Solid or Liquid ? - Kinetically induced phase transition of a confined liquid

TL;DR

This study demonstrates that the phase behavior of confined liquids depends on the approach rate of confining surfaces, with solidification occurring kinetically at a critical slow rate rather than thermodynamic equilibrium.

Contribution

It reveals that confinement-induced solidification is a kinetic phenomenon, not an equilibrium phase transition, depending on the approach rate of confining surfaces.

Findings

Confined liquids can behave as liquids or pseudo-solids based on approach rate.

Solidification occurs kinetically at a critical rate of about 6 Å/s.

No confinement-induced solidification in thermodynamic equilibrium.

Abstract

There has been long-standing debate about the physical state and possible phase transformations of confined liquids. In this report we show that a model confined liquid can behave both as a Newtonian liquid with very little change in its dynamics or as a pseudo-solid depending solely on the {\it rate} of approach of the confining surfaces. Thus, the confined liquid does {\it not} exhibit any confinement induced solidification in thermodynamic equilibrium. Instead, solidification is induced kinetically, when the two confining surfaces are approached with a minimum critical rate. This critical rate is surprisingly slow, of the order of 6 \AA /s, explaining the frequent observation of confinement induced solidification.