Department of Chemical Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, UK.
Int J Mol Sci. 2013 Aug 8;14(8):16414-42. doi: 10.3390/ijms140816414.
We employ a generalized van der Waals-Onsager perturbation theory to construct a free energy functional capable of describing the thermodynamic properties and orientational order of the isotropic and nematic phases of attractive disc particles. The model mesogen is a hard (purely repulsive) cylindrical disc particle decorated with an anisotropic square-well attractive potential placed at the centre of mass. Even for isotropic attractive interactions, the resulting overall inter-particle potential is anisotropic, due to the orientation-dependent excluded volume of the underlying hard core. An algebraic equation of state for attractive disc particles is developed by adopting the Onsager trial function to characterize the orientational order in the nematic phase. The theory is then used to represent the fluid-phase behaviour (vapour-liquid, isotropic-nematic, and nematic-nematic) of the oblate attractive particles for varying values of the molecular aspect ratio and parameters of the attractive potential. When compared to the phase diagram of their athermal analogues, it is seen that the addition of an attractive interaction facilitates the formation of orientationally-ordered phases. Most interestingly, for certain aspect ratios, a coexistence between two anisotropic nematic phases is exhibited by the attractive disc-like fluids.
我们采用广义范德瓦尔斯-翁萨格微扰理论构建一个自由能泛函，能够描述各向同性相和向列相的热动力学性质和取向有序性。模型介晶是一个带有各向异性方阱吸引势的硬（纯排斥）圆柱形碟粒子，位于质心处。即使对于各向同性的吸引相互作用，由于基础硬芯的取向相关的排斥体积，导致粒子间的整体相互作用势具有各向异性。采用翁萨格试探函数来描述向列相中取向有序性，开发出一个用于吸引碟粒子的状态方程。然后，该理论被用于表示各向同性相-向列相、气相-液相和各向同性相-各向同性相的扁长形吸引粒子的流体相行为，同时考虑到分子纵横比和吸引势参数的变化。与无热近似类似物的相图进行比较后，我们发现，引入吸引相互作用有助于形成取向有序相。最有趣的是，对于某些纵横比，吸引碟状流体表现出两个各向异性向列相共存的现象。
