Evidence for Size Effects on Interfacial Widths in Confined Thin Films

When a film of thickness D of a binary mixture on a substrate segregates into two coexisting phases, an interface between the phases parallel to the substrate may form due to preferential surface attraction of one of them. It is argued then that the correlation length ${\xi }_{\parallel }$ for interfacial fluctuations parallel to this interface $\left(\ln {\xi }_{\parallel }\propto D\right)$ leads to a size-dependent interfacial width $w\propto \sqrt{D}$. Nuclear reaction depth profiling experiments on polymer mixtures as well as Ising model simulations both support this prediction.