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Kinetics of near-critical quenches in homogeneous binary polymer mixtures.

01 January 1986

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The dynamical response of a binary mixture of homopolymers in the vicinity of its critical point is investigated. We consider the situation in which the mixture is subjected to a rapid quench, with both initial and final equilibrium states in the homogeneous one-phase region, but near tau(c). The theory of Kawasaki and Ohta for mixtures of small molecules is extended to the present case of high molecular weight polymer mixtures. The resulting equation of motion for the structure factor is expected to accurately describe the results of neutron and light scattering experiments subsequent to a rapid quench of a two-component polymer melt. Mode coupling terms in the kinetic equations that were neglected in previous treatments of critical dynamics in polymer mixtures are shown to be important for scattering wavelengths larger than the size of a coil and for temperatures and compositions sufficiently close to the critical point. In a narrow region surrounding the critical point we find that the mode coupling corrections lead to several new predictions for the linear dynamical response of polymer mixtures.