TEMPERATURE AND MOLECULAR-WEIGHT DEPENDENCE OF INTERFACIAL-TENSION BETWEEN IMMISCIBLE POLYMER PAIRS BY THE SQUARE GRADIENT THEORY COMBINED WITH THE FLORY-ORWOLL-VRIJ EQUATION-OF-STATE THEORY

Interfacial tension between immiscible polymer pairs was predicted by using a square gradient theory in conjunction with the Flory-Orwoll-Vr ij equation-of-state expression for the free energy of mixing. The con tact interaction parameter was determined by fitting the equation-of-s tate theory to experimental cloud points taken from the literature, an d the square gradient coefficient was estimated from the relation deri ved from a scattering function. The modified square gradient theory co uld successfully predict both the magnitude and temperature dependence of interfacial tension between polystyrene and poly(methyl methacryla te), although no adjustable parameters were used in calculating interf acial tension. The molecular weight dependence of interfacial tension was also successfully predicted. The contribution of free volume on in terfacial tension is analyzed for two systems: polystyrene/poly(methyl methacrylate) and polystyrene/poly(dimethyl siloxane) blends. (C) 199 8 John Wiley & Sons, Inc.