Centre for Condensed Matter Theory, Department of Physics, Indian Institute of Science, Bangalore 560064, India.
Sci Rep. 2017 Jan 5;7:40059. doi: 10.1038/srep40059.
For isotropic fluids, classical nucleation theory predicts the nucleation rate, barrier height and critical droplet size by ac- counting for the competition between bulk energy and interfacial tension. The nucleation process in liquid crystals is less understood. We numerically investigate nucleation in monolayered nematogenic films using a mesoscopic framework, in par- ticular, we study the morphology and kinetic pathway in spontaneous formation and growth of droplets of the stable phase in the metastable background. The parameter κ that quantifies the anisotropic elastic energy plays a central role in determining the geometric structure of the droplets. Noncircular nematic droplets with homogeneous director orientation are nucleated in a background of supercooled isotropic phase for small κ. For large κ, noncircular droplets with integer topological charge, accompanied by a biaxial ring at the outer surface, are nucleated. The isotropic droplet shape in a superheated nematic background is found to depend on κ in a similar way. Identical growth laws are found in the two cases, although an unusual two-stage mechanism is observed in the nucleation of isotropic droplets. Temporal distributions of successive events indi- cate the relevance of long-ranged elasticity-mediated interactions within the isotropic domains. Implications for a theoretical description of nucleation in anisotropic fluids are discussed.
对于各向同性流体,经典成核理论通过考虑体相能量和界面张力之间的竞争来预测成核速率、势垒高度和临界液滴尺寸。液晶中的成核过程理解较少。我们使用介观框架数值研究单层向列型膜中的成核,特别是研究在亚稳背景中稳定相液滴自发形成和生长的形态和动力学途径。量化各向异性弹性能量的参数κ在确定液滴的几何结构中起着核心作用。对于小κ,在过冷各向同性相中会形成具有均匀指向矢的非圆形向列液滴。对于大κ,会形成具有整数拓扑电荷的非圆形液滴,并伴有外表面的双轴环。在过热向列型背景中各向同性液滴的形状发现与κ以相似的方式有关。尽管在各向同性液滴成核中观察到不寻常的两阶段机制,但在这两种情况下都发现了相同的生长规律。连续事件的时间分布表明在各向同性域内长程弹性介导相互作用的相关性。讨论了各向异性流体中成核的理论描述的意义。