Study of the pitch of fluids of electrostatically chiral anisotropic molecules: mean-field theory and simulation
Study of the pitch of fluids of electrostatically chiral anisotropic molecules: mean-field theory and simulation
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DOI：
10.1080/00268970601058556
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发表时间：
2006-11
影响因子：
1.7
通讯作者：
S. Varga;G. Jackson
中科院分区：
文献类型：
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作者：
S. Varga;G. Jackson
导出了静电手征硬高斯重叠(HGO)粒子系统的节距解析表达式。计算是针对平面几何进行的，即HGO粒子被限制在垂直于螺旋轴的平面内，并且它们定向于给定平面的局部向列相指向矢的方向。分子间的手性贡献用Goossens引入的伪张量来描述[W.J.Goossens，Mol.克赖斯特。LIQCryst，12,237(1971)]。硬体排斥力的贡献是用Parsons-Lee[J.D.Parsons，Phys.Rev.A，19,1225(1979)；S.D.Lee，J.Chem.Phys.，87,4972(1987)]自由旋转杆在完全局域向列排列(平面几何)的极限下的理论，而平均场近似被用来解释手性色散相互作用的贡献。这提供了第一个真正的微观描述之一，即扭矩场、扭转弹性常数和手性向列相的节距与分子参数和热力学变量的显式依赖关系。手性HGO流体的螺距明显依赖于温度(手性强度)、长宽比和体系的密度。最有趣的结果是，即使最近邻距离的减小会增加手性对能量的贡献，间距也会随着堆积分数的增加而增加(对应于较弱的有效手性相互作用)。用作者先前发展的方法获得了手性硬球衬里自由旋转体系的节距的蒙特卡罗模拟数据[S.Varga和G.Jackson，Chem.太棒了。Let.，377，6(2003)]与理论计算的预测完全一致。
An analytical expression is derived for the pitch of a system of electrostatically chiral hard Gaussian overlap (HGO) particles. The calculations are performed for a planar geometry, i.e. the HGO particles are confined in a plane perpendicular to the helical axis and they are oriented in the direction of the local nematic director of a given plane. The chiral contribution between molecules is described in terms of the pseudo tensor introduced by Goossens [W.J. Goossens, Mol. Cryst. Liq. Cryst., 12, 237 (1971)]. The contribution of hard-body repulsion is treated using the Parsons–Lee [J.D. Parsons, Phys. Rev. A, 19, 1225 (1979); S.D. Lee, J. Chem. Phys., 87, 4972 (1987)] theory for the freely rotating rods in the limit of perfect local nematic alignment (planar geometry), while the mean-field approximation is used to account for the contribution due to the chiral dispersion interactions. This provides one of the first truly microscopic descriptions of the explicit dependence of the torque-field, twist-elastic constant, and the pitch of the chiral nematic phase on the molecular parameters and thermodynamic variables. The pitch of the chiral HGO fluid exhibits a significant dependence on the temperature (chiral strength), aspect ratio, and density of the system. The most interesting result is that the pitch increases with increasing packing fraction (corresponding to a weaker effective chiral interaction) even when a decrease in the nearest neighbour distance tends to increase the chiral contribution to the energy. Monte Carlo simulation data for the pitch of a freely rotating system of chiral hard spherocylinders obtained with a method previously developed by the authors [S. Varga and G. Jackson, Chem. Phys. Lett., 377, 6 (2003)] are fully consistent the predictions of the theoretical calculations.