Segregation in aqueous methanol enhanced by cooling and compression

TL;DR

This study investigates how cooling and compression enhance molecular segregation in aqueous methanol, revealing increased heterogeneity and potential critical solution behavior that is hidden below the freezing line.

Contribution

It provides detailed insights into segregation behavior in methanol-water mixtures under varying conditions using neutron diffraction and molecular dynamics simulations.

Findings

Segregation increases with cooling and compression.

Water cluster topology changes with conditions.

Evidence suggests an approach to an upper critical solution point.

Abstract

Molecular segregation in methanol-water mixtures is studied across a wide concentration range as a function of temperature and pressure. Cluster distributions obtained from both neutron diffraction and molecular dynamics simulations point to significantly enhanced segregation as the mixtures are cooled or compressed. This evolution toward greater molecular heterogenity in the mixture accounts for the observed changes in the water-water radial distribution function and there are indications also of a change in the topology of the water clusters. The observed behavior is consistent with an approach to an upper critical solution point. Such a point would appear to be ``hidden'' below the freezing line, thereby precluding observation of the two-fluid region.