Phase separation of mixtures after a second quench: composition heterogeneities

TL;DR

This paper explores how binary mixtures undergo complex, multi-stage phase separation after a second deep temperature quench, revealing new effects like long-lived heterogeneities and filamentous morphologies.

Contribution

It extends previous lattice theory to predict novel phenomena in phase separation dynamics after a second quench, including long-lived structures and interface behaviors.

Findings

Long-lived composition heterogeneities at interfaces

Wetting of interfaces by oppositely fractionated layers

Filamentous morphologies in three-phase coexistence

Abstract

We investigate binary mixtures undergoing phase separation after a second (deeper) temperature quench into two- and three-phase coexistence regions. The analysis is based on a lattice theory previously developed for gas-liquid separation in generic mixtures. Our previous results, which considered an arbitrary number of species and a single quench, showed that, due to slow changes in composition, dense colloidal mixtures can phase-separate in two stages. Moreover, the denser phase contains long-lived composition heterogeneities that originate as the interfaces of shrunk domains. Here we predict several new effects that arise after a second quench, mostly associated with the extent to which crowding can slow down 'fractionation', i.e. equilibration of compositions. They include long-lived regular arrangements of secondary domains; wetting of fractionated interfaces by oppositely fractionated layers; 'surface'-directed spinodal 'waves' propagating from primary interfaces; a 'dead zone' where no phase separation occurs; and, in the case of three-phase coexistence, filamentous morphologies arising out of secondary domains.