The effect of shear flow on the mesoscopic structure of partially misciblepolymer blends

Shear flow may have a significant effect on liquid mixtures such as polymer solutions but also polymer blends. The study of the effect of shear on the microscopic and mesoscopic structure of partially miscible polymer blends has recently been the focus of much theoretical and experimental work. Diff erent theoretical approaches used to explain the observed shear induced enh ancement or decay of concentration fluctuations in polymer blends are prese nted here and compared with the available data on several systems. In parti cular some of our most recent data for a polystyrene/poly(vinyl methyl ethe r) blend are presented. Our main conclusion is that, to describe all the ph enomena encountered when shearing polymer blends, three sometimes competiti ve factors must be taken into account: the change in the equilibrium thermo dynamics of the system due to molecular conformational changes, the couplin g between concentration fluctuations and shear stress and the shear droplet break-up effect.