del Río Elvira Martín, de Miguel Enrique
Department of Chemical Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom.
Phys Rev E Stat Nonlin Soft Matter Phys. 2005 May;71(5 Pt 1):051710. doi: 10.1103/PhysRevE.71.051710. Epub 2005 May 11.
The smectic phase is studied for a thermotropic fluid model consisting of aligned hard ellipsoids with superimposed square-well attractive interactions of variable range. The system is analyzed using a density functional theory in which the hard-core contributions to the free-energy functional are treated within a nonlocal weighted density approximation and the attractive contributions are considered at a mean-field level. In the absence of attractions the model reduces, under appropriate scaling, to a fluid of hard spheres and therefore does not exhibit smectic ordering. It is shown that above a certain value of the square-well range, smectic ordering is stable relative to the nematic state at densities well inside the fluid region. The nematic-smectic-A transition is found to be continuous at high temperatures and first order at low temperatures, these two regimes being separated by a tricritical point at an intermediate temperature. These predictions have been confirmed by computer simulation of the model fluid. The results highlight that smectic ordering can be stabilized by coupling anisotropic short-range repulsions with the isotropic contribution of the soft attractive interactions. By increasing the pressure, the range of stability of the smectic phase is seen to decrease. At sufficiently high pressure, the smectic phase is suppressed, and the solid phase dominates. Our calculations show that smectic ordering is no longer stable if the range of the attractions is made too long ranged.
研究了一种热致液晶流体模型的近晶相，该模型由排列的硬椭球体组成，具有可变范围的叠加方阱吸引相互作用。使用密度泛函理论对该系统进行分析，其中对自由能泛函的硬核贡献在非局部加权密度近似下处理，而吸引贡献在平均场水平上考虑。在没有吸引力的情况下，在适当的标度下，该模型简化为硬球流体，因此不表现出近晶有序。结果表明，在方阱范围超过某一值时，在流体区域内密度处，近晶有序相对于向列相是稳定的。发现向列-近晶-A转变在高温下是连续的，在低温下是一级的，这两种状态由中间温度下的三临界点分隔。这些预测已通过对模型流体的计算机模拟得到证实。结果突出表明，通过将各向异性短程排斥与软吸引相互作用的各向同性贡献耦合，可以使近晶有序稳定。通过增加压力，近晶相的稳定范围会减小。在足够高的压力下，近晶相被抑制，固相占主导。我们的计算表明，如果吸引力范围变得太长，近晶有序就不再稳定。
