Studies On The Synthesis Of γ-Fe₂O₃/polyacrylate Composite Particles And The Relationship Between The Electrorheological Effect Mechanism And The Sub-cluster Parameters

Electrorheological(ER) fluids are materials which have the ability to increase their viscosity in the presence of an electric field. The fluid becomes solidified at high enough field and returns to its original flow state when the field is removed. This fast response and reversible change between fluid and solidified state make it possible to apply the fluid in switch, brakes, clutch, valve and other mechanical-electrical control areas.Most ER fluids consist of polarizable particles dispersed in insulating base liquids. A lot of materials are discovered with ER effect. However, no commercial ER devices are available so far because of the lack of effective ER fluids and poor understanding of the mechanism.In the thesis, for the first time, the γ-Fe₂O₃/polyacrylate composite particles were synthesized by emulsion polymerization technique. The particles were then dispersed in silicone oil or other base liquids. The influences of the chemical composition of the particle including the neutralization percentage and the counter ion type of the polyacrylic acid, the content of the crosslinking agent and the comonomer maleic anhydride on the ER effect of composite particles in silicone oil were studiedWith increasing the γ-Fe₂O₃ content of the composite particles, the ER effect of the fluids varied in different way under DC and AC electric field. All the particles containing y-Fe₂O₃ demonstrate stronger ER effect than the lithium polyacrylate without γ-Fe₂O₃. The permittivity, conductance and dielectric loss of the ER fluids with different γ-Fe₂O₃ and conductive carbon black content were measured to illustrate the relationship between ER effect and the electrical properties of the particles. The results show that not the single permittivity but the permittivity, the conductance and the dielectric loss altogether control the ER effect.Besides the dispersed particle, the property of the base liquid is also very important to the ER effect, but little work has been done in this subject. The influence of the permittivity and the viscosity, the content of the polar molecule of the base liquid on the ER effect of the same composite particles were investigated systematically. Some meaningful conclusions were obtained. The ER effect obeys the permittivity dismatch principle if greater differences exist among the permittivity of various base liquids. While if the permittivity of the base liquids are similar, the situation is different. The viscosity of the base liquid influences the ER effect through competing between the viscous force of the...