Instituto de Química Física Rocasolano, Consejo Superior de Investigaciones Cientficas, CSIC, Calle Serrano 119, 28026 Madrid, Spain.
Soft Matter. 2017 May 3;13(17):3221-3229. doi: 10.1039/c7sm00217c.
Using computer simulations, we study the phase diagram of a two-dimensional system of disk particles with three patches distributed symmetrically along the particle equator. The geometry of the particles is compatible with a honey-comb lattice at moderately low temperature and pressure, whereas it is expected that the system forms a close-packed triangular lattice at high temperature and pressure. The effect of patch size within the single bond per patch regime was investigated, and it was found that the topology of the phase diagram changes drastically with patch size. Interestingly, in particles with small patches (with a half opening angle of 10°), the fluid transforms upon increasing the pressure into a rather exotic phase that can be understood as a honey-comb lattice whose voids are filled continuously with additional particles that remain, on average, unbound. Eventually, all the voids are occupied so that particles are located at the positions of a triangular lattice, but only two thirds of the particles are orientationally ordered whereas the remaining one third can rotate almost freely as in a plastic crystal. At moderately low temperature, the fluid transforms into a nearly empty honey-comb lattice, whereas at high temperature it transforms directly into the almost filled lattice. Interestingly, for particles with big patches (with a half opening angle of 20°), the honey-comb and triangular lattices are separated by a liquid phase that remains stable down to fairly low temperatures. Less surprisingly, only particles with big patches exhibit an equilibrium gas-liquid separation.
利用计算机模拟，我们研究了具有三个补丁的二维圆盘粒子系统的相图，这些补丁沿粒子赤道对称分布。在中等温度和压力下，粒子的几何形状与蜂巢晶格兼容，而在高温和高压下，预计系统将形成紧密堆积的三角形晶格。我们研究了单键每补丁区域内补丁大小的影响，发现相图的拓扑结构随着补丁大小的变化而剧烈变化。有趣的是，在具有小补丁（半开口角度为 10°）的粒子中，随着压力的增加，流体转变为一种相当奇特的相，可以理解为一个蜂巢晶格，其空隙连续填充额外的粒子，这些粒子平均仍然是未结合的。最终，所有的空隙都被占据，所以粒子位于三角形晶格的位置，但只有三分之二的粒子在方向上有序，而其余的三分之一可以几乎自由旋转，就像在塑料晶体中一样。在中等温度下，流体转变为几乎为空的蜂巢晶格，而在高温下，它直接转变为几乎充满的晶格。有趣的是，对于具有大补丁（半开口角度为 20°）的粒子，蜂巢晶格和三角形晶格之间被一个液相分离隔开，该液相在相当低的温度下仍然稳定。不足为奇的是，只有具有大补丁的粒子才表现出平衡的气液分离。
