INTERFACIAL SEGREGATION IN 2-PHASE POLYMER BLENDS WITH DIBLOCK COPOLYMER ADDITIVES - THE EFFECT OF HOMOPOLYMER MOLECULAR-WEIGHT

Segregation to interfaces in two-phase blends containing diblock copolymers is fundamental to understanding the properties of these interfaces. In this study, the effect of homopolymer molecular weight on the segregation is examined by forward recoil spectrometry (FRES). In the case of P(a) > N(a), where P(a) and N(a) are the polymerization indices of the homopolymer A and the A block of the copolymer, respectively, it is found that the interfacial areal density of block copolymer chains (nu(i)) at saturation is not affected significantly by P(a). This situation corresponds to the case where the "brush" of A block chains is not penetrated strongly by the A homopolymer, the so-called dry brush case. However, a lower nu(i) is observed in the case of P(a) < N(a), the so-called wet brush case. While Leibler's brush theory1 can reproduce the shape of the segregation isotherm if the Flory interaction parameter chi-is allowed to vary with P(a), a self-consistent mean-field theory2 can predict the observed isotherm using a single value of chi. The critical micelle concentration, phi(cmc), is obtained from the onset of surface segregation and is found to decrease as the molecular weight of the homopolymer matrix increases.