Mean-field theory of the interface between a homopolymer and a binary-polymer mixture

In this paper we investigate the properties of the interface between a homopolymer (A) and a binary polymer mixture (B:C). We have extended the self-consistent field (SCF) model of Helfand [Macromolecules 25, 1676 (1992)] by including the effects of the numbers of segments of polymers on the polymer volume fractions, the interfacial excess of B, (-*)(similar to B), the interfacial tension, gamma(ABC), the interfacial width, w(ABC), and the A-B interfacial overlap, w(AB). Other parameters include the polymer interaction parameters, chi(AB), chi(AC), and chi(BC), and the B volume fraction in the B:C mixture, phi(B infinity). As expected, the B component segregates to the A/B:C interface when A-B interactions are more favorable than the A-C ones (chi(AB)<chi(AC)) This interfacial adsorption lowers the interfacial tension and width compared to the pure AIC case, demonstrating the compatibilizing effect of B. As chi(BC) varies from favorable to unfavorable, a segregation is found to increase. Similarly, al constant interaction parameters, B segregation increases as the number of the B segments increases. Furthermore, the addition of a small amount of high molecular weight B to an immiscible AJC blend is found to reduce greatly gamma(ABC) and thus stabilize the system, Calculations for the case of an athermal mixture B:C with chi(AB)=chi(AC) reveals that the shorter chains are ''entropically driven'' to the A/B:C: interface. (C) 1996 American Institute of Physics.