of the resultant textile surface, although, as was observed for the solution polymerization
method, this increase had little or no effect on the conductivity. The fluorescent intensities of textile samples produced by the nanoencapsulation method, with increasing molar equivalents of pyrene are shown in Fig. 7, in which the maximum fluorescence intensity is reached when 3 mol. equiv. pyrene were nano-encapsulated on a textiles surface by 1 mol. equiv. PPy. Our previous publications on conducting polymer coatings reported a range of results on the abrasion resistance of various coating methods [17–21]. Effects of coating methods, reaction parameters and substrates have been investigated in detail, including abrasion resistance and electrical properties. We have shown that conductivity of the final coated textile depended on the thickness of the coating. Thinner coatings resulted in a higher surface resistivity of the coated fabric and generally revealed the colour of the fabric substrate, whereas textiles with a thicker coating are generally are highly conductive, black fabric. Solution polymerization methods resulted in thicker coatings with higher conductivity than vapour phase methods. The prolonged reaction times in the solution polymerization resulted in thicker coatings and higher conductivity. The vapour phase method gave rise to thinner but smoother coatings. Martindale abrasion test results showed that all solution and vapour phase PPy-coated textiles had relatively low abrasion resistance and hence there were some loss of electrical and fluorescent properties. With the removal of the polypyrrole coating, the textile became lighter in colour. These samples generally had higher fluorescent intensity, indicating that the fluorescent dye had pen-
Fig. 6. Solution polymerization of pyrrole in the presence of pyrene (left); nano-encapsulation of pyrene in PPy (right).
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etrated deeper into the woven textile. The damage and reduction of conductivity of the textiles tested for abrasion resistance was comparable to those previously tested [17–18]. When wool and polyester fabrics were pretreated with atmospheric plasma glow discharge (APGD) the abrasion resistance of doped PPy coatings on these fabrics were considerably improved [22]. APGD-treated fabrics were tested for surface contact angle, wettability and surface energy change and the results confirmed that APGD had considerably improved the abrasion resistance with the 95% helium/5% nitrogen gas mixture yielding the best results with respect to coating uniformity, abrasion resistance and conductivity [22].
these textiles were not as high as those formed from the encapsulation method, however, they were much greater than coatings produced by the solution polymerization method. The SEM images of the mist polymerization method (Fig. 1) onto textiles show a greater dispersion, thus the coatings of these textiles were more homogeneous. The results of the current investigation are encouraging and further research is currently underway.
4. Conclusion
References
The results of this investigation were promising both in terms of fluorescence properties and conductivity values. Solution polymerization onto textiles and the pre-dyeing of textiles with a fluorescent dye resulted in the synthesis of textiles with moderate conductivity and fluorescent intensity values. The best results for the coatings of textiles were obtained from the encapsulation of fluorescent dyes in PPy. Compared to the solution polymerization method that produced coated textiles with either a high fluorescent intensity or high conductivity, the encapsulation of pyrene in PPy produced highly conductivity and fluorescent textile samples. The encapsulation process allowed highly conductive textiles to be produced possibly due to the fluorescent dopant being encapsulated in a thin pocket of PPy, thus the fluorescent species was close to the surface. A comparison of the pre-dyeing solution method vs. encapsulation method (Fig. 6) showed that both of these textile samples had similar low resistance values however, the fluorescence intensity of the fabric formed by dye encapsulation was far superior to that produced using the pre-dyeing method. The pre-dyed textiles coated using the mist polymerization method produced the second best results. The conductivities of
[1] D. Aldakov, P. Anzenbacher, J. Chem. Commun. (2003) 1394. [2] J. Jang, J.H. Oh, Adv. Mater. 15 (2003) 977. [3] Ger. Gebrauchsmusterschrift, 2004, 34 pp., DE 202004012607, application: DE 2004 202004012607. [4] H. Wang, T. Lin, A. Kaynak, Synth. Met. 151 (2005) 136. [5] H. Kato, S. Takemura, Y. Nakajima, Thin Solid Films 317 (1998) 367. [6] C. Eiras, V. Zucolotto, O.N. Oliveira, D. Goncalves, Synth. Met. 135 (2003) 161. [7] T. Ghosh, B.G. Maiya, M.W. Wong, J. Phys. Chem. A 108 (2004) 11249. [8] T. Ghosh, B.G. Maiya, J. Chem. Sci. (Bangalore, India) 116 (2004) 17. [9] S. Nespurek, P. Toman, J. Sworakowski, J. Lipinski, NATO Sci. Ser. II Math. Phys. Chem. 59 (2002) 37. [10] T. Nagata, T. Matsui, M. Ozaki, K. Yoshino, F. Kajzar, Synth. Met. 119 (2001) 607. [11] T. Matsui, T. Nagata, M. Ozaki, A. Fujii, M. Onoda, M. Teraguchi, T. Masuda, K. Yoshino, Synth. Met. 119 (2001) 599. [12] M.M. Krayushkin, A.L. Rusanov, Polym. Prep. (Am. Chem. Soc., Div. Polym. Chem.) 44 (2003) 367. [13] T. Koshido, T. Kawai, K. Yoshino, Synth. Met. 73 (1995) 257. [14] T. Kawai, T. Koshida, M. Nakazono, K. Yoshino, Chem. Lett. (1993) 697. [15] K. Huang, H. Qiu, M. Wan, Macromolecules 35 (2002) 8653. [16] M.A. De Paolia, G. Casalbore-Miceli, E.M. Girotto, W.A. Gazotti, Electrochim. Acta 44 (1999) 2983. [17] R.C. Foitzik, A. Kaynak, F.M. Pfeffer, Synth. Met. 156 (2006) 637. [18] R.C. Foitzik, A. Kaynak, F.M. Pfeffer, J. Beckman, Synth. Met. 156 (2006) 1333. [19] R.C. Foitzik, A. Kaynak, F.M. Pfeffer, Synth. Met. 157 (2007) 534. [20] R.C. Foitzik, A. Kaynak, J. Beckmann, F. Pfeffer, Synth. Met. 155 (2005) 185. [21] R.C. Foitzik, A. Kaynak, F.M. Pfeffer, Synth. Met. 63 (2007) 4237. [22] S. Garg, C. Hurren, A. Kaynak, Synth. Met. 157 (2007) 41.
Acknowledgements The authors wish to acknowledge Australian Wool Innovation (AWI) for the financial support of the research.
Contents lists available at ScienceDirect
Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys
Fluorescence and conductivity studies on wool Akif Kaynak a,∗ , Richard C. Foitzik b , Frederick M. Pfeffer c a
Deakin University, School of Engineering & Information Technology, Pigdons Road, Geelong, Victoria 3217, Australia Medicinal Chemistry and Drug Action, Monash Institute of Pharmaceutical Sciences, Monash University, 381 Royal Parade, Parkville, Victoria 3052, Australia c Deakin University, School of Life and Environmental Science, Geelong, Victoria 3217, Australia b
a r t i c l e
i n f o
Article history: Received 15 February 2008 Received in revised form 14 July 2008 Accepted 17 July 2008 Keywords: Conducting polymers Conducting textiles Fluorescent polymers
a b s t r a c t An optimized synthetic method for the production of fluorescent conductive wool using pyrene, rhodamine B and fluorescein is reported. The application of fluorescent conductive polymers to wool was studied using solution and mist polymerization techniques. The effects of incorporating fluorescent dopants into the polymerization solution as well as the encapsulation of fluorescent dyes in a polypyrrole (PPy) micelle were also investigated. It was determined on the basis of both conductivity and fluorescence measurements that the encapsulation of dyes in PPy onto the surface of textiles gave the best results. © 2008 Elsevier B.V. All rights reserved.
1. Introduction Apart from sensor technologies, the combining of fluorescence dyes with conductive polymers has received little attention [1]. Indeed the fabrication of fluorescent conductive polymer-coated textiles, to the best of our knowledge has not been attempted. Fluorescent conductive textiles could be valuable in the apparel industry where one application would be the production of security clothing labels that exhibit both fluorescence and conductivity, thus allowing the easy detection of imitation items. Fluorescent dyes were first encapsulated in a polypyrrole (PPy) shell by Jang and Oh [2] The particle size was controlled by the reaction conditions and the work required low temperatures for the synthesis of an emulsion of fluorescent conductive nano-particles [2]. Additional research has been performed (and patented) by WellaTM , where fluorescent nano-particles were used to increase the brightness of hair dyes [3]. Recently, coloured conductive polymers were produced by polymerization in the presence of dyes [4–6]. Research published on coloured conductive polymers, involved covalent attachment of photo-chromic dyes to pyrrole [1,7–8]. Photo-chromic conductive polymers are of interest due to the polymer’s ability to exhibit light switching tendencies [9]. The majority of work on conductive photo-chromic polymers utilizes monomers other than pyrrole, such as polyaniline and poly(3,4-ethylenedioxythiophenes) [9–16].
Herein were report an optimized synthetic method for the production of fluorescent conductive wool. The fluorescent dyes used in this investigation were pyrene, rhodamine B and fluorescein. Several methods were studied including solution polymerization, mist polymerization, the use of fluorescent dopants and finally the encapsulation of fluorescent dyes in a PPy micelle. 2. Experimental 2.1. General experimental All solvents used were AR grade or higher. The pyrrole, iron(III) chloride and fluorescent dyes were purchased from Sigma–Aldrich and had a purity of 98% or greater. All textiles were tested for abrasion resistance using a Martindale abrasion tester. Each specimen was tested for 2000 abrasion cycles with a pressure of 9 kPa. Scanning electron microscope (SEM) images were generated by sputter coating a thin layer of gold (∼7–10 nm) onto the textile surface. Surface resistance was measured by a Fluke multimeter with a probe distance of 10.0 mm. All wool samples used were 40 mm × 40 mm of a woven material. The wool samples were cleaned and degreased prior to use by stirring for 3 h in 1 L of water at 60 ◦ C with decon 90 (2 mL). The pH of the solution was maintained around a value of 1 by the addition of hydrochloric acid (HCl). The wool substrates were then washed with water followed by rinsing with acetonitrile. A fine mist or vapour was sprayed directly onto the textile samples by using a solution of the monomer in ethanol with a commercially available Preval Sprayer® [17–19]. The fluorescence intensities of the textile samples were measured using a Cary Eclipse spectrofluorometer, or visually using a powerful poly-light. The excitation wavelength and emission of rhodamine B on the surface of wool were 356 nm and 600 nm respectively whereas for the pyrene-coated textile surface these excitation and emission values were 336 nm and 395 nm, respectively. 2.2. Preparation of fluorescent conductive textiles by pre-treatment of a textile sample followed by solution polymerization
∗ Corresponding author. E-mail address: [email protected] (A. Kaynak). 0254-0584/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2008.07.098
A fluorescent dyeing solution was prepared by dissolving dye (1 g of pyrene or rhodamine B) in acetone (20 mL). A woven textile was soaked in this solution
A. Kaynak et al. / Materials Chemistry and Physics 113 (2009) 480–484 for 15 min, then removed and dried, to produce a fluorescent textile. The textile was then submerged in water (100 mL) and held by a wire frame to fix its location. Pyrrole (0.50 g, 7.46 mmol) and FeCl3 (1.21 g, 7.46 mmol) were added in quick succession, and the reaction stirred for 3 h. The textile sample was washed with copious amounts of warm water (to remove excess polymer and FeCl3 ). The textile was rinsed with a dilute solution of HCl (pH ∼2) then again washed with water. The coated textile was dried under reduced pressure (∼0.1 mmHg) for 4 h before being tested for fluorescence, surface resistance, and surface abrasion durability.
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polymer and FeCl3 ). The textile was rinsed with a dilute solution of HCl (pH ∼2) then again washed with water. The coated textile was dried under reduced pressure (∼0.1 mmHg) for 4 h before being tested for fluorescence, surface resistance, and surface abrasion durability.
3. Results and discussion 3.1. Conductive fluorescent textiles by pre-dyeing the wool
2.3. Preparation of fluorescent conductive textiles by pre-treatment of a textile sample followed by mist polymerization A fluorescent dyeing solution was prepared by dissolving a dye (1 g of pyrene or rhodamine B) in acetone (20 mL). A woven textile was soaked in this solution for 15 min, then removed and dried, leaving a fluorescent textile. The textile sample was then sprayed with pyrrole in ethanol (1:2, w/w). The textile was slowly heated with a heat gun to induce polymerization. When the sample was completely dried the coating process was repeated two times, starting from the application of FeCl3 . The sample was then washed with copious amounts of warm water until the washings were clear. The sample was then washed in a solution of HCl in water with the pH maintained at ∼2 followed by washing with water. The coated textile was dried under reduced pressure (∼0.1 mmHg) for 4 h before being tested for fluorescence, surface resistance, and surface abrasion durability. 2.4. A one-pot preparation of fluorescent conductive textiles by solution polymerization A textile sample was submerged in water (100 mL) and held by a wire frame to fix its location. Pyrrole (0.50 g, 7.46 mmol) and a fluorescent dye (1–4 mol. equiv. pyrene, rhodamine B or fluorescein) in acetone (10 mL) were added and stirred for 5 min. Iron(III) chloride (1.21 g, 7.46 mmol) was added in one portion and the reaction stirred for 3 h. The resulting textile sample was washed with copious amounts of warm water (to remove excess polymer and FeCl3 ). The textile was rinsed with a dilute solution of HCl (pH ∼2) then washed with water. The coated textile was dried under reduced pressure (∼0.1 mmHg) for 4 h before being tested for fluorescence, surface resistance, and surface abrasion durability. 2.5. Encapsulation of fluorescent dyes in PPy for the preparation of fluorescent conductive textiles A textile sample was submerged in ice-cold water (100 mL) and held by a wire frame to fix its location. Pyrrole (0.50 g, 7.46 mmol), a surfactant (decon 90, 10 mL) and varying amounts of a fluorescent dye in acetone (1 g of pyrene or rhodamine B in 10 mL), were added and stirred for 15 min, where upon iron(III) chloride (1.21 g, 7.46 mmol) was added in one portion and the reaction vigorously stirred at 0 ◦ C for 5 h. The textile sample was washed with copious amounts of warm water (to remove excess polymer and FeCl3 ). The textile was rinsed with a dilute solution of HCl (pH ∼2) and again washed with water. The coated textile was dried under reduced pressure (∼0.1 mmHg) for 4 h before being tested for fluorescence, surface resistance, and surface abrasion durability. 2.6. Preparation of fluorescent conductive textiles using fluorescent dopants A textile sample was submerged in water (100 mL) and held by a wire frame to fix its location. Pyrrole (0.50 g, 7.46 mmol) and 1-pyrenesulfonic acid (1.05 g, 3.73 mmol) were added and stirred for 5 min. Iron(III) chloride (1.21 g, 7.46 mmol) was then added in one portion and the reaction stirred for 3 h. The textile sample was removed then washed with copious amounts of warm water (to remove excess
The first method employed for the production of fluorescent conductive textiles involved pre-dyeing the samples with fluorescent dyes, followed by the polymerization of pyrrole onto the textiles surface. The samples were pre-dyed by soaking in a solution containing fluorescent dyes. The dyes that worked efficiently for this method were pyrene and rhodamine B. The textile samples that were pre-dyed with a fluorescent dye were coated with PPy by either the solution or mist polymerization method. The solution polymerization of the pre-dyed textiles was done in water to avoid organic solvent leaching the dye out of the textiles. Mist polymerization was also employed to coat the predyed textiles with PPy. Both the solution and mist polymerization methods produced even polymer coatings on the textiles surface; however, fluorescent textiles coated by the mist polymerization method retained greater fluorescence intensity. Investigation utilizing SEM showed little change in the surface appearance of wool. Coating the textile samples by mist polymerization showed little dendritic PPy formation (Fig. 1). This was in line with our previous findings in relation to PPy coatings [17]. The coated textile surfaces were also investigated after administrating the sample to abrasion testing, these results appeared visually to have little or no change in the polymer coating thickness, thus it was concluded that the polymer was strongly attached to the wool surface (good fastness), again in line with previous findings [17]. 3.2. Preparation of the conductive fluorescent textiles by solution polymerization Fluorescent conductive textiles were also produced by modifications to the solution polymerization method. Addition of a fluorescent dye to a reaction mixture of FeCl3 and textile sample was followed by the addition of pyrrole. Once the pyrrole was added, polymerization occurred immediately on the textile surface. It was originally postulated that this method would have the same effect as the solution polymerization of a pre-dyed sample. Increasing the concentrations of the fluorescent dyes increased the fluorescence intensities of the resultant textile samples. It was found that the optimum fluorescence intensity was produced when a dye to pyrrole ratio of 4:1 was used. In general for every 2 g of
Fig. 1. Mist polymerization of pyrrole onto fluorescent pre-dyed woven wool.
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Fig. 2. Solution polymerization of pyrrole in the presence of a fluorescent dye and woven wool.
woven wool 1 g of pyrrole was added to the solution for polymerization onto the textiles surface. Polymerization in the presence of fluorescent dopants was also trialled however the resultant surface showed only isolated areas of fluorescence. Unlike the mist polymerization method the coating thickness of the solution polymerization method appeared thicker by SEM imaging (Fig. 2). There appeared to be a high level of dendritic PPy formation on the textiles surface, which is common with the solution polymerization technique [17]. The fastness and feel of the coatings of these textile samples was poor with rapid removal of excess PPy from the surface. 3.3. Preparation of the conductive fluorescent textiles by encapsulation The encapsulation of fluorescent dyes in PPy is achieved by the use of surfactants. Rapid stirring of a reaction mixture containing, a fluorescent dye, FeCl3 , pyrrole and a surfactant at low temperatures produced conductive fluorescent polymers. The fluorescent dyes become encapsulated in PPY due to the formation of micelles, which cause the organic dye and pyrrole monomer to cluster together. When the oxidizing agent is added, the fluorescent dyes become encapsulated or trapped in a PPy shell. The solvent has a crucial role in the nano-encapsulation process; some solvents inhibit the formation of micelles and also prevent the adherence of the polymer to the textiles surface. Indeed the fastness of the polymer coating was poor when organic solvents were used. When tetrahydrofuran was used the quality of the polymer coating on textile surface was very poor, whereas polymerization in water produced a homogeneous coating with good adherence to the wool surface. The temperature of the solution in which the encapsulated particles were produced had a large effect on the fluorescence intensity and conductivity of the resultant polymer coatings. Lower temperatures produced grey coatings with low conductivity and high fluorescence intensity after a polymerization time of 5 h, whereas at room temperature black-coated textiles were observed after 30 min, exhibiting high conductivity and low fluorescence intensities. The lower temperature polymerizations also resulted in textiles that had better handling properties due to the reduced deposits of bulk polymerized PPy (Fig. 3).
Fig. 3. Encapsulated rhodamine B in PPy on the surface of wool.
ization method. This is due to the clean textile sample being dyed before polymerization onto the surface was performed. The choice of solvent and dyes used was important, as many organic solvents dissolve the dyes, thereby removing them from the surface of the textiles. The properties of conductivity and fluorescence were inversely related, a coating that was highly conductive exhibited little fluorescence and vice versa. Increasing the thickness of the PPy coating on the textiles surface decreased or even blocked the fluorescence emission. Fig. 4 shows two textile samples, produced by solution polymerization of pyrrole in the presence of rhodamine B. The coated textile sample on the left had a very thin coating of PPy, allowing the fluorescent properties of the dye to be observed, how-
3.4. Fluorescence and conductivity testing of coated textiles Pre-dyeing of the textile samples with a florescent dye before the solution or mist polymerization of pyrrole onto the textiles surface, gave the same results as the standard solution polymer-
Fig. 4. Wool samples with a thin (left) and thick (right) coating of PPy. The textiles were pre-dyed with rhodamine B, coated with PPy by solution polymerization and exposed under a 505-m light and viewed using a green filter.
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Fig. 7. Fluorescence intensity measurement by increasing the molar ratios of pyrene to 1 mol. equiv. pyrrole. Fig. 5. Fluorescent response of PPy-coated textiles with increasing rhodamine B concentrations.
ever the conductivity of this sample was very poor, with a surface resistance of around 15 M. On the other hand a thick coating of PPy on a textile sample is shown on the right in Fig. 4, which had no fluorescence response but a much lower surface resistance (0.8 k). Thus the pre-dyeing method has limitations, a compromise between conductivity and fluorescent must be made. Increasing the molar ratio of rhodamine B to pyrrole increased the intensity of the fluorescence response without altering the conductivity. The fluorescent intensity reached a maximum when a 4:1 ratio of rhodamine B to pyrrole was used (Fig. 5). Unfortunately, fluorescence was only observed if the PPy coating was thin enough to allow the excitation and emission process. Nano-encapsulation of fluorescent dyes in PPy gave the best results for the synthesis of fluorescent conductive textiles. A comparison of fluorescent textiles produced by the solution polymerization of pyrrole in the presence of pyrene and the nanoencapsulation of pyrene in PPy can be seen in Fig. 6. The same ratio of pyrrole to pyrene was used for both samples shown in Fig. 6, however the fluorescence response of the nano-encapsulated pyrene samples has a much higher intensity than that emitted from the sample formed from the solution polymerization method. The conductivity of the samples produced by these two methods is comparable (3–5 M). Increasing the molar ratio of pyrrole to pyrene had a considerable effect on the fluorescent intensities of the resultant textile surface, although, as was observed for the solution polymerization
method, this increase had little or no effect on the conductivity. The fluorescent intensities of textile samples produced by the nanoencapsulation method, with increasing molar equivalents of pyrene are shown in Fig. 7, in which the maximum fluorescence intensity is reached when 3 mol. equiv. pyrene were nano-encapsulated on a textiles surface by 1 mol. equiv. PPy. Our previous publications on conducting polymer coatings reported a range of results on the abrasion resistance of various coating methods [17–21]. Effects of coating methods, reaction parameters and substrates have been investigated in detail, including abrasion resistance and electrical properties. We have shown that conductivity of the final coated textile depended on the thickness of the coating. Thinner coatings resulted in a higher surface resistivity of the coated fabric and generally revealed the colour of the fabric substrate, whereas textiles with a thicker coating are generally are highly conductive, black fabric. Solution polymerization methods resulted in thicker coatings with higher conductivity than vapour phase methods. The prolonged reaction times in the solution polymerization resulted in thicker coatings and higher conductivity. The vapour phase method gave rise to thinner but smoother coatings. Martindale abrasion test results showed that all solution and vapour phase PPy-coated textiles had relatively low abrasion resistance and hence there were some loss of electrical and fluorescent properties. With the removal of the polypyrrole coating, the textile became lighter in colour. These samples generally had higher fluorescent intensity, indicating that the fluorescent dye had pen-
Fig. 6. Solution polymerization of pyrrole in the presence of pyrene (left); nano-encapsulation of pyrene in PPy (right).
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etrated deeper into the woven textile. The damage and reduction of conductivity of the textiles tested for abrasion resistance was comparable to those previously tested [17–18]. When wool and polyester fabrics were pretreated with atmospheric plasma glow discharge (APGD) the abrasion resistance of doped PPy coatings on these fabrics were considerably improved [22]. APGD-treated fabrics were tested for surface contact angle, wettability and surface energy change and the results confirmed that APGD had considerably improved the abrasion resistance with the 95% helium/5% nitrogen gas mixture yielding the best results with respect to coating uniformity, abrasion resistance and conductivity [22].
these textiles were not as high as those formed from the encapsulation method, however, they were much greater than coatings produced by the solution polymerization method. The SEM images of the mist polymerization method (Fig. 1) onto textiles show a greater dispersion, thus the coatings of these textiles were more homogeneous. The results of the current investigation are encouraging and further research is currently underway.
4. Conclusion
References
The results of this investigation were promising both in terms of fluorescence properties and conductivity values. Solution polymerization onto textiles and the pre-dyeing of textiles with a fluorescent dye resulted in the synthesis of textiles with moderate conductivity and fluorescent intensity values. The best results for the coatings of textiles were obtained from the encapsulation of fluorescent dyes in PPy. Compared to the solution polymerization method that produced coated textiles with either a high fluorescent intensity or high conductivity, the encapsulation of pyrene in PPy produced highly conductivity and fluorescent textile samples. The encapsulation process allowed highly conductive textiles to be produced possibly due to the fluorescent dopant being encapsulated in a thin pocket of PPy, thus the fluorescent species was close to the surface. A comparison of the pre-dyeing solution method vs. encapsulation method (Fig. 6) showed that both of these textile samples had similar low resistance values however, the fluorescence intensity of the fabric formed by dye encapsulation was far superior to that produced using the pre-dyeing method. The pre-dyed textiles coated using the mist polymerization method produced the second best results. The conductivities of
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Acknowledgements The authors wish to acknowledge Australian Wool Innovation (AWI) for the financial support of the research.