Hynninen A-P, Panagiotopoulos A Z
J Phys Condens Matter. 2009 Nov 18;21(46):465104. doi: 10.1088/0953-8984/21/46/465104. Epub 2009 Oct 26.
We present full phase diagrams (including solid phases) of spherical charged colloids, using Monte Carlo sampling and thermodynamic integration of the Helmholtz free energy. Colloids and their co- and counterions are described by the primitive model for ionic systems that consists of hard-spheres with central point charges, while the solvent is taken into account solely through its dielectric constant. Two systems are considered: (i) a size-asymmetric system of oppositely charged spheres with size ratios q = 0.3 and 0.5 and (ii) a charge- and size-asymmetric system with colloid charge Q = 10 and counterions of charge -1 in the presence of monovalent added salt. In system (i), for both size ratios, the stable solid phase is equivalent to the NaCl crystal where the oppositely charged spheres take the lattice positions of Na and Cl ions. In system (ii), the phase diagram consists of gas-liquid and fluid-solid coexistence regions. We show that added salt stabilizes the fluid phase and shrinks the fluid-solid coexistence region, in agreement with experimental and theoretical results.
我们利用蒙特卡罗抽样法和亥姆霍兹自由能的热力学积分，给出了球形带电胶体的完整相图（包括固相）。胶体及其共离子和反离子由离子系统的原始模型描述，该模型由带有中心电荷的硬球组成，而溶剂仅通过其介电常数来考虑。我们考虑了两个系统：（i）大小比q = 0.3和0.5的带相反电荷球体的大小不对称系统，以及（ii）在存在单价添加盐的情况下，胶体电荷Q = 10且反离子电荷为 -1的电荷和大小不对称系统。在系统（i）中，对于两种大小比，稳定的固相等同于NaCl晶体，其中带相反电荷的球体占据Na和Cl离子的晶格位置。在系统（ii）中，相图由气-液和液-固共存区域组成。我们表明，添加盐使流体相稳定并缩小了液-固共存区域，这与实验和理论结果一致。
