Rheology of homogeneous block copolymers near the microphase separation transition

Abstract

Mode coupling and fluctuation effects on the low frequency linear viscoelastic properties of homogeneous diblock copolymers are investigated. Attention is restricted to temperatures near, but not below the microphase separation transition (MST), where a homogeneous block copolymer melt first transforms to a spatially periodic, compositionally inhomogeneous morphology. We find that long‐wavelength transverse momentum fluctuations couple only weakly to compositional order parameter fluctuations; the latter are predominantly on the scale of the radius of gyration. Crossover expressions are obtained for the renormalized transport and viscometric coefficients. The fluctuation contributions to these various coefficients are smaller than originally predicted at the MST, a consequence of refined calculations showing the MST to be a weakly first order phase transition.