Department of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, IN 46556, USA.
Soft Matter. 2019 Oct 23;15(41):8219-8226. doi: 10.1039/c9sm01395d.
Bent-shaped liquid crystals have attracted significant attention recently due to their novel mesostructure and the intriguing behavior of their elastic constants, which are strongly anisotropic and have an unusual temperature dependence. Though theories explain the onset of the twist-bend nematic phase (NTB) through spontaneous symmetry breaking concomitant with transition to a negative bend (K3) elastic constant, this has not been observed as yet in experiments. There, the small bend elastic constant has a strongly non-monotonic temperature dependence, which first increases after crossing the isotropic (I)-nematic (N) transition, then dips near the nematic (N)-twist-bend (NTB) transition before it increases again as the transition is crossed. The molecular mechanisms responsible for this exotic behavior are unclear. Here, we utilize density of states algorithms in Monte Carlo simulation applied to a variant of the Lebwohl-Lasher model which includes bent-shaped-like interactions to analyze the mechanism behind elastic response in this novel mesostructure and understand the temperature dependence of its Frank-Oseen elastic constants.
由于其新颖的介观结构和弹性常数的有趣行为，弯曲状液晶最近引起了人们的极大关注，这些弹性常数具有强烈的各向异性和异常的温度依赖性。尽管理论通过自发对称性破缺解释了扭曲 - 弯曲向列相（NTB）的起始，同时转变为负弯曲（K3）弹性常数，但这在实验中尚未观察到。在实验中，小弯曲弹性常数具有强烈的非单调温度依赖性，在经过各向同性（I）-向列（N）转变后首先增加，然后在向列（N）-扭曲 - 弯曲（NTB）转变附近下降，然后再次增加，因为转变已经通过。导致这种奇特行为的分子机制尚不清楚。在这里，我们利用蒙特卡罗模拟中的态密度算法应用于包括弯曲状相互作用的 Lebwohl-Lasher 模型的变体，以分析这种新型介观结构中弹性响应的机制，并了解其弗兰克 - 奥森弹性常数的温度依赖性。
