Electrorheology of filled silicone elastomers

Date of Completion

January 1999

Keywords

Chemistry, Polymer|Physics, Electricity and Magnetism|Engineering, Materials Science

Degree

Ph.D.

Abstract

Electrorheological (ER) materials have potential applications in electromechanical control as they change their rheological properties upon application of an electrical field. The ER behavior of silicone elastomers filled with three types of particles including silica, titania and iron was studied. 2-D numerical simulations were conducted to investigate the influence of structure parameters, material composition and field parameters. Electrical field was applied to align silica and titania particles during the cure of the silicone prepolymer. Dielectric measurements suggested that surface conductivity of silica particles dominated the polarization of the silicone-silica elastomers. The alignment of silica particles increased the dielectric permittivity and the Maxwell-Wagner dispersion. The ER response of the silicone with aligned silica exhibited a deviation from the quadratic dependence on field intensity at high fields accompanied by nonlinear conductivity. The results were consistent with the computations in that the saturation of the field between particles due to nonlinear conductivity of polymer matrix resulted in a decreased ER response. Silicone-silica elastomers showed an enhancement of ER effect when the particle concentration was increased. For silicone-titania elastomers, the ER response increased with particle permittivity. Silicone-BaTiO3 elastomer showed a shear-strain dependent ER response as interparticle force decreases with the increase of spacing between adjacent particles. The ER response of the silicone-BaTiO3 elastomer increased with field frequency as expected from high permittivity of BaTiO3 relative to silicone. A novel method was developed to prepare ER solids containing iron particles. A magnetic field was employed to align iron particles in a silicone prepolymer. After cure, silicone oil was used to swell the silicone-iron gel. Both microscope observation and conductivity measurements showed that the particles separated after swelling. Silicone-iron gels showed a quadratic dependence of ER response on the field intensity. The ER responses of the silicone-iron gels were two orders of magnitude larger than the prediction of the dipole approximation. When increasing orientation angle of particle chain relative to the field, the ER effect of the silicone-iron gels decreased, which was in a qualitative agreement with the calculation based on the dipole approximation. ^

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