CROSSOVER TO STRONG SHEAR IN A LOW-MOLECULAR-WEIGHT CRITICAL POLYMER BLEND

Small-angle neutron scattering has been used to measure the influence of shear flow on a low-molecular-weight polymer blend near the critical point. When combined with light scattering measurements of the equilibrium (gamma=0) critical dynamics, these measurements reveal that the long-range critical fluctuations begin to break apart when the shear rate becomes comparable to the characteristic relaxation rate tau(c)-1, where tau(c), is the equilibrium lifetime of the critical fluctuations. This effect is directly related to the decrease in the critical temperature caused by the flow, and the data are found to be in very good agreement with the theoretical predictions of Onuki and Kawasaki.