Tunable liquid-liquid critical point in an ionic model of silica

TL;DR

This study shows that by adjusting ion charges in an ionic silica model, a liquid-liquid critical point can be induced, which could be observed experimentally in charged colloids, revealing insights into silica's phase behavior.

Contribution

We demonstrate that varying ion charges in the WAC silica model induces a liquid-liquid critical point, linking coordination numbers to phase transition phenomena.

Findings

Increasing ion charge separates maxima of response functions.

Reducing ion charge merges maxima into a LLCP.

Low Si/O coordination ratio is necessary for LLCP.

Abstract

Recently it was shown that the WAC model for liquid silica [L. V. Woodcock, C. A. Angell, and P. Cheeseman, J. Chem. Phys. 65, 1565 (1976)] is remarkably close to having a liquid-liquid critical point (LLCP). We demonstrate that increasing the ion charge separates the global maxima of the response functions, while reducing the charge smoothly merges them into a LLCP; a phenomenon that might be experimentally observable with charged colloids. An analysis of the Si and O coordination numbers suggests that a sufficiently low Si/O coordination number ratio is needed to attain a LLCP.