Colloid–polymer mixtures in the presence of quenched disorder: a theoretical and computer simulation study

Abstract

We use theory and computer simulation to study the structure and phase behavior of colloid-polymer mixtures in the presence of quenched disorder. The Asakura-Oosawa model (AO) (Asakura and Oosawa 1954 J. Chem. Phys. 22 1255) is used to describe the colloid-colloid, colloid-polymer, and polymer-polymer pair interactions. We then investigate the behavior of this model in the presence of frozen-in (quenched) obstacles. The obstacles will be placed according to two different scenarios, both of which are experimentally feasible. In the first scenario, polymers are distributed at positions drawn from an ideal gas configuration. In the second scenario, colloidal particles are distributed at positions drawn from an equilibrium hard sphere configuration. We investigate how the unmixing transition of the AO model is affected by the type of quenched disorder. The theoretical formalism is based on the replica method of Given and Stell (1994 Physica A 209 495). Our foremost aim is to test the accuracy of three common closures to the replica Ornstein-Zernike equations, namely the hypernetted chain, the Percus-Yevick, and the Martinov-Sarkisov equations. The accuracy is determined by comparison with grand canonical Monte Carlo simulations. We find that, for quenched polymer disorder, all three closures perform remarkably well. However, when quenched colloid disorder is considered, i.e. the second mentioned scenario, the predictions of all three closures worsen dramatically.

Fluid–fluid demixing curves for colloid–polymer mixtures in a random colloidal matrix

“…We have thus fixed q = 0.8, as in Ref. [48], at the boundary between the colloid and the protein regimes.…”

“…We can compare our results with those obtained in Refs. [45,48]. By using densityfunctional methods, Ref.…”

“…We will not instead perform a detailed study of the q dependence and we shall set q = 0.8 as in Ref. [48]. This work complements the results of Ref.…”

“…AO colloid-polymer mixtures in a porous matrix have been studied in Refs. [45][46][47][48][49] by means of density-functional theory, integral equations, and…”

Demixing and confinement of non-additive hard-sphere mixtures in slit pores

“…The effects of randomness and confinement on demixing of colloidpolymer systems have also been extensively investigated. 14,15 Moreover, Fortini and Dijsktra 16 explored the possibility of manipulating colloidal crystal structures by confinement in slit pores, stressing the potential technological implications of this class of studies. These colloid-polymer mixtures are mostly treated in terms of the Asakura-Oosawa model, 17 by which the mixture is reduced to an effective one-component fluid and the demixing transition is in turn mapped onto a vapor-liquid transition.…”