Observation of surface layering in a nonmetallic liquid

TL;DR

This study demonstrates that surface layering occurs in a nonmetallic molecular liquid at low temperatures, confirming theoretical predictions and expanding understanding of surface phenomena beyond metallic liquids.

Contribution

It provides the first experimental evidence of surface layering in a dielectric liquid, previously observed only in liquid metals, using x-ray reflectivity.

Findings

Surface layering appears at T/Tc~0.25 in the molecular liquid.

Lateral order within layers remains liquid-like.

Surface layering occurs in dielectric liquids at low temperatures.

Abstract

Oscillatory density profiles (layers) have previously been observed at the free surfaces of liquid metals, but not in other isotropic liquids. We have used x-ray reflectivity to study a molecular liquid, tetrakis(2-ethylhexoxy)silane. When cooled to T/Tc~0.25 (well above the freezing point for this liquid), density oscillations appear at the surface. Lateral order within the layers is liquid-like. Our results confirm theoretical predictions that a surface-layered state will appear even in dielectric liquids at sufficiently low temperatures, if not preempted by freezing.