TY - JOUR
T1 - Composition inversion in mixtures of binary colloids and polymer
AU - Zhang, Isla
AU - Pinchaipat, Rattachai
AU - Wilding, Nigel B.
AU - Faers, Malcolm A.
AU - Bartlett, Paul
AU - Evans, Robert
AU - Royall, Cp
PY - 2018/5/14
Y1 - 2018/5/14
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=85046889808&partnerID=8YFLogxK
U2 - 10.1063/1.5023393
DO - 10.1063/1.5023393
M3 - Article (Academic Journal)
C2 - 29764136
AN - SCOPUS:85046889808
SN - 0021-9606
VL - 148
JO - Journal of Chemical Physics
JF - Journal of Chemical Physics
IS - 18
M1 - 184902
ER -