| This thesis studies a novel rheo-dielectric effect, dielectrostriction, in viscoelastic materials including pure polymers, liquid polymeric suspensions and solid polymeric composites. Dielectrostriction is the variation of dielectric properties of material with deformation. As a starting point, the phenomenology of dielectrostriction of viscoelastic materials is formulated consistently with that in linear elastic solids. Each strain- or stress-description requires two independent coefficients characterizing dielectrostriction responses of an isotropic material. Experimental approach is developed to observe dielectrostriction effect and to measure strain- or stress-dielectric coefficients. The dielectrostriction response in small amplitude oscillatory shear deformation/flow is studied. Both strain- and stress-descriptions are verified against experimental data. However, unlike for linear elastic solids where the strain- and stress-dielectric coefficients are constant, in viscoelastic materials such coefficients are process-dependent. In addition, the strain- and stress-dielectric coefficients have been found sensitive to particle size distributions. The investigation of dielectrostriction effect in this study renders dielectrostriction measurement a potential powerful tool for rheological study and material characterization. |
