Electrorheology of miscible blended liquid crystalline polymer: A dielectric property approach

The Effect of Dielectric Polarization Rate Difference of Filler and Matrix on the Electrorheological Responses of Poly(ionic liquid)/Polyaniline Composite Particles

By using different conductivity of polyaniline as filler, a kind of poly(ionic liquid)/polyaniline composite particles was synthesized to investigate the influence of dielectric polarization rate difference between filler and matrix on the electrorheological response and flow stability of composite-based electrorheological fluids under simultaneous effect of shear and electric fields. The composite particles were prepared by a post ion-exchange procedure and then treated by ammonia or hydrazine to obtain different conductivity of polyaniline. Their electrorheological response was measured by dispersing these composite particles in insulating carrier liquid under electric fields. It showed that the composite particles treated by ammonia had the strongest electrorheological response and most stable flow behavior in a broad shear rate region from 0.5 s⁻¹ to 1000 s⁻¹. By using dielectric spectroscopy, it found that the enhanced electrorheological response with stable flow depended on the matching degree of the dielectric polarization rates between poly(ionic liquid) matrix and polyaniline filler. The closer their polarization rates are, the more stable the flow curves are. These results are helpful to design optimal composite-based electrorheological materials with enhanced and stable ER performance.

Low-Temperature Interfacial Polymerization and Enhanced Electro-Responsive Characteristic of Poly(ionic liquid)s@polyaniline Core-shell Microspheres

The synthesis of monodisperse poly(ionic liquid)s (PILs) microspheres coated with semiconducting polyaniline (PANI) shell is reported, which shows enhanced electro-responsive electrorheological (ER) effect but decreased power consumption compared to neat PIL microspheres. The monodisperse PIL microspheres are first prepared via dispersion polymerization and then PANI is coated via low-temperature interfacial polymerization of aniline on the surface of hydrophobic PIL microspheres without additional modification. The stimulus-responsive ER effect of the core-shell microspheres when dispersing in insulating oil are investigated under electric fields. The power-law of yield stress versus electric field strength and the dielectric relaxation spectroscopy are analyzed to understand the ER effect and the origin of property enhancement. It demonstrates that the semiconducting PANI shell can well limit the irreversible ion leakage of PIL microspheres and improve the particle polarizability, resulting in decreased power consumption but enhanced electro-responsive ER effect.

Electrorheological Fluids with High Shear Stress Based on Wrinkly Tin Titanyl Oxalate

Electrorheological (ER) fluids are considered as a type of smart fluids because their rheological characteristics can be altered through an electric field. The discovery of giant ER effect revived the researchers' interest in the ER technological area. However, the poor stability including the insufficient dynamic shear stress, the large leakage current density, and the sedimentation tendency still hinders their practical applications. Herein, we report a facile and scalable coprecipitation method for synthesizing surfactant-free tin titanyl oxalate (TTO) particles with tremella-like wrinkly microstructure (W-TTO). The W-TTO-based ER fluids exhibit enhanced ER activity compared to that of the pristine TTO because of the improved wettability between W-TTO and the silicone oil. In addition, the static yield stress and leakage current of W-TTO ER fluids also show a fine time stability during the 30 day tests. More importantly, the dynamic shear stress of W-TTO ER fluids can remain stable throughout the shear rate range, which is valuable for their use in engineering applications. The results in this work provided a promising strategy to solving the long-standing problem of ER fluid stability. Moreover, this convenient route of synthesis may be considered a green approach for the mass production of giant ER materials.

Enhanced temperature effect of electrorheological fluid based on cross-linked poly(ionic liquid) particles: rheological and dielectric relaxation studies

Recent research of using poly(ionic liquid) (PIL) particles as the dispersal phase has provided a new strategy to develop a high-performance anhydrous polyelectrolyte-based electrorheological (ER) fluid. However, the working temperature range of the ER fluid of PIL particles is still narrow due to an inherently low glass transfer temperature caused by the plasticization of polyatomic organic counter ions in PILs. In this paper, we develop a new ER system based on cross-linked PIL (C-PIL) particles and demonstrate that crosslinking with a suitable degree only slightly degrades the ER properties but significantly improves the working temperature range of the ER fluid of PIL particles. By using differential scanning calorimetry, rheology, and dielectric spectroscopy, we systematically study the ER properties of C-PILs and their temperature dependence at different crosslinking levels and understand the mechanism behind the improved temperature effect. The results indicate that crosslinking can effectively increase the glass transition temperature of PIL particles and enhance local ion-motion induced interfacial polarization by suppressing the thermally promoted long-range drift of mobile counter ions in the PIL matrix, and this results in the improved temperature effect of the ER fluid of C-PIL particles.

Enhanced dielectric polarization and electro-responsive characteristic of graphene oxide-wrapped titania microspheres

Electric field-induced particle polarization is essential to the electro-responsive electrorheological (ER) effect of particle suspensions. In this work, we use graphene oxide (GO) as a soft and polar coating shell to prepare GO-wrapped titania dielectric microspheres for use as the dispersal phase of an ER suspension. Under a DC electric field, the ER characteristic of GO-wrapped titania microspheres dispersed in silicone oil is investigated by rheological tests, and then compared with that of a suspension of bare titania microspheres. The results show that the suspension of GO-wrapped titania microspheres possesses an enhanced ER characteristic. Its field-induced shear yield stress and storage modulus are much higher than those of the suspension of bare titania microspheres. The soft and polar GO shell is regarded as the origin of the ER enhancement. Dielectric analysis indicates that wrapping GO can enhance the interfacial polarization and thus improve the ER characteristics of titania microspheres. Wrapping GO onto the surface of titania microspheres can also reduce the particle sedimentation velocity of the suspension.

Electrorheological activity generation by graphene oxide coating on low-dielectric silica particles

A recent challenge in the field of electrorheology is to generate or to enhance the electrorheological (ER) activity of an inactive or lowly active suspension using core–shell structured particles.

Enhanced Electrorheological Activity of Mesoporous Cr-Doped TiO2 from Activated Pore Wall and High Surface Area

To enhance electrorheological (ER) activity by improving interfacial polarization, we prepared a new mesoporous Cr-doped TiO2 ER material by a copolymer-templated sol-gel method. The material was characterized by differential scanning calorimeter and thermogravimetric (DSC-TG) analysis, Fourier transform infrared (FT-IR), X-ray powder diffraction (XRD), transmission electron microscopy (TEM), N2 adsorption, and X-ray photoelectron spectroscopy (XPS) techniques. The ER activity was studied by the rheological curve and yield stress under an electric field. The results showed that the mesoporous Cr-doped TiO2 ER material possessed a high surface area over 200 m2/g and a crystalline anatase pore wall doped by different valent Cr ions. The ER activity of mesoporous Cr-doped TiO2 was higher than that of nonporous Cr-doped TiO2. The yield stress and ER efficiency of the mesoporous Cr-doped TiO2 ER suspension was 3 times as high as that of the nonporous Cr-doped TiO2 ER suspension, 7 times as high as that of the mesoporous undoped TiO2 ER suspension, and 20 times as high as that of the nonporous pure TiO2 ER suspension. Furthermore, the ER activity of mesoporous Cr-doped TiO2 showed a dependence on surface area, and the high porosity or surface area samples showed higher ER activity. The dielectric spectra analysis showed that the mesoporous Cr-doped TiO2 ER suspension possessed a significantly larger interfacial polarizability compared with the nonporous Cr-doped TiO2 ER suspension, and the regular change of polarizability with surface area or porosity was in accordance with the change of ER activity with surface area or porosity. The improvement of dielectric properties or polarization could well explain the enhancement of the ER activity of mesoporous Cr-doped TiO2.

Preparation of montmorillonite/titania nanocomposite and enhanced electrorheological activity

We prepared a new type of electrorheological particle composed of TiO2 nanocrystallites-coated montmorillonite (MMT/TiO2) nanocomposite by the sol-gel technique. The characterizations including TGA, XRD, TEM, SEM, EDS, and FTIR showed that TiO2 was deposited on the surface of the MMT flakes with anatase nanocrystallite. An obviously enhanced ER effect was found in the MMT/TiO2 nanocomposites based ER fluids compared with pure MMT and TiO2. Furthermore, the temperature and sedimentation stabilities of the MMT/TiO2 ER fluids had also been improved greatly. Interestingly, the content of TiO2 was demonstrated to have an important influence on the ER effect. When the content of TiO2 was about 20 wt%, the ER effect of MMT/TiO2 ER fluid reached its maximum, which was about 5 times that of pure MMT ER fluid and 27 times that of pure TiO2 ER fluid. Based on dielectric analysis, the significant ER enhancement by formation nanocrystallites-coated montmorillonite was attributed to the enhanced interfacial polarization in this nanocomposite particle due to the effective limitation of the long-range drift of active ions in montmorillonite particles.

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.