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Preparation and Properties of Janus SiO2Based Electroheological Fluid

Author: WangZuoZuo
Tutor: GuoJianJun;LiangHongZe
School: Ningbo University
Course: Physical and chemical
Keywords: Electrorheological fluid Janus Silica Polar molecule
CLC: TQ127.2
Type: Master's thesis
Year: 2013
Downloads: 1
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Abstract


Electrorheological （ER） fluid is a type of intelligent colloids regularly composed of solidparticles with high-dielectric constant and low-conductivity dispersed in insulating carrier oil. Itcan exhibit drastic and reversible changes in its rheological properties in response to an appliedelectric field in a few milliseconds. This novel property makes it an excellent candidate forapplications in broad fields, such as actuators, shock absorbers, active devices, human musclesimulations, ER tactile displays, photonic crystal, and various other control systems. Since thediscovery of ER phenomena in1947, various types of ER materials have been studied in detail.However, the ER fluids are still lack of obtaining wide applications due to their low yield stress.When it comes to2003, a new series of ER materials called Giant Electrorheological Fluid werediscovered. Since then, several giant ER fluids have been fabricated, of which the yield stressesexceed the predicted upper bounds of dielectric ER fluids significantly. Many theories about giantER effect are based on core–shell structure model, wherein the hard core is made of inorganicmaterials, and the coating shell is composed of polar molecules. Many researches focus on thepolar molecules adsorbed on the shell layer, but the study on the role and the interaction betweendielectric core and polar molecules is few.Janus particles with different surface structures on the two sides are perfect candidates forstudy of the detail interaction of the surface molecules and dielectric cores. Accordingly,monodisperse SiO2spheres, which have good dispersity and well defined morphology, are selectedas the core material and modified by different polar molecules to obtain core–shell structural SiO2Janus particles. The structure, composition, and morphology have been characterized by FTIR,XRD, and SEM. The resulting productions were then adopted to prepare ER fluids, and their ERproperties were investigated.1.“Raspberry” core-shell SiO2/polyaniline nanocomposite particles were prepared by in situpolymerization of aniline monomer and commercial ultrafine silica sols in aqueous solution in thepresence of hydrochloric acid as dopant and ammonium persulfate as initiator and oxidant. It wasfound that well-defined nanocomposites between SiO2and polyaniline were formed. A strongyield stress up to14.1KPa was observed for the SiO2/polyaniline nanocomposites suspensions at5KV DC electric field, which is much higher than those of polyaniline and silica nanoparticles. Thenear linear dependence of the yield stress on the electric field is different from the conventional ER fluids which can be explained by giant electrorheological effect. It is likely a result of both thesmall size effect of SiO2and strong polarizability of polyaniline. This indicates that the SiO2-polarmolecules composites can be used as an model for the study of the mechanism of Giant ERphenomena.2. We present the wet-chemical synthesis of rod-like silica colloids with aspect ratios from810to study the influence of particle morphology on the activity of electrorheological fluidsystematically. The ER activity of the silica suspension was studied under DC electric field. Theobtained rod-like silica particles exhibited superior ER activity compared to the isotropicalspherical silica particles, and the dynamic rheological measurement suggested the rod-like silicaparticles have a good response to the shear stress. The dielectric test showed that the rod-likeparticles possess higher dielectric constant, which means greater polarization ability, and finallyinduced a stronger interaction force. Under the electric field, the polarized particles in the ER fluidsattracted each other and aligned along the field direction to form chain structure. The one-dimensional rod-like silica particles can link together to form stable geometrical construction. It ismore difficult to break this chain than to isotropic particles. Particles overlap would preventparticles from slipping past one another, therefore inhibit the chain structure, and thus enhance eheyield stress stiffness modulus.3. We prepared polar molecule modified Janus SiO2particles with diameters about200nm1.0μm and1.5μm., which were modified selectively by acetamide via Pickering emulsion. Themorphology was determined by absorbing nano gold colloidal particles and fluorescein FITC, andthe characterization result turned out to confirm its anisotropical structure effectively; FT-IR andorganic element analyze data showed the polar molecule acetamide have modified on the silicasurface successfully. The ER activity was studied by yield stress under DC electric field. As aresult, the200nm Janus SiO2/acetamide ER fluid showed notable ER activity, a strong yield stressup to4.26KPa was observed at3KV DC electric field, according to they were easier to align uponthe application of electric field, thus anisotropical particles showed head to tail arrangementmacroscopically, form a microscopic view the polar molecule have an interaction with thedielectric core. The local electric field between the particles could be three orders higher than theexternal field, and high local field caused the polar molecules in the gap to turn to the fielddirection and interact with the polarization charges of the neighboring particles. At the same time,1.0μm and1.5μm silica particles modified with acetamide turned out to have higher ER effectcompared to the corresponding Janus particles, this should attribute to their dielectric loss factorpeak and the higher dielectric constant differentials between102-105Hz. This result could serve asa promising direction for achieving highly active materials and understanding the detailedmechanism.

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CLC: > Industrial Technology > Chemical Industry > Non-metallic elements and their inorganic compounds, the chemical industry > Part Ⅳ family of non-metallic element and its inorganic compounds > Silicon and its inorganic compounds
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