Synchronized Fractionation and Phase Separation in Binary Colloids

TL;DR

This study demonstrates how controlled supersaturation in binary colloids induces synchronized fractionation and phase separation, revealing a mechanism relevant to biological membraneless organelles.

Contribution

It introduces a reversible fractionation method in binary colloids driven by competition between size-dependent repulsion and tunable attraction.

Findings

Deep supersaturation forms uniform gels.

Gradual supersaturation causes two-step crystallization.

Fractionation occurs during melting of gels.

Abstract

Fractionation is necessary for self-assembly in multicomponent mixtures. Here, reversible fractionation and crystallization are realized and studied in a two-dimensional binary colloids which is supersaturated by enhancing the attraction between colloidal particles. As a deep and fast supersaturation results in gels with a uniform distribution of binary particles, a gradual quasistatic supersaturating process leads to a two-step crystallization in which small particles and large particles are fractionated as coexisting crystal and liquid phases respectively. Fractionation occurs as well in the quasistatic melting of gel. We show that the synchronized fractionation and phase separation arises from the competition between the size-dependent repulsion and the tunable attraction. The results in this study demonstrate a robust mechanism of fractionation via phase separation, and have important implication in understanding the reversible formation of membraneless organelles in living cells.