Zausch Jochen, Virnau Peter, Binder Kurt, Horbach Jürgen, Vink Richard L
Institut für Physik, Johannes Gutenberg-Universität Mainz, 55099 Mainz, Staudinger Weg 7, Germany.
J Chem Phys. 2009 Feb 14;130(6):064906. doi: 10.1063/1.3071197.
We propose a new coarse-grained model for the description of liquid-vapor phase separation of colloid-polymer mixtures. The hard-sphere repulsion between colloids, and between colloids and polymers, which is used in the well-known Asakura-Oosawa (AO) model, is replaced with Weeks-Chandler-Andersen potentials. Similarly, a soft potential of height comparable to thermal energy is used for the polymer-polymer interaction, rather than treating polymers as ideal gas particles. It is shown by grand-canonical Monte Carlo simulations that this model leads to a coexistence curve that almost coincides with that of the AO model and that the Ising critical behavior of static quantities is reproduced. Then the main advantage of the model is exploited-its suitability for Molecular Dynamics simulations-to study the dynamics of mean square displacements of the particles, transport coefficients such as the self-diffusion and interdiffusion coefficients, and dynamic structure factors. While the self-diffusion of polymers increases slightly when the critical point is approached, the self-diffusion of colloids decreases and at criticality the colloid self-diffusion coefficient is about a factor of 10 smaller than that of the polymers. Critical slowing down of interdiffusion is observed, which is qualitatively similar to symmetric binary Lennard-Jones mixtures, for which no dynamic asymmetry of self-diffusion coefficients occurs.
我们提出了一种新的粗粒化模型，用于描述胶体-聚合物混合物的液-气相间分离。在著名的朝仓-大泽（AO）模型中使用的胶体之间以及胶体与聚合物之间的硬球排斥力，被维克斯-钱德勒-安德森势所取代。同样，聚合物-聚合物相互作用采用了高度与热能相当的软势，而不是将聚合物视为理想气体粒子。通过巨正则蒙特卡罗模拟表明，该模型得到的共存曲线几乎与AO模型的共存曲线重合，并且再现了静态量的伊辛临界行为。然后利用该模型的主要优点——其适用于分子动力学模拟——来研究粒子均方位移的动力学、诸如自扩散和互扩散系数等输运系数以及动态结构因子。当接近临界点时，聚合物的自扩散略有增加，而胶体的自扩散则减小，在临界状态下，胶体自扩散系数比聚合物的自扩散系数小约10倍。观察到互扩散的临界慢化，这在定性上与对称二元 Lennard-Jones 混合物相似，对于后者，自扩散系数不存在动态不对称性。
