# Phase behavior of charged colloids at a fluid interface

## TL;DR

This study investigates the phase transitions of charged colloids at a fluid interface, confirming KTHNY theory predictions through experimental observations of different phases and their topological defects.

## Contribution

The paper provides experimental validation of KTHNY theory in a colloidal system with detailed analysis of phase behavior and defect structures.

## Key findings

- Identification of solid, hexatic, and fluid phases
- Observation of topological defects matching KTHNY predictions
- Distinct dynamical behaviors for each phase

## Abstract

We study the phase behavior of a system of charged colloidal particles that are electrostatically bound to an almost flat interface between two fluids. We show that, despite the fact that our experimental system consists of only $10^{3}$ - $10^{4}$ particles, the phase behavior is consistent with the theory of melting due to Kosterlitz, Thouless, Halperin, Nelson and Young (KTHNY). Using spatial and temporal correlations of the bond-orientational order parameter, we classify our samples into solid, isotropic fluid, and hexatic phases. We demonstrate that the topological defect structure we observe in each phase corresponds to the predictions of KTHNY theory. By measuring the dynamic Lindemann parameter, $\gamma_{L}(\tau)$, and the non-Gaussian parameter, $\alpha_{2}(\tau)$, of the displacements of the particles relative to their neighbors, we show that each of the phases displays distinctive dynamical behavior.