MODE SELECTION IN THE DYNAMICS OF SHEARED POLYMER-SOLUTIONS

We report transient light scattering measurements upon the cessation of shear for a semidilute polymer solution under theta conditions. The polymer solution demonstrates two modes of relaxation for concentration fluctuations in equilibrium. The transient measurements show that the mechanism that couples the concentration fluctuations to the shear flow, and thereby enhances concentration fluctuations, selectively enhances only the slower of the two equilibrium modes. This selective enhancement generates a long-wavelength peak in the shear-enhanced structure.