# Formation of Laves Phases in Repulsive and Attractive Hard Sphere Suspensions

## TL;DR

This study demonstrates the formation of colloidal Laves phases in binary hard sphere mixtures, showing that their crystallization can be accelerated and improved by adding non-adsorbing polymer, with implications for photonic materials.

## Contribution

First experimental observation of Laves phases in hard sphere binary mixtures, confirming theoretical predictions and showing effects of attractive interactions on crystallization.

## Key findings

- Laves phases of MgZn2 structure form over weeks to months.
- Addition of non-adsorbing polymer accelerates crystallization.
- Attractive interactions improve crystal quality.

## Abstract

Colloidal Laves phases (LPs) of $MgCu_2$ type are promising precursors for diamond structure photonic materials. They have been predicted for hard sphere binary mixtures, but not yet observed. We here report a time resolved static light scattering study on their formation in a binary mixture of buoyant experimental hard sphere approximants (size ratio $\Gamma=0.77$, molar fraction of small spheres $x_S = 0.76$) for volume fractions between melting and the glass transition. In line with theoretical expectation, all samples form LPs of $MgZn_2$ structure on the time scale of weeks to months. $MgNi_2$ structures are absent, $MgCu_2$ structures and randomly stacked LPs prevail at elevated volume fraction. The addition of small amounts of non-adsorbing polymer switches the interaction to depletion attractive and results in significantly accelerated crystallization kinetics and improved crystal quality.

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Source: https://tomesphere.com/paper/1702.05817