Rheological and morphological study of cocontinuous polymer blends during coarsening

Abstract

One of the challenges in the study of cocontinuous blends is to relate their rheological behavior with their morphology. This is due to the inherent instability of cocontinuous structures. We have studied the morphological and rheological time evolution of cocontinuous blends with different interfacial tension and viscosity ratio during annealing. In general, the presence of an interface generates an extra contribution to the elastic modulus, G′int. We have found that both the initial value of G′int and its rate of evolution during coarsening are proportional to the ratio between interfacial tension and blend viscosity. We have related time evolution of the elastic modulus to that of the interfacial area via a simplification of Doi–Ohta model for the case of small amplitude oscillatory shear flow. This simplification is based on the experimental evidence that the degree of anisotropy generated during small amplitude oscillations is negligible [López-Barrón and Macosko, Langmuir 26, 14284–14293 (2010b)]. The simplification gives a linear relation between the characteristic size and time and an asymptotic decrease of the elastic modulus with a limit behavior at long times: G′|t→∞∝t−1. This behavior was observed on blends with low interfacial tension. However, blends with high interfacial tension underwent a transition toward a decrease in the rate of coarsening, which is accompanied by a slower decrease of the elastic modulus. Doi–Ohta model is not sensitive to this transition and fails in predicting the time evolution of the characteristic length and elasticity of high interfacial tension blends.