Experimental validation of correlation peak universality in classical fluids

Abstract

The radial distribution function (RDF) in condensed matter provides a key link between structural and thermodynamic properties. A recently developed fluid interpolation method allows the reconstruction of the RDF over a wide temperature range in fluids. This method is based on the observed “universality” of the correlation peaks in the pair correlation function $g\left(r\right)$, which holds despite variations in density, temperature, interparticle potentials and system types - from ideal gases to complex biological fluid-like systems. However, so far this universality has only been identified by computer simulations for two-dimensional systems and has not been experimentally validated. This work is dedicated to a more comprehensive analysis of this ‘universality’, including experiments on colloidal suspensions with tunable interactions in external rotating electric fields and 3D systems such Lennard-Jones fluid, and fluid state of Hg and Fe. In particular, we found that the peak norms, their mean values and dispersion show identical behaviour, while differences between peaks are mainly due to non-Gaussian parameters. Furthermore, the obtained dependencies reveal a clear transition between the crystal- and gas-like correlation regimes at close and far distances, suggesting that our approach may provide a new way to analyse fluids of different nature, from atomic and molecular to protein and colloidal systems.