SMALL-ANGLE X-RAY-SCATTERING STUDY OF THE MICROPHASE SEPARATION TRANSITION IN ASYMMETRIC DIBLOCK COPOLYMERS - A MODEL B KINETIC PHENOMENON

We report the results of a time-resolved small-angle X-ray scattering (SAXS) study of the kinetics of the microphase separation transition i n asymmetric styrene-butadiene diblock copolymers in semidilute soluti on. Following a quench to below the transition temperature, the scatte red intensity at early stages is found to increase exponentially with time according to a time-dependent Ginzburg-Landau (TDGL) model, model ''B'' in the Hohenberg-Halperin notation. Over a range of scattering vectors near the SAXS peak, the exponential rate constants are modeled using the TDGL theory. The form of the wavevector dependence of the m easured rate constants is used to test the fundamental predictions of the TDGL model. No lower and upper critical wavevectors are identified , although valid results for the static parameters are provided within the context of the model.