Freezing and correlations in fluids with competing interactions

TL;DR

This paper investigates how competing attractive and repulsive interactions in fluids influence phase stability and correlations, revealing that repulsive forces extend the metastability of the liquid-vapor transition and significantly alter correlation decay near criticality.

Contribution

The study extends previous work by analyzing the impact of long-range repulsive interactions on phase behavior and correlation decay in fluids with competing forces.

Findings

Long-range repulsion expands the metastable region of fluid-solid transition.

Large density fluctuations are enhanced and cover a wider region near the critical point.

Correlation decay involves two characteristic lengths, deviating from Ornstein-Zernike behavior.

Abstract

We consider fluids where the attractive interaction at distances slightly larger than the particle size is dominated at larger distances by a repulsive contribution. A previous investigation of the effects of the competition between attraction and repulsion on the liquid-vapour transition and on the correlations is extended to the study of the stability of liquid-vapour phase separation with respect to freezing. We find that this long-range repulsive part of the interaction expands the region where the fluid-solid transition preempts the liquid-vapour one, so that the critical point becomes metastable at longer attraction ranges than those required for purely attractive potentials. Moreover, the large density fluctuations that occur near the liquid-vapour critical point are greatly enhanced by the competition between attractive and repulsive forces, and encompass a much wider region than in the attractive case. The decay of correlations for states where the compressibility is large is governed by two characteristic lengths, and the usual Ornstein-Zernike picture breaks down except for the very neighborhood of the critical point, where one length reduces to the commonly adopted correlation length, while the other one saturates at a finite value.