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Issue 33, 2017
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Phase separation dynamics of polydisperse colloids: a mean-field lattice-gas theory

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Abstract

New insights into phase separation in colloidal suspensions are provided via a dynamical theory based on the polydisperse lattice-gas model. The model gives a simplified description of polydisperse colloids, incorporating a hard-core repulsion combined with polydispersity in the strength of the attraction between neighbouring particles. Our mean-field equations describe the local concentration evolution for each of an arbitrary number of species, and for an arbitrary overall composition of the system. We focus on the predictions for the dynamics of colloidal gas–liquid phase separation after a quench into the coexistence region. The critical point and the relevant spinodal curves are determined analytically, with the latter depending only on three moments of the overall composition. The results for the early-time spinodal dynamics show qualitative changes as one crosses a ‘quenched’ spinodal that excludes fractionation and so allows only density fluctuations at fixed composition. This effect occurs for dense systems, in agreement with a conjecture by Warren that, at high density, fractionation should be generically slow because it requires inter-diffusion of particles. We verify this conclusion by showing that the observed qualitative changes disappear when direct particle–particle swaps are allowed in the dynamics. Finally, the rich behaviour beyond the spinodal regime is examined, where we find that the evaporation of gas bubbles with strongly fractionated interfaces causes long-lived composition heterogeneities in the liquid phase; we introduce a two-dimensional density histogram method that allows such effects to be easily visualized for an arbitrary number of particle species.

Graphical abstract: Phase separation dynamics of polydisperse colloids: a mean-field lattice-gas theory

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Publication details

The article was received on 16 Jun 2017, accepted on 02 Aug 2017 and first published on 02 Aug 2017


Article type: Paper
DOI: 10.1039/C7CP04062H
Citation: Phys. Chem. Chem. Phys., 2017,19, 22509-22527
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    Phase separation dynamics of polydisperse colloids: a mean-field lattice-gas theory

    P. de Castro and P. Sollich, Phys. Chem. Chem. Phys., 2017, 19, 22509
    DOI: 10.1039/C7CP04062H

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