INFLUENCE OF COMPRESSIBILITY AND MONOMER STRUCTURE ON SMALL-ANGLE NEUTRON-SCATTERING FROM BINARY POLYMER BLENDS

The compressible random phase approximation (RPA) is combined with the lattice cluster theory to study how compressibility and monomer molecular structure affect small angle neutron coherent scattering intensities and quantities like the apparent radius of gyration and correlation length in binary polymer blends. Blend compressibility implies that the partial structure factors S(alpha-beta)(k) depend on three macroscopic interaction parameters chi(alpha-beta), which, in turn, are functions of (at least) three microscopic van der Waals energies, temperature, pressure, polymerization indices, and monomer molecular structures. The {chi(alpha-beta)} are determined from the lattice cluster theory for the extended lattice model of compressible, structured monomer binary blends. The traditional incompressible RPA analysis is applied to our computed S(alpha-beta)(k) and uncovers deficiencies in extracting the apparent radius of gyration and correlation length. The calculated structure factor, apparent radius of gyration, and correlation length for polystyrene/polyvinylmethylether blends are compared with the experimental data of Han et al. without using new adjustable parameters.