Triplet correlations in two-dimensional colloidal model liquids

TL;DR

This study measures three-body correlation functions in two-dimensional colloidal liquids, revealing how triplet correlations lead to local crystalline order as particle coupling increases, despite differing interaction potentials.

Contribution

First experimental measurement of three-point correlation functions in colloidal fluids, demonstrating the emergence of local order due to triplet correlations.

Findings

Triplet correlations increase with particle coupling.

Local crystal-like order forms due to packing effects.

Similar results observed in systems with different interactions.

Abstract

Three-body distribution functions in classical fluids have been theoretically investigated many times, but have never been measured directly. We present experimental three-point correlation functions that are computed from particle configurations measured by means of video-microscopy in two types of quasi-two-dimensional colloidal model fluids: a system of charged colloidal particles and a system of paramagnetic colloids. In the first system the particles interact via a Yukawa potential, in the second via a potential $\Gamma/r^{3}$. We find for both systems very similar results: on increasing the coupling between the particles one observes the gradual formation of a crystal-like local order due to triplet correlations, even though the system is still deep inside the fluid phase. These are mainly packing effects as is evident from the close resemblance between the results for the two systems having completely different pair-interaction potentials.