团簇增强了四方相的稳定性
Enhanced stability of tetratic phase due to clustering
摘要：
我们表明，相对于通常的单轴晶相的相对稳定性的四晶相可以大大提高集群效应。二维矩形的纵横比$κ$通过硬相互作用被认为是相互作用，和稳定性的两个双相（单轴和四相）使用扩展的缩放粒子理论适用于多分散流体混合物的$n$物种进行检查。这里，第$i$种与$i$矩形的簇相关联，簇被定义为包含近似平行矩形的矩形的堆叠，具有冻结的内部自由度。该理论假设一个指数簇大小分布（一个假设完全支持蒙特卡罗模拟和一个简单的化学反应模型），与固定值的二阶矩。相应的面积分布呈现出一个肩部，有时甚至是一个明确定义的峰值，在簇大小近似对应于正方形形状（即$i\simeqκ$），这意味着正方形簇有一个主要贡献的硬矩形流体的自由能。该理论预测的增强区域的稳定性的四相相对于标准的缩放-粒子理论，更接近模拟和实验结果，表明在这种流体中的聚类的重要性。
英文摘要：
We show that the relative stability of the nematic tetratic phase with respect to the usual uniaxial nematic phase can be greatly enhanced by clustering effects. Two--dimensional rectangles of aspect ratio $κ$ interacting via hard interactions are considered, and the stability of the two nematic phases (uniaxial and tetratic) is examined using an extended scaled--particle theory applied to a polydispersed fluid mixture of $n$ species. Here the $i$--th species is associated with clusters of $i$ rectangles, with clusters defined as stacks of rectangles containing approximately parallel rectangles, with frozen internal degrees of freedom. The theory assumes an exponential cluster size distribution (an assumption fully supported by Monte Carlo simulations and by a simple chemical--reaction model), with fixed value of the second moment. The corresponding area distribution presents a shoulder, and sometimes even a well-defined peak, at cluster sizes approximately corresponding to square shape (i.e. $i\simeqκ$), meaning that square clusters have a dominant contribution to the free energy of the hard--rectangle fluid. The theory predicts an enhanced region of stability of the tetratic phase with respect to the standard scaled--particle theory, much closer to simulation and to experimental results, demonstrating the importance of clustering in this fluid.
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