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Composition inversion in mixtures of binary colloids and polymer

Research output: Contribution to journalArticle

Original languageEnglish
Article number184902
Number of pages10
JournalJournal of Chemical Physics
Issue number18
Early online date9 May 2018
DateAccepted/In press - 19 Apr 2018
DateE-pub ahead of print - 9 May 2018
DatePublished (current) - 14 May 2018


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.

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