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polyaniline nanocomposite particles by oxidative polymerization and their electrorheology
CLAY-03308; No of Pages 8 Applied Clay Science xxx (2015) xxx–xxx
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Research Paper
Synthesized palygorskite/polyaniline nanocomposite particles by oxidative polymerization and their electrorheology Hyun Sik Chae, Wen Ling Zhang, Shang Hao Piao, Hyoung Jin Choi ⁎ Department of Polymer Science and Engineering, Inha University, Incheon 402-751, Korea
a r t i c l e
i n f o
Article history: Received 4 July 2014 Received in revised form 18 January 2015 Accepted 21 January 2015 Available online xxxx Keywords: Electrorheological fluid Polyaniline Palygorskite Nanocomposite
a b s t r a c t Palygorskite (Pal) clay coated with semiconducting polyaniline (PANI) nanocomposite particles was prepared by oxidative polymerization using aniline monomer in the presence of Pal. The morphological characteristics of the synthesized Pal/PANI composite particles were examined by both field emission scanning electron microscopy and transmission electron microscopy. A rotational rheometer was also used to examine the rheological behavior of the Pal/PANI composite-based electrorheological (ER) fluid when the nanocomposite particles were dispersed in silicone oil. From its flow curve of shear stress vs. shear rate investigated under an applied electric field, the typical ER behavior of the Pal/PANI-based ER fluid was observed. In addition, polarizability and relaxation time of the ER system obtained from the dielectric spectra were well correlated with its ER performance. © 2015 Elsevier B.V. All rights reserved.
1. Introduction Inorganic–organic nanocomposites have attracted considerable attention for their enhanced mechanical, electrical, optical, and other functional properties (Yilmaz et al., 2007; Kim & Kim, 2008; Meheust et al., 2011; Yin et al., 2011). In particular, clay/polymer nanocomposite particles often exhibit excellent electrical properties when fabricated appropriately (Yilmaz et al., 2007; Meheust et al., 2011). These materials have been adopted as electrorheological (ER) materials (Cheng et al., 2008; Kim & Kim, 2008; Stenicka et al., 2008; Liu & Choi, 2012), in which an insulating medium, such as silicone oil or mineral oil, containing ER particles underwent a structural phase change from a liquid-like to a solid-like form under an applied electric field. A typical type of ER fluid was a colloidal suspension of polarizable solid dielectric or conducting particles dispersed in an insulating fluid, which often exhibits Newtonian fluid behavior in the absence of an applied electric field (Trlica et al., 2000). On the other hand, when an electric field was applied to ER fluids, the dispersed particles became polarized immediately and align along the direction of the electric field, resulting in an increased shear viscosity. Therefore, the rheological behavior of the ER fluid can usually be explained using the Bingham fluid model with the yield stress (Zhao & Yin, 2002; Hiamtup et al., 2006). Among the various polarizable particles for anhydrous ER materials, semiconducting polymers including polyaniline (PANI) (Adachi et al., 2004; Pavlinek et al., 2005; Hiamtup et al., 2006; Sung et al., 2006), Nsubstituted copolyaniline (Cho et al., 1998), sulfonated poly(styreneco-divinylbenzene) (Ikazaki et al., 1998), PANI coated polystyrene ⁎ Corresponding author. E-mail address: [email protected] (H.J. Choi).
particles (Kuramoto et al., 1995), poly(aniline-co-o-ethoxyaniline) (Choi et al., 1999), and poly(acene quinone) radicals (Cho et al., 2005) have been reported. Recently, polymer-inorganic nanocomposites (Yoshimoto, 2005; Maity & Biswas, 2006) and conducting polymer/ mesoporous silica hybrids (Cheng et al., 2006) were adopted as drybased ER materials in addition to various inorganic materials. Among these, the PANI has attracted considerable attention because of its low cost, unique oxidation–reduction chemistry, environmental stability, and excellent optical and electrical properties (Wei & Wan, 2002). The colloidal synthesis of PANI, such as microspheres and nanofibers, can overcome its poor processability. Moreover, assembly structures of these colloids will further improve its properties and expand its applications (Liang et al., 2002; Nandan et al., 2007). PANI and various electroresponsive materials, such as inorganics with high dielectric properties, organic or polymeric semiconducting materials and their composites have been used as ER particles (Yin et al., 2009). Palygorskite (Pal) is a Mg-rich phyllosilicate with fibrous morphological characteristics, and it can be approximated by the formula, yMg5Si8O20(OH)2·(1 − y)[xMg2Fe2·(1 − x)Mg2Al2] Si8O20(OH)2 (Chryssikos et al., 2009). Pal consists of a three-dimensional network of densely packed rods with diameters less than 100 nm and lengths between hundreds of nanometers and several micrometers for each single rod (Pan & Chen, 2007). Pal has a large specific surface area, a moderate cation exchange capacity, and reactive OH-groups groups on its surface that can adsorb and trap metal ions from wastewater (Chen and Wang, 2007). To reduce the cost and improve the comprehensive waterabsorbing properties of this material, it is important to fabricate a composite that consists of a polymer and Pal micro-powder (Cui et al., 2012). To enhance the adsorption capacity and selectivity of Pal, considerable attention has been paid to special treatments or modifications
http://dx.doi.org/10.1016/j.clay.2015.01.018 0169-1317/© 2015 Elsevier B.V. All rights reserved.
Please cite this article as: Chae, H.S., et al., Synthesized palygorskite/polyaniline nanocomposite particles by oxidative polymerization and their electrorheology, Appl. Clay Sci. (2015), http://dx.doi.org/10.1016/j.clay.2015.01.018
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Aniline (5.58 g, 93.13 g/mol, DC chemical, Korea) as a monomer and 200 mL of sulfuric acid (2 mol/l) were used. Palygorskite (7 g, 411.35 g/mol, Fluorochem, UK) was adopted for the nanocomposite preparation. 0.4 M ammonium peroxodisulfate (APS, (NH4)2 S2O 8, Daejung, Korea) solution was used as an oxidizing agent.
to 90° with Cu Kα (λ = 1.5418 Å) incident radiation at a step size of 0.02°. Scan speed, counting time and slit width of XRD were 0.067°/s, 0.3 s, and 0.8°, respectively. The density of the synthesized composite particles was measured using a gas pycnometer (AccuPyc 1330, Micromeritics Instruments Co., USA). The electrical conductivity was measured by a standard four-pin probe technique using a resistivity meter (Mitsubishi Loresta-GP and Hiresta-UP). An optical microscope (OM, Olympus BX-51, USA) equipped with a DC voltage generator was used to observe the formed chain-like structure of the ER fluid. To characterize the typical ER properties of the ATP/PANI nanocomposite particles (10 vol%) dispersed in silicone oil (ShinEtsu, density = 0.96 g/cm3) with a kinematic viscosity of 30 cS from the controlled shear rate (CSR) measurements, in which the range of shear rate ranged from 0.01 to 1,000 [1/s] on a log–log scale, the rheological properties were measured using a rotational rheometer (Physica MCR 300, Stuttgart, Germany) equipped with a high voltage generator under different electric strengths. The measurements were at least in duplicate and the experimental error range was within 3%. The dielectric spectra of the ER fluid were also measured using an LCR meter (HP 4284A Precision) with a liquid test fixture (HP 16452A) for liquids to examine their interfacial polarization mechanism. The frequency of the AC electric fields was varied from 20 Hz to 1 MHz.
2.2. Preparation of Pal/PANI composite particle
3. Results and discussion
The Pal/PANI composite particles were synthesized by an oxidative polymerization process and used without a post-treatment step except for the doping process. To initiate the polymerization of aniline, sulfuric acid was added drop-wise. At the surface of Pal, the sulfuric acidmodified aniline monomer was polymerized with the aid of APS. The APS solution was slowly added drop-wise into the mixture with vigorous stirring over a period 6 h at room temperature. The obtained Pal/PANI composite particles were centrifuged with deionized water to remove the excess initiator, monomer, and free Pal templates and then dried in a vacuum oven at 60 °C for 24 h. The electrical conductivity of the Pal/PANI composite particles was about 10− 3 S/cm measured using a resistivity meter. This value was too high to prepare the Pal/PANI ER fluid. If the sample had too high electrical conductivity, an electric short would damages the rheometer device. The electrical conductivity of the composite particle was then controlled by the de-doping process where the pH was increased to 9.0 by adding a 1 M NaOH solution to an aqueous Pal/PANI solution, and then dried the sample in an oven for 24 h (Strounina et al., 2003; Fang et al., 2007, 2011). The obtained Pal/PANI particles were sieved (mesh size of 38 μm) to remove agglomerated Pal/PANI composite particles for better dispersion of the composite particles as for the ER fluid. As a result, the electrical conductivity of the Pal/PANI composite particles was changed from 10−3 S/cm to 10−8 S/cm. The 10−8 S/cm was in the appropriate range of the electrical conductivity in this ER test.
The morphologies of both Pal/PANI and Pal were examined by TEM to characterize the surface morphology of the pristine Pal (Fig. 1(a)) and Pal/PANI composite particles (Fig. 1(b)). The surface of Pal was fairly smooth (Fig. 1(a)). Pal has a highly fibrous morphology, forming bundles. The length of each fiber varied from the submicrometer to the micrometer range with an average diameter of approximately 20 nm. In contrast, the Pal/PANI composite particles exhibited a much rougher surface due to the wrapping of PANI (Fig. 1(b)). This means that the polymerization of aniline via a chemical oxidation method onto the Pal template have successfully changed the outside surface. The chemical interaction between Pal and PANI was confirmed by the FT-IR spectra of Pal/PANI, PANI, and Pal (Fig. 2), which showed marked variations of the absorption bands after modification. Although the Pal/PANI bands had a slight shift owing to the amorphous nature of PANI synthesized by this polymerization, Pal/PANI bands included both their individual characteristic bands of PANI and Pal. In the spectrum of Pal, the bands at 3620 cm−1, 3550 cm−1, and 3420 cm−1 were assigned to the stretching vibrations of the Al-OH unit, Mg-OH unit, and stretching vibration of zeolitic water, respectively (Fan et al., 2009; Yin and Zhao, 2011). For Pal/PANI, the wide absorption band at approximately 3446 cm−1 was assigned to the stretching vibration of − NH2 and −OH groups (Wang & Wang, 2010), and the Al-OH and Mg-OH vibrations were still visible as minor inflexions in the Pal/PANi spectrum, indicating that PANI had coated Pal. Pal exhibited a band at 1650 cm−1, which was assigned to the bending vibration of zeolitic water and absorbed water molecules (Li et al., 2011). This band was reduced in the Pal/PANI spectrum, suggesting that the zeolitic water and absorbed water in Pal decreased. The characteristic absorption bands of Pal were observed at 1025 cm−1 for Si-O-Si, and the band at 980 cm−1 corresponding to the stretching vibration of Al–O–Si (Cui et al., 2012). The new bands of Pal/PANI were representative of the C = C stretching vibrations of quinine and benzene rings at 1560 cm−1 and 1480 cm−1, respectively. The spectrum of Pal/PANI also showed C-O stretching vibrations at 1300 cm−1, C-N stretching vibrations at 1235 cm−1 and C-H out of plane bending vibrations at 800 cm−1, respectively. These results confirm that the Pal surface had been coated successfully with PANI. The EDS data of Pal/PANI nanocomposite particles are indicated in Fig. 3. This graph shows that the Pal/PANI is composed of C, N, O, Mg, Al, and Si. The synthesized Pal/PANI particle had weight and atomic percentage of C (10.82%, 15.66%), N (9.83%, 12.21%), O (48.60%,
such as heat treatment, acid treatment (Chen et al., 2007), or graft reactions. (Liu et al., 2007; Chen and Wang, 2009; Shao et al., 2010) Recently, polymers could be grafted successfully onto the surfaces of Pal to achieve the enhanced removal of heavy metals from aqueous solutions (Chen et al., 2009; Liu and Wang, 2007; Wang et al., 2009). In this study, Pal/PANI composite particles were synthesized by chemical oxidative polymerization. The electrical conductivity of PANI, which is still not high enough for many engineering applications, actually becomes a positive factor for an ER study. An ER fluid was prepared by dispersing the Pal/PANI composite particles in silicone oil, and their ER responses were then investigated using a rotational rheometer under various electric field strengths. 2. Experimental 2.1. Materials
2.3. Characterization The particle size and surface morphology were observed by transmission electron microscope (TEM) (CM 200, Philips). To prepare the TEM sample, a grid coated carbon was used. The accelerating voltage of TEM used was 120 kV. The molecular structure of the Pal/PANI composites was detected by Fourier transform infrared (FT-IR, Perkin Elmer System 2000) spectroscopy using KBr pellets in the spectral range from 4000 to 400 cm−1, with a spectral resolution of 4 cm−1 and the number of scans of 16. To prepare the FT-IR sample, the sample concentration ratio was 1: 100 (wt%). The elemental analysis of the sample was obtained by scanning electron microscopy (SEM) (S-4300, Hitachi, Japan) equipped with an energy-dispersive X-ray spectroscopy (EDS) (Horiba, Japan) accessory. The accelerating voltage of EDS used was 15 kV. Both Pal/PANI and Pal were further characterized by a powder X-ray diffraction (XRD, DMAX-2500, Rigaku) ranging from at 2θ = 5°
Please cite this article as: Chae, H.S., et al., Synthesized palygorskite/polyaniline nanocomposite particles by oxidative polymerization and their electrorheology, Appl. Clay Sci. (2015), http://dx.doi.org/10.1016/j.clay.2015.01.018
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Fig. 1. TEM images of (a) Pal and (b) Pal/PANI composite particles, respectively.
52.82%), Mg (1.78%, 1.27%), Al (3.97%, 2.56%), and Si (25%, 15.48%). Also, based on the EDS data, it was confirmed that C and N come from only attached PANI compared to the fact that the Pal is composed of neither C nor N.
Fig. 2. FT-IR spectra of Pal/PANI composites, PANI, and Pal.
The XRD patterns of Pal, PANI, and synthesized Pal/PANI nanocomposite particles are shown in Fig. 4. The crystalline PANI possessed reflections at 2θ = 18.4° and 25.7°. The reflection centered at 2θ = 18.4° was ascribed to the periodicity in the direction parallel to the polymer chain, while the reflection at 2θ = 18.4° was due to the periodicity in the direction perpendicular to the polymer chain (Jin et al., 2010). For Pal, the typical reflections at 2θ = 8.3°, 13.6°, 19.7°, and 26.6° were observed, which were in good agreement with the reflections of the (1 1 0), (2 0 0), (0 4 0), and (4 0 0) planes of Pal, respectively (Wang et al., 2011). A similar set of characteristic reflections was also observed for the Pal/PANI, which suggests that the crystal structure of Pal is well maintained under polymerization reaction. The PANI reflection in Pal/PANI is almost invisible because Pal/PANI has a relative thin layer of amorphous PANI synthesized by this polymerization reaction (Wang et al., 2011). The densities of Pal (2.27 g/cm3), PANI (1.30 g/cm3), and Pal/PANI composite particles (1.77 g/cm3) were also measured using a gas pycnometer. The density mismatch between the Pal/PANI composite particles and the continuous silicone oil with a kinematic viscosity of 30 cS (0.96 g/cm3) was reduced significantly compared to pure Pal. Therefore, the suspension stability of the ER fluid including the dispersion stability and sedimentation stability will be improved by using Pal/PANI. The ER fluids consist of semiconducting or polarizable materials dispersed in a non-conducting liquid. A microstructural transition of the ER fluid from a fluid-like to solid-like can be obtained under an electric field. In this study, an ER fluid was prepared by dispersing Pal/PANI nanocomposite particles (10 vol.% particle concentration) in 30 cS silicone oil. The microstructural changes in the Pal/PANI ER fluid were observed by optical microscopy under an applied electric field with a DC high voltage source (Fig. 5) (Cho et al., 2003). The gap between the two parallel electrodes was fixed to 150 μm. In the absence of an electric field, the synthesized particles were dispersed randomly in silicone oil, showing liquid-like state characteristics (Fig. 5(a)). On the other hand, when an electric field is present, Pal/PANI nanoparticles begin to move immediately and form a chain structure with the adjacent particles (Fig. 5(b)). Finally, the dispersed particles formed a chain structure that aligned along the applied electric field direction, in which the anisotropic rod-like shape of the ATP might enhance the chain formation. The ER fluid behavior was similar to that of pseudo-Newtonian fluid behavior without an external electric field, in which the shear stress is proportional to the shear rate with a slope of approximately 0.8 in a log–log plot (Cho et al., 2003). On the other hand, under an applied external electric field, the ER fluid exhibited plastic behavior with increased shear stress. In particular, when the electric field was changed from 0 to 0.5 kV/mm, the enhancement in shear stress was extremely distinct as a result of the formation of chain-like particle structures, as shown in the optical microscope images in Fig. 5(b), which can be called Bingham-like behavior (Cho et al., 2003).
Please cite this article as: Chae, H.S., et al., Synthesized palygorskite/polyaniline nanocomposite particles by oxidative polymerization and their electrorheology, Appl. Clay Sci. (2015), http://dx.doi.org/10.1016/j.clay.2015.01.018
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Fig. 3. EDS data of palygorskite/polyaniline composite particles.
Interestingly, the synthesized particle-based ER fluid indicated a slightly decreasing trend in the shear stress in the low shear rate region, and an increasing shear stress with increasing shear rate, which can be explained by the following mechanism. The aligned chain structures began to break with hydrodynamic shear deformation, and broken structures tended to reform the chains by the applied electric field, depending on the magnitude of the applied shear and particle–particle
interaction in the fibrils. In the low shear rate region, the electrostatic interactions were dominant (Cho et al., 2003, 2005). That is, the aligned particles reduced the shear deformation and the broken structure tended to reform the chain-like structure repeatedly. Therefore, the shear stress generated decreased with increasing shear rate. In the high shear rate region, where the hydrodynamic interaction was dominant, the broken chain particles had no to time to reform and the ER
(a)
(b)
300 V
50 μm
Fig. 4. XRD diffraction patterns for pristine (a) PANI, (b) Pal, and (c) Pal/PANI.
Fig. 5. Optical microscope the ER fluid based on Pal/PANI (a) without an electric field and (b) with an electric field.
Please cite this article as: Chae, H.S., et al., Synthesized palygorskite/polyaniline nanocomposite particles by oxidative polymerization and their electrorheology, Appl. Clay Sci. (2015), http://dx.doi.org/10.1016/j.clay.2015.01.018
H.S. Chae et al. / Applied Clay Science xxx (2015) xxx–xxx
suspension behaved like a pseudo-Newtonian fluid (Cho et al., 2003). Therefore, the Bingham model and Cho–Choi–Jhon (CCJ) model were used to describe the shear stress behavior and yield stress (Cho et al., 2005). The Bingham model is widely used to explain the shear stress behavior. The Bingham model, shown in Eq. (1), has two parameters originating from the Newtonian viscosity (η0) and yield stress (τ0) and is adopted widely as a model for not only ER suspensions but also conventional suspension systems. τ ¼ τ0 þ η0 γ̇ γ̇ ¼ 0
ðτ ≥τ0 Þ
ðτbτ0 Þ
ð1Þ
where τ is the shear stress, τ0 is the yield stress, which is a function of the electric field, γ̇ is the shear rate, and η0 is the shear viscosity. The Bingham model has two flow regimes: a rigid pre-yield behavior for shear stresses less than the field-dependent yield stress and Newtonian flow characteristics beyond the yield stress τ0 (post-yield region). The dotted lines in Fig. 6(a) were from Eq. (1), and the Bingham model, however, did not fit the flow curve of Pal/PANI ER fluid. Therefore, a recently reported CCJ model shown in Eq. (2) was used to re-plot the shear stress behaviors by fitting the curves using six parameters (Cho et al., 2005). τ0 1 τ¼ þ η∞ 1 þ 1 þ ðt1 γ̇ Þα ðt2 γ̇ Þβ
! γ̇
ð2Þ
(a)
where τ0 is the static yield stress, which is defined as the extrapolated stress from the low shear rate region, and η∞ is the viscosity at the infinite shear rate that is interpreted as the viscosity without an external electric field. The exponents α and β are related to the decrease and increase in shear stress; β has the range 0 b β ≤ 1, due to dτ ≥0. The γ̇ parameters t1 and t2 are time constants. Fig. 6(a) showed the fitting of the two model equations for the 10 vol.% Pal/PANI composite particlebased ER fluid. Table 1 lists the optimal fitting parameters used for these two models. The CCJ model, which has six parameters, described the flow curves better than the Bingham model through the entire shear rate range (Cho et al., 2003). Fig. 6(b) shows the shear viscosity as a function of the shear rate. The shear thinning behavior was confirmed not only in each electric field strength but also in the absence of electric field (Zhu et al., 2010). In general, the non-Newtonian behavior in the absence of an electric field is attributed to the poor dispersed state in the high concentration ER fluid. In Fig. 7, the dynamic yield stress was plotted as a function of the electric field strength in log–log scale curves. In general, the dependence of the dynamic yield stress on the electric field strength can be presented by a power law relationship: m
τ∝E
(b)
ð3Þ
The exponent m can be obtained from the yield stress over a broad electric field range. The dependence of the dynamic yield stress was found to be expressed as τ ∝ E2, which is a polarization model of the ER mechanism (Fang et al., 2011). The polarizability of Pal/PANI ER fluids is known to be depended on their dielectric characteristic (Fig. 8). The dielectric spectra (Fig. 8(a)) and the Cole–Cole plot which is useful for examining the relationship between dielectric and ER properties (Fig. 8(b)) were obtained, where the permittivity (ε′) and loss factor (ε″) were a functions of the frequency (from 20 Hz to 1 MHz). Generally, this can be described using the following equation (Cho et al., 2003):
Slope ~ 0.8
5
0
ε ¼ ε þ ε} ¼ ε∞ þ
ε0 −ε∞ 1 þ ðiωλÞ1−α
ð0 ≤ αb1Þ
ð4Þ
where ε* is the complex dielectric constant, ε0 is the dielectric constant at 0, and ε∞ is the dielectric constant at infinite frequency. Δε = ε0 − ε∞ is the achievable polarizability in ER fluids, which is related to the electrostatic interactions between particles. The ε0 and ε∞ obtained were 3.82 and 1.78, respectively, so that Δε was 2.04 for the Pal/PANI-based ER fluid. λ (λ = 1 / 2πfc; fc, the critical frequency) is the relaxation time for the interfacial polarization of ER fluids at the frequency of which the dielectric loss reaches the maximum value (Kim et al., 2013). The relaxation time is also related to the yield stress and stress enhancement under an applied electric field strength. Here, the relaxation time of Pal/PANIbased ER fluid is 0.21 ms. This is in the range of 102–105 Hz, which is Table 1 Fitting parameters of Bingham and CCJ model equations to the flow curves of ER fluid based on Pal/PANI (10 vol.% particle concentration). Electric filed strength (kV/mm) Parameters Model Bingham CCJ
Fig. 6. Shear stress (a) and viscosity (b) curves vs shear rate for Pal/PANI-based ER fluids (10 vol.%) under various electric field strengths, the dashed lines were fitted via a conventional Bingham model; the solid lines were fitted via a suggested CCJ model.
τ0 η0 τ0 t1 α η∞ t2 β
0.5
1
1.5
2
2.5
3
18 0.087 18 0.01 0.3 0.087 0.8 0.4
60 0.115 60 0.001 0.05 0.115 0.9 0.9
111 0.164 111 0.10 0.4 0.164 0.1 0.3
176 0.227 176 0.04 0.3 0.227 0.25 0.9
252 0.281 252 0.03 0.5 0.281 0.8 0.8
512 0.358 512 0.18 0.41 0.358 0.9 0.66
Please cite this article as: Chae, H.S., et al., Synthesized palygorskite/polyaniline nanocomposite particles by oxidative polymerization and their electrorheology, Appl. Clay Sci. (2015), http://dx.doi.org/10.1016/j.clay.2015.01.018
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Fig. 7. Dynamic yield stress as a function of electric field of the Pal/PANI composite particle-based ER fluid. The solid line is fitted by the equation, τy ∝ E2.
needed for a good ER fluid (Stenicka et al., 2009; Yin et al., 2011). The exponent (1 − α) determines the broadness of the relaxation time distribution. When α is zero, Eq. (4) reduces to Debye's well-known single relaxation time model (Kim et al., 2007; Zhang et al., 2012). The α of Pal/PANI particle-based ER fluid was 0.711. Fig. 9 To examine the stability and sensitivity of the Pal/PANI nanocomposite particle-based ER fluid, the shear viscosity was measured at a
Fig. 9. Shear stress of ER fluid (10 vol.%) based on Pal/PANI composite particles in the electric field with a square voltage pulse (t = 20 s) at a fixed shear rate of 1 s−1.
fixed shear rate of 1 [1/s] with a square voltage pulse (t = 20 s) (Fig. 9). When the external electric field was applied (turn on), the shear stress increased suddenly, whereas the electric field (turn off) sharply declined to a zero field level when the applied electric field was removed. Therefore, the transformation of the shear stress can change easily from the off-state to the on-state. This well-controlled ER characteristic was sensitive and reversible. Applications to controlled mechanical systems may be possible by taking advantage of the ER phenomenon (Tan et al., 2007). The dynamic oscillation test was conducted to examine the viscoelastic properties of an ER fluid. Before the dynamic oscillation test, an amplitude sweep test was conducted at various strains from 10−3% to 102% to determine the linear viscoelastic region (γLVE) at a fixed angular frequency of 6.28 rad/s (Fig. 10(a)). At the low strain region, the storage modulus, G′ (energy stored in the sample during the oscillatory shear process), is always higher than that of the loss modulus, G″ (energy dissipated during the oscillatory shear process). Between 10−3% and 10−1%, the G′ and G″ values are independent of strain in the linear viscoelastic region, and the γLVE was chosen as 0.005% for the frequency sweep test (Hwang et al., 2012). At γLVE, the elastic response was dominant (G′ N G″) and the structures generated from the electric fields were unchanged. When the applied strain exceeded γLVE, both G′ and G″ decreased sharply due to the chain breaking. Moreover, G″ became larger than G′, suggesting that the structures, which were formed by an electric field, began to break down beyond a certain degree of deformation with increasing strain (Cho et al., 2005). The selected mean γLVE value was applied to the frequency sweep measurements. G′ and G″ were measured over an angular frequency, ranging from 1 to 100 [rad/s] with a strain of 0.005% at γLVE (Fig. 10(b)). The G′ and G″ values increased with increasing electric field. The G′ values representing an elastic response were higher than that of G″ representing viscous property, indicating the dominance of solid-like behavior over viscous behaviors in the ER fluid. In addition, the constant G′ values suggested that the chain structure of the ER fluid was not deformed in the given frequency range, whereas G′ values with increasing electric field strength indicated the enhanced solidification properties of the Pal/PANI composite particle-based ER fluid. 4. Conclusions
Fig. 8. (a) Permittivity and loss factor as a function of the frequency; (b) Cole–Cole arc for Pal/PANI-based ER fluids. The lines were obtained from Eq. (4).
Pal/PANI nanocomposite particles were synthesized using an oxidative polymerization technique. The morphology and particle size of the synthesized product were confirmed by TEM images. Through the FT-IR spectra and XRD patterns of Pal, PANI, and synthesized Pal/PANI
Please cite this article as: Chae, H.S., et al., Synthesized palygorskite/polyaniline nanocomposite particles by oxidative polymerization and their electrorheology, Appl. Clay Sci. (2015), http://dx.doi.org/10.1016/j.clay.2015.01.018
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Fig. 10. Amplitude sweep (a) and frequency sweep (b) close symbols for G′(storage modulus) and open symbols for G″ (loss modulus) of ER fluid based on Pal/PANI composite particles (10 vol.%).
nanocomposite particles, it was confirmed that the Pal surface had been coated successfully with PANI. The ER fluid based on the Pal/PANI nanocomposite particles exhibited typical ER behavior. A stepwise increase in yield stress was observed and shear thinning in the flow curve was confirmed. The shear stress curves were analyzed using a CCJ model with six parameters. The CCJ model showed a better fit to the flow curve than the Bingham model. In the electric field sweep, the yield stress has a dependence on the electric field strength as a power law, τ0 ∝ Ε2.0. Furthermore, the dielectric spectra revealed polarizability in the nanocomposite particles based on an ER fluid, which is also consistent with their ER effects. Acknowledgment This work was supported by a research grant from the National Research Foundation, Korea (NRF-2013R1A1A2057955). References Adachi, M., Murata, Y., Takao, J., Jiu, J.T., Sakamoto, M., Wang, F.M., 2004. Highly efficient dye-sensitized solar cells with a titania thin-film electrode composed of a network structure of single-crystal-like TiO2 nanowires made by the “oriented attachment” mechanism. J. Am. Chem. Soc. 126, 14943–14949. Chen, H., Wang, A.Q., 2007. Kinetic and isothermal studies of lead ion adsorption onto palygorskite clay. J. Colloid Interface Sci. 307, 309–316.
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Chen, H., Wang, A.Q., 2009. Adsorption characteristics of Cu(II) from aqueous solution onto poly(acrylamide)/attapulgite composite. J. Hazard. Mater. 165, 223–231. Chen, H., Zhao, Y.G., Wang, A.Q., 2007. Removal of Cu(II) from aqueous solution by adsorption onto acid-activated palygorskite. J. Hazard. Mater. 149, 346–354. Chen, Y., Zhao, Y.J., Zhou, S.Y., Chu, X.Z., Yang, L.L., Xing, W.H., 2009. Preparation and characterization of polyacrylamide/palygorskite. Appl. Clay Sci. 46, 148–152. Cheng, Q.L., Pavlinek, V., Li, C.Z., Lengalova, A., He, Y., Saha, P., 2006. Synthesis and characterization of new mesoporous material with conducting polypyrrole confined in mesoporous silica. Mater. Chem. Phys. 98, 504–508. Cheng, Y.C., Guo, J.J., Xu, G.J., Cui, P., Liu, X.H., Liu, F.H., 2008. Electrorheological property and microstructure of acetamide-modified TiO2 nanoparticles. Colloid Polym. Sci. 286, 1493–1497. Cho, M.S., Choi, H.J., To, K.W., 1998. Effect of ionic pendent groups on a polyaniline-based electrorheological fluid. Macromol Rapid Commun. 19, 271–273. Cho, M.S., Cho, Y.H., Choi, H.J., Jhon, M.S., 2003. Synthesis and electrorheological characteristics of polyaniline-coated poly(methyl methacrylate) microsphere: Size effect. Langmuir 19, 5875–5881. Cho, M.S., Choi, H.J., Jhon, M.S., 2005. Shear stress analysis of a semiconducting polymer based electrorheological fluid system. Polymer 46, 11484–11488. Choi, H.J., Kim, J.W., To, K., 1999. Synthesis and electrorheological behavior of semiconducting poly(aniline-co-o-ethoxyaniline). Synth. Met. 101, 697–698. Chryssikos, G.D., Gionis, V., Kacandes, G.H., Stathopoulou, E.T., Suarez, M., García-Romero, E., Sánchez Del Río, M., 2009. Octahedral cation distribution in palygorskite. Am. Mineral. 94, 200–203. Cui, H., Qian, Y., Li, Q., Zhang, Q., Zhai, J.P., 2012. Adsorption of aqueous Hg(II) by a polyaniline/attapulgite composite. Chem. Eng. J. 211, 216–223. Fan, Q.H., Li, Z., Zhao, H.G., Jia, Z.H., Xu, J.Z., Wu, W.S., 2009. Adsorption of Pb(II) on palygorskite from aqueous solution: effects of pH, ionic strength and temperature. Appl. Clay Sci. 45, 111–116. Fang, F.F., Kim, J.H., Choi, H.J., Seo, Y., 2007. Organic/inorganic hybrid of polyaniline/BaTiO3 composites and their electrorheological and dielectric characteristics. J. Appl. Polym. Sci. 105, 1853–1860. Fang, F.F., Liu, Y.D., Lee, I.S., Choi, H.J., 2011. Well controlled core/shell type polymeric microspheres coated with conducting polyaniline: fabrication and electrorheology. RSC Adv. 1026–1032. Hiamtup, P., Sirivat, A., Jamieson, A.M., 2006. Electrorheological properties of polyaniline suspensions: field-induced liquid to solid transition and residual gel structure. J. Colloid Interface Sci. 295, 270–278. Hwang, J.K., Shin, K., Lim, H.S., Cho, J.C., Kim, J.W., Suh, K.D., 2012. The effects of particle conductivity on the electrorheological properties of functionalized MCNT-coated doublet-shaped anisotropic microspheres. Macromol. Res. 20, 391–396. Ikazaki, F., Kawai, A., Uchida, K., Kawakami, T., Edamura, K., Sakurai, K., 1998. Mechanisms of electrorheology: the effect of the dielectric property. J. Phys. D. Appl. Phys. 31, 336–347. Jin, E., Lu, X.F., Bian, X.J., Kong, L.R., Zhang, W.J., Wang, C., 2010. Unique tetragonal starlike polyaniline microstructure and its application in electrochemical biosensing. J. Mater. Chem. 20, 3079–3083. Kim, Y.D., Kim, J.H., 2008. Synthesis of polypyrrole-polycaprolactone composites by emulsion polymerization and the electrorheological behavior of their suspensions. Colloid Polym. Sci. 286, 631–637. Kim, S.G., Lim, J.Y., Sung, J.H., Choi, H.J., Seo, Y., 2007. Emulsion polymerized polyaniline synthesized with dodecylbenzenesulfonic acid and its electrorheological characteristics: Temperature effect. Polymer 48, 6622–6631. Kim, Y.J., Liu, Y.D., Choi, H.J., Park, S.J., 2013. Facile fabrication of Pickering emulsion polymerized polystyrene/laponite composite nanoparticles and their electrorheology. J. Colloid Interface Sci. 394, 108–114. Kuramoto, N., Yamazaki, M., Nagai, K., Koyama, K., Tanaka, K., Yatsuzuka, K., 1995. The electrorheological property of a polyaniline-coated copolystyrene particle suspension. Rheol. Acta 34, 298–302. Li, M., Wu, Z.S., Kao, H.T., 2011. Study on preparation, structure and thermal energy storage property of capric-palmitic acid/attapulgite composite phase change materials. Appl. Energy 88, 3125–3132. Liang, L., Liu, J., Windisch, C.F., Exarhos, G.J., Lin, Y.H., 2002. Direct assembly of large arrays of oriented conducting polymer nanowires. Angew. Chem. Int. Ed. 41, 3665–3668. Liu, Y.D., Choi, H.J., 2012. Electrorheological fluids: smart soft matter and characteristics. Soft Matter 8, 11961–11978. Liu, P., Wang, T.M., 2007. Adsorption properties of hyperbranched aliphatic polyester. grafted attapulgite towards heavy metal ions. J. Hazard. Mater. 149, 75–79. Liu, Y.S., Liu, P., Su, Z.X., 2007. Core-shell attapulgite@polyaniline composite particles via in situ oxidative polymerization. Synth. Met. 157, 585–591. Maity, A., Biswas, M., 2006. Recent progress in conducting polymer, mixed polymerinorganic hybrid nanocomposites. J. Ind. Eng. Chem. 12, 311–351. Meheust, Y., Parmar, K.P.S., Schjelderupsen, B., Fossum, J.O., 2011. The electrorheology of suspensions of Na-fluorohectorite clay in silicone oil. J. Rheol. 55, 809–833. Nandan, B., Hsu, J.Y., Chiba, A., Chen, H.L., Liao, C.S., Chen, S.A., 2007. Highly oriented nanowires from the hierarchical self-assembly in supramolecular complex of polyaniline with omega-methoxypoly(ethylene oxide) phosphates. Macromolecules 40, 395–398. Pan, H.X., Chen, D.J., 2007. Preparation and characterization of waterborne polyurethane/ attapulgite nanocomposites. Eur. Polym. J. 43, 3766–3772. Pavlinek, V., Saha, P., Kitano, T., Stejskal, J., Quadrat, O., 2005. The effect of polyaniline layer deposited on silica particles on electrorheological and dielectric properties of their silicone-oil suspensions. Phys. A 353, 21–28. Shao, L.A., Qiu, J.H., Liu, M.Z., Feng, H.X., Zhang, G.H., Lu, S.Y., 2010. Preparation and characterization of attapulgite/polyaniline nanofibers via self-assembling and graft polymerization. Chem. Eng. J. 161, 301–307.
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8
H.S. Chae et al. / Applied Clay Science xxx (2015) xxx–xxx
Stenicka, M., Pavlinek, V., Saha, P., Blinova, N.V., Stejskal, J., Quadrat, O., 2008. Conductivity of flowing polyaniline suspensions in electric field. Colloid Polym. Sci. 286, 1403–1409. Stenicka, M., Pavlinek, V., Saha, P., Blinova, N.V., Stejskal, J., Quadrat, O., 2009. The electrorheological efficiency of polyaniline particles with various conductivities suspended in silicone oil. Colloid Polym. Sci. 287, 403–412. Strounina, E.V., Shepherd, R., Kane-Maguire, L.A.P., Wallace, G.G., 2003. Conformational changes in sulfonated polyaniline caused by metal salts and OH-. Synth. Met. 135, 289–290. Sung, B.H., Choi, U.S., Jang, H.G., Park, Y.S., 2006. Novel approach to enhance the dispersion stability of ER fluids based on hollow polyaniline sphere particle. Colloids Surf. A 274, 37–42. Tan, K.P., Johnson, A.R., Stanway, R., Bullough, W.A., 2007. Model validation of the output reciprocating dynamic responses of a twin electro-rheological (ER) clutch mechanism. Mech. Mach. Theory 42, 1547–1562. Trlica, J., Saha, P., Quadrat, O., Stejskal, J., 2000. Electrorheology of polyaniline-coated silica particles in silicone oil. J. Phys. D. Appl. Phys. 33, 1773–1780. Wang, X.H., Wang, A.Q., 2010. Adsorption characteristics of chitosan-g-poly(acrylic acid)/ attapulgite hydrogel composite for Hg(II) ions from aqueous solution. Sep. Sci. Technol. 45, 2086–2094. Wang, X.H., Zheng, Y., Wang, A.Q., 2009. Fast removal of copper ions from aqueous solution by chitosan-g-poly(acrylic acid)/attapulgite composites. J. Hazard. Mater. 168, 970–977. Wang, J.H., Han, X.J., Ma, H.R., Ji, Y.F., Bi, L.J., 2011. Adsorptive removal of humic acid from aqueous solution on polyaniline/attapulgite composite. Chem. Eng. J. 173, 171–177. Wei, Z.X., Wan, M.X., 2002. Hollow microspheres of polyaniline synthesized with an aniline emulsion template. Adv. Mater. 14, 1314–1317.
Yilmaz, H., Unal, H.I., Sari, B., 2007. Synthesis, characterization and electrorheological properties of poly(o-toluidine)/Zn conducting composites. J. Appl. Polym. Sci. 103, 1058–1065. Yin, J., Zhao, X., 2011. Electrorheology of nanofiber suspensions. Nanoscale Res. Lett. 6, 1–17. Yin, J.B., Zhao, X.P., Xiang, L.Q., Xia, X., Zhang, Z.S., 2009. Enhanced electrorheology of suspensions containing sea-urchin-like hierarchical Cr-doped titania particles. Soft Matter 5, 4687–4697. Yin, J.B., Xia, X.A., Xiang, L.Q., Zhao, X.P., 2011. Temperature effect of electrorheological fluids based on polyaniline derived carbonaceous nanotubes. Smart Mater. Struct. 20, 015002. Yoshimoto, S., 2005. A commentary on “Synthesis and electrorheological properties of polyaniline-Na + − montmorillonite suspensions” by J. W. Kim, S. G. Kim, H. J. Choi, M. S. Jhon (Macromol. Rapid Commun. 1999, 20, 450–452). Macromol. Rapid Commun. 26, 857–861. Zhang, W.L., Liu, Y.D., Choi, H.J., Kim, S.G., 2012. Electrorheology of graphene oxide. ACS Appl. Mater. Interfaces 4, 2267–2272. Zhao, X.P., Yin, J.B., 2002. Preparation and electrorheological characteristics of rare-earthdoped TiO2 suspensions. Chem. Mater. 14, 2258–2263. Zhu, J.H., Wei, S.Y., Ryu, J., Budhathoki, M., Liang, G., Guo, Z.H., 2010. In situ stabilized carbon nanofiber (CNF) reinforced epoxy nanocomposites. J. Mater. Chem. 20, 4937–4948.
Please cite this article as: Chae, H.S., et al., Synthesized palygorskite/polyaniline nanocomposite particles by oxidative polymerization and their electrorheology, Appl. Clay Sci. (2015), http://dx.doi.org/10.1016/j.clay.2015.01.018
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Research Paper
Synthesized palygorskite/polyaniline nanocomposite particles by oxidative polymerization and their electrorheology Hyun Sik Chae, Wen Ling Zhang, Shang Hao Piao, Hyoung Jin Choi ⁎ Department of Polymer Science and Engineering, Inha University, Incheon 402-751, Korea
a r t i c l e
i n f o
Article history: Received 4 July 2014 Received in revised form 18 January 2015 Accepted 21 January 2015 Available online xxxx Keywords: Electrorheological fluid Polyaniline Palygorskite Nanocomposite
a b s t r a c t Palygorskite (Pal) clay coated with semiconducting polyaniline (PANI) nanocomposite particles was prepared by oxidative polymerization using aniline monomer in the presence of Pal. The morphological characteristics of the synthesized Pal/PANI composite particles were examined by both field emission scanning electron microscopy and transmission electron microscopy. A rotational rheometer was also used to examine the rheological behavior of the Pal/PANI composite-based electrorheological (ER) fluid when the nanocomposite particles were dispersed in silicone oil. From its flow curve of shear stress vs. shear rate investigated under an applied electric field, the typical ER behavior of the Pal/PANI-based ER fluid was observed. In addition, polarizability and relaxation time of the ER system obtained from the dielectric spectra were well correlated with its ER performance. © 2015 Elsevier B.V. All rights reserved.
1. Introduction Inorganic–organic nanocomposites have attracted considerable attention for their enhanced mechanical, electrical, optical, and other functional properties (Yilmaz et al., 2007; Kim & Kim, 2008; Meheust et al., 2011; Yin et al., 2011). In particular, clay/polymer nanocomposite particles often exhibit excellent electrical properties when fabricated appropriately (Yilmaz et al., 2007; Meheust et al., 2011). These materials have been adopted as electrorheological (ER) materials (Cheng et al., 2008; Kim & Kim, 2008; Stenicka et al., 2008; Liu & Choi, 2012), in which an insulating medium, such as silicone oil or mineral oil, containing ER particles underwent a structural phase change from a liquid-like to a solid-like form under an applied electric field. A typical type of ER fluid was a colloidal suspension of polarizable solid dielectric or conducting particles dispersed in an insulating fluid, which often exhibits Newtonian fluid behavior in the absence of an applied electric field (Trlica et al., 2000). On the other hand, when an electric field was applied to ER fluids, the dispersed particles became polarized immediately and align along the direction of the electric field, resulting in an increased shear viscosity. Therefore, the rheological behavior of the ER fluid can usually be explained using the Bingham fluid model with the yield stress (Zhao & Yin, 2002; Hiamtup et al., 2006). Among the various polarizable particles for anhydrous ER materials, semiconducting polymers including polyaniline (PANI) (Adachi et al., 2004; Pavlinek et al., 2005; Hiamtup et al., 2006; Sung et al., 2006), Nsubstituted copolyaniline (Cho et al., 1998), sulfonated poly(styreneco-divinylbenzene) (Ikazaki et al., 1998), PANI coated polystyrene ⁎ Corresponding author. E-mail address: [email protected] (H.J. Choi).
particles (Kuramoto et al., 1995), poly(aniline-co-o-ethoxyaniline) (Choi et al., 1999), and poly(acene quinone) radicals (Cho et al., 2005) have been reported. Recently, polymer-inorganic nanocomposites (Yoshimoto, 2005; Maity & Biswas, 2006) and conducting polymer/ mesoporous silica hybrids (Cheng et al., 2006) were adopted as drybased ER materials in addition to various inorganic materials. Among these, the PANI has attracted considerable attention because of its low cost, unique oxidation–reduction chemistry, environmental stability, and excellent optical and electrical properties (Wei & Wan, 2002). The colloidal synthesis of PANI, such as microspheres and nanofibers, can overcome its poor processability. Moreover, assembly structures of these colloids will further improve its properties and expand its applications (Liang et al., 2002; Nandan et al., 2007). PANI and various electroresponsive materials, such as inorganics with high dielectric properties, organic or polymeric semiconducting materials and their composites have been used as ER particles (Yin et al., 2009). Palygorskite (Pal) is a Mg-rich phyllosilicate with fibrous morphological characteristics, and it can be approximated by the formula, yMg5Si8O20(OH)2·(1 − y)[xMg2Fe2·(1 − x)Mg2Al2] Si8O20(OH)2 (Chryssikos et al., 2009). Pal consists of a three-dimensional network of densely packed rods with diameters less than 100 nm and lengths between hundreds of nanometers and several micrometers for each single rod (Pan & Chen, 2007). Pal has a large specific surface area, a moderate cation exchange capacity, and reactive OH-groups groups on its surface that can adsorb and trap metal ions from wastewater (Chen and Wang, 2007). To reduce the cost and improve the comprehensive waterabsorbing properties of this material, it is important to fabricate a composite that consists of a polymer and Pal micro-powder (Cui et al., 2012). To enhance the adsorption capacity and selectivity of Pal, considerable attention has been paid to special treatments or modifications
http://dx.doi.org/10.1016/j.clay.2015.01.018 0169-1317/© 2015 Elsevier B.V. All rights reserved.
Please cite this article as: Chae, H.S., et al., Synthesized palygorskite/polyaniline nanocomposite particles by oxidative polymerization and their electrorheology, Appl. Clay Sci. (2015), http://dx.doi.org/10.1016/j.clay.2015.01.018
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Aniline (5.58 g, 93.13 g/mol, DC chemical, Korea) as a monomer and 200 mL of sulfuric acid (2 mol/l) were used. Palygorskite (7 g, 411.35 g/mol, Fluorochem, UK) was adopted for the nanocomposite preparation. 0.4 M ammonium peroxodisulfate (APS, (NH4)2 S2O 8, Daejung, Korea) solution was used as an oxidizing agent.
to 90° with Cu Kα (λ = 1.5418 Å) incident radiation at a step size of 0.02°. Scan speed, counting time and slit width of XRD were 0.067°/s, 0.3 s, and 0.8°, respectively. The density of the synthesized composite particles was measured using a gas pycnometer (AccuPyc 1330, Micromeritics Instruments Co., USA). The electrical conductivity was measured by a standard four-pin probe technique using a resistivity meter (Mitsubishi Loresta-GP and Hiresta-UP). An optical microscope (OM, Olympus BX-51, USA) equipped with a DC voltage generator was used to observe the formed chain-like structure of the ER fluid. To characterize the typical ER properties of the ATP/PANI nanocomposite particles (10 vol%) dispersed in silicone oil (ShinEtsu, density = 0.96 g/cm3) with a kinematic viscosity of 30 cS from the controlled shear rate (CSR) measurements, in which the range of shear rate ranged from 0.01 to 1,000 [1/s] on a log–log scale, the rheological properties were measured using a rotational rheometer (Physica MCR 300, Stuttgart, Germany) equipped with a high voltage generator under different electric strengths. The measurements were at least in duplicate and the experimental error range was within 3%. The dielectric spectra of the ER fluid were also measured using an LCR meter (HP 4284A Precision) with a liquid test fixture (HP 16452A) for liquids to examine their interfacial polarization mechanism. The frequency of the AC electric fields was varied from 20 Hz to 1 MHz.
2.2. Preparation of Pal/PANI composite particle
3. Results and discussion
The Pal/PANI composite particles were synthesized by an oxidative polymerization process and used without a post-treatment step except for the doping process. To initiate the polymerization of aniline, sulfuric acid was added drop-wise. At the surface of Pal, the sulfuric acidmodified aniline monomer was polymerized with the aid of APS. The APS solution was slowly added drop-wise into the mixture with vigorous stirring over a period 6 h at room temperature. The obtained Pal/PANI composite particles were centrifuged with deionized water to remove the excess initiator, monomer, and free Pal templates and then dried in a vacuum oven at 60 °C for 24 h. The electrical conductivity of the Pal/PANI composite particles was about 10− 3 S/cm measured using a resistivity meter. This value was too high to prepare the Pal/PANI ER fluid. If the sample had too high electrical conductivity, an electric short would damages the rheometer device. The electrical conductivity of the composite particle was then controlled by the de-doping process where the pH was increased to 9.0 by adding a 1 M NaOH solution to an aqueous Pal/PANI solution, and then dried the sample in an oven for 24 h (Strounina et al., 2003; Fang et al., 2007, 2011). The obtained Pal/PANI particles were sieved (mesh size of 38 μm) to remove agglomerated Pal/PANI composite particles for better dispersion of the composite particles as for the ER fluid. As a result, the electrical conductivity of the Pal/PANI composite particles was changed from 10−3 S/cm to 10−8 S/cm. The 10−8 S/cm was in the appropriate range of the electrical conductivity in this ER test.
The morphologies of both Pal/PANI and Pal were examined by TEM to characterize the surface morphology of the pristine Pal (Fig. 1(a)) and Pal/PANI composite particles (Fig. 1(b)). The surface of Pal was fairly smooth (Fig. 1(a)). Pal has a highly fibrous morphology, forming bundles. The length of each fiber varied from the submicrometer to the micrometer range with an average diameter of approximately 20 nm. In contrast, the Pal/PANI composite particles exhibited a much rougher surface due to the wrapping of PANI (Fig. 1(b)). This means that the polymerization of aniline via a chemical oxidation method onto the Pal template have successfully changed the outside surface. The chemical interaction between Pal and PANI was confirmed by the FT-IR spectra of Pal/PANI, PANI, and Pal (Fig. 2), which showed marked variations of the absorption bands after modification. Although the Pal/PANI bands had a slight shift owing to the amorphous nature of PANI synthesized by this polymerization, Pal/PANI bands included both their individual characteristic bands of PANI and Pal. In the spectrum of Pal, the bands at 3620 cm−1, 3550 cm−1, and 3420 cm−1 were assigned to the stretching vibrations of the Al-OH unit, Mg-OH unit, and stretching vibration of zeolitic water, respectively (Fan et al., 2009; Yin and Zhao, 2011). For Pal/PANI, the wide absorption band at approximately 3446 cm−1 was assigned to the stretching vibration of − NH2 and −OH groups (Wang & Wang, 2010), and the Al-OH and Mg-OH vibrations were still visible as minor inflexions in the Pal/PANi spectrum, indicating that PANI had coated Pal. Pal exhibited a band at 1650 cm−1, which was assigned to the bending vibration of zeolitic water and absorbed water molecules (Li et al., 2011). This band was reduced in the Pal/PANI spectrum, suggesting that the zeolitic water and absorbed water in Pal decreased. The characteristic absorption bands of Pal were observed at 1025 cm−1 for Si-O-Si, and the band at 980 cm−1 corresponding to the stretching vibration of Al–O–Si (Cui et al., 2012). The new bands of Pal/PANI were representative of the C = C stretching vibrations of quinine and benzene rings at 1560 cm−1 and 1480 cm−1, respectively. The spectrum of Pal/PANI also showed C-O stretching vibrations at 1300 cm−1, C-N stretching vibrations at 1235 cm−1 and C-H out of plane bending vibrations at 800 cm−1, respectively. These results confirm that the Pal surface had been coated successfully with PANI. The EDS data of Pal/PANI nanocomposite particles are indicated in Fig. 3. This graph shows that the Pal/PANI is composed of C, N, O, Mg, Al, and Si. The synthesized Pal/PANI particle had weight and atomic percentage of C (10.82%, 15.66%), N (9.83%, 12.21%), O (48.60%,
such as heat treatment, acid treatment (Chen et al., 2007), or graft reactions. (Liu et al., 2007; Chen and Wang, 2009; Shao et al., 2010) Recently, polymers could be grafted successfully onto the surfaces of Pal to achieve the enhanced removal of heavy metals from aqueous solutions (Chen et al., 2009; Liu and Wang, 2007; Wang et al., 2009). In this study, Pal/PANI composite particles were synthesized by chemical oxidative polymerization. The electrical conductivity of PANI, which is still not high enough for many engineering applications, actually becomes a positive factor for an ER study. An ER fluid was prepared by dispersing the Pal/PANI composite particles in silicone oil, and their ER responses were then investigated using a rotational rheometer under various electric field strengths. 2. Experimental 2.1. Materials
2.3. Characterization The particle size and surface morphology were observed by transmission electron microscope (TEM) (CM 200, Philips). To prepare the TEM sample, a grid coated carbon was used. The accelerating voltage of TEM used was 120 kV. The molecular structure of the Pal/PANI composites was detected by Fourier transform infrared (FT-IR, Perkin Elmer System 2000) spectroscopy using KBr pellets in the spectral range from 4000 to 400 cm−1, with a spectral resolution of 4 cm−1 and the number of scans of 16. To prepare the FT-IR sample, the sample concentration ratio was 1: 100 (wt%). The elemental analysis of the sample was obtained by scanning electron microscopy (SEM) (S-4300, Hitachi, Japan) equipped with an energy-dispersive X-ray spectroscopy (EDS) (Horiba, Japan) accessory. The accelerating voltage of EDS used was 15 kV. Both Pal/PANI and Pal were further characterized by a powder X-ray diffraction (XRD, DMAX-2500, Rigaku) ranging from at 2θ = 5°
Please cite this article as: Chae, H.S., et al., Synthesized palygorskite/polyaniline nanocomposite particles by oxidative polymerization and their electrorheology, Appl. Clay Sci. (2015), http://dx.doi.org/10.1016/j.clay.2015.01.018
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Fig. 1. TEM images of (a) Pal and (b) Pal/PANI composite particles, respectively.
52.82%), Mg (1.78%, 1.27%), Al (3.97%, 2.56%), and Si (25%, 15.48%). Also, based on the EDS data, it was confirmed that C and N come from only attached PANI compared to the fact that the Pal is composed of neither C nor N.
Fig. 2. FT-IR spectra of Pal/PANI composites, PANI, and Pal.
The XRD patterns of Pal, PANI, and synthesized Pal/PANI nanocomposite particles are shown in Fig. 4. The crystalline PANI possessed reflections at 2θ = 18.4° and 25.7°. The reflection centered at 2θ = 18.4° was ascribed to the periodicity in the direction parallel to the polymer chain, while the reflection at 2θ = 18.4° was due to the periodicity in the direction perpendicular to the polymer chain (Jin et al., 2010). For Pal, the typical reflections at 2θ = 8.3°, 13.6°, 19.7°, and 26.6° were observed, which were in good agreement with the reflections of the (1 1 0), (2 0 0), (0 4 0), and (4 0 0) planes of Pal, respectively (Wang et al., 2011). A similar set of characteristic reflections was also observed for the Pal/PANI, which suggests that the crystal structure of Pal is well maintained under polymerization reaction. The PANI reflection in Pal/PANI is almost invisible because Pal/PANI has a relative thin layer of amorphous PANI synthesized by this polymerization reaction (Wang et al., 2011). The densities of Pal (2.27 g/cm3), PANI (1.30 g/cm3), and Pal/PANI composite particles (1.77 g/cm3) were also measured using a gas pycnometer. The density mismatch between the Pal/PANI composite particles and the continuous silicone oil with a kinematic viscosity of 30 cS (0.96 g/cm3) was reduced significantly compared to pure Pal. Therefore, the suspension stability of the ER fluid including the dispersion stability and sedimentation stability will be improved by using Pal/PANI. The ER fluids consist of semiconducting or polarizable materials dispersed in a non-conducting liquid. A microstructural transition of the ER fluid from a fluid-like to solid-like can be obtained under an electric field. In this study, an ER fluid was prepared by dispersing Pal/PANI nanocomposite particles (10 vol.% particle concentration) in 30 cS silicone oil. The microstructural changes in the Pal/PANI ER fluid were observed by optical microscopy under an applied electric field with a DC high voltage source (Fig. 5) (Cho et al., 2003). The gap between the two parallel electrodes was fixed to 150 μm. In the absence of an electric field, the synthesized particles were dispersed randomly in silicone oil, showing liquid-like state characteristics (Fig. 5(a)). On the other hand, when an electric field is present, Pal/PANI nanoparticles begin to move immediately and form a chain structure with the adjacent particles (Fig. 5(b)). Finally, the dispersed particles formed a chain structure that aligned along the applied electric field direction, in which the anisotropic rod-like shape of the ATP might enhance the chain formation. The ER fluid behavior was similar to that of pseudo-Newtonian fluid behavior without an external electric field, in which the shear stress is proportional to the shear rate with a slope of approximately 0.8 in a log–log plot (Cho et al., 2003). On the other hand, under an applied external electric field, the ER fluid exhibited plastic behavior with increased shear stress. In particular, when the electric field was changed from 0 to 0.5 kV/mm, the enhancement in shear stress was extremely distinct as a result of the formation of chain-like particle structures, as shown in the optical microscope images in Fig. 5(b), which can be called Bingham-like behavior (Cho et al., 2003).
Please cite this article as: Chae, H.S., et al., Synthesized palygorskite/polyaniline nanocomposite particles by oxidative polymerization and their electrorheology, Appl. Clay Sci. (2015), http://dx.doi.org/10.1016/j.clay.2015.01.018
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Fig. 3. EDS data of palygorskite/polyaniline composite particles.
Interestingly, the synthesized particle-based ER fluid indicated a slightly decreasing trend in the shear stress in the low shear rate region, and an increasing shear stress with increasing shear rate, which can be explained by the following mechanism. The aligned chain structures began to break with hydrodynamic shear deformation, and broken structures tended to reform the chains by the applied electric field, depending on the magnitude of the applied shear and particle–particle
interaction in the fibrils. In the low shear rate region, the electrostatic interactions were dominant (Cho et al., 2003, 2005). That is, the aligned particles reduced the shear deformation and the broken structure tended to reform the chain-like structure repeatedly. Therefore, the shear stress generated decreased with increasing shear rate. In the high shear rate region, where the hydrodynamic interaction was dominant, the broken chain particles had no to time to reform and the ER
(a)
(b)
300 V
50 μm
Fig. 4. XRD diffraction patterns for pristine (a) PANI, (b) Pal, and (c) Pal/PANI.
Fig. 5. Optical microscope the ER fluid based on Pal/PANI (a) without an electric field and (b) with an electric field.
Please cite this article as: Chae, H.S., et al., Synthesized palygorskite/polyaniline nanocomposite particles by oxidative polymerization and their electrorheology, Appl. Clay Sci. (2015), http://dx.doi.org/10.1016/j.clay.2015.01.018
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suspension behaved like a pseudo-Newtonian fluid (Cho et al., 2003). Therefore, the Bingham model and Cho–Choi–Jhon (CCJ) model were used to describe the shear stress behavior and yield stress (Cho et al., 2005). The Bingham model is widely used to explain the shear stress behavior. The Bingham model, shown in Eq. (1), has two parameters originating from the Newtonian viscosity (η0) and yield stress (τ0) and is adopted widely as a model for not only ER suspensions but also conventional suspension systems. τ ¼ τ0 þ η0 γ̇ γ̇ ¼ 0
ðτ ≥τ0 Þ
ðτbτ0 Þ
ð1Þ
where τ is the shear stress, τ0 is the yield stress, which is a function of the electric field, γ̇ is the shear rate, and η0 is the shear viscosity. The Bingham model has two flow regimes: a rigid pre-yield behavior for shear stresses less than the field-dependent yield stress and Newtonian flow characteristics beyond the yield stress τ0 (post-yield region). The dotted lines in Fig. 6(a) were from Eq. (1), and the Bingham model, however, did not fit the flow curve of Pal/PANI ER fluid. Therefore, a recently reported CCJ model shown in Eq. (2) was used to re-plot the shear stress behaviors by fitting the curves using six parameters (Cho et al., 2005). τ0 1 τ¼ þ η∞ 1 þ 1 þ ðt1 γ̇ Þα ðt2 γ̇ Þβ
! γ̇
ð2Þ
(a)
where τ0 is the static yield stress, which is defined as the extrapolated stress from the low shear rate region, and η∞ is the viscosity at the infinite shear rate that is interpreted as the viscosity without an external electric field. The exponents α and β are related to the decrease and increase in shear stress; β has the range 0 b β ≤ 1, due to dτ ≥0. The γ̇ parameters t1 and t2 are time constants. Fig. 6(a) showed the fitting of the two model equations for the 10 vol.% Pal/PANI composite particlebased ER fluid. Table 1 lists the optimal fitting parameters used for these two models. The CCJ model, which has six parameters, described the flow curves better than the Bingham model through the entire shear rate range (Cho et al., 2003). Fig. 6(b) shows the shear viscosity as a function of the shear rate. The shear thinning behavior was confirmed not only in each electric field strength but also in the absence of electric field (Zhu et al., 2010). In general, the non-Newtonian behavior in the absence of an electric field is attributed to the poor dispersed state in the high concentration ER fluid. In Fig. 7, the dynamic yield stress was plotted as a function of the electric field strength in log–log scale curves. In general, the dependence of the dynamic yield stress on the electric field strength can be presented by a power law relationship: m
τ∝E
(b)
ð3Þ
The exponent m can be obtained from the yield stress over a broad electric field range. The dependence of the dynamic yield stress was found to be expressed as τ ∝ E2, which is a polarization model of the ER mechanism (Fang et al., 2011). The polarizability of Pal/PANI ER fluids is known to be depended on their dielectric characteristic (Fig. 8). The dielectric spectra (Fig. 8(a)) and the Cole–Cole plot which is useful for examining the relationship between dielectric and ER properties (Fig. 8(b)) were obtained, where the permittivity (ε′) and loss factor (ε″) were a functions of the frequency (from 20 Hz to 1 MHz). Generally, this can be described using the following equation (Cho et al., 2003):
Slope ~ 0.8
5
0
ε ¼ ε þ ε} ¼ ε∞ þ
ε0 −ε∞ 1 þ ðiωλÞ1−α
ð0 ≤ αb1Þ
ð4Þ
where ε* is the complex dielectric constant, ε0 is the dielectric constant at 0, and ε∞ is the dielectric constant at infinite frequency. Δε = ε0 − ε∞ is the achievable polarizability in ER fluids, which is related to the electrostatic interactions between particles. The ε0 and ε∞ obtained were 3.82 and 1.78, respectively, so that Δε was 2.04 for the Pal/PANI-based ER fluid. λ (λ = 1 / 2πfc; fc, the critical frequency) is the relaxation time for the interfacial polarization of ER fluids at the frequency of which the dielectric loss reaches the maximum value (Kim et al., 2013). The relaxation time is also related to the yield stress and stress enhancement under an applied electric field strength. Here, the relaxation time of Pal/PANIbased ER fluid is 0.21 ms. This is in the range of 102–105 Hz, which is Table 1 Fitting parameters of Bingham and CCJ model equations to the flow curves of ER fluid based on Pal/PANI (10 vol.% particle concentration). Electric filed strength (kV/mm) Parameters Model Bingham CCJ
Fig. 6. Shear stress (a) and viscosity (b) curves vs shear rate for Pal/PANI-based ER fluids (10 vol.%) under various electric field strengths, the dashed lines were fitted via a conventional Bingham model; the solid lines were fitted via a suggested CCJ model.
τ0 η0 τ0 t1 α η∞ t2 β
0.5
1
1.5
2
2.5
3
18 0.087 18 0.01 0.3 0.087 0.8 0.4
60 0.115 60 0.001 0.05 0.115 0.9 0.9
111 0.164 111 0.10 0.4 0.164 0.1 0.3
176 0.227 176 0.04 0.3 0.227 0.25 0.9
252 0.281 252 0.03 0.5 0.281 0.8 0.8
512 0.358 512 0.18 0.41 0.358 0.9 0.66
Please cite this article as: Chae, H.S., et al., Synthesized palygorskite/polyaniline nanocomposite particles by oxidative polymerization and their electrorheology, Appl. Clay Sci. (2015), http://dx.doi.org/10.1016/j.clay.2015.01.018
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Fig. 7. Dynamic yield stress as a function of electric field of the Pal/PANI composite particle-based ER fluid. The solid line is fitted by the equation, τy ∝ E2.
needed for a good ER fluid (Stenicka et al., 2009; Yin et al., 2011). The exponent (1 − α) determines the broadness of the relaxation time distribution. When α is zero, Eq. (4) reduces to Debye's well-known single relaxation time model (Kim et al., 2007; Zhang et al., 2012). The α of Pal/PANI particle-based ER fluid was 0.711. Fig. 9 To examine the stability and sensitivity of the Pal/PANI nanocomposite particle-based ER fluid, the shear viscosity was measured at a
Fig. 9. Shear stress of ER fluid (10 vol.%) based on Pal/PANI composite particles in the electric field with a square voltage pulse (t = 20 s) at a fixed shear rate of 1 s−1.
fixed shear rate of 1 [1/s] with a square voltage pulse (t = 20 s) (Fig. 9). When the external electric field was applied (turn on), the shear stress increased suddenly, whereas the electric field (turn off) sharply declined to a zero field level when the applied electric field was removed. Therefore, the transformation of the shear stress can change easily from the off-state to the on-state. This well-controlled ER characteristic was sensitive and reversible. Applications to controlled mechanical systems may be possible by taking advantage of the ER phenomenon (Tan et al., 2007). The dynamic oscillation test was conducted to examine the viscoelastic properties of an ER fluid. Before the dynamic oscillation test, an amplitude sweep test was conducted at various strains from 10−3% to 102% to determine the linear viscoelastic region (γLVE) at a fixed angular frequency of 6.28 rad/s (Fig. 10(a)). At the low strain region, the storage modulus, G′ (energy stored in the sample during the oscillatory shear process), is always higher than that of the loss modulus, G″ (energy dissipated during the oscillatory shear process). Between 10−3% and 10−1%, the G′ and G″ values are independent of strain in the linear viscoelastic region, and the γLVE was chosen as 0.005% for the frequency sweep test (Hwang et al., 2012). At γLVE, the elastic response was dominant (G′ N G″) and the structures generated from the electric fields were unchanged. When the applied strain exceeded γLVE, both G′ and G″ decreased sharply due to the chain breaking. Moreover, G″ became larger than G′, suggesting that the structures, which were formed by an electric field, began to break down beyond a certain degree of deformation with increasing strain (Cho et al., 2005). The selected mean γLVE value was applied to the frequency sweep measurements. G′ and G″ were measured over an angular frequency, ranging from 1 to 100 [rad/s] with a strain of 0.005% at γLVE (Fig. 10(b)). The G′ and G″ values increased with increasing electric field. The G′ values representing an elastic response were higher than that of G″ representing viscous property, indicating the dominance of solid-like behavior over viscous behaviors in the ER fluid. In addition, the constant G′ values suggested that the chain structure of the ER fluid was not deformed in the given frequency range, whereas G′ values with increasing electric field strength indicated the enhanced solidification properties of the Pal/PANI composite particle-based ER fluid. 4. Conclusions
Fig. 8. (a) Permittivity and loss factor as a function of the frequency; (b) Cole–Cole arc for Pal/PANI-based ER fluids. The lines were obtained from Eq. (4).
Pal/PANI nanocomposite particles were synthesized using an oxidative polymerization technique. The morphology and particle size of the synthesized product were confirmed by TEM images. Through the FT-IR spectra and XRD patterns of Pal, PANI, and synthesized Pal/PANI
Please cite this article as: Chae, H.S., et al., Synthesized palygorskite/polyaniline nanocomposite particles by oxidative polymerization and their electrorheology, Appl. Clay Sci. (2015), http://dx.doi.org/10.1016/j.clay.2015.01.018
H.S. Chae et al. / Applied Clay Science xxx (2015) xxx–xxx
Fig. 10. Amplitude sweep (a) and frequency sweep (b) close symbols for G′(storage modulus) and open symbols for G″ (loss modulus) of ER fluid based on Pal/PANI composite particles (10 vol.%).
nanocomposite particles, it was confirmed that the Pal surface had been coated successfully with PANI. The ER fluid based on the Pal/PANI nanocomposite particles exhibited typical ER behavior. A stepwise increase in yield stress was observed and shear thinning in the flow curve was confirmed. The shear stress curves were analyzed using a CCJ model with six parameters. The CCJ model showed a better fit to the flow curve than the Bingham model. In the electric field sweep, the yield stress has a dependence on the electric field strength as a power law, τ0 ∝ Ε2.0. Furthermore, the dielectric spectra revealed polarizability in the nanocomposite particles based on an ER fluid, which is also consistent with their ER effects. Acknowledgment This work was supported by a research grant from the National Research Foundation, Korea (NRF-2013R1A1A2057955). References Adachi, M., Murata, Y., Takao, J., Jiu, J.T., Sakamoto, M., Wang, F.M., 2004. Highly efficient dye-sensitized solar cells with a titania thin-film electrode composed of a network structure of single-crystal-like TiO2 nanowires made by the “oriented attachment” mechanism. J. Am. Chem. Soc. 126, 14943–14949. Chen, H., Wang, A.Q., 2007. Kinetic and isothermal studies of lead ion adsorption onto palygorskite clay. J. Colloid Interface Sci. 307, 309–316.
7
Chen, H., Wang, A.Q., 2009. Adsorption characteristics of Cu(II) from aqueous solution onto poly(acrylamide)/attapulgite composite. J. Hazard. Mater. 165, 223–231. Chen, H., Zhao, Y.G., Wang, A.Q., 2007. Removal of Cu(II) from aqueous solution by adsorption onto acid-activated palygorskite. J. Hazard. Mater. 149, 346–354. Chen, Y., Zhao, Y.J., Zhou, S.Y., Chu, X.Z., Yang, L.L., Xing, W.H., 2009. Preparation and characterization of polyacrylamide/palygorskite. Appl. Clay Sci. 46, 148–152. Cheng, Q.L., Pavlinek, V., Li, C.Z., Lengalova, A., He, Y., Saha, P., 2006. Synthesis and characterization of new mesoporous material with conducting polypyrrole confined in mesoporous silica. Mater. Chem. Phys. 98, 504–508. Cheng, Y.C., Guo, J.J., Xu, G.J., Cui, P., Liu, X.H., Liu, F.H., 2008. Electrorheological property and microstructure of acetamide-modified TiO2 nanoparticles. Colloid Polym. Sci. 286, 1493–1497. Cho, M.S., Choi, H.J., To, K.W., 1998. Effect of ionic pendent groups on a polyaniline-based electrorheological fluid. Macromol Rapid Commun. 19, 271–273. Cho, M.S., Cho, Y.H., Choi, H.J., Jhon, M.S., 2003. Synthesis and electrorheological characteristics of polyaniline-coated poly(methyl methacrylate) microsphere: Size effect. Langmuir 19, 5875–5881. Cho, M.S., Choi, H.J., Jhon, M.S., 2005. Shear stress analysis of a semiconducting polymer based electrorheological fluid system. Polymer 46, 11484–11488. Choi, H.J., Kim, J.W., To, K., 1999. Synthesis and electrorheological behavior of semiconducting poly(aniline-co-o-ethoxyaniline). Synth. Met. 101, 697–698. Chryssikos, G.D., Gionis, V., Kacandes, G.H., Stathopoulou, E.T., Suarez, M., García-Romero, E., Sánchez Del Río, M., 2009. Octahedral cation distribution in palygorskite. Am. Mineral. 94, 200–203. Cui, H., Qian, Y., Li, Q., Zhang, Q., Zhai, J.P., 2012. Adsorption of aqueous Hg(II) by a polyaniline/attapulgite composite. Chem. Eng. J. 211, 216–223. Fan, Q.H., Li, Z., Zhao, H.G., Jia, Z.H., Xu, J.Z., Wu, W.S., 2009. Adsorption of Pb(II) on palygorskite from aqueous solution: effects of pH, ionic strength and temperature. Appl. Clay Sci. 45, 111–116. Fang, F.F., Kim, J.H., Choi, H.J., Seo, Y., 2007. Organic/inorganic hybrid of polyaniline/BaTiO3 composites and their electrorheological and dielectric characteristics. J. Appl. Polym. Sci. 105, 1853–1860. Fang, F.F., Liu, Y.D., Lee, I.S., Choi, H.J., 2011. Well controlled core/shell type polymeric microspheres coated with conducting polyaniline: fabrication and electrorheology. RSC Adv. 1026–1032. Hiamtup, P., Sirivat, A., Jamieson, A.M., 2006. Electrorheological properties of polyaniline suspensions: field-induced liquid to solid transition and residual gel structure. J. Colloid Interface Sci. 295, 270–278. Hwang, J.K., Shin, K., Lim, H.S., Cho, J.C., Kim, J.W., Suh, K.D., 2012. The effects of particle conductivity on the electrorheological properties of functionalized MCNT-coated doublet-shaped anisotropic microspheres. Macromol. Res. 20, 391–396. Ikazaki, F., Kawai, A., Uchida, K., Kawakami, T., Edamura, K., Sakurai, K., 1998. Mechanisms of electrorheology: the effect of the dielectric property. J. Phys. D. Appl. Phys. 31, 336–347. Jin, E., Lu, X.F., Bian, X.J., Kong, L.R., Zhang, W.J., Wang, C., 2010. Unique tetragonal starlike polyaniline microstructure and its application in electrochemical biosensing. J. Mater. Chem. 20, 3079–3083. Kim, Y.D., Kim, J.H., 2008. Synthesis of polypyrrole-polycaprolactone composites by emulsion polymerization and the electrorheological behavior of their suspensions. Colloid Polym. Sci. 286, 631–637. Kim, S.G., Lim, J.Y., Sung, J.H., Choi, H.J., Seo, Y., 2007. Emulsion polymerized polyaniline synthesized with dodecylbenzenesulfonic acid and its electrorheological characteristics: Temperature effect. Polymer 48, 6622–6631. Kim, Y.J., Liu, Y.D., Choi, H.J., Park, S.J., 2013. Facile fabrication of Pickering emulsion polymerized polystyrene/laponite composite nanoparticles and their electrorheology. J. Colloid Interface Sci. 394, 108–114. Kuramoto, N., Yamazaki, M., Nagai, K., Koyama, K., Tanaka, K., Yatsuzuka, K., 1995. The electrorheological property of a polyaniline-coated copolystyrene particle suspension. Rheol. Acta 34, 298–302. Li, M., Wu, Z.S., Kao, H.T., 2011. Study on preparation, structure and thermal energy storage property of capric-palmitic acid/attapulgite composite phase change materials. Appl. Energy 88, 3125–3132. Liang, L., Liu, J., Windisch, C.F., Exarhos, G.J., Lin, Y.H., 2002. Direct assembly of large arrays of oriented conducting polymer nanowires. Angew. Chem. Int. Ed. 41, 3665–3668. Liu, Y.D., Choi, H.J., 2012. Electrorheological fluids: smart soft matter and characteristics. Soft Matter 8, 11961–11978. Liu, P., Wang, T.M., 2007. Adsorption properties of hyperbranched aliphatic polyester. grafted attapulgite towards heavy metal ions. J. Hazard. Mater. 149, 75–79. Liu, Y.S., Liu, P., Su, Z.X., 2007. Core-shell attapulgite@polyaniline composite particles via in situ oxidative polymerization. Synth. Met. 157, 585–591. Maity, A., Biswas, M., 2006. Recent progress in conducting polymer, mixed polymerinorganic hybrid nanocomposites. J. Ind. Eng. Chem. 12, 311–351. Meheust, Y., Parmar, K.P.S., Schjelderupsen, B., Fossum, J.O., 2011. The electrorheology of suspensions of Na-fluorohectorite clay in silicone oil. J. Rheol. 55, 809–833. Nandan, B., Hsu, J.Y., Chiba, A., Chen, H.L., Liao, C.S., Chen, S.A., 2007. Highly oriented nanowires from the hierarchical self-assembly in supramolecular complex of polyaniline with omega-methoxypoly(ethylene oxide) phosphates. Macromolecules 40, 395–398. Pan, H.X., Chen, D.J., 2007. Preparation and characterization of waterborne polyurethane/ attapulgite nanocomposites. Eur. Polym. J. 43, 3766–3772. Pavlinek, V., Saha, P., Kitano, T., Stejskal, J., Quadrat, O., 2005. The effect of polyaniline layer deposited on silica particles on electrorheological and dielectric properties of their silicone-oil suspensions. Phys. A 353, 21–28. Shao, L.A., Qiu, J.H., Liu, M.Z., Feng, H.X., Zhang, G.H., Lu, S.Y., 2010. Preparation and characterization of attapulgite/polyaniline nanofibers via self-assembling and graft polymerization. Chem. Eng. J. 161, 301–307.
Please cite this article as: Chae, H.S., et al., Synthesized palygorskite/polyaniline nanocomposite particles by oxidative polymerization and their electrorheology, Appl. Clay Sci. (2015), http://dx.doi.org/10.1016/j.clay.2015.01.018
8
H.S. Chae et al. / Applied Clay Science xxx (2015) xxx–xxx
Stenicka, M., Pavlinek, V., Saha, P., Blinova, N.V., Stejskal, J., Quadrat, O., 2008. Conductivity of flowing polyaniline suspensions in electric field. Colloid Polym. Sci. 286, 1403–1409. Stenicka, M., Pavlinek, V., Saha, P., Blinova, N.V., Stejskal, J., Quadrat, O., 2009. The electrorheological efficiency of polyaniline particles with various conductivities suspended in silicone oil. Colloid Polym. Sci. 287, 403–412. Strounina, E.V., Shepherd, R., Kane-Maguire, L.A.P., Wallace, G.G., 2003. Conformational changes in sulfonated polyaniline caused by metal salts and OH-. Synth. Met. 135, 289–290. Sung, B.H., Choi, U.S., Jang, H.G., Park, Y.S., 2006. Novel approach to enhance the dispersion stability of ER fluids based on hollow polyaniline sphere particle. Colloids Surf. A 274, 37–42. Tan, K.P., Johnson, A.R., Stanway, R., Bullough, W.A., 2007. Model validation of the output reciprocating dynamic responses of a twin electro-rheological (ER) clutch mechanism. Mech. Mach. Theory 42, 1547–1562. Trlica, J., Saha, P., Quadrat, O., Stejskal, J., 2000. Electrorheology of polyaniline-coated silica particles in silicone oil. J. Phys. D. Appl. Phys. 33, 1773–1780. Wang, X.H., Wang, A.Q., 2010. Adsorption characteristics of chitosan-g-poly(acrylic acid)/ attapulgite hydrogel composite for Hg(II) ions from aqueous solution. Sep. Sci. Technol. 45, 2086–2094. Wang, X.H., Zheng, Y., Wang, A.Q., 2009. Fast removal of copper ions from aqueous solution by chitosan-g-poly(acrylic acid)/attapulgite composites. J. Hazard. Mater. 168, 970–977. Wang, J.H., Han, X.J., Ma, H.R., Ji, Y.F., Bi, L.J., 2011. Adsorptive removal of humic acid from aqueous solution on polyaniline/attapulgite composite. Chem. Eng. J. 173, 171–177. Wei, Z.X., Wan, M.X., 2002. Hollow microspheres of polyaniline synthesized with an aniline emulsion template. Adv. Mater. 14, 1314–1317.
Yilmaz, H., Unal, H.I., Sari, B., 2007. Synthesis, characterization and electrorheological properties of poly(o-toluidine)/Zn conducting composites. J. Appl. Polym. Sci. 103, 1058–1065. Yin, J., Zhao, X., 2011. Electrorheology of nanofiber suspensions. Nanoscale Res. Lett. 6, 1–17. Yin, J.B., Zhao, X.P., Xiang, L.Q., Xia, X., Zhang, Z.S., 2009. Enhanced electrorheology of suspensions containing sea-urchin-like hierarchical Cr-doped titania particles. Soft Matter 5, 4687–4697. Yin, J.B., Xia, X.A., Xiang, L.Q., Zhao, X.P., 2011. Temperature effect of electrorheological fluids based on polyaniline derived carbonaceous nanotubes. Smart Mater. Struct. 20, 015002. Yoshimoto, S., 2005. A commentary on “Synthesis and electrorheological properties of polyaniline-Na + − montmorillonite suspensions” by J. W. Kim, S. G. Kim, H. J. Choi, M. S. Jhon (Macromol. Rapid Commun. 1999, 20, 450–452). Macromol. Rapid Commun. 26, 857–861. Zhang, W.L., Liu, Y.D., Choi, H.J., Kim, S.G., 2012. Electrorheology of graphene oxide. ACS Appl. Mater. Interfaces 4, 2267–2272. Zhao, X.P., Yin, J.B., 2002. Preparation and electrorheological characteristics of rare-earthdoped TiO2 suspensions. Chem. Mater. 14, 2258–2263. Zhu, J.H., Wei, S.Y., Ryu, J., Budhathoki, M., Liang, G., Guo, Z.H., 2010. In situ stabilized carbon nanofiber (CNF) reinforced epoxy nanocomposites. J. Mater. Chem. 20, 4937–4948.
Please cite this article as: Chae, H.S., et al., Synthesized palygorskite/polyaniline nanocomposite particles by oxidative polymerization and their electrorheology, Appl. Clay Sci. (2015), http://dx.doi.org/10.1016/j.clay.2015.01.018