Fluctuations and Pattern Formation in Fluids with Competing Interactions

TL;DR

This paper investigates how competing attractive and repulsive forces in 2D fluids lead to pattern formation and microphase structures, revealing the role of temperature and external fields in these phenomena.

Contribution

It provides simulation-based insights into the effects of microscopic force competition on phase behavior and pattern formation in soft-matter fluids.

Findings

Competition inhibits liquid-vapor phase separation at lower temperatures.

Presence of intra- and inter-cluster correlations in fluid structure.

Large density fluctuations occur even without microphase formation, enabling patterning with external fields.

Abstract

One of the most interesting phenomena in the soft-matter realm consists in the spontaneous formation of super-molecular structures (microphases) in condition of thermodynamic equilibrium. A simple mechanism responsible for this self-organization or pattern formation is based on the competition between attractive and repulsive forces with different length scales in the microscopic potential, typically, a short-range attraction against a longer-range repulsion. We analyse this problem by simulations in 2D fluids. We find that, as the temperature is lowered, liquid-vapor phase separation is inhibited by the competition between attraction and repulsion, and replaced by a transition to non-homogeneous phases. The structure of the fluid shows well defined signatures of the presence of both intra- and inter-cluster correlations. Even when the competition between attraction and repulsion is not so strong as to cause microphase formation, it still induces large density fluctuations in a wide region of the temperature-density plane. In this large-fluctuation regime, pattern formation can be triggered by a weak external modulating field.