Institut für Phsyik, Johannes Gutenberg-Universität Mainz, Staudingerweg 7, D-55099 Mainz, Germany.
J Chem Phys. 2012 Apr 7;136(13):134710. doi: 10.1063/1.3699981.
The Asakura-Oosawa model for colloid-polymer mixtures is studied by Monte Carlo simulations at densities inside the two-phase coexistence region of fluid and solid. Choosing a geometry where the system is confined between two flat walls, and a wall-colloid potential that leads to incomplete wetting of the crystal at the wall, conditions can be created where a single nanoscopic wall-attached crystalline cluster coexists with fluid in the remainder of the simulation box. Following related ideas that have been useful to study heterogeneous nucleation of liquid droplets at the vapor-liquid coexistence, we estimate the contact angles from observations of the crystalline clusters in thermal equilibrium. We find fair agreement with a prediction based on Young's equation, using estimates of interface and wall tension from the study of flat surfaces. It is shown that the pressure versus density curve of the finite system exhibits a loop, but the pressure maximum signifies the "droplet evaporation-condensation" transition and thus has nothing in common with a van der Waals-like loop. Preparing systems where the packing fraction is deep inside the two-phase coexistence region, the system spontaneously forms a "slab state," with two wall-attached crystalline domains separated by (flat) interfaces from liquid in full equilibrium with the crystal in between; analysis of such states allows a precise estimation of the bulk equilibrium properties at phase coexistence.
采用蒙特卡罗模拟方法研究了胶体-聚合物混合物的朝仓-大泽模型，模拟密度处于流体相和固体相共存区域内。选择系统被限制在两个平面壁之间的几何形状，并采用导致晶体在壁处不完全润湿的壁-胶体势，就可以在模拟盒的其余部分中创建与流体共存的单个纳米级壁附着结晶簇的条件。根据在研究气液共存时对液滴异质成核有用的相关思想，我们从热平衡时结晶簇的观测结果估计接触角。我们发现，使用从平面研究中得出的界面张力和壁张力的估计值，与基于杨方程的预测值吻合良好。结果表明，有限系统的压力-密度曲线呈现出一个环，但是压力最大值表示“液滴蒸发-凝结”转变，因此与范德华型环没有任何共同之处。在填充分数深入两相共存区域的系统中，系统会自发形成“薄片状态”，两个壁附着的结晶域通过（平面）界面与完全处于平衡状态的液体隔开，中间是晶体；对这种状态的分析可以精确估计相共存时的体相平衡性质。
