INTERFACIAL BEHAVIOR OF COMPRESSIBLE POLYMER BLENDS - MONTE-CARLO SIMULATION AND THE LATTICE FLUID THEORY

Monte Carlo (MC) lattice simulation studies have been performed for co mpressible polymer-polymer interfaces showing a density dip at the int erface of an immiscible polymer pair. The dependence of the interfacia l properties on the cross interaction energy and pressure is investiga ted. The simulations are compared with theoretical calculations. There fore a theory is developed using the lattice fluid (LF) theory applied to polymer interfaces according to Helfand's ideas, using anisotropy factors (probabilities) for the polymer bond directions to account for the inhomogeneity at the interface. The free energy is expressed in t erms of these anisotropy factors, polymer densities, and segment-segme nt contact energies. It is minimized under a number of constraints usi ng the technique of Lagrange multipliers. Between simulations and theo ry a gratifying qualitative agreement is found. Systems asymmetric in density can be treated, which is important for application to real sys tems. Application of Helfand's lattice approach is not restricted to b road interfaces and therefore presents a good alternative to gradient term interface theories.