Composition inversion in mixtures of binary colloids and polymer

Isla Zhang, Rattachai Pinchaipat, Nigel B. Wilding, Malcolm A. Faers, Paul Bartlett, Robert Evans, Cp Royall

Research output: Contribution to journalArticle (Academic Journal)

5 Citations (Scopus)
522 Downloads (Pure)

Abstract

Understanding the phase behaviour of mixtures continues to pose challenges, even for systems that might be considered “simple”. Here we consider a very simple mixture of two colloidal and one non-adsorbing polymer species which can be simplified even further to a size-asymmetrical binary mixture, in which the effective colloid-colloid interactions depend on the polymer concentration. We show that this basic system exhibits surprisingly rich phase behaviour. In particular, we enquire whether such a system features only a liquid- vapor phase separation (as in one-component colloid-polymer mixtures) or whether, additionally, liquid-liquid demixing of two colloidal phases can occur. Particle-resolved experiments show demixing-like behaviour, but when combined with bespoke Monte Carlo simulations, this proves illusory, and we reveal that only a single liquid-vapor transition occurs. Progressive migration of the small particles to the liquid phase as the polymer concentration increases gives rise to composition inversion — a maximum in the large particle concentration in the liquid phase. Near criticality the density fluctuations are found to be dominated by the larger colloids.
Original languageEnglish
Article number184902
Number of pages10
JournalJournal of Chemical Physics
Volume148
Issue number18
Early online date9 May 2018
DOIs
Publication statusPublished - 14 May 2018

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