| Electrorheological fluid(ERF) is a new type of intelligent material. Excellent electrorheological properties of ERF may induce a peculiar electrorheological effect, namely may carry on the continuous and reversible transition between liquid state and solid state within millisecond, and will restore to the original state again in the twinkling of an eye after withdrawing the electric field. The research and development technology of electrorheological fluid with excellent ER properties involves such a lot of disciplines as physics, chemistry, computer, material, etc. Hi-Tech intelligent products developed by the electrorheological technology, such as electrorheological shock absorber, electrorheological clutch, electrorheological valve, etc., have a good performance which is superior to the traditional brake rigging device greatly. These apparatuses have the performance of change in stepless and succession. They have simple structures, small wears and tears in the job parts, high speed of response and low energy consumption in the course of controls, and so on. Electrorheological fluid is considered as a kind of new material which may produce remarkable changes in many fields such as machine-building, auto industry, hydraulic pressure control project and spaceflight aviation etc. all the time these decades. So its development and research have won a great attention from industry and defence in the world. The electrorheological fluid is usually made up of disperse medium with the non-conductor and disperse phase particles with the higher dielectric constant. At the end of the eighties of the 20th century, Block and Kelly reported that ER fluids made by using some organic macromolecular compounds such as poly (pyrene-quinone), poly(naphthalene-quinine), etc. as disperse phase may do not at all contain water and have a high working temperature. Therefore, extensive attention has been caught to organic polymer disperse phase particles. For examples, polyaniline and polypyrrole, etc. were studied as disperse phase particles. But so far, electrorheological fluid has some scarcities, such as not high enough yield stress, not wide enough working temperature range, and not good enough subside ability. This article will report the results of our research that selects conjugated polymer which contains aromatic ring and have suitable range of dielectric constant, moderate density and hardness as base materials. Some conjugated polymer disperse particle was synthesized and their electrorheological properties were .characterized. Synthesis methods of three poly (p-phenylene vinylene) derivatives have been studied. Results show that, compared to classic methods, our ultrasonic irradiation method takes on significantly the high efficiency of the synthetic process with a higher production yield and a shorter process time. We have designed and synthesized seven conjugated polymers containing bithiazole group and amphoteric group. Five of the seven polymers were first synthesized and reported among the conjugated polymers. We have studied the modified condition of microcrystalline cellulose. The conjugated polymers were characterized with IR, elemental analysis, etc. The surface morphology of the polymers was measured with a scanning electron microscope. Thermal stability of the polymer was measured with thermal analyzer. Results show the synthesized polymers are in well agreement with the design requirement. Meanwhile, we first use three of the synthesized polymers as disperse phase particals and the bromodiphenylmethane or silicone oil as a disperse medium to prepare suspensions with different concentration. Shear stress, shear viscosity, conductivity, dielectric loss constant and stability of the suspensions under different electric field strengths were studied respectively. Results indicate (1) that the suspension made from poly (p-phenylene vinylene) derivatives, or the polymers containing bithiazole group or amphoteric group and the modified microcrystalline cellulose have a good electrorheological effect. The suspension made from 20% of poly[N,N'-(2-amino-5-carboxy-1,3-phenylenedimethylene)-2,2'-diamino-4,4'-bithiazole] dispersed in bromodiphenylmethane showed a shear stress above 3.3 kPa and poly[N,N'-(2-amino-5-sulfo group-1,3-phenylenedimethylene) -2,2'-diamino-4,4'-bithiazole] dispersed in bromodiphenylmethane showed a shear stress above 2.3 kPa at an electric field of 4.2 kV/mm respectively, and good stability due to a close match of the densities between the disperse phase and disperse medium . (2) Strength of electrorheological effect was controlled by the properties of the polymer micro-particles in suspension, such as the molecular structure, the group polarity and the concentration. Electrorheological effect of the ERF with the polymer micro-particles bearing polar groups is higher than with the polymer micro-particles not bearing polar groups. The higher of the polarity of amphoteric group of polymer as dispersed phase particles in suspension, the greater of the ability of polarization and the better of the electrorheological effect. The higher of steric hindrance, the weaker of electrorheological effect of the polymers. The higher concentration of polymer particles in the disperse medium, the stronger impact to ER properties. When the polymer micro-particle surface is poriferous, its electrorheological effect become stronger. (3) Poly (p-phenylene vinylene) derivatives with great conjugation systems can be convenient for the migration of the electron in the system that results in good conductivity. There is a moderate electrorheological effect when poly (p-phenylene vinylene) derivatives were dispersed in silicone oil under electric field. It also shows some leakage current density even under lower electric field. When electric field rise or the concentration of polymer particles in the disperse medium increase to a certain volume, leakage current density increase accordingly, resulting discharge, even the system being destroyed. We also found that there was a negative electrorheological effect of suspension that poly (2-methoxy-5-butoxy) phenylene vinylene were dispersed in bromodiphenylmethane under electric field. (4) The conjugated polymers with π–πconjugation and amphoteric group as dispersed phase particles could form an internal chain-like structure or net-like structure by the rearrangements of dispersed particles within the ER fluids under the imposed electric field so that the suspension shows better electrorheological effect. Results show that the mechanism of electrorheological effect of suspension containing conjugated polymers can be explained by a polarization model. Results show that suspension made from polymers containing bithiazole group and amphoteric group take on excellent electrorheological effect and have good antisubside ability. It can overcome precipitation of dispersed particles and abrasion to equipment, which cannot be overcome by the materials made of inorganic dispersed particles or metal dispersed particles. |
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