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41.

Capillary condensation and interface structure of a model colloid-polymer mixture in a porous medium P. P. F. Wessels, M. Schmidt, and H. Löwen, Phys. Rev. E 68, 061404 (2003). Locate in [bare] [illustrated] list. Get [full paper] as pdf. Abstract. We consider the Asakura-Oosawa model of hard sphere colloids and ideal polymers in contact with a porous matrix modeled by immobilized configurations of hard spheres. For this ternary mixture a fundamental measure density functional theory is employed, where the matrix particles are quenched and the colloids and polymers are annealed, i.e., allowed to equilibrate. We study capillary condensation of the mixture in a small sample of matrix as well as demixing and the fluid-fluid interface inside a bulk matrix. Density profiles normal to the interface and surface tensions are calculated and compared to the case without matrix. Two kinds of matrices are considered: (i) colloid-sized matrix particles at low packing fractions and (ii) large matrix particles at high packing fractions. These two cases show fundamentally different behavior and should both be experimentally realizable. Furthermore, we argue that capillary condensation of a colloidal suspension could be experimentally accessible. We find that in case (ii), even at high packing fractions, the main effect of the matrix is to exclude volume and, to high accuracy, the results can be mapped onto those of the same system without matrix via a simple rescaling. [figures] Read the [full paper] as pdf.

Fluid interfaces

Colloid-polymer mixtures display fluid-fluid interfaces [21] [44], relevant for laser-induced condensation [35], capillary condensation [43] and evaporation [48], immersion in porous media [41], the appearance of the floating liquid phase [52], the competition between sedimentation and phase coexistence [51], tension at a substrate [45], the experimental observation of thermal capillary waves [47], and the contact angle of the liquid-gas interface and a wall [50]. In colloidal rod-sphere mixtures fluid-fluid interfaces were investigated with theory [30] and simulation [42]. Hard sphere fluids were considered at surfaces of porous media [37], in random fiber networks [39], and in one dimensional cases [46].



Fluids in random media

The density functional theory for quenched-annealed mixtures [24] relates the quenched components to a random porous medium and the annealed components model to an adsorbate fluid (mixture). See [46] for the explicit relation to the the replica trick. Colloid-polymer mixtures were studied in bulk random matrices [32], exhibiting (gas-liquid) interfaces [41], and wetting properties at porous substrates [56]. Rods were immersed in quenched sphere matrices [54], and spheres were immersed in random fibre networks [39]. Freezing is hindered in the presence of disorder [38]. See [33] for the related non-equilibrium process of random sequential adsorption.

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