论文标题

灾难性液晶的平衡阶段和域生长动力学

Equilibrium phases and domain growth kinetics of calamitic liquid crystals

论文作者

Birdi, Nishant, Underwood, Tom L., Wilding, Nigel B., Puri, Sanjay, Banerjee, Varsha

论文摘要

当媒体元素并排放置在终端或端到端时,CALAMITIC LC颗粒的各向异性形状会产生不同的能量值。由参数K'控制的能量各向异性对平衡和非平衡性能产生了深刻的影响。使用GB模型,该模型显示了NM和低温SM顺序,我们进行了大规模的MC&MD模拟,以探测K'对温度t淬灭后的平衡相图和非平衡结构域生长的效果(块状)。模型中有2个过渡,在Tc1&nm-> SM处的i-> nm在Tc2 <tc1处。 K'显着降低了TC1,但对TC2的影响相对较小。 NM相中的域生长表现出众所周知的LAC定律,L(t)〜t^0.5&进化是通过灭绝弦缺损的。该系统表现出动态缩放,相对于K'也很强。我们发现,在淬灭温度t(t> t> tc1-> t <tc2)处的SM相,我们认为我们的SMB顺序具有层中LC分子的示型排列。在这一阶段的粗化表现出惊人的两次尺度场景:首先,LC分子对齐和开发定向顺序,然后出现特征分层以及在层中的示型键取向阶。因此,生长遵循LAC LAC L(T)〜t^0.5在早期,然后在以后的时间显示出较慢的生长状态。我们的观察结果强烈表明在此制度中l(t)〜t^0.25。有趣的是,相关函数在制度和缩放函数中均显示了动态缩放。对于K'的变化,动力学也很健壮,但是在较大的值下,近晶型更为明显。此外,早期动态受弦缺陷的控制,而晚期的演变则由界面缺陷决定。我们认为,即使SM层中的其他类型的本地顺序,这种情况也是SM阶段的通用。

The anisotropic shape of calamitic LC particles results in distinct energy values when nematogens are placed side-by-side or end-to-end. The energy anisotropy governed by parameter K' has deep consequences on equilibrium & non-equilibrium properties. Using GB model, which shows Nm & low temperature Sm order, we undertake large-scale MC & MD simulations to probe effect of K' on the equilibrium phase diagram & the non-equilibrium domain growth following a quench in the temperature T (coarsening). There are 2 transitions in the model, I->Nm at Tc1 & Nm->Sm at Tc2<Tc1. K' decreases Tc1 significantly, but has relatively little effect on Tc2. Domain growth in Nm phase exhibits the well-known LAC law, L(t)~t^0.5 & evolution is via annihilation of string defects. The system exhibits dynamical scaling that is also robust with respect to K'. We find that Sm phase at quench temperatures T (T>Tc1->T<Tc2) that we consider has SmB order with a hexatic arrangement of the LC molecules in the layers. Coarsening in this phase exhibits a striking two-time-scale scenario: first the LC molecules align & develop orientational order, followed by emergence of characteristic layering along with the hexatic bond-orientational-order within layers. Consequently, the growth follows the LAC law L(t)~t^0.5 at early times & then shows a sharp crossover to a slower growth regime at later times. Our observations strongly suggest L(t)~t^0.25 in this regime. Interestingly, the correlation function shows dynamical scaling in both the regimes & the scaling function is universal. The dynamics is also robust with respect to changes in K', but the smecticity is more pronounced at larger values. Further, the early-time dynamics is governed by string defects, while the late-time evolution is dictated by interfacial defects. We believe this scenario is generic to Sm phase even with other kinds of local order within Sm layers.

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