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 γ̇_cx, at which the light scattering intensity starts to increase in our experimental geometry, and on a critical shear stress, σ_xy,cx, at γ̇ = γ̇_cx. We found that γ̇_cx is not well correlated with χ but rather that σ_xy,cx is better correlated with χ, where χ is the Flory-Huggins interaction parameter between polystyrene and solvents. σ_xy,cx increases with decreasing χ. 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 γ̇_cx in the context of Onuki's linear theory, and found that γ̇_cx can be scaled by K_os/η₀, where K_os is the osmotic modulus and η₀ the zero-shear viscosity.