Effect of molecular weight on the interfacial excess, tension, and width in a homopolymer binary polymer blend system

The interfacial properties of a three-component, two-phase A/B:C blend are investigated to understand the effect of the A and B chain lengths on the interfacial excess of B, z(B)*, the interfacial tension, gamma(ABC), and the interfacial width, w(ABC). The A/B:C components are polystyrene/poly(d(8)-styrene-co-4-bromostyrene):poly(styrene-co-4-bromostyrene), where B and C have 4-bromostyrene mole fractions of 0.154 and 0.177, respectively. Low-energy forward recoil spectrometry (LE-FRES) is used to measure z(B)* as a function of the B volume fraction in the B:C blend, phi B-infinity. The experimental z(B)*'s are found to be in excellent agreement with those calculated using the self-consistent field (SCF) model of the A/B:C interface. In addition, the SCF model is used to evaluate gamma(ABC) and the widths for the A/B:C, A/B, and A/C interfaces (i.e., w(ABC), w(AB), and w(AC), respectively). Our results demonstrate that increasing the number of B segments, N-B, greatly increases the magnitude of z(B)*, particularly at low phi(B infinity). On the other hand, varying N-A has only a minor effect on z(B)*. Concurrent with the segregation of B, gamma(ABC) and w(AB) rapidly decrease and increase, respectively, as phi(B infinity) initially increases. Upon calculation of the entanglement length, w(e), for each component, w(AB) is found to approach w(e) when phi(B infinity) approximate to 0.30. As a result the mechanical strength of the interface should greatly improve. The optimum amount of B to achieve good compatibilization correlates with the phi B-infinity at which z(B)* is a maximum.