Electrorheological characteristics of polyaniline/titanate composite nanotube suspensions

In this paper, one-dimensional polyaniline/titanate (PANI/TN) composite nanotubes were synthesized by in situ chemical oxidative polymerization directed by block copolymer. These novel nanocomposite particles were used as a dispersed phase in electrorheological (ER) fluids, and the ER properties were investigated under both steady and dynamic shear. It was found that the ER activity of PANI/TN fluids varied with the ratio of aniline to titanate, and the PANI/TN suspensions showed a higher ER effect than that made by sphere-like PANI/TiO₂ nanoparticles. These observations were well interpreted by their dielectric spectra analysis; a larger dielectric loss enhancement and a faster rate of interfacial polarization were responsible for a higher ER activity of nanotubular PANI/TN-based fluids.     

Electrorheological characteristics of polyaniline and its copolymer suspensions with ionic and nonionic substituents

Electrorheological (ER) characteristics of ER fluids, composed of suspensions of semiconducting polyaniline and two different copolyaniline particles in silicone oil, were determined experimentally. Ionic sodium diphenylamine sulfonate and nonionic o-ethoxyaniline were used to synthesize copolyanilines, i.e. N-substituted copolyaniline and poly(aniline-co-o-ethoxyaniline), respectively. ER fluids composed of these three different polymers were compared with respect to their rheological properties under an applied electric field. It was found that ER fluids containing a copolymer with an ionic group exhibited the highest ER performance among polyaniline and its copolymer systems in a shear-rate region above 1 s⁻¹. Received: 22 February 1999 /Accepted in revised form: 25 August 1999     

Electrorheological behavior of copper phthalocyanine-doped MCM-41 suspensions

A type of anhydrous electrorheological (ER) material of copper phthalocyanine (CuPC)-doped MCM-41 was synthesized by in situ micelle-assisted incorporation of CuPC during MCM-41 synthesis. The ER behavior of the suspensions of CuPC-doped MCM-41 particles in paraffin liquid with a 30 wt.% was investigated under an applied electric field. It is found that the ER effect increased with increasing the CuPC-doping ratio. The dopants of CuPC molecules within the mesochannel of MCM-41 mesoporous sieve improved the conductivity of the particles, and produced a proper conductivity of 10⁻⁷ S m⁻¹. Dielectric spectra of the fluids were also measured to examine their possible correlation with the ER behavior, and the results were explained based on Ikazaki's criterion that the relaxation frequency must be in the range 100–10⁵ Hz and the difference in the dielectric constant must be large below and above the relaxation frequency for an appreciable ER effect.     

Compression behavior of Langmuir-Blodgett monolayers of regioselectively substituted cellulose ethers with long alkyl side chains

Regioselectively substituted alkylcellulose ethers having long alkyl side chains, 6-O- (6C18), 2,3-di-O- (23C18), and tri-O-octadecyl-cellulose (triC18) were successfully synthesized. The key step of these syntheses was removal of the residual alkylation reagent by an isothermal crystallization procedure to isolate and purify the compounds, since a physical entanglement between the long alkyl side chains in the cellulose derivatives and the reagent had caused difficulty in obtaining the purified derivatives. After the monolayers from these cellulose ethers were fabricated on a water surface, they were deposited on substrates by a vertical dipping method to be Langmuir-Blodgett (LB) monolayers. During the compression process of each monolayer, a surface pressure (pi)-area (A) isotherm behaved in a different way. Atomic force microscopy (AFM) was employed to interpret changes of the surface topography of the obtained LB monolayers depending on the surface pressure. The compressed 23C18 LB monolayer was observed to be more homogeneous than other samples. On the basis of the LB monolayer thickness estimated by AFM as well as X-ray reflection measurements, the 23C18 LB monolayer was assumed to possibly possess the vertical arrangement of an up-ordering of all the alkyl side chains on the individual glucose ring against the water surface. In other words, with increase in the surface pressure, the usual conformation of a 2(1) screw of cellulose backbone may be changed into an unusual conformation with a certain phi-psi dihedral angle resulting in 1-fold axis without a symmetry element. These results suggest that the formation of such compressed LB monolayers was strongly influenced by the hydrophobic interaction among the distribution of the long alkyl side chains in the anhydroglucose unit and further lack of inter- and/or intramolecular hydrogen bonds engaged in cellulose ethers, and as a result, those effects may even change the main chain conformation.     

Electrorheological behavior of copper phthalocyanine-doped mesoporous TiO2 suspensions

A type of anhydrous electrorheological (ER) material of copper phthalocyanine (CuPC)-doped mesoporous TiO2 was synthesized by in situ micelle-assisted incorporation CuPC during mesoporous TiO2 synthesis. TEM, XRD and the nitrogen adsorption-desorption isotherms demonstrated that the material had mesoporous structure and an anatase framework. The ER behavior of the suspensions of CuPC-doped mesoporous TiO2 in silicone oil with the different volume fractions was investigated under an applied electric field. It is found that the suspensions showed visible electrorheological behavior which were compared with that of pure TiO2. The dopants of CuPC molecules within the mesochannel of TiO2 mesoporous sieve improved the conductivity of the particles and produced a proper conductivity of approximately 10(-7) S m(-1). Dielectric spectra of the ER fluid were measured to examine the peak of epsilon' should appear in the frequency range of 10(2)-10(5) Hz and have a large Deltaepsilon' in this frequency range. Therefore, the both properties may make a conjunct effect on electrorheological behavior.     

Electrorheological properties of suspensions of monodispersed micron‐sized polyaniline composite particles

Monodispersed micron‐sized polyaniline (PANi) composite particles were synthesized by chemically oxidative polymerization of aniline in the presence of functional porous polymer particles. The formation of the PANi‐coated composite particles was confirmed by scanning electron microscopy. Electrorheological (ER) properties of the monosized composite particle suspensions were then investigated under different DC electric fields by altering the particle characteristics. The ER effect of the PANi composite suspensions was largely dependent on the composition ratio (PANi loading), the particle conductivity, and the particle concentration. Dynamic oscillation measurements revealed that the applied electric field induced the viscoelastic property of the ER suspensions by generating the chain structures of the suspended particles. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1163–1170, 2002     

Electrorheological behavior of urea-doped mesoporous TiO2 suspensions

A type of anhydrous electrorheological (ER) material of urea-doped mesoporous TiO₂ is synthesized by in micelle-assisted incorporation urea molecules during mesoporous TiO₂ synthesis. TEM, XRD demonstrate that the material had mesoporous structure, while the FT-IR spectra and the nitrogen adsorption–desorption isotherms show urea molecules have been fixed in the channel of the mesoporous TiO₂. The ER behavior of the suspensions of urea-doped mesoporous TiO₂ in silicone oil with the different volume fractions was investigated under an applied electric field. It is found that the suspensions show visible electrorheological behavior which are compared with that of pure TiO₂. The dopants of urea molecules change the conductivity of the particles, and produce a proper conductivity of 10⁻⁷ S m⁻¹ with the molar ratio of urea/Ti = 0.2. Dielectric spectra of the ER fluid was measured to examine the peak of ″ should appear in the frequency range of 10²–10⁵ Hz and have a large Δ′ in this frequency range. The interfacial particle polarization model can exactly explain the ER behavior of this material.     

Electrorheological properties of polyaniline suspensions: field-induced liquid to solid transition and residual gel structure

Polyaniline (PANI) was synthesized via oxidative coupling polymerization in acid conditions and de-doped in solution of ammonia. The electrorheological (ER) properties of the PANI/silicone oil suspensions were investigated in oscillatory shear as functions of electric field strength, particle concentration, and host fluid viscosity. Consistent with literature, the PANI ER fluid exhibits viscoelastic behavior under the applied electric field and the ER response is strongly enhanced with increasing electric field strength and particle concentration. The dynamic moduli, G' and G' increase dramatically, by 5 orders of magnitude, as the electric field strength is increased to 2 kV/mm. A viscoelastic liquid to solid transition occurs at a critical electric field strength, in the range Ec = 50-200 V/mm, whose value depends on particle concentration and host fluid viscosity. The fibrillar structure formed in the presence of the applied field has a static yield strength tau(y), whose value scales with electric field strength as tau(y) approximately E(1.88). When the field is switched off a residual structure remains, whose yield stress increases with the strength of the applied field and particle concentration. When the applied stress exceeds the yield stress of the residual structure, fast, fully reversible switching of the ER response is obtained.     

Soluble alkyl substituted polygermanes: Thermochromic behavior

We have prepared a number of high molecular weight, soluble, symmetrical dialkyl substituted germanium homopolymers and germanium-silicon copolymers. In solution, the absorption of the homopolymers was ～ 20 nm red shifted from the crossponding silicon derivatives. This was somewhat unexpected based on theoretical predictions and has been rationalized on the basis of conformational arguments. In the solid state, samples of poly(di-n-hexylgermane) and poly(di-n-octylgermane) are strongly thermochromic. The effect is attributed to the conformational locking of the backbone which is caused by the crystallization of the side groups. In this regard, the germanium derivatives behave similarly to the corresponding silicon polymers, and the convergence of the long wavelength absorptions for both types of polymers is consistent with theoretical predictions. The germanium-silicon copolymers are also strongly thermochromic, but the long wavelength absorption is somewhat blue shifted (8 nm) from the respective homopolymers. As expected, the new germanium homo and copolymers are quite sensitive to light and readily undergo chain scission to produce lower molecular weight materials.     

Electrorheological properties of PMMA-b-PSt copolymer suspensions

In this study, a block copolymer of methyl methacrylate (MMA) and styrene (St) synthesized by combined ultrasonic irradiation and reverse atom transfer radical polymerization (RATRP) processes was used. PMMA-b-PSt was partially hydrolyzed and converted to a lithium salt, PMMA-b-PSt-Li, before the electrorheological (ER) measurements carried out. Average particle diameter of PMMA-b-PSt-Li polymeric salt was determined by dynamic light scattering (DLS) as 22 mum. Suspensions of PMMA-b-PSt-Li polymeric salts were prepared in silicone oil. ER properties of PMMA-b-PSt-Li/silicone oil suspensions were studied as a function of electric field strength, dispersed phase concentration, shear rate, shear stress, temperature, frequency, and polar promoter. Further dielectric properties of PMMA-b-PSt-Li ionomer were also investigated.     

Electrorheological analysis of nano laden suspensions

The synthesis and characterization of Pb3O2Cl2 nanowires and the electrorheological (ER) properties of carbon nanofiber (CNF), carbon nanotube (CNT) and Pb3O2Cl2 nanowire (NW) laden suspensions is presented. The ER properties were investigated through oscillatory shear experiments. The viscoelastic response in the presence of dc electric fields was analyzed. Actuation behavior for the CNF and NW laden suspensions was observed at low voltages and low concentration of the reinforcements (0.05 wt%). In the case of the CNT laden suspensions, an effect was observed at a concentration of 0.0125 wt%. Positive and negative electrorheological behaviors were observed due to differences in electrical conductivity and polarization mechanisms.     

Comment on "Electrorheological behavior of copper phthalocyanine-doped mesoporous TiO2 suspensions"

We comment on the electrorheological (ER) behavior of copper phthalocyanine (CuPC)-doped mesoporous TiO(2) suspensions. Our Cole-Cole plot not only fits the dielectric spectra of the two CuPC-doped mesoporous TiO(2) templated ER fluids with CuPC/cetyltrimethylammonium (CTAB) molar ratios of 0.10 and 0.15, respectively, but also provides a better explanation of their polarizability by differentiating their ER performance.     

Electrorheological response of polyaniline and its hybrids

One of the remarkable applications of conducting polymers is as an electrorheological (ER) fluid which is a smart suspension of polarisable particles dispersed in an insulating liquid with the capacity to effect a phase transition from a liquid-like to a solid-like state. Polyaniline (PANI) and its hybrids with inorganics or other polymers are active candidates for ER materials due to their various advantages, e.g., easy synthesis, controllable conductivity, and less friction than pure inorganics. In this short review, we review recent progress in the synthesis of semi-conducting PANI and its hybrids with diverse morphologies and their ER performance measured by a rotational rheometer using the applied electric field strength. The dielectric properties of these ER fluids, as an important analytical method for their ER performance, are also discussed.     

Electrorheological properties and microstructure of silica suspensions

We present experimental and theoretical results on the electrorheological response and microstructure of colloidal suspensions composed of silica nanoparticles dispersed in a silicon oil, as a function of electric field strength and silica water content. Using small-angle neutrons scattering experiments, we determined the evolution of the static structure factor of the suspensions when an electric field is applied. Experimental data were fitted with model calculations using the Percus-Yevick solution for Baxter's hard-sphere adhesive potential. The obtained stickiness parameter is directly related to the polarization interactions that depend on the water content of silica particles. The influence of the polarization interparticle potential on the rheology of the silica dispersions was investigated in a second time. A microscopic theory for the shear viscosity of adhesive hard-sphere suspensions was successfully used which describes the steady shear viscosity of suspension in terms of the fractal concept.     

Electrorheological properties of perchloric acid-doped polythiophene suspensions

Poly(3-thiopheneacetic acid), PTAA, was synthesized via an oxidative polymerization and doped with perchloric acid to control its conductivity. The rheological properties of the HClO₄-doped PTAA/silicone oil suspensions were measured in oscillatory shear to investigate the effects of electric field strength, particle concentration, and particle conductivity on electrorheological (ER) characteristics. The PTAA-based ER fluids exhibit viscoelastic behavior under an applied electric field and the ER response is amplified with increase of electric field strength. The dynamic moduli, G and G, increase dramatically by ten orders of magnitude when the field strength is increased to 2 kV/mm. The suspensions exhibit a transition from fluid-like to solid-like behavior as the field strength increases, and reach a saturated ER response at a field strength of 1 kV/mm. Increase of particle concentration and particle conductivity result in a lower transition field strength. Scaling arguments are presented which successfully superpose the scaled moduli at various electric field strengths onto a single master function of the dimensionless frequency.     

十八烷基取代吲哚啉螺吡喃衍生物的合成及光谱性质

本文合成了十种新的十八烷基取代的吲哚螺吡喃衍生物,拟进一步研究这类化合物在LB膜中的光致变色性质.     

Combinations of alkyl radicals with alkyl and substituted allyl radicals

In contrast with expectations based upon simple collision theory, reactions of alkyl radicals with substituted allyl radicals yield cross-combination ratios of =2. Reactions of CH ₃ ^\ with some C₅ radicals give >2, in accordance with theory.

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, =2. CH₃ ^\ C₅ >2, .

     

Synthesis and solution properties of poly(vinyl ether)s with long alkyl chain,biphenyl, and cholesteryl pendants

The judicious choice of reaction conditions permitted living cationic polymerization of vinyl ethers with bulky and strongly interacting pendant groups, such as crystalline long alkyl chains and liquid crystalline mesogenic structures, using appropriate combinations of Lewis acids with added bases. Thus, well‐defined random and block copolymers with various pendants were also synthesized. Highly sensitive UCST‐type phase separation in various organic solvents was achieved employing crystallization of octadecyl pendants of homopolymers and random copolymers. This phase separation behavior is unusual for a polymer‐organic solvent system. Furthermore, thermally induced reversible physical gelation was conducted using this thermosensitive behavior. These specific pendants were very effective not only in organic media but also in water, in obtaining hydrogels with relatively low polymer concentrations. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4392–4406, 2008     

Photochemical and thermal behavior of light-driven unidirectional molecular motor with long alkyl chains

In order to utilize molecular motors in a molecular device or smart materials, their dynamic behavior when other groups are introduced at key positions has to be examined. A C₁₆ hydrocarbon chain has been introduced at the stereogenic centers of the first generation light-driven molecular motor based on sterically overcrowded biphenanthrylidene. It was found that this derivatization does not affect the unidirectional rotary capability of the motor and does not cause a reduction of its speed, opening new possibility for future functionalizations and applications.     

Electrorheological suspensions of laponite in oil: rheometry studies

We have studied the effect of an external direct current (DC) electric field ( approximately 1 kV/mm) on the rheological properties of colloidal suspensions consisting of aggregates of laponite particles in a silicone oil. Microscopy observations show that, under application of an electric field greater than a triggering electric field Ec approximately 0.6 kV/mm, laponite aggregates assemble into chain- and/or columnlike structures in the oil. Without an applied electric field, the steady-state shear behavior of such suspensions is Newtonian-like. Under application of an electric field larger than Ec, it changes dramatically as a result of the changes in the microstructure: a significant yield stress is measured, and under continuous shear the fluid is shear-thinning. The rheological properties, in particular the dynamic and static shear stress, were studied as a function of particle volume fraction for various strengths (including null) of the applied electric field. The flow curves at constant shear rate can be scaled with respect to both the particle fraction and electric field strength onto a master curve. This scaling is consistent with simple scaling arguments. The shape of the master curve accounts for the system's complexity; it approaches a standard power-law model at high Mason numbers. Both dynamic and static yield stresses are observed to depend on the particle fraction Phi and electric field E as PhibetaEalpha, with alpha approximately 1.85 and beta approximately 1 and 1.70 for the dynamic and static yield stresses, respectively. The yield stress was also determined as the critical stress at which there occurs a bifurcation in the rheological behavior of suspensions that are submitted to a constant shear stress; a scaling law with alpha approximately 1.84 and beta approximately 1.70 was obtained. The effectiveness of the latter technique confirms that such electrorheological (ER) fluids can be studied in the framework of thixotropic fluids. The method is very reproducible; we suggest that it could be used routinely for studying ER fluids. The measured overall yield stress behavior of the suspensions may be explained in terms of standard conduction models for electrorheological systems. Interesting prospects include using such systems for guided self-assembly of clay nanoparticles.