Linear viscoelasticity of a polymeric bicontinuous microemulsion

Ternary polymer blends of immiscible homopolymers and the corresponding diblock copolymer are useful models for studying equilibrium and nonequilibrium behavior of self-assembled fluids. We report linear viscoelastic data for a polymeric bicontinuous microemulsion, experiments that are possible due to the comparatively high viscosities of the principal components. After subtracting a viscous background contribution from the pure constituents, the microemulsion exhibits "excess" viscoelastic behavior similar in character to that resulting from the Rouse model of polymer dynamics. The data are compared to the predictions of a time-dependent Landau-Ginzburg model developed by Pätzold and Dawson, using structural parameters derived from neutron scattering as input. This model captures the essential characteristics of the viscoelastic behavior very well. However, using independent dynamic light scattering measurements of the Onsager coefficient for these blends, it appears that the model fails to predict either the magnitude or the temperature dependence of the zero shear viscosity and relaxation time of the microemulsion accurately. Possible origins for these discrepancies are discussed.