Neutron reflectometry and small-angle neutron scattering - Two complementary techniques for polymer blend investigations

Several incompatible polymer blend systems have been investigated by neutron reflectometry (NR) to obtain the interfacial width (typically 3-8 nm) as a function of temperature and molecular weight. A comparison with small-angle neutron scattering (SANS) is possible for blends of PS with a statistical copolymer of P(CHA-stat-nBMA), where the miscibility can be changed in a wide range by variation of the copolymer composition. The values for the interfacial width provide information on the segment interaction parameter, which describes blend compatibility in the framework of mean field theory. Analysing the molecular weight dependence of interfacial width allows also the determination of the Kuhn segment length from a fit to the interfacial width data. The excellent agreement of the interaction parameter and segment length determined by NR in the two-phase region with results from SANS in the one-phase region demonstrates the potential of NR as a continuation of SANS into the two-phase region in order to achieve a more comprehensive understanding of polymer miscibility.