Crystallization and gelation in colloidal systems with short-ranged attractive interactions

TL;DR

This study investigates how short-range attractive colloids crystallize or gel depending on interaction strength and density, revealing a two-stage crystallization process and the conditions leading to gelation or glassy states.

Contribution

It provides a detailed simulation-based analysis of the phase behavior and crystallization pathways in short-range attractive colloids, highlighting the role of metastable phases and arrest mechanisms.

Findings

Enhanced crystallization occurs near the gas-liquid binodal.

Gelation results from arrested phase separation at high interaction strength.

Crystalline clusters form at low energy, glassy clusters at high energy.

Abstract

We systematically study the relationship between equilibrium and non-equilibrium phase diagrams of a system of short-ranged attractive colloids. Using Monte Carlo and Brownian dynamics simulations we find a window of enhanced crystallization that is limited at high interaction strength by a slowing down of the dynamics and at low interaction strength by the high nucleation barrier. We find that the crystallization is enhanced by the metastable gas-liquid binodal by means of a two-stage crystallization process. First, the formation of a dense liquid is observed and second the crystal nucleates within the dense fluid. In addition, we find at low colloid packing fractions a fluid of clusters, and at higher colloid packing fractions a percolating network due to an arrested gas-liquid phase separation that we identify with gelation. We find that this arrest is due to crystallization at low interaction energy and it is caused by a slowing down of the dynamics at high interaction strength. Likewise, we observe that the clusters which are formed at low colloid packing fractions are crystalline at low interaction energy, but glassy at high interaction energy. The clusters coalesce upon encounter.