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Interfacial profiles between coexisting phases in thin films: Cahn Hilliard treatment versus capillary waves

K. Binder·M. Mueller·F. Schmid·A. Werner
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Abstract

We consider an interface between two demixed A and B phases, confined in a thin film between two antisymmetric walls, one of which prefers A and the other B. Above the wetting transition, the interface is stabilized in the center of the film. Based on a suitable extension of the Cahn-Hilliard gradient-square theory in combination with the capillary wave theory, we argue that the confinement influences the interfacial structure in two ways: It squeezes the intrinsic structure and cuts off the capillary wave spectrum. As a result, the interfacial width is proportional to the film thickness D in very thin films, and proportional to the square root of D in thicker films. These effects are then discussed in detail for the special case of an interface between demixed homopolymer phases. The width of the intrinsic profile is calculated analytically as a function of film thickness in the Cahn-Hilliard approximation (weak segregation limit) and in the Helfand theory (strong segregation limit), and numerically in the self-consistent field approximation. The results are confirmed by Monte Carlo simulations of a lattice model for a polymer mixture.

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K. Binder, M. Mueller, F. Schmid, A. Werner. 1998-10-06. Interfacial profiles between coexisting phases in thin films: Cahn Hilliard treatment versus capillary waves. https://doi.org/10.1023/a%3A1004510702716

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