Polymer chain dynamics in dilute solution under Couette flow: Behavior of poly(α-methylstyrene) in good solvent

Abstract

Chain dynamics of poly(α-methylstyrene) of high molecular weight in benzene, a good solvent, in dilute solution was investigated by dynamic light scattering under Couette flow, or the one-dimensional simple shear flow. At the velocity gradient γ=0.34–5.2 s−1 measured, two modes of the translational diffusion and the intramolecular motions were detected. However, the latter was suppressed with the increase of γ. The suppression occurred only in the amplitude without any change in the inherent internal-mode frequencies. The universal ratio Ω/D0q2, estimated as a γ-independent characteristic value in good solvents, agreed well with the theoretical curve predicted for the nondraining Gaussian chain with the microscopic description of chain dynamics, and differed from the macroscopic one with the preaveraged Oseen hydrodynamics. This quantitative agreement suggests that (1) the coupled kinetic equations for chain segments and solvent in the same dynamic level are indispensable for describing rigorous chain dynamics in dilute solution, and (2) the internal motions in the shear field suffer the hydrodynamic interaction strongly (to the level of the Zimm limit), the interaction being compensated for the intramolecular excluded volume effect and making the chain quasi-ideal even in good solvents.