On the Structure of Liquids: More order than expected

TL;DR

This paper reveals that liquids possess a complex, large-scale structural order characterized by alternating symmetries, detectable through novel correlation functions and temperature-dependent length scales, challenging previous notions of disorder.

Contribution

The study introduces a new four-point correlation function to uncover large-scale order in liquids, demonstrating more extensive structural organization than previously recognized.

Findings

Liquids exhibit alternating layers with icosahedral and dodecahedral symmetries.

Structural order extends to surprisingly large distances in liquids.

Temperature influences the length scale of this order, observable via scattering experiments.

Abstract

Disordered systems like liquids, gels, glasses, or granular materials are not only ubiquitous in daily life and in industrial applications but they are also crucial for the mechanical stability of cells or the transport of chemical and biological agents in living organisms [1-3]. Despite the importance of these systems, their microscopic structure is understood only on a rudimentary level, thus in stark contrast to the case of gases and crystals [1,4]. Experimental and theoretical investigations indicate that disordered systems have a structural order on the length scale of a few particle diameters but which then quickly vanishes at larger distances [5]. This conclusion is, however, based mainly on the behavior of two-point correlation functions such as the static structure factor or the radial distribution function [5.6]. Whether or not disordered systems have an order that extents to larger length scales is therefore a highly important question that is still open [7-10]. Here we use computer simulations to show that liquids have an intricate structural order given by alternating layers with icosahedral and dodecahedral symmetries and which extends to surprisingly large distances. We show that the temperature dependence of the corresponding length scale can be detected in the static structure factor, making it directly accessible to scattering experiments. These results, obtained by a novel type of four point correlation function that probes directly the particle density in three dimensions, show that liquids are far more ordered than envisaged so far but that this structural information is encoded in non-standard correlation functions.