From capillary condensation to interface localization transitions in colloid-polymer mixtures confined in thin-film geometry
De Virgiliis, Andres and Vink, Richard L. C. and Horbach, Jürgen and Binder, Kurt (2008) From capillary condensation to interface localization transitions in colloid-polymer mixtures confined in thin-film geometry. Physical Review E, 78, . DOI: 10.1103/PhysRevE.78.041604.
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Monte Carlo simulations of the Asakura-Oosawa model for colloid-polymer mixtures confined between two parallel repulsive structureless walls are presented and analyzed in the light of current theories on capillary condensation and interface localization transitions. Choosing a polymer-to-colloid size ratio of q=0.8 and studying ultrathin films in the range of D=3 to D=10 colloid diameters thickness, grand canonical Monte Carlo methods are used; phase transitions are analyzed via finite size scaling, as in previous work on bulk systems and under confinement between identical types of walls. Unlike the latter work, inequivalent walls are used here: While the left wall has a hard-core repulsion for both polymers and colloids, at the right-hand wall an additional square-well repulsion of variable strength acting only on the colloids is present. We study how the phase separation into colloid-rich and colloid-poor phases occurring already in the bulk is modified by such a confinement. When the asymmetry of the wall-colloid interaction increases, the character of the transition smoothly changes from capillary condensation type to interface localization type. For very thin films (i.e., for D=3) and a suitable choice of the wall-colloid interactions, evidence is found that the critical behavior falls in the universality class of the two-dimensional Ising model. Otherwise, we observe crossover scaling between different universality classes (namely, the crossover from the three-dimensional to the two-dimensional Ising model universality class). The colloid and polymer density profiles across the film in the various phases are discussed, as well as the correlation of interfacial fluctuations in the direction parallel to the confining walls. The broadening of the interface between the coexisting colloid-rich and polymer-rich phases (located parallel to the confining walls) is understood in terms of capillary wave fluctuations. The experimental observability of all these phenomena is briefly discussed.
|Title:||From capillary condensation to interface localization transitions in colloid-polymer mixtures confined in thin-film geometry|
|Date:||09 October 2008|
|Journal or Publication Title:||Physical Review E|
|In ISI Web of Science:||Yes|
|Keywords:||demixing transition in confinement, colloid-polymer mixtures, Monte-Carlo simulation|
|HGF - Research field:||Aeronautics, Space and Transport|
|HGF - Program:||Space|
|HGF - Program Themes:||W FR - Forschung unter Weltraumbedingungen|
|DLR - Research area:||Space|
|DLR - Program:||W FR - Forschung unter Weltraumbedingungen|
|DLR - Research theme (Project):||W - Vorhaben Materialwissenschaftliche Forschung (old)|
|Institutes and Institutions:||Institute of Materials Physics in Space|
|Deposited By:||Dr.rer.nat. Jürgen Horbach|
|Deposited On:||20 Oct 2008|
|Last Modified:||27 Apr 2009 15:17|
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