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, zB*, the interfacial tension, γABC, and the interfacial width, wABC. The A/B:C components are polystyrene/poly(d8-styreneco-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 zB* as a function of the B volume fraction in the B:C blend, φB∞. The experimental zB*’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 γABC and the widths for the A/B:C, A/B, and A/C interfaces (i.e.,wABC,wAB, andwAC, respectively). Our results demonstrate that increasing the number of B segments, NB, greatly increases the magnitude of zB*, particularly at low φB∞. On the other hand, varying NA has only a minor effect on zB*. Concurrent with the segregation of B, γABC and wAB rapidly decrease and increase, respectively, as φB∞ initially increases. Upon calculation of the entanglement length, we, for each component, wAB is found to approach we when φB∞ ≈ 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 φB∞ at which zB* is a maximum.