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    52. Floating liquid phase in sedimenting colloid-polymer mixtures
    M. Schmidt, M. Dijkstra, and J.-P. Hansen, Phys. Rev. Lett. 93, 088303 (2004).
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    Abstract. Density functional theory and computer simulation are used to investigate sedimentation equilibria of colloid-polymer mixtures within the Asakura-Oosawa-Vrij model of hard sphere colloids and ideal polymers. When the ratio of buoyant masses of the two species is comparable to the ratio of differences in density of the coexisting bulk (colloid) gas and liquid phases, a stable "floating liquid" phase is found, i.e., a thin layer of liquid sandwiched between upper and lower gas phases. The full phase diagram of the mixture under gravity shows coexistence of this floating liquid phase with a single gas phase or a phase involving liquid-gas equilibrium; the phase coexistence lines meet at a triple point. This scenario remains valid for general asymmetric binary mixtures undergoing bulk phase separation. [figures]


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    Colloid-polymer mixtures

    The density functional theory for the Asakura-Oosawa model of colloid-polymer mixtures [11] was used to find the "floating liquid" phase [52]. Phew, I am exhausted! All these relations drive me crazy.. See [29] for an investigation of bulk fluid phases. See [22] for an answer to the question whether effective interactions depend on the choice of coordinates.

    Colloid-polymer mixtures: Beyond the AOV model

    Extensions include taking into account an explicit solvent of point particles [27], penetrability of (small) colloids into polymers [28], colloid-induced polymer compression [31], the influence of polymer interactions on fluid-demixing [34] and on the contact angle of the colloidal liquid-gas interface and a hard wall [50], as well as the stability of the floating liquid phase in sedimenting colloid-polymer mixtures for non-ideal polymers [52].

    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].

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MS, 20 Apr 2009.