Direct Observation in 3d of Structural Crossover in Binary Hard Sphere Mixtures

TL;DR

This study provides direct 3D experimental evidence of structural crossover in binary hard sphere mixtures, confirming theoretical predictions and simulations, and clarifies that crossover is not linked to percolation phenomena.

Contribution

First direct 3D experimental observation of structural crossover in binary mixtures, aligning with theory and simulations, and distinguishing it from percolation effects.

Findings

Crossover exists and matches theoretical predictions.

Location of crossover in phase diagram is quantitatively accurate.

Crossover is unrelated to percolation phenomena.

Abstract

For binary fluid mixtures of spherical particles in which the two species are sufficiently different in size, the dominant wavelength of oscillations of the pair correlation functions is predicted to change from roughly the diameter of the large species to that of the small species along a sharp crossover line in the phase diagram [C. Grodon, M. Dijkstra, R. Evans & R. Roth, J.Chem.Phys. 121, 7869 (2004)]. Using particle-resolved colloid experiments in 3d we demonstrate that crossover exists and that its location in the phase diagram is in quantitative agreement with the results of both theory and our Monte-Carlo simulations. In contrast with previous work [J. Baumgartl, R. Dullens, M. Dijkstra, R. Roth & C. Bechinger, Phys.Rev.Lett. 98, 198303 (2007)], where a correspondence was drawn between crossover and percolation of both species, in our 3d study we find that structural crossover is unrelated to percolation.