Electric Fields: From Copolymer Orientation to Phase-Transitions and Chemical Reactions in Liquid Mixtures

Yoav Tsori

Dept. of Chemical Engineering, Ben Gurion University

Electric field can have a strong effect in many soft-matter systems, such as liquids, polymers, colloids, etc. We first show that an electric field can orient mesophases of block-copolymers. Based on a so-called "dielectric mechanism", proportional to the permittivity difference squared, external field can also provoke an order-order or order-disorder phase-transition. However, generally the influence on the critical temperature is quite small, since composition fluctuations couple with electric field fluctuations. In contrast, spatially nonuniform fields can have a dramatic effect on the phase behavior because of the direct coupling between composition fluctuations and externally-imposed field gradients. The new type of phase-transitions is demonstrated for block-copolymers and liquid mixtures in nonuniform electric fields, with and without dissociated ions. We illustrate several important applications of these transitions in electric-field-controlled lubrication and controlled chemical reactions.