Shear-induced structures in semidilute polystyrene solution: Effect of solvent quality

The effect of solvent quality on shear-induced structures in semidilute polystyrene solutions are investigated by using light-scattering and rheological methods. We found that the shear-induced structures are universally formed in various solvents employed in this experiment. We especially focus on a critical shear rate (gamma)over dot(cx) at which the light scattering intensity starts to increase in our experimental geometry, and on a critical shear stress, sigma(xy,cx), and (gamma)over dot = (gamma)over dot(cx). We found that (gamma)over dot(cx) is not well correlated with chi but rather that is better correlated with X, where X is the Flory-Huggins interaction parameter between polystyrene and solvents. sigma(xy,cx) increases with decreasing chi. This indicates that the structure formation is strongly affected by solvent quality, mainly through the thermodynamic state of the solution. We also analyzed the solvent quality dependence of (gamma)over dot(cx) in the context of Onuki's linear theory, and found that (gamma)over dot(cx) can be scaled by K(os)/eta(0), where K(os) is the osmotic modulus and eta(0) the zero-shear viscosity.