SHEAR-ENHANCED CONCENTRATION FLUCTUATIONS IN POLYMER-SOLUTIONS AS OBSERVED BY FLOW LIGHT-SCATTERING

The effects of simple shear flow on concentration fluctuations in polymer solutions are investigated as a function of S, T, c, and N by the flow light scattering method. Here, S is the shear rate, T the temperature, c the polymer concentration, and N the degree of polymerization of the polymer. Over the range of the concentration studied in this experiment (a semidilute regime covering c/c* = 4 to 20, where c* is the overlap concentration), strong shear-enhanced concentration fluctuations were observed above a certain critical shear rate S(c). For S > S(c), the integrated scattered intensity J perpendicular-to in the direction perpendicular to the flow increases at least by two orders of magnitude compared to that of the homogeneous solution. The scattering patterns observed for S > S(c) have two main characteristics: (i) they are very diffuse, extending up to high scattering vectors and (ii) they have a sharp and strong destructive interference in the direction perpendicular to the flow.