Critical adsorption at chemically structured substrates

TL;DR

This paper investigates how binary liquid mixtures near critical points behave near chemically patterned flat substrates, revealing universal scaling functions that describe order parameter profiles and adsorption.

Contribution

It introduces calculated universal scaling functions for order parameters and adsorption profiles near chemically structured substrates at criticality.

Findings

Order parameter profiles show frustration across chemical steps that heal in the bulk.

Universal scaling functions govern the temperature dependence of order parameters.

Adsorption behavior can be described relative to reference systems using these scaling functions.

Abstract

We consider binary liquid mixtures near their critical consolute points and exposed to geometrically flat but chemically structured substrates. The chemical contrast between the various substrate structures amounts to opposite local preferences for the two species of the binary liquid mixtures. Order parameters profiles are calculated for a chemical step, for a single chemical stripe, and for a periodic stripe pattern. The order parameter distributions exhibit frustration across the chemical steps which heals upon approaching the bulk. The corresponding spatial variation of the order parameter and its dependence on temperature are governed by universal scaling functions which we calculate within mean field theory. These scaling functions also determine the universal behavior of the excess adsorption relative to suitably chosen reference systems.