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 in asymmetric styrene−butadiene diblock copolymers in semidilute solution. Following a quench to below the transition temperature, the scattered 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 measured 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.