(742c) Interface Anisotropy and Rheology of Immiscible Blends with Cocontinuous Morphologies

One of the challenges in the study of cocontinuous blends is to relate their rheological response with their morphology. Doi and Ohta [J. Chem. Phys. 95, 1242 (1991)] proposed a semiphenomenological model that relates the rheology of 50/50 mixtures of two immiscible Newtonian liquids of equal viscosity with the morphology (i.e. size and anisotropy). Although this model was developed for cocontinuous blends, it has been tested almost exclusively in systems with droplet-matrix morphologies. We propose a simplification of Doi-Ohta's model for the case of oscillatory flow under small amplitudes (SAOS). This simplification is based on the experimental evidence that the degree of anisotropy generated during small amplitude oscillations is negligible. The simplification gives a linear relation between the characteristic size and time and an asymptotic decrease of the elastic modulus with a limit at long times given as G' ~ t-1. Cocontinuous blends made of fluorescently labeled polystyrene (FLPS) and styrene-ran-acrylonitrile copolymer (SAN) were imaged with laser scanning confocal microscopy. We developed a methodology to compute the normal vector field of the blend interface using differential geometry of 3D images of the blend microstructure. The normal vector field was used to compute, for the first time, the anisotropy tensor of the cocontinuous interfaces. The anisotropy tensor is key in Doi-Ohta's model. Thus, we were able to compared experimental data of the evolution of the morphology and rheology with the predictions of the Doi-Ohta's model simplification. Good agreement was obtained for blends with relatively low interfacial tension.