Critical point of symmetric binary homopolymer blends

Abstract

Monte Carlo field-theoretic simulations (MC-FTS) are performed on structurally symmetric binary homopolymer blends for invariant polymerization indexes of N > 10^3. It is shown that the ultraviolet (UV) divergence that plagues MC-FTS at small N can be removed by an appropriate renormalization of the Flory-Huggins interaction parameter, chi, allowing one to extract meaningful results that are independent of the wavevector cutoff. Once the divergence is taken care of, the fluctuation corrections to mean-field theory are found to be exceptionally small. In particular, the disordered-state structure function, S(k), is virtually indistinguishable from the RPA prediction, and there is a slight shift in the critical point, (chi N)_c, that roughly scales as N^-0.5. An implication of the small corrections is that previous experimental determinations of chi based on homopolymer blends should be relatively accurate.