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50.

The contact angle of the colloidal liquid-gas interface and a hard wall P. P. F. Wessels, M. Schmidt, and H. Löwen, J. Phys.: Condens. Matt. 16, S4169 (2004). Locate in [bare] [illustrated] list. Get [full paper] as pdf. Abstract. We consider the Asakura-Oosawa-Vrij model of hard sphere colloids and ideal polymer coils in contact with a planar hard wall at (colloidal) liquid-gas coexistence. Using extensive numerical density functional calculations, the liquid-gas, wall-liquid and wall-gas interfacial free energies are calculated. The results are inserted into Young's equation to obtain the contact angle between the liquid-gas interface and the wall. As a function of the polymer fugacity this angle exhibits discontinuities of slope ('kinks') upon crossing first-order surface phase transitions located on the gas branch of the bulk binodal. Each kink corresponds to a transition from n-1 to n colloid layers adsorbed at the wall, referred to as the nth layering transition. The corresponding adsorption spinodal points from n-1 to n layers upon reducing the polymer fugacity along the bulk binodal were found in a previous study (Brader et al 2002 J. Phys.: Condens. Matter. 14 L1; Brader et al 2003 Mol. Phys. 101 3349). Remarkably, we find desorption spinodal points from n to n-1 layers to be absent upon increasing polymer fugacity at bulk coexistence, and many branches (containing up to seven colloid layers) remainmetastable. Results for the first layering binodal and both spinodal branches off bulk coexistence hint at a topology of the surface phase diagram consistent with these findings. Both the order of the transition to complete wetting and whether it is preceded by a finite or an infinite number of layering transitions remain open questions. We compare the locations of the first layering binodal line and of the second layering binodal point at bulk coexistence with recent computer simulation results by Dijkstra and van Roij (2002 Phys. Rev. Lett. 89 208303) and discuss our results for the contact angle in the light of recent experiments. [figures] Read the [full paper] as pdf.

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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