Open Access is an initiative that aims to make scientific research freely available to all. To date our community has made over 100 million downloads. It’s based on principles of collaboration, unobstructed discovery, and, most importantly, scientific progression. As PhD students, we found it difficult to access the research we needed, so we decided to create a new Open Access publisher that levels the playing field for scientists across the world. How? By making research easy to access, and puts the academic needs of the researchers before the business interests of publishers.
We are a community of more than 103,000 authors and editors from 3,291 institutions spanning 160 countries, including Nobel Prize winners and some of the world’s most-cited researchers. Publishing on IntechOpen allows authors to earn citations and find new collaborators, meaning more people see your work not only from your own field of study, but from other related fields too.
To purchase hard copies of this book, please contact the representative in India:
CBS Publishers & Distributors Pvt. Ltd.
www.cbspd.com
|
customercare@cbspd.com
Smart fluids are stimuli-responsive materials whose rheological properties can be changed drastically by applying either an external electric or magnetic field strength. Smart fluids are dispersions comprised of dispersed particles in a carrier liquid that transform from liquid-like state to solid-like state within milliseconds reversibly with an application of external field due to the structural chain formation of the dispersed particles. Owing to this outstanding controllable transformation capability, smart fluids are utilized in various potential applications where an electro/magneto-mechanical interface is required, such as dampers, clutches, shock absorbers, robotics, haptic devices, microfluidics, etc. Various kinds of materials have been proposed and used by researchers for applications that require the electrorheological (ER) and magnetorheological (MR) effects. Polyaniline (PAn) is considered a remarkable material as a dispersed phase of ER fluids due to its easy synthesis, low cost, adjustable conductivity through doping/de-doping processes, and excellent environmental stability. PAn is an attractive material in MR fluids as well due to its contribution to the improvement of dispersion stability and protection against corrosion and oxidation of the soft-magnetic particles. In this chapter, the recent advances in the usage of various kinds of PAn-based materials as electric and magnetic field responsive materials and their ER/MR behaviors are summarized.
Chemistry Department, Science Faculty, Gazi University, Ankara, Turkey
*Address all correspondence to: oerol@gazi.edu.tr
1. Introduction
Electrorheological (ER) and magnetorheological (MR) fluids are stimuli-responsive smart dispersions with rheological properties (yield stress, viscosity, shear modulus, etc.) that are reversible and controllable in a continuous manner with the usage of an externally applied electric field (E) or magnetic field (H), respectively. The ER fluids are commonly composed of polarizable/semiconducting micron/nano-sized particles as a dispersing phase, in an insulating dispersing medium with low volatility and high chemical/thermal stability, whereas their magnetic counterpart, the MR fluids generally consist of highly magnetizable micron-sized dispersed particles in a nonmagnetizable carrier fluid such as mineral oil, silicone oil, polyesters, polyethers, synthetic hydrocarbons, or water. Additives can also be added to enhance the ER/MR effect and/or to increase dispersion stability of the whole stimuli-responsive fluids. These smart fluids transform reversibly and rapidly from a liquid-like state to a solid-like state within a millisecond with the aid of an E or a H. Smart fluids, therefore, can be used as electrical and mechanical interfaces in various applications that require active control of vibrations or the transmission of torque, including the fast-acting valves, clutches, brakes, shock absorbers, accurate polishing, robotics, and tactile displays [1, 2].
For ER fluids, when an E is applied, the randomly dispersed particles are polarized forming a dipole moment due to the difference between the dielectric constant of the dispersant and dispersed particles. These particles attract each other along the field between the parallel electrodes to construct chain and/or columnar-like structures along the field direction. Similarly, when MR fluids are exposed to a H, dispersed particles are magnetized and oriented along the direction of the H and generate anisotropic aggregates. As a result, for both smart fluids, the field-induced structuration in the fluid leads to resist the flow of the carrier fluid, which results in an enhanced apparent viscosity and viscoelasticity of the fluid. This phenomenon is known as the ER or MR effect. The schematic representation of the microstructure of ER or MR fluids under on/off state of the E or H is shown in the Figure 1.
Figure 1.
Schematic representation of the microstructure of ER or MR fluids under off-state (a) and on-state (b) of E or H.
A deeper understanding of the field-induced structuring mechanism may lead us to design and prepare high-performance field responsive fluids. The mechanism of the electric field-induced rheological changes has been studied intensively since the invention of the ER fluids [3]. Several mechanisms or models were proposed previously to explain the ER effect, including fibrillation, electrical double layer, water/surfactant bridge, polarization, conduction, and dielectric loss model [4]. On the other hand, particle magnetization model is the most acceptable mechanism to account for the magnetic field-induced structuring in MR fluids. According to the particle magnetization model, the MR effect is ascribed to the magnetic permeability mismatch between the dispersed particles and continuous phases [2]. There are several critical key factors that influence the behavior of the ER fluids. Thus, it is difficult to develop desired high-performance ER fluids in consideration of all variables such as dispersed particle size, shape and overall morphology, particle conductivity and dielectric properties, particle surface properties, particle volume fraction of the ER fluid, the E, temperature, properties of dispersing medium, and dispersion stability. A proper electrical conductivity range is desired to be 10−6–10−12 S/cm [5]. For MR fluids, the H, carrier fluid, additives, temperature, dispersion stability, durability, magnetic permeability, particle surface roughness, volume fraction, density, and size/shape of the dispersed particles are the major parameters on MR effect [6].
As a dispersed phase, a wide range of ER or MR active materials are developed to eliminate the impediments that limit the use of stimuli-responsive fluids in the literature. Various polarizable particles ranging from ceramics to polymers have been applied as the dispersed phase of ER fluids, including SiO2, TiO2, corn starch, aluminosilicate, carbonaceous particles, conducting polymers, etc. [1]. In addition, recent efforts on various hybrid materials with different hierarchical morphologies have been made to improve the dispersion stability and polarizability. As a dispersed phase, Fe3O4, Fe2O3, iron particles, carbonyl iron (CI) particles, iron alloy particles (nickel-iron, cobalt-iron, magnetized stainless steel alloys), and ferrite nanoparticles were used to fabricate MR fluids [7]. MR active particles are desired to have large saturation magnetization and small coercivity value over a wide temperature range, high dispersion, and chemical stability [2]. Although these MR active materials have reasonable mechanical properties, they generally have lack of dispersion stability against settling and poor anticorrosion properties. Thus, surface modification, coating of magnetic particles, or the addition of different additives are usually required. The optimum particle size of dispersed phase is usually in the range of 0.1–10 μm.
Among conductive polymers, PAn has been widely used in the research on ER materials so far due to its possessing excellent chemical and environmental stability and tunable conductivity. Additionally, PAn has been utilized for enhancing the dispersion stability of MR fluids and obtaining dual ER/MR response. In this chapter, the recently developed PAn-based materials as electric and magnetic field responsive materials and their ER/MR behaviors are reviewed.
As an anhydrous ER active material, PAn and PAn-based materials have been extensively investigated in previous studies due to their adjustable electrical conductivity, easy synthesis, low cost, good environmental, thermal, and chemical stability, and nonabrasive for the device. Various efforts have been made to increase the ER efficiency of PAn, including synthetization of PAn with different morphologies, preparing its derivatives, and combining PAn with various kinds of materials such as inorganic particles or polymers by preparing composites, nanocomposites, core/shell structures, etc. In this section, constituents of PAn-based ER fluids have been reported so far and their general ER characteristics are summarized. The main parameters of PAn-based ER fluids can be found in a brief table in a recent review reported by Kuznetsov et al. [8].
2.1 Development and diversification of polyaniline-based ER fluids
2.1.1 Polyaniline, its derivatives, and copolymers
Among conjugated conductive polymers, PAn has drawn great attention due to its easy and cost-effective production. PAn is synthesized in different morphologies, including fibrillar, tubular, belt-like, porous, hollow structures, etc. PAn exists in different forms in terms of its oxidation state as fully oxidized, half-oxidized, and fully reduced states, namely, pernigraniline, emeraldine base, and leucomeraldine, respectively. For ER application, the level of conductivity of the fabricated PAn is important and depends on the degree of doping, synthesis conditions such as temperature, monomer: oxidatant ratio, presence of surfactant, and other components. If the conductivity of the PAn is not within the proper semiconductive level, dedoping process is generally applied to PAn before preparing ER fluids. The doping process by organic/inorganic acids also impacts the control of wettability of PAn, which plays a role in ER efficiency by influencing the compatibility between solid phase and liquid phase [9, 10].
The doping degree of PAn can be controlled by adjusting the pH of the aqueous solution containing the PAn particles to 9.0 to make it suitable for ER fluids. Additionally, Xie et al. reported the effect of different dedoping methods on ER properties of PAn, namely equilibrium and nonequilibrium. In the reported equilibrium method, the PAn particles were immersed in a diluted aqueous ammonia solution with a certain pH value and stirred for a defined time. On the other hand, in the reported nonequilibrium method, the PAn particles were immersed in a concentrated aqueous ammonia solution for a certain time. Although similar conductivity values were reached for both methods, the greater yield stress value was observed in case of the PAn prepared via nonequilibrium method. The reason for this observation was attributed to the possible formation of more insulating shell coating on PAn particles via nonequilibrium method, which led to more electron movement within the particles rather than electron hopping between them [11]. However, when the PAn is even dedoped, the current density may still be higher than that of desired for ER fluid and cause consumption of power and electrical discharge. Thus, PAn derivatives and copolymers have taken attention owing to eliminate the limitations of PAn.
Substituted derivatives of PAn are obtained by the introducing of substituted groups on the benzene ring and/or amino N of PAn. The conjugation length and electrochemical behaviors are both affected by the substituent nature and its position on the ring [12]. The PAn derivatives usually show reduced intrinsic conductivities by several orders of magnitude compared to PAn due to steric hindrance of the substituent groups or the disruption of the conjugated backbone or difference in the interchain interactions [13]. Thus, further dedoping process, which is generally required for PAn-based ER fluids, may not be required for PAn derivatives, and the efficiency of the processing of ER fluid can be increased. The most extensively investigated introduced substituents are methyl, ethyl, methoxy, ethoxy, and phenyl groups. There are vast amount of different homopolymers and copolymers have been prepared from substituted anilines for ER application in the literature, including poly(2-methoxyaniline) or poly(o-anisidine) [14], poly(2-ethoxyaniline), poly(N-methylaniline), poly(N-ethylaniline), poly(2-methylaniline) or poly(o-toluidine) [15, 16], poly(2-ethylaniline) [16, 17], poly(diphenylamine) (N-aryl-substituted PAn) [18], substituted PAn with long alkyl pendants (poly(2-dodecyloxyaniline) [19], poly(aniline-co-diphenylamine) [20], poly(aniline-co-o-ethoxyaniline) [21], poly(aniline-co-1,4-phenylenediamine) [22], PAn copolymer containing N-substituted benzene sulfonic acid group [23], and aniline/pyrrole copolymer [24]. In addition, oligomeric aniline particles were demonstrated to exhibit greater ER activity than PAn [25].
An irregular particulate morphology is generally obtained from chemical oxidative polymerization of aniline and used as ER active material. Additionally, well-defined hollow [26], nanofibrous [27, 28], nanotubular [29], nanorod covered rectangular tubular [30], urchin-like [31], and clip-like [32] shaped PAn have been developed using a variety of synthesis methods, such as template synthesis, rapid mixing polymerization or interface polymerization, chemical oxidation dilute polymerization in an aqueous acidic solution with an anionic surfactant, the in-situ chemical oxidative polymerization assisted with a surfactant mixed system. In a study, the effect of morphology and size, that is nanofiber, nanoparticle, and microparticle PAn prepared by modified oxidative polymerization method in the citric acid aqueous solution, on the sedimentation and ER properties of PAn has been reported the highest dispersion stability and the strongest ER effect were observed for nanofiber morphology compared to that of the nanoparticle and microparticle ones due to its possession of high aspect ratio [33]. In another study, porous PAn was prepared via chemical oxidation polymerization at various synthesis temperatures between 37°C to 95°C and reduced pore size, increased porosity, and specific surface area, and stronger ER response with lower leakage current density were reported with increasing synthesis temperature. It has been stated that the increased specific surface area and porosity lead to an increase in the interaction area between the carrier fluid and the PAn particles in the ER fluid, resulting in enhanced interfacial polarization and ER performance [34]. On the other hand, the highest ER activity was reported for the dispersion of particles obtained at the lowest synthesis temperature due to possessing higher molar mass and longer main chains of PAn, at the same time, having greater the dielectric permittivity and dielectric loss coefficient has been observed in a different study where the effect of lower polymerization temperatures in the range from −10°C to 5°C was studied [35].
2.1.2 Polyaniline/inorganic hybrid materials
PAn and PAn derivatives have been hybridized with inorganic materials in order to achieve the synergistic contribution of constituent materials, which cannot be provided from one another, to improve ER characteristics and dispersion stability of the fluid and adjust the conductivity in a desired range for ER applications [36]. Several methods have been applied to fabricate PAn/inorganic hybrid materials including in-situ chemical oxidative polymerization, emulsion polymerization, microemulsion polymerization, and Pickering emulsion polymerization of PAn and PAn derivatives with the presence of inorganic material. As an inorganic part of the PAn/inorganic hybrid material, titanate [37, 38], titania [39, 40], TiO2 [41, 42, 43], kaolinite [44], silica [14, 45, 46, 47], halloysite [48], sepiolite [49, 50], Fe2O3 [51, 52], Fe3O4 [53, 54], palygorskite [55], BaTiO3 [56, 57, 58], bentonite [59], montmorillonite [60, 61, 62], organoclay [63, 64], organo-montmorillonite [65], laponite [66], mesoporous SiO2 [67, 68, 69, 70], mesoporous TiO2 [71], anisotropic TiO2 [72], attapulgite [73], nanoporous zeolite [74], metal-organic framework (MOF) [75], MoS2 [76, 77], WS2 [78], K-feldspar [79], red mud [80], aluminum hydroxide and talc [81], and zinc ferrite [82] have been used. Among these inorganic compounds, since silica is a well-defined uniform structured compound that can be fabricated on large scale, it has been widely studied as a typical ER active material. In addition, ER fluid containing mesoporous form of silica has demonstrated improved dispersion stability, dielectric property, and ER activity due to its additional advantages, such as low density and high surface area compared to bare silica [69]. However, since silica has low conductivity, its ER response is limited. Researchers have enhanced ER activity of silica by controlling its size and morphology, and via coating the silica with conducting polymers and carbonaceous materials using different methods. For example, Noh et al. fabricated vapor deposition polymerized PAn-coated mesoporous silica particles with different aspect ratios to investigate the particle geometry effect on ER activity and demonstrated that the ER performance of the dedoped PAn-coated mesoporous silica was significantly enhanced due to the increase of the aspect ratio of the silica core [70].
Among the natural clay minerals, inherent 1D nanostructured sepiolite, palygorskite (attapulgite), and halloysite have high aspect ratio and surface charge, large specific surface area, good mechanical strength, outstanding chemical, thermal and dimensional stability, low cost, abundant natural resources, and easy processing and have been hybridized with PAn to utilize their 1D shape effect. In another study, porous zeolite allowed the PAn to fill into microstructural pores resulting in complex nanostructures, leading PAn composite to have better dielectric properties and ER performance due to stronger polarization and fibrillar formation under E [74]. A thin conducting layer of PAn is also one of the best ways of reducing the cost of conducting polymers in these inorganic/PAn nanostructured particles.
Carbon-based nanostructures such as carbon nanoparticles, multi-walled carbon nanotubes (MWCNT), graphene, and graphene oxide (GO) have been utilized for the preparation of ER materials due to their unique and versatile electrical and morphological properties. The carbon-based materials, which stand out with their high conductivity, have been combined with polymers or inorganic compounds in order to reach the appropriate conductivity range for ER studies. These studies were in the form of coating carbon-based material on polymer or inorganic material, or, on the contrary, coating carbon-based material with polymer or inorganic material. Among the carbon-based materials, GO sheets, considered as an oxidation state of graphene, have the most remarkable result since these materials possess relatively reduced electrical conductivity even without any posttreatment and good dispersion stability in carrier fluid due to the large amount of hydroxyl, carboxylic, and epoxide functional groups on its basal planes and edges [83, 84]. PAn has been combined with various carbon-based materials for ER studies, including MWCNT [85], GO [86, 87, 88], graphene [89, 90], and carbon particles [91], in addition, 2D carbonaceous particles were fabricated from annealing of PAn-coated GO sheets in vacuum [92] and core–shell particles of carbonized PAn base was coated with PAn base [93].
In a study, nitrogen-enriched carbonaceous nanotubes with large aspect ratio and tunable conductivity were prepared by heat treatment of PAn nanotubes at elevated temperatures and used as ER active material. Thus, with this approach, to achieve the desired high polarizability and dispersion stability for ER fluids, the high aspect ratio of 1D morphology has been maintained with appropriate electrical conductivity, which is difficult to achieve in highly conductive carbon-based nanostructures. Furthermore, nitrogen-enriched carbonaceous nanotubes displayed better dispersion stability and higher ER performance compared to their granular analogue [29]. In another study, to display the morphology and conductivity effect on ER performance of composite nanoplates, in-situ fabricated GO-supported PAn emeraldine salt nanoplates were treated either with ammonia or hydrazine to obtain nonconducting-GO-supported PAn base nanoplates (rGO/PAn) or conducting reduced-GO-supported PAn base nanoplates (GO/PAn), respectively. The dielectric and ER properties of both composite nanoplates, with the same morphology and shell property but with different core conductivities, were compared with granular-shaped PAn. In case of using conducting rGO as the core instead of nonconducting one enhanced the intensity and the rate of interfacial polarization of composite nanoplates and thus resulted in stronger ER response. Furthermore, both anisotropic nanoplate composites displayed much greater ER performance than that of PAn base [90]. This reported study clearly indicated that the anisotropic GO structure had an influential role in improved polarization and ER effect, whereas the conductive core gave further favorable contribution to ER effect. Apart from this study, PAn-coated GO sheet prepared with a similar approach mentioned above was subjected to heat treatment at 550°C under inert atmosphere to fabricate two-dimensional (2D) structures composed of graphene-supported amorphous carbon. The electric field-induced yield stress values of 2D-graphene-supported carbonaceous sheets were reported to be about three times greater than that of dispersion of pure carbonaceous particles obtained from annealing of PAn due to the increased polarization with the aid of the presence of the graphene core. Additionally, the interparticle friction and viscous drag force have been enhanced owing to the high-aspect-ratio of 2D-plate-like morphology [92]. Instead of amorphous carbon coating, PAn base coated on graphitic carbon prepared from carbonized PAn base particles at 650°C under inert atmosphere was used as a dispersed phase of ER fluid. This composite structure was reported to lower the interactions between the carrier liquid and the dispersed particles and enhance the ER efficiency compared with the dispersion of the bare PAn base and carbonized PAn base in silicone oil [93].
2.1.4 Polyaniline/polymer composites
For ER application, the conductivity of PAn has to be adjusted to desired level to prevent electrical short upon application of the E. There are various alternative strategies to maintain the electrical characteristics of PAn at a safe and proper level for ER purposes and enhance the ER performance, such as dedoping process, co-polymerization, encapsulating of PAn with polymers or inorganic materials with low conductivity, fabricating of core/shell hybrid structures, nanocomposites, composites, and blends. The conductivity of the PAn incorporated materials can be controlled in a wide range by altering the amount of PAn. The increasing PAn content increases the density and mobility of the charge carriers until the optimum saturation level is reached depending on the conducting network formation in the dielectric polymer matrix [94]. Many researchers have devoted themselves to combining PAn particles with an insulating polymer for ER studies. Especially, core/shell structured uniform polymer microspheres coated PAn with controlled thickness have been extensively studied to combine the morphological effect of core nonconducting polymer with the electrical properties of conducting PAn layer. As a general approach, monodispersed micron-sized PAn or PAn derivative composites are synthesized via oxidative polymerization of aniline or aniline derivative monomer in the presence of micron-sized polymer spheres such as poly(styrene) (PS) [95, 96], poly(methyl methacrylate) (PMMA) [97, 98], poly(glycidyl methacrylate) (PGMA)/PMMA [99], or poly(styrene-co-glycidyl methacrylate-co-divinylbenzene) [100]. The ER effect of the PAn-coated polymer core/shell composite particles containing dispersions depends on the PAn loading, the dispersed particle conductivity, and concentration [100]. In a study, among the homopolymer PAn, PMMA(core)/PAn(shell), and PAn(core)/PMMA(shell) particles, the ER effect of the PAn(core)/PMMA(shell) particles was demonstrated to be stronger than that of PMMA(core)/PAn(shell) particles whereas similar with that of homopolymer PAn. As a result, an insulating shell on conductive PAn core was found to be effective to obtain improved ER performance without dedoping process [97]. Additionally, the particle size of the insulating polymer core with similar PAn shell thickness and electrical properties have been reported to influence the ER performance. The larger particle size in the range from 1 to 10 μm resulted in the greater ER effect [101]. In the literature, besides the isotropic spherical PAn/insulating polymer core/shell structures, the fabrication of anisotropic PAn-coated snowman-like core/shell particles was reported via seed emulsion polymerization method [98]. To enhance the mechanical strength of the core/shell structure, the crosslinking agent like ethylene glycol dimethacrylate has also been introduced to the PMMA core before being coated by the conducting PAn derivative overlayer via grafting polymerization [102]. Another approach to produce semiconducting core/shell-type nonconducting polymer coated on PAn particles is via Pickering emulsion-type polymerization, using polymer particles as a solid polymeric surfactant, such as poly(divinylbenzene-alt-maleic anhydride) [103].
2.1.5 Polyaniline/poly(ionic liquid) composites
Organic polymer-based materials have been most frequently studied as ER materials compared to the inorganic ones due to their low density, soft texture, and relatively high ER activity. Among various organic polymer-based polymers, polyelectrolytes are more extensively applied in ER fluids due to their low cost, facile fabrication, and high ER response in the presence of promoter, such as a small amount of water or moisture. The small amount of water required for ER activation leads the traditional polyelectrolytes to face the electrical and thermal problems. To overcome these drawbacks, a novel anhydrous polyelectrolyte-based ER system based on hydrophobic poly(ionic liquid)s (PILs) has been developed recently [104].
PILs are a type of functional polyelectrolyte obtained by polymerization of ionic liquids, a typical organic molten salt bearing hydrophobic counterions at room temperature. PILs can exhibit strong ER activity and high dielectric polarizability without affinity to water due to comprising of high-density cation/anion counterions endowing polarized easily upon application of the E. Additionally, crosslinking can be applied to improve the mechanical and thermal properties of PILs due to possessing low glass transition temperature. The ER activity of PILs with linear backbone depends on the type and the nature of the hydrophobic counterions [105]. If the PILs are self-crosslinked, the ER effect rises with the length of the alkyl spacer due to enhanced ion mobility and induced interfacial polarization whereas the operating temperature range is narrowed resulting in current leakage at higher temperature [106]. Hydrophobic PILs can be prepared by direct polymerization of hydrophobic ionic liquid monomers or subsequent post-ion-exchange treatment after polymerization of hydrophilic ionic liquid monomers. Although, the post ion-exchange treatment is a facile procedure with higher yield, hydrophobic PILs prepared by post ion-exchange procedure are easily surface charged. In order to eliminate the surface charging and thus enhance the ER effect, the preparation of the composite particles composed of conducting PAn core encapsulated by PIL, poly(vinylbenzyl)trimethylammonium hexafluorophosphate (P[VBTMA]PF6) was reported via post-ion-exchange procedure. The P[VBTMA]PF6-capsulated PAn particles were demonstrated to have an enhanced ER effect due to partially suppressing the positively charged state of P[VBTMA]PF6 particles by wrapping PAn into P[VBTMA]PF6 when compared with that of pure PIL, pure PAn, and their simple mixture [107].
At higher E values, the irreversible leakage of mobile ions from particles into carrier liquid can be encountered for PIL-based ER fluids. Another approach to block ion leakage from PILs can be semiconducting PAn coating on the surface of ionically conductive PIL core since PAn mainly allows the transport of the electron or the hole. In a study, Zheng et al. demonstrated that core/shell structured poly[2-(methacryloyloxy)ethyl] trimethylammonium bis(trifluoromethanesulfonyl) imide (P[MTMA][TFSI])/PAn fabricated via low-temperature interfacial polymerization of PAn on the P[MTMA][TFSI] microspheres limited the irreversible ion leakage of P[MTMA][TFSI] microspheres and improved the particle polarizability and ER effect [108].
The influence of oxidation state of PAn on the ER response of PIL/PAn composite composed of P[VBTMA][PF6] as a matrix and different forms of semiconducting PAn as a filler, prepared by ion-exchange and subsequently treated by ammonia or hydrazine to obtain different forms of PAn filler, such as emeraldine salt, emeraldine base, and leucoemeraldine was studied by Zheng et al. Thus, the researchers could adjust the difference in polarization rate between filler and matrix and reported that when the closer their polarization rates were, the more stable the flow curve was in a broad shear rate region, and enhanced ER response was achieved only for the ammonia-treated P[VBTMA][PF6]/PAn particles at room temperature. On the other hand, the flow curves of the hydrazine-treated P[VBTMA][PF6]/PAn displayed more stable flow curve with increasing temperature [109]. In another study, ionic liquid crystal PAn prepared via microwave-assisted reaction using leucoemeraldine PAn as polymer skeleton, naphthalene disulfonic acids as ionic crosslinkers, and diisonicotinates as mesogenic groups demonstrated integrated behaviors of PIL, liquid crystal, and PAn-base and strong ER dependency on operating temperature [110]. Emeraldine base form of PAn was doped by the synthesized series of main-chain liquid-crystalline polymers (LCPs) with pendant sulfonic acid groups using biphenyl-4,40-diol, 6,7-dihydroxynaphthalene-2-sulfonic acid, and bis(4-(chlorocarbonyl)phenyl) decanedioate in a one-step esterification reaction. The resulting sulfonic acid-containing PAn–LCP ionomer dispersions showed better ER effect than PAn dispersions [111].
2.2 ER characteristics of polyaniline-based materials
Within the realm of ER fluids, the ER characteristics have been extensively examined by rheological measurements including steady shear, on/off switch test at constant shear rate, and oscillatory test under E and dielectric analysis in terms of understanding the behavior of ER fluid and response to external electrical stimuli. ER properties investigated are mainly yield stress, storage, and loss modulus under different E values. Without E, the shear stress of ER fluid usually increases linearly with increasing shear rate displaying Newtonian fluid behavior (Figure 2a). In the presence of the E, the shear stress remains constant over a low shear rate range and increases with increasing the shear rate in the high shear rate range according to the Bingham model (Figure 2a). The yield stress (τy) is defined as the minimum shear stress required to completely disrupt the field-induced solid-like structure under continuous shear. However, in many cases, Bingham model is not sufficient for describing the flow curves of ER fluids over a large range of the shear rate. Therefore, other models such as De Kee-Turcotte model, the Hershel-Bulkley model, Cho-Choi-Jhon (CCJ) model (Figure 2a), and Seo-Seo model have been applied [112]. The τy can be determined by above-mentioned models using experimental data. The correlation of the τy and applied electric field follows power law,τy∝Eα. The value of index, α, is 1.5 or 2.0 corresponding to the conduction model and ideal polarization model, respectively [5]. On the other hand, in some cases, this relationship is not fully consistent with the corresponding models due to the effect of dispersed particle size, morphology, surface properties and concentration, and dielectric properties of ER fluid on the τy.
Figure 2.
Representative shear stress versus shear rate curves of an ER fluid that fits the Newtonian model under off-field, the Bingham or CCJ model under on-field, and corresponding schematic microstructure under shear flow (a) and representative dielectric spectrum (b) of an ER fluid.
The viscoelastic properties and phase transition of ER fluids can be examined by dynamic oscillation test in which a sinusoidal strain or stress is applied, and the ER fluid is sheared back and forth at a given strain amplitude and frequency [5]. In order to do so, a linear viscoelastic region (LVE), where stress and strain are proportional, is initially determined by stress or strain amplitude sweep test at a fixed frequency value. Within the low-strain region, elastic (G′) and viscous (G″) modulus are independent of the applied strain or stress and show a constant plateau. When the applied strain or stress is inadequate and leads to structural breakdown of the field-induced structures, the important microstructural properties are being measured. Out of the LVE, nonlinearities arise and measurements can no longer be easily correlated with microstructural properties. Within the predetermined LVE for the given ER fluid, the angular frequency sweep test is performed to analyze the time-dependent behavior of the ER fluid in the nondestructive deformation range and to determine the behavior and inner structure, and the long-term stability of the ER fluid [113]. In the absence of the E, G′<G″ is observed at low frequencies indicating liquid-like behavior predominates, then the crossover point of G′ and G″ is appeared, which is related to the relaxation time, and at high-frequency region G′>G″ is displayed indicating solid-like behavior predominates for viscoelastic liquids. Upon application of electric field, G′>G″ is displaced and G′ and G″ are observed as parallel throughout the entire frequency range indicating stable gel-like structure with solid-like behavior. With increasing the E, the modulus values increase indicating raised structural strength.
Furthermore, the microstructural changes in the ER fluid can be directly determined by optical microscopy under E. The particles are dispersed in the carrier fluid randomly whereas they rapidly align parallel to the direction of the E and form a chain-like structure spinning towards the electrodes. Depending on the concentration of the ER fluid and the magnitude of E, columnar or network structure can also be observed.
Dielectric spectra of ER fluids, the frequency-dependent dielectric constant (ε′) and dielectric loss factor (ε″) curves (Figure 2b), provide important information about the polarization mechanism, polarizability, and polarization relaxation time (λ) of ER fluids on analyzing of electrical polarization properties and interpreting the flow behavior under the E [13]. Response time of the dispersed particles to the E and formation of stable fibrillar structures are related to the relaxation frequency of the ER fluid. A high relaxation frequency results in a short relaxation time and a rapid response time to an E. Generally, a higher polarizability corresponds to strong interactions between particles and ER performance. For achieving stable flow behavior under an E, the response rate of the dispersed particles to E was presented in the range of 10–5–10–2 s. If the response rate is too low, during shear deformation, the reconstruction of the chain-like structures in time may be hindered. If the response time value is too high, the repulsions between the particles dominate, resulting in a decrease in the stability of the chain-like structure arisen. The dielectric spectra of ER fluids can usually be explained by the Cole–Cole equation and the Havriliak–Negami model [5].
MR fluids whose rheological properties tuned reversibly and rapidly (in a fraction of millisecond) from a liquid to a nearly solid state under the presence of the H are composed of dispersing micron-sized, soft-magnetic particles (up to 50 vol%) in a nonmagnetizable carrier liquid. Soft-magnetic particles used as a dispersed phase for MR fluids generally possess inevitable sedimentation problems due to the large density mismatch between the magnetic particles and the carrier fluid, which restricts further MR applications. Additionally, corrosion, low reversibility, and remnant magnetization of the dispersed particles are other impediments to be considered. Most common approaches to reduce density and prevent magnetic particle aggregation are application of core/shell structures with the aid of polymers and addition of surfactants or submicron-sized additives such as MWCNT, graphite nanotubes, fumed silica, and organo-clay [6]. Fabrication of core/shell structure is taken more attention compared to using additives to improve the dispersion stability of MR fluids since introducing additives requires further other parameters to be considered such as size, morphology, and affinity of the additive. Also, additives may interfere with the induced chain structure of the magnetic particles in H [114]. For core/shell structures, if the core is a magnetic particle, the coating shell will provide chemical and oxidation stability. On the other hand, the ultimate disintegration in shearing can be obtained when the magnetic particle is a shell and thus the interaction between magnetic shell and nonmagnetic core should be strong. Nevertheless, both approaches improve the dispersion stability [115]. As a polymer, PAn was attractive recently for enhancing the dispersion stability and obtaining dual ER/MR response [116]. Various synthetic approaches for the preparation of PAn-based MR particles are displayed in Figure 3. In this section, the use of PAn in MR fluids in recent studies is summarized and the comparison of various properties of PAn-based materials used for MR fluids is tabulated in Table 1.
Figure 3.
Synthetic approaches for the preparation of PAn-based MR particles.
Material
Magnetic particle (its Ms)
Additive
Morphology
Synthesis method
Density (g/cm3)
Ms
MR fluid concentration
Optimum H
Yield stress at optimum H
Index α
Dual response
Ref
PAn@Fe3O4
Fe3O4 (70 emu/g)
—
Nano-sized Fe3O4-coated PAn tubes, approximately 148 nm in diameter and several μm in length
PAn/Fe composite nanofibers approximately 80–150 nm in diameter with rough surface used as additive for microspherical Cl
Two-step process for additive: i. Rapid mixing, oxidative polymerization, ii. Reduction of the polymerization by-products FeCl2/FeCl3 by NaBH4 solution
The comparison of various properties of PAn-based materials used for MR fluids.
3.1 Development and diversification of polyaniline-based MR fluids
Various soft-magnetic particles such as Fe3O4, carbonyl iron (CI), CoNi, zinc-ferrite (ZnFe2O4), and MnFe2O4 have been used as a dispersed phase for MR fluids. Their organic/inorganic composites have attracted considerable interest in terms of increasing dispersion stability of fluid, protecting magnetic particles against corrosion, and improving reversible behavior in field on/off states while maintaining intrinsic MR properties of soft-magnetic particles. However, fabricating hybrid structures have their pros and cons. Hybrid structures show slightly inferior magnetic properties compared to bare soft-magnetic particles as the aforementioned improvements are gained.
PAn having fibrous structure was coated with Fe3O4 by an in-situ self-assembly method and much lower magnetic properties were observed for the magnetic composite compared to that of pure Fe3O4 due to high percent composition of PAn. In a study, a magnetic composite consisting of Fe3O4 nanoparticles inserted in PAn matrix was fabricated and much lower magnetic properties were observed for the magnetic composite compared to that of pure Fe3O4 due to the high percent composition of PAn in the composite [118]. On the other hand, when a hierarchically structured composite was prepared by the deposition of Fe3O4 on fibrous structured PAn, fibrous PAn coated by Fe3O4 exhibited greater magnetic properties than that of particulate Fe3O4 embedded in PAn matrix [117]. The Fe3O4 particles have also been considered to fabricate a dual stimulus-responsive material to the E and the H. Fe3O4 coated monodispersed poly(N-methylaniline) microspheres were prepared with proper conductivity without undergoing dedoping and good magnetic susceptibility for ER and MR performance, respectively [126].
CI particles obtained from the decomposition of iron pentacarbonyl are most used for MR fluids due to their large saturation magnetization, small coercivity magnetization, and appropriate size. However, CI-based MR fluids generally have serious sedimentation problems due to the large density mismatch between the CI particles and the carrier fluid. One of the strategies to reduce the density or prevent particle aggregation is polymer coating on the particle surface. PAn coating has been introduced to reduce the density or prevent CI particle aggregation. Core-shell structured CI-PAn composite particles, prepared by dispersing CI particles in pre-synthesized PAn colloidal dispersion in chloroform, were reported to have similar magnetic properties with CI particles whereas enhanced dispersion stability, decreased field off viscosity and increased MR effect were observed compared to bare CI MR fluid [115]. To increase interfacial interaction and affinity between magnetic particles and PAn, Cl surface can be modified by suitable grafting agents. In a study, dopamine-attached CI particles were coated by PAn by dispersion polymerization process and the formed homogenous rough surface and low density of the core/shell PAn/CI particles resulted in improved dispersion stability [120]. For the same purposes, in another study, p-toluenesulfonic acid monohydrate was used as a surface modifier and showed the increase in chemical affinity between CI and polymer layer through hydrogen bonding and electrostatic interactions, resulting in a better core-shell morphology and improved dispersion stability, compared to the bare CI due to decreasing the density mismatch between composite particle and carrier oil [121]. Another strategy to sustain the dispersion stability was introducing carboxylic acid-functionalized MWCNT as a second layer on the PAn-coated CI core/shell particles by a two-step coating process [116]. Instead of being a shell of Cl core, iron nanoparticle-supported PAn nanofibers were used as an additive for the preparation of CI-based MR fluids and both MR properties and the dispersion stability of the MR fluid were reported to be improved [119].
Magnetic ZnFe2O4 particles coated with conducting PAn particles with raspberry-like core/shell morphology synthesized by Pickering emulsion polymerization were reported to exhibit dual ER/MR active material [122]. In another study, rough surfaces were observed when ZnFe2O4 was coated with dedoped-PAn with dual-field responsive properties [123]. Also, PAn derivatives poly(N-methyl aniline) [124] and poly(diphenylamine) [125] were also reported to be as a shell layer on magnetic ZnFe2O4 particles without any requirement of an additional de-doping process. PAn-coated spherical MnFe2O4 nanoparticles were reported with dual characteristics of ER/MR fluids [127].
3.2 MR characteristics of polyaniline-based materials
MR fluids often show a Newtonian fluid behavior, in which shear stress increases linearly with shear rate without the H. However, when a H is applied to MR fluids, the dispersed particles will get aligned along the direction of magnetic field forming fibrous structure, which leads to a solid-like state. Hence, a yield stress is necessary to make the fluid flow again. Above the yield stress, the fibrous structure breaks and yields fluidity, which means the MR fluids show a fluid-like behavior. In general, the yield stress depends on the volume fraction and the strength of H as well as the intrinsic properties of MR materials. The properties of MR fluids under the H have similarities to that of ER fluids under an electric field in terms of steady shear and oscillatory tests. However, the Herschel-Bulkley model and Bingham model are generally used to explain the flow curve of an MR fluid. The τy dependent on the magnetic field strength can also be expressed as τy∝Hα [128]. Instead of dielectric properties, the saturation magnetization (Ms) of a material is an important parameter predicting the MR performance that can be achieved in an MR fluid. Generally, a larger Ms value indicates higher MR performance of the MR fluid at the same particle concentration. Furthermore, the hysteresis of magnetic particles has a direct influence on the recovery of an MR fluid upon the removal of the H. If there is no hysteresis loop, the MR fluid exhibits soft magnetic properties and thus the magnetostatic interactions between particles in the carrier fluid form rapidly upon application of the H resulting in solid-like state and disappearing when the field is removed showing liquid-like state.
This chapter presents an overview of the status and recent studies in PAn-based materials used in electro/magneto-responsive smart fluids. Electro/magneto-responsive smart fluids have tremendous applications such as shock absorbers, robotics, clutches, valves, dampers, and microfluidics due to their possessing an ability to change their rheological properties reversibly and promptly under externally applied electric or magnetic fields in a controlled manner. The electro-responsive smart fluid, namely, ER fluids mainly consists of polarizable particles dispersed in nonconductive liquid dispersant and furthermore, various polar additives may be inserted to increase polarizability or dispersion stability of the ER fluid. But, instead of incorporating additives due to their drawbacks such as leading electrical breakdown and device corrosion, inherently anhydrous polarizable particles are desired to be used as an ER active material. Thus, inherently polarizable PAn has been one of the most promising and extensively studied conducting polymers in the research of ER materials for many years due to its tunable conductivity, ease of synthesis, adequate chemical and thermal stability, noncorrosiveness, and less friction than pure inorganic compounds. The morphology, size, shape, surface characteristics, dedoping level, and incorporation of other compounds with PAn have a significant influence on the ER properties. In this chapter, PAn-based ER fluids with various compositions are categorized in terms of constituent components and discussed in detail. Various inorganic compounds, insulating polymers, PILs, and carbon-based nanomaterials have been hybridized with PAn and PAn derivatives to improve the ER performance and the dispersion stability.
The magnetic field analog of ER fluids, MR fluids are basically made up of soft magnetizable dispersed particles, carrier fluid, and additives. The researchers have focused on enhancing the dispersion stability of soft-magnetizable dispersed particles in MR fluid, preventing particle corrosion, and improving the overall MR effect by reduction in density mismatch between carrier fluid and dispersed particles, the addition of various additives and particle coating with inorganic, organic or polymeric components. Even though PAn has no soft magnetic properties, PAn and its derivatives have also been used for enhancing the dispersion stability of MR fluids and obtaining dual ER/MR response. For that reason, there have been fewer studies on the use of PAn in MR fluids compared to its use in the ER fluids. The literature studies have indicated that while introducing PAn in MR materials enhanced the sedimentation stability, the magnetic saturation of the resulting structure was decreased. Therefore, there are still major opportunities for the development of PAn with low magnetic masking property in the future research.
According to the recent studies reported so far, it has been concluded that owing high surface area, good wettability, rough surface compared to smooth surface, hierarchical anisotropic structures compared to isotropic ones, suitable conductivity, and reduced density mismatch with carrier fluid led to enhanced ER/MR performances of PAn-based stimuli responsive fluids.
References
1.Hao T. Electrorheological fluids. Advanced Materials. 2001;13(24):1847-1857
2.de Vicente J, Klingenberg DJ, Hidalgo-Alvarez R. Magnetorheological fluids: A review. Soft Matter. 2011;7(8):3701-3710
3.Winslow WM. Induced fibration of suspensions. Journal of Applied Physics. 1949;20(12):1137-1140
4.Hao T. Electrorheological suspensions. Advances in Colloid and Interface Science. 2002;97(1):1-35
5.Dong YZ, Kim HM, Choi HJ. Conducting polymer-based electro-responsive smart suspensions. Chemical Papers. 2021;75(10):5009-5034
6.Kumar JS, Paul PS, Raghunathan G, Alex DG. A review of challenges and solutions in the preparation and use of magnetorheological fluids. International Journal of Mechanical and Materials Engineering. 2019;14(1):13
7.Rabbani Y, Hajinajaf N, Shariaty-Niassar M. The effect of microparticles/nanoparticles surface modification on the magnetorheological fluid properties: A review. Journal of Intelligent Material Systems and Structures. 2023;0(0):1045389X221147667
8.Kuznetsov NM, Kovaleva VV, Belousov SI, Chvalun SN. Electrorheological fluids: from historical retrospective to recent trends. Materials Today Chemistry. 2022;26:101066
9.Stenicka M, Pavlinek V, Saha P, Blinova NV, Stejskal J, Quadrat O. The effect of compatibility of suspension particles with the oil medium on electrorheological efficiency. Journal of Intelligent Material Systems and Structures. 2012;23(9):1055-1059
10.Stěnička M, Pavlínek V, Sáha P, Blinova NV, Stejskal J, Quadrat O. Effect of hydrophilicity of polyaniline particles on their electrorheology: Steady flow and dynamic behaviour. Journal of Colloid and Interface Science. 2010;346(1):236-240
11.Xie H-Q, Guan J-G, Guo J-S. Three ways to improve electrorheological properties of polyaniline-based suspensions. Journal of Applied Polymer Science. 1997;64:1641-1647
12.Sebastian J, Samuel JM. Recent advances in the applications of substituted polyanilines and their blends and composites. Polymer Bulletin. 2020;77(12):6641-6669
13.Fang FF, Lee BM, Choi HJ. Electrorheologically intelligent polyaniline and its composites. Macromolecular Research. 2010;18(2):99-112
14.Kuramoto N, Takahashi Y, Nagai K, Koyama K. Electrorheological properties of poly(o-anisidine) and poly(o-anisidine)-coated silica suspensions. Reactive and Functional Polymers. 1996;30(1):367-373
15.Liu J, Wen X, Liu Z, Tan Y, Yang S, Zhang P. Electrorheological performances of poly(o-toluidine) and p-toluenesulfonic acid doped poly(o-toluidine) suspensions. Colloid and Polymer Science. 2015;293(5):1391-1400
16.Gercek B, Yavuz M, Yilmaz H, Sari B, Unal HI. Comparison of electrorheological properties of some polyaniline derivatives. Colloids and Surfaces A: Physicochemical and Engineering Aspects. 2007;299(1):124-132
17.Kim JW, Jang WH, Choi HJ, Joo J. Synthesis and electrorheological characteristics of polyaniline derivatives with different substituents. Synthetic Metals. 2001;119(1):173-174
18.Kim MH, Bae DH, Choi HJ, Seo Y. Synthesis of semiconducting poly(diphenylamine) particles and analysis of their electrorheological properties. Polymer. 2017;119:40-49
19.Woo DJ, Suh MH, Shin ES, Lee CW, Lee SH. Electrorheological behavior of suspensions of a substituted polyaniline with long alkyl pendants. J Colloid Interface Sci. 2005;288(1):71-74
20.Han WJ, Choi HJ. Synthesis of conducting polymeric nanoparticles in the presence of a polymerizable surfactant and their electrorheological response. Colloid and Polymer Science. 2019;297(5):781-784
21.Choi HJ, Kim JW, To K. Electrorheological characteristics of semiconducting poly(aniline-co-o-ethoxyaniline) suspension. Polymer. 1999;40(8):2163-2166
22.Trlica J, Sáha P, Quadrat O, Stejskal J. Electrical and electrorheological behavior of poly(aniline-co-1,4-phenylenediamine) suspensions. European Polymer Journal. 2000;36(11):2313-2319
23.Cho MS, Kim TW, Choi HJ, Jhon MS. N-substituted copolyaniline for electrorheological material. Journal of Materials Science Letters. 1997;16:672-673
24.Cho CH, Choi HJ, Kim JW, Jhon MS. Synthesis and electrorheology of aniline/pyrrole copolymer. Journal of Materials Science. 2004;39(5):1883-1885
25.Mrlik M, Sedlacik M, Pavlinek V, Bober P, Trchová M, Stejskal J, et al. Electrorheology of aniline oligomers. Colloid and Polymer Science. 2013;291(9):2079-2086
26.Sung BH, Choi US, Jang HG, Park YS. Novel approach to enhance the dispersion stability of ER fluids based on hollow polyaniline sphere particle. Colloids and Surfaces A: Physicochemical and Engineering Aspects. 2006;274(1):37-42
27.Yin J, Zhao X, Xia X, Xiang L, Qiao Y. Electrorheological fluids based on nano-fibrous polyaniline. Polymer. 2008;49(20):4413-4419
28.Fang FF, Dong Y-Z, Choi HJ. Effect of oxidants on morphology of interfacial polymerized polyaniline nanofibers and their electrorheological response. Polymer. 2018;158:176-182
29.Yin J, Xia X, Xiang L, Zhao X. Conductivity and polarization of carbonaceous nanotubes derived from polyaniline nanotubes and their electrorheology when dispersed in silicone oil. Carbon. 2010;48(10):2958-2967
30.Lee BM, Kim JE, Fang FF, Choi HJ, Feller J-F. Rectangular-shaped polyaniline tubes covered with nanorods and their electrorheology. Macromolecular Chemistry and Physics. 2011;212(21):2300-2307
31.Kim MJ, Liu YD, Choi HJ. Urchin-like polyaniline microspheres fabricated from self-assembly of polyaniline nanowires and their electro-responsive characteristics. Chemical Engineering Journal. 2014;235:186-190
32.Wen Q, He K, Wang C, Wang B, Yu S, Hao C, et al. Clip-like polyaniline nanofibers synthesized by an insitu chemical oxidative polymerization and its strong electrorheological behavior. Synthetic Metals. 2018;239:1-12
33.Yin J, Xia X, Xiang L, Qiao Y, Zhao X. The electrorheological effect of polyaniline nanofiber, nanoparticle and microparticle suspensions. Smart Materials and Structures. 2009;18(9):095007
34.Lin DD, Zhang ZJ, Zhao BY, Chen LS, Hu K. Rapid synthesis of porous polyaniline and its application in electrorheological fluid. Smart Materials and Structures. 2006;15(6):1641
35.Choi HJ, Cho MS, To K. Electrorheological and dielectric characteristics of semiconductive polyaniline-silicone oil suspensions. Physica A: Statistical Mechanics and its Applications. 1998;254(1):272-279
36.Liu YD, Choi HJ. Electrorheological response of polyaniline and its hybrids. Chemical Papers. 2013;67(8):849-859
37.Ji L, Zhang J. Synthesis, characterization and electrorheological properties of polyaniline/titanate core-shell composite. Journal of Macromolecular Science, Part A. 2009;46(7):688-693
38.Cheng Q, Pavlinek V, He Y, Li C, Saha P. Electrorheological characteristics of polyaniline/titanate composite nanotube suspensions. Colloid and Polymer Science. 2009;287(4):435-441
39.Yin J, Xia X, Wang X, Zhao X. The electrorheological effect and dielectric properties of suspensions containing polyaniline@titania nanocable-like particles. Soft Matter. 2011;7(22):10978-10986
40.Wang B, Liu C, Yin Y, Yu S, Chen K, Liu P, et al. Double template assisting synthesized core–shell structured titania/polyaniline nanocomposite and its smart electrorheological response. Composites Science and Technology. 2013;86:89-100
41.Lee IS, Lee JY, Sung JH, Choi HJ. Synthesis and electrorheological characteristics of polyaniline-titanium dioxide hybrid suspension. Synthetic Metals. 2005;152(1):173-176
42.Tang J, Wen X, Liu Z, Wang J, Zhang P. Synthesis and electrorheological performances of 2D PANI/TiO2 nanosheets. Colloids and Surfaces A: Physicochemical and Engineering Aspects. 2018;552:24-31
43.Lee S, Noh J, Jekal S, Kim J, Oh W-C, Sim H-S, et al. Hollow TiO2 nanoparticles capped with polarizability-tunable conducting polymers for improved electrorheological activity. Nanomaterials. 2022;12(19):3521
44.Wang B, Liu C, Yin Y, Tian X, Yu S, Chen K, et al. The electrorheological properties of polyaniline nanofiber/kaolinite hybrid nanocomposite. Journal of Applied Polymer Science. 2013;130(2):1104-1113
45.Lengálová A, Vr P, Sáha P, Stejskal J, Kitano T, Quadrat O. The effect of dielectric properties on the electrorheology of suspensions of silica particles coated with polyaniline. Physica A: Statistical Mechanics and its Applications. 2003;321(3):411-424
46.Liu YD, Zhang WL, Choi HJ. Pickering emulsion polymerization of core–shell-structured polyaniline@SiO2 nanoparticles and their electrorheological response. Colloid and Polymer Science. 2012;290(9):855-860
47.Jang HS, Kwon SH, Lee JH, Choi HJ. Facile fabrication of core-shell typed silica/poly(diphenylamine) composite microparticles and their electro-response. Polymer. 2019;182:121851
48.Zhang WL, Choi HJ. Fabrication of semiconducting polyaniline-wrapped halloysite nanotube composite and its electrorheology. Colloid and Polymer Science. 2012;290(17):1743-1748
49.Marins JA, Giulieri F, Soares BG, Bossis G. Hybrid polyaniline-coated sepiolite nanofibers for electrorheological fluid applications. Synthetic Metals. 2013;185-186:9-16
50.Jang DS, Choi HJ. Conducting polyaniline-wrapped sepiolite composite and its stimuli-response under applied electric fields. Colloids and Surfaces A: Physicochemical and Engineering Aspects. 2015;469:20-28
51.Tian X, He K, Wang B, Yu S, Hao C, Chen K, et al. Flower-like Fe2O3/polyaniline core/shell nanocomposite and its electroheological properties. Colloids and Surfaces A: Physicochemical and Engineering Aspects. 2016;498:185-193
52.Zhu X, Zhao Q, Zhang T, Pang X. Electrorheological response of novel polyaniline-Fe2O3 nanocomposite particles. Polymer-Plastics Technology and Materials. 2019;58(5):573-577
54.Lu Q, Lee JH, Lee JH, Choi HJ. Magnetite/poly(ortho-anisidine) composite particles and their electrorheological response. Materials. 2021;14(11):2900
55.Chae HS, Zhang WL, Piao SH, Choi HJ. Synthesized palygorskite/polyaniline nanocomposite particles by oxidative polymerization and their electrorheology. Applied Clay Science. 2015;107:165-172
56.Fei Fang F, Hye Kim J, Jin Choi H, Seo Y. Organic/inorganic hybrid of polyaniline/BaTiO3 composites and their electrorheological and dielectric characteristics. Journal of Applied Polymer Science. 2007;105(4):1853-1860
57.Yan H, Liao ZJ, Zhu X, Wang XM, Chen Y, Zhang B, et al. Synthesis and electrorheological properties of polyaniline-coated barium titanate composite particles. Journal of Applied Polymer Science. 2008;107(3):1960-1966
58.Linzhi LI, Shujuan GAO. Polyaniline (PANI) and BaTiO3 composite nanotube with high suspension performance in electrorheological fluid. Materials Today Communications. 2020;24:100993
59.Wang B, Yin Y, Liu C, Yu S, Chen K. Synthesis and characterization of clay/polyaniline nanofiber hybrids. Journal of Applied Polymer Science. 2013;128(2):1304-1312
60.Kim JW, Kim SG, Choi HJ, Jhon MS. Synthesis and electrorheological properties of polyaniline-Na+-montmorillonite suspensions. Macromolecular Rapid Communications. 1999;20(8):450-452
61.Lu J, Zhao X. Electrorheological properties of a polyaniline–montmorillonite clay nanocomposite suspension. Journal of Materials Chemistry. 2002;12(9):2603-2605
62.Song DH, Lee HM, Lee K-H, Choi HJ. Intercalated conducting polyaniline–clay nanocomposites and their electrical characteristics. Journal of Physics and Chemistry of Solids. 2008;69(5):1383-1385
63.Lim YT, Park JH, Park OO. Improved electrorheological effect in polyaniline nanocomposite suspensions. Journal of Colloid and Interface Science. 2002;245(1):198-203
64.Fang FF, Liu YD, Choi HJ. Synthesis and electrorheological characteristics of polyaniline/organoclay nanoparticles via Pickering emulsion polymerization. Smart Materials and Structures. 2010;19(12):124002
65.Sung JH, Choi HJ. Effect of pH on physical characteristics of conducting poly(o-ethoxyaniline) nanocomposites. Journal of Macromolecular Science, Part B. 2005;44(3):365-375
66.Jun CS, Sim B, Choi HJ. Fabrication of electric-stimuli responsive polyaniline/laponite composite and its viscoelastic and dielectric characteristics. Colloids and Surfaces A: Physicochemical and Engineering Aspects. 2015;482:670-677
67.Cho MS, Choi HJ, Kim KY, Ahn WS. Synthesis and characterization of polyaniline/mesoporous SBA-15 nanocomposite. Macromolecular Rapid Communications. 2002;23(12):713-716
68.Cho MS, Choi HJ, Ahn W-S. Enhanced electrorheology of conducting polyaniline confined in MCM-41 channels. Langmuir. 2004;20(1):202-207
69.Fang FF, Choi HJ, Ahn WS. Electroactive response of mesoporous silica and its nanocomposites with conducting polymers. Composites Science and Technology. 2009;69(13):2088-2092
70.Noh J, Yoon C-M, Jang J. Enhanced electrorheological activity of polyaniline coated mesoporous silica with high aspect ratio. Journal of Colloid and Interface Science. 2016;470:237-244
71.Wei C, Zhu Y, Yang X, Li C. One-pot synthesis of polyaniline-doped in mesoporous TiO2 and its electrorheological behavior. Materials Science and Engineering: B. 2007;137(1):213-216
72.Tian X, He K, Wang C, Wen Q, Wang B, Yu S, et al. Preparation and electrorheological behavior of anisotropic titanium oxide/polyaniline core/shell nanocomposite. Composites Science and Technology. 2016;137:118-129
73.Han WJ, Piao SH, Choi HJ. Synthesis and electrorheological characteristics of polyaniline@attapulgite nanoparticles via Pickering emulsion polymerization. Materials Letters. 2017;204:42-44
74.Chattopadhyay A, Rani P, Srivastava R, Dhar P. Electro-elastoviscous response of polyaniline functionalized nano-porous zeolite based colloidal dispersions. Journal of Colloid and Interface Science. 2018;519:242-254
75.Wen Q, Ma L, Wang C, Wang B, Han R, Hao C, et al. Preparation of core–shell structured metal–organic framework@PANI nanocomposite and its electrorheological properties. RSC Advances. 2019;9(25):14520-14530
76.Zhang WL, Jiang D, Wang X, Hao BN, Liu YD, Liu J. Growth of polyaniline nanoneedles on MoS2 nanosheets, tunable electroresponse, and electromagnetic wave attenuation analysis. The Journal of Physical Chemistry C. 2017;121(9):4989-4998
77.Li C, Chen Y, Wang L, Wang Z, Lin Y, Xiong K, et al. Electrorheological response behavior of PANI@MoS2 core–shell nanocomposites. Advanced Engineering Materials. 2023;25:2300029
78.Stejskal J, Mrlík M, Plachý T, Trchová M, Kovářová J, Li Y. Molybdenum and tungsten disulfides surface-modified with a conducting polymer, polyaniline, for application in electrorheology. Reactive and Functional Polymers. 2017;120:30-37
79.Erol O, Karakisla M, Unal HI, Sacak M. Electrorheological properties of polyaniline/K-feldspar conducting composite. Journal of Composite Materials. 2012;46(11):1295-1304
80.Yavuz M, Gok A, Sen S, Unal HI. Electrorheological properties of polyaniline/red mud composite. International Journal of Polymer Analysis and Characterization. 2008;13(1):9-24
81.Lengálová A, Pavlı́nek Vr, Sáha P, Stejskal J, Quadrat O. Electrorheology of polyaniline-coated inorganic particles in silicone oil. Journal of Colloid and Interface Science. 2003;258(1):174-178
82.Munteanu L, Munteanu A, Sedlacik M, Kutalkova E, Kohl M, Kalendova A. Zinc ferrite/polyaniline composite particles: Pigment applicable as electro-active paint. J Ind Eng Chem. 2022;115:440-448
83.Zhang WL, Liu J, Choi HJ. Graphene and graphene oxide composites and their electrorheological applications. Journal of Nanomaterials. 2015;2015:574637
84.Lu Q, Jang HS, Han WJ, Lee JH, Choi HJ. Stimuli-responsive graphene oxide-polymer nanocomposites. Macromolecular Research. 2019;27(11):1061-1070
85.Park SJ, Park SY, Cho MS, Choi HJ, Jhon MS. Synthesis and electrorhelogy of multi-walled carbon nanotube/polyaniline nanoparticles. Synthetic Metals. 2005;152(1):337-340
86.Sim B, Zhang WL, Choi HJ. Graphene oxide/poly(2-methylaniline) composite particle suspension and its electro-response. Materials Chemistry and Physics. 2015;153:443-449
87.Zhang K, Li H, Dong YZ, Zhang H, Zhao W, Zhao S, et al. Jellyfish-shaped p-phenylenediamine functionalized graphene oxide-g-polyaniline fibers and their electrorheology. Polymer. 2019;168:29-35
88.Gao CY, Kim MH, Jin H-J, Choi HJ. Synthesis and electrorheological response of graphene oxide/polydiphenylamine microsheet composite particles. Polymers. 2020;12(9):1984
89.Yin J, Wang X, Chang R, Zhao X. Polyaniline decorated graphene sheet suspension with enhanced electrorheology. Soft Matter. 2012;8(2):294-297
90.Yuan J, Wang Y, Xiang L, Zhao X, Yin J. Understanding the enhanced electrorheological effect of reduced graphene oxide-supported polyaniline dielectric nanoplates by a comparative study with graphene oxide as the support core. IET Nanodielectrics. 2021;4(3):143-154
91.Sedlacik M, Almajdalawi S, Mrlik M, Pavlinek V, Saha P, Stejskal J. Viscoelastic properties of electrorheological suspensions of core-shell (carbon/polyaniline) particles in silicone oil. Journal of Physics: Conference Series. 2013;412(1):012006
92.Yin J, Shui Y, Chang R, Zhao X. Graphene-supported carbonaceous dielectric sheets and their electrorheology. Carbon. 2012;50(14):5247-5255
93.Sedlacik M, Pavlinek V, Mrlik M, Morávková Z, Hajná M, Trchová M, et al. Electrorheology of polyaniline, carbonized polyaniline, and their core–shell composites. Materials Letters. 2013;101:90-92
94.Abu Hassan Shaari H, Ramli MM, Mohtar MN, Abdul Rahman N, Ahmad A. Synthesis and conductivity studies of poly(methyl methacrylate) (PMMA) by co-polymerization and blending with polyaniline (PANi). Polymers. 2021;13(12):1939
95.Kim MH, Choi HJ. Core–shell structured semiconducting poly(diphenylamine)-coated polystyrene microspheres and their electrorheology. Polymer. 2017;131:120-131
96.Sung SK, Hyoung JC. Poly(2,5-dimethoxyaniline) coated polystyrene microspheres and their electrorheological characteristics. Colloids and Surfaces A: Physicochemical and Engineering Aspects. 2020;605:125375
97.Park SY, Cho MS, Kim CA, Choi HJ, Jhon MS. Polyaniline microsphere encapsulated by poly(methyl methacrylate) and investigation of its electrorheological properties. Colloid and Polymer Science. 2003;282(2):198-202
98.Liu YD, Fang FF, Choi HJ. Core−shell structured semiconducting PMMA/polyaniline snowman-like anisotropic microparticles and their electrorheology. Langmuir. 2010;26(15):12849-12854
99.Lee IS, Cho MS, Choi HJ. Preparation of polyaniline coated poly(methyl methacrylate) microsphere by graft polymerization and its electrorheology. Polymer. 2005;46(4):1317-1321
100.Jun J-B, Kim J-W, Suh K-D. Monodisperse micron-sized polyaniline composite particles for electrorheological fluid material. Macromolecular Chemistry and Physics. 2002;203(7):1011-1017
101.Cho MS, Cho YH, Choi HJ, Jhon MS. Synthesis and electrorheological characteristics of polyaniline-coated poly(methyl methacrylate) microsphere: Size effect. Langmuir. 2003;19(14):5875-5881
102.Moon IJ, Choi HJ. Core-shell-structured copolyaniline-coated polymeric nanoparticle suspension and its viscoelastic response under various electric fields. Materials. 2015;8(8):4932-4942
103.Jun CS, Kwon SH, Choi HJ, Seo Y. Polymeric nanoparticle-coated Pickering emulsion-synthesized conducting polyaniline hybrid particles and their electrorheological study. ACS Applied Materials & Interfaces. 2017;9(51):44811-44819
104.Dong Y, Yin J, Zhao X. Microwave-synthesized poly(ionic liquid) particles: A new material with high electrorheological activity. Journal of Materials Chemistry A. 2014;2(25):9812-9819
105.Dong Y, Liu Y, Wang B, Xiang L, Zhao X, Yin J. Influence of counterion type on dielectric and electrorheological responses of poly(ionic liquid)s. Polymer. 2017;132:273-285
106.Liu Y, Zhao J, He F, Zheng C, Zhao X, Yin J. Influence of alkyl spacer length on ion transport, polarization and electro-responsive electrorheological effect of self-crosslinked poly(ionic liquid)s. Polymer. 2019;171:161-172
107.Zheng C, Dong Y, Liu Y, Zhao X, Yin J. Enhanced stimuli-responsive electrorheological property of poly(ionic liquid)s-capsulated polyaniline particles. Polymers. 2017;9(9):385
108.Zheng C, Liu Y, Dong Y, He F, Zhao X, Yin J. Low-temperature interfacial polymerization and enhanced electro-responsive characteristic of poly(ionic liquid)s@polyaniline core-shell microspheres. Macromolecular Rapid Communications. 2019;40(17):1800351
109.Zheng C, Lei Q, Zhao J, Zhao X, Yin J. The effect of dielectric polarization rate difference of filler and matrix on the electrorheological responses of poly(ionic liquid)/polyaniline composite particles. Polymers. 2020;12(3):703
110.Li X, Yan G, Wang J, Kong W, Chang X, Zhuang Y, et al. Effect of a temperature threshold on the electrorheological performance of ionic liquid crystal polyanilines. Journal of Molecular Liquids. 2021;326:115299
111.Meng F-B, Zhou N-Y, Du C, Gao H-M, He X-Z. Synthesis, characterization and electrorheological effect of sulfosalt-type liquid-crystalline ionomers containing polyaniline units. Journal of Applied Polymer Science. 2013;130(5):3395-3403
112.Seo YP, Choi HJ, Lee JR, Seo Y. Modeling and analysis of an electrorheological flow behavior containing semiconducting graphene oxide/polyaniline composite particles. Colloids and Surfaces A: Physicochemical and Engineering Aspects. 2014;457:363-367
113.Ramli H, Zainal NFA, Hess M, Chan CH. Basic principle and good practices of rheology for polymers for teachers and beginners. Chemistry Teacher International. 2022;4(4):307-326
114.Fang FF, Choi HJ, Choi WS. Two-layer coating with polymer and carbon nanotube on magnetic carbonyl iron particle and its magnetorheology. Colloid and Polymer Science. 2010;288(3):359-363
115.Sedlačík M, Pavlínek V, Sáha P, Švrčinová P, Filip P, Stejskal J. Rheological properties of magnetorheological suspensions based on core–shell structured polyaniline-coated carbonyl iron particles. Smart Materials and Structures. 2010;19(11):115008
116.Fang FF, Liu YD, Choi HJ, Seo Y. Core–shell structured carbonyl iron microspheres prepared via dual-step functionality coatings and their magnetorheological response. ACS Applied Materials & Interfaces. 2011;3(9):3487-3495
117.Kwon SH, Sim B, Choi HJ. Magnetorheological characteristics of nano-sized iron oxide coated polyaniline composites. IEEE Transactions on Magnetics. 2016;52(7):1-4
118.Kim JH, Fang FF, Choi HJ, Seo Y. Magnetic composites of conducting polyaniline/nano-sized magnetite and their magnetorheology. Materials Letters. 2008;62(17):2897-2899
119.Piao SH, Bhaumik M, Maity A, Choi HJ. Polyaniline/Fe composite nanofiber added softmagnetic carbonyl iron microsphere suspension and its magnetorheology. Journal of Materials Chemistry C. 2015;3(8):1861-1868
120.Moon IJ, Kim MW, Choi HJ, Kim N, You C-Y. Fabrication of dopamine grafted polyaniline/carbonyl iron core-shell typed microspheres and their magnetorheology. Colloids and Surfaces A: Physicochemical and Engineering Aspects. 2016;500:137-145
121.Min TH, Choi HJ, Kim N-H, Park K, You C-Y. Effects of surface treatment on magnetic carbonyl iron/polyaniline microspheres and their magnetorheological study. Colloids and Surfaces A: Physicochemical and Engineering Aspects. 2017;531:48-55
122.Kim JN, Dong YZ, Choi HJ. Pickering emulsion polymerized polyaniline/zinc-ferrite composite particles and their dual electrorheological and magnetorheological responses. ACS Omega. 2020;5(13):7675-7682
123.Kim HM, Kang SH, Choi HJ. Polyaniline coated ZnFe2O4 microsphere and its electrorheological and magnetorheological response. Colloids and Surfaces A: Physicochemical and Engineering Aspects. 2021;626:127079
124.Kim HM, Jeong JY, Kang SH, Jin H-J, Choi HJ. Dual electrorheological and magnetorheological behaviors of poly(N-methyl aniline) coated ZnFe2O4 composite particles. Materials. 2022;15(7):2677
125.Kim TH, Choi HJ. Fabrication and shear response of conducting polymer-coated zinc ferrite particles under magnetic/electric field. IEEE Transactions on Magnetics. 2022;58(2):1-5
126.Dong Y, Wang S, Choi HJ. Poly(N-methylaniline)/magnetite microsphere and its electrical and magnetic dual responses. Polymer. 2022;240:124492
127.Jeong JY, Kim S, Baek E, You CY, Choi HJ. Suspension rheology of polyaniline coated manganese ferrite particles under electric/magnetic fields. Colloids and Surfaces A: Physicochemical and Engineering Aspects. 2023;656:130438
128.Dong YZ, Choi K, Kwon SH, Nam J-D, Choi HJ. Nanoparticles functionalized by conducting polymers and their electrorheological and magnetorheological applications. Polymers. 2020;12(1):204
Written By
Ozlem Erol
Submitted: 27 May 2023Reviewed: 29 May 2023Published: 21 August 2023
Open access peer-reviewed chapter
