Measuring the equation of state of a hard-disc fluid

TL;DR

This study experimentally measures the pressure-density relationship of a 2D colloidal fluid, validating theoretical models and simulations with high precision using optical tweezers and video microscopy.

Contribution

It provides the first precise experimental measurement of the equation of state for a 2D hard-disc fluid, confirming theoretical and simulation predictions.

Findings

Good agreement between experimental data and theoretical models.

Accurate determination of the fluid-solid transition point.

Validation of Monte Carlo simulation results.

Abstract

We use video microscopy to study a two-dimensional (2D) model fluid of charged colloidal particles suspended in water and compute the pressure from the measured particle configurations. Direct experimental control over the particle density by means of optical tweezers allows the precise measurement of pressure as a function of density. We compare our data with theoretical predictions for the equation of state, the pair-correlation function and the compressibility of a hard-disc fluid and find good agreement, both for the fluid and the solid phase. In particular the location of the transition point agrees well with results from Monte Carlo simulations.