Electrorheological determination of the Leslie viscosity coefficient (alpha(2)) of a main-chain liquid crystal polymer in a nematic solvent

Analysis of the electrorheological response of thermotropic solutions of a main-chain liquid crystal polymer (MCLCP) in a low molar mass nematic solve nt is performed at a fixed shear rate as a function of the applied field st rength. The Leslie viscosity coefficient alpha(2) can be obtained by least squares fits to an equation describing the balance between the viscous and electric torques, formulated via the two dimensional Leslie-Ericksen-Parodi theory. We find that the increment Delta alpha(2) on dissolving the MCLCP increases linearly with molecular weight, consistent with earlier light sca ttering measurements of the increment in the twist viscosity, Delta gamma(1 ), and also with previous electrorheological measurements of the increment in the Miesowicz viscosity Delta eta(c).