Complex phase behavior near the Lifshitz line in a ternary polymer blend

With small-angle neutron scattering (SANS) we measured thermal composition fluctuations in a homopolymer blend, PB/PS, of critical composition mixed with different amounts of the symmetric diblockcopolymer PB–PS (PB and PS being polybutadiene (1,4) and polystyrene, respectively) in the disordered state along the isopleths. The diblockcopolymer acts as a surfactant enhancing the compatibility of both homopolymers up to the Lifshitz line and simultaneously changes the critical university class from 3D-Ising to isotropic Lifshitz critical behavior. Above Φ≈0.3 diblock content the samples show diblock-like behavior with a first-order ordering transition. The intermediate regime between Φ≈0.075 and 0.3 can be characterized by a micro-emulsion phase. The temperature dependence of the Lifshitz line, the disorder line and the critical line is non-monotonous.