Crossover from 3D ising to isotropic Lifshitz critical behavior in a mixture of a homopolymer blend and diblock copolymer

Thermal composition fluctuations and the associated crossover from the 3D I sing to the isotropic Lifshitz universality class have been studied in a th ree component mixture made of a critical polymer blend and the correspondin g diblock copolymer. The critical exponents were found to be appreciably la rger than these of the 3D Ising, in agreement with expectations from the la rger upper critical dimension. Very near the critical temperature a crossov er to a renormalized Lifshitz critical behavior was observed possibly cause d by fluctuation induced rearrangements of the diblock copolymers.