Electric-Field Induced Phase Transitions of Dielectric Colloids : Impact of Multiparticle Effects

Abstract

The thermodynamic framework for predicting the electric-field induced fluid like-solid like phase transition of dielectric colloids developed by Khusid and Acrivos [Phys. Rev. E. 54, 5428 (1996)] is extended to examine the impact of multiscattering/multiparticle effects on the resulting phase diagrams. This was accomplished using effective permittivity models suitable both over the entire composition region for hard spheres (0≤c<cmax0≤c<cmax) and for multiple types of solid packing structures (random close-packed structure, FCC, BCC). The Sihvola-Kong model and the self-consistent permittivity model of Sen et al. [Geophysics 46, 781 (1981)] were used to generate the coexistence (slow phase transition) and spinodal (rapid phase transition) boundaries for the system and compared to assuming Maxwell-Garnett permittivity. It was found that for larger dielectric contrasts between medium and particle that the impact of accounting for multiscattering effects increased and that there was a significant shift in the resulting phase diagrams. Results obtained for model colloidal systems of silica-dimethylsulfoxide and silica-isopropanol showed that critical electric field strength required for phase transitions could rise by up to approximately 20% when considering multiparticle effects versus the isolated dipole case. The impact of multiparticle effects on the phase diagrams was not only limited purely to the direct effect of volume fraction on permittivity and particle dipoles but also on the curvature of the volume fraction dependence. This work stresses the importance of accounting for particle effects on the polarization of colloidal suspensions, which has large implications for predicting the behavior of electro rheological fluids and other electric-field driven phenomena.

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