Intrinsic profiles and capillary waves at homopolymer interfaces:: A Monte Carlo study

A popular concept that describes the structure of polymer interfaces by "intrinsic profiles'' centered around a two-dimensional surface, the "local interface position," is tested by extensive Monte Carlo simulations of interfaces between demixed homopolymer phases in symmetric binary (AB) homopolymer blends, using the bond fluctuation model. The simulations are done in an LxLxD geometry. The interface is forced to run parallel to the LxL planes by imposing periodic boundary conditions in these directions and fixed boundary conditions in the D direction, with one side favoring A and the other side favoring B. Intrinsic profiles are calculated as a function of the "coarse graining length" B by splitting the system into columns of size BxBxD and averaging in each column over profiles relative to the local interface position. The results are compared to predictions of the self-consistent field theory. It is shown that the coarse graining length can be chosen such that the interfacial width matches that of the self-consistent field profiles and that for this choice of B the "intrinsic'' profiles compare well with the theoretical predictions. Our simulation data suggest that this ''optimal'' coarse graining length Bo exhibits a dependence of the form B-0 = 3.8w(SCF)(1 - 3.1/chi N), where W-SCF is the interfacial width, N the chain length, and chi the Flory-Huggins parameter. [S1063-651X(99)05801-8].