Critical phenomena in binary and ternary polymer blends

We have studied the dynamic and static properties of binary and ternary polymer blends in temperature and concentration domains that include the critical temperature. The ternary blends consisted of A and B homopolymers and an A-B diblock copolymer. In binary blends and in ternary blends with lower content of the diblock copolymer, we have observed critical divergence of dynamic and static correlation lengths and of static susceptibility, as measured by dynamic light scattering and small-angle neutron scattering. The critical divergence for the binary blends could be analyzed in terms of a crossover between a mean-field and a nonclassical, Ising-type critical behavior. For ternary blends, the addition of a block copolymer stabilizes the system by decreasing the extent of composition fluctuations and by lowering the critical temperature. At a particular composition of the ternary blend, the appearance of a bicontinuous microemulsion was established by small-angle neutron scattering. It was shown that a maximum in the dynamic correlation length derived from dynamic light scattering and observed under these conditions is a characteristic signature of the microemulsion structure.