Hiding in plain view: Colloidal self-assembly from polydisperse populations

TL;DR

This study demonstrates that polydisperse colloidal silica dispersions can self-assemble into multiple crystal phases due to intermediate-range forces, revealing new pathways for designing complex colloidal structures.

Contribution

It provides experimental evidence of fractional crystallization and multi-phase coexistence in polydisperse colloids, highlighting the role of interparticle forces in complex self-assembly.

Findings

Polydisperse silica particles form distinct crystal phases.

Multiple-phase coexistence observed in dispersions.

Intermediate-range forces enable complex self-assembly.

Abstract

We report small-angle x-ray scattering (SAXS) experiments on aqueous dispersions of colloidal silica with a broad monomodal size distribution (polydispersity 18%, size 8 nm). Over a range of volume fractions the silica particles segregate to build first one, then two distinct sets of colloidal crystals. These dispersions thus demonstrate fractional crystallization and multiple-phase (bcc, Laves AB$_2$, liquid) coexistence. Their remarkable ability to build complex crystal structures from a polydisperse population originates from the intermediate-range nature of interparticle forces, and suggests routes for designing self-assembling colloidal crystals from the bottom-up.