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

Abstract

We study fluid-fluid phase separation in a colloid-polymer mixture adsorbed in a colloidal porous matrix close to the θ point. For this purpose we consider the Asakura-Oosawa model in the presence of a quenched matrix of colloidal hard spheres. We study the dependence of the demixing curve on the parameters that characterize the quenched matrix, fixing the polymer-to-colloid size ratio to 0.8. We find that, to a large extent, demixing curves depend only on a single parameter f , which represents the volume fraction which is unavailable to the colloids. We perform Monte Carlo simulations for volume fractions f equal to 40% and 70%, finding that the binodal curves in the polymer and colloid packing-fraction plane have a small dependence on disorder. The critical point instead changes significantly: for instance, the colloid packing fraction at criticality increases with increasing f . Finally, we observe for some values of the parameters capillary condensation of the colloids: a bulk colloid-poor phase is in chemical equilibrium with a colloid-rich phase in the matrix. PACS: 61.25. Hq, 82.35.Lr

Structure of phase-separated athermal colloid-polymer systems in the protein limit

“…While there have been theoretical attempts to treat such systems at coexistence with liquid-state integral equation theory [24][25][26], such theories can only predict the spinodal curve, rather than the binodal. Due to computational limitations, previous simulations have also not been able to capture structural details of large many-body systems, nor have they been explicitly linked to phase behavior as they are often at the limit of either one or two colloids [27,28], or have restricted colloid translational degrees of freedom such as in quenched matrices [29].…”

Virial coefficients and demixing in the Asakura–Oosawa model

“…Finally, simulations have also been performed using either the effective one-component depletion potential or the full AO binary mixture. [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] Our motivation to carry out the present study rests, however, on different grounds. Three of us have considered fluid-fluid demixing in binary AHS mixtures using the available information on the virial coefficients of those mixtures.…”

Colloids and polymers in random colloidal matrices: Demixing under good-solvent conditions

“…However, as we already discussed in Ref. [18], it is much more useful to characterize the amount of disorder by using the volume fraction f which is not accessible to the colloids due to the matrix. To define it precisely, consider the region R in which the (centers of the) colloids are allowed:…”

“…AOV colloidpolymer mixtures in a porous matrix have been studied in Refs. [13][14][15][16][17][18] by means of densityfunctional theory, integral equations, and Monte Carlo (MC) simulations. The nature of the critical transition has been fully clarified [14][15][16][17]: if the obstacles are random and there is a preferred affinity of the quenched obstacles to one of the phases, the transition is in the same universality class as that occurring in the random-field Ising model, in agreement with a general argument by de Gennes [19].…”

“…If, instead, q 1 (the protein regime), demixing occurs for η p 1, hence one must use more sophisticated CG multiblob models [25] in which each polymer is represented by a polyatomic molecule and each atom corresponds to a polymer blob of size of the order of that of the colloid. In this paper, we investigate the case q = 0.8, as in our previous work [18]. Since colloids are larger than polymers, a CG approach based on a single-blob representation of the polymers should be adequate.…”