Rheology of lamellar liquid crystals in two and three dimensions: a simulation study
Rheology of lamellar liquid crystals in two and three dimensions: a simulation study
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DOI：
10.1039/c2sm07374a
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发表时间：
2011-12
期刊：
影响因子：
3.4
通讯作者：
O. Henrich;O. Henrich;K. Stratford;D. Marenduzzo;P. Coveney;M. Cates
中科院分区：
文献类型：
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作者：
O. Henrich;O. Henrich;K. Stratford;D. Marenduzzo;P. Coveney;M. Cates
我们对片层相(近晶液晶)在中等到大的剪切速率(Peclet数为10-100)下的二维和三维非线性整体流变学进行了大规模的计算机模拟。在两个维度上，我们发现适度的剪切速率使系统排列，并稳定了几乎规则的片层相，但高剪切速率导致缺陷的形核和扩散，而在稳态，这被相反符号的缺陷的湮灭所平衡。第二阶段开始时的切变率c由热力学和动力学参数控制；我们提供了一个标度分析，它将c与涉及这些变量的一个临界“毛细管数”联系起来。在缺陷扩散区域内，缺陷可以通过缓慢降低施加的剪切速率来部分退火；这会导致显著的记忆效应和与历史相关的流变性。三维模拟显示，即使在这里研究的最高剪切速率下，剪切诱导的有序化也是如此。这表明，随着维度的增加，c明显向上移动。这可能在一定程度上反映了对缺陷运动的限制减少，允许它们更容易地找到和消灭彼此。三维对准状态下的残余边缘缺陷主要指向流速方向，这在二维情况下是不可能的。
We present large scale computer simulations of the nonlinear bulk rheology of lamellar phases (smectic liquid crystals) at moderate to large values of the shear rate (Peclet numbers 10–100), in both two and three dimensions. In two dimensions we find that modest shear rates align the system and stabilise an almost regular lamellar phase, but high shear rates induce the nucleation and proliferation of defects, which in steady state is balanced by the annihilation of defects of opposite sign. The shear rate c at onset of this second regime is controlled by thermodynamic and kinetic parameters; we offer a scaling analysis that relates c to a critical “capillary number” involving those variables. Within the defect proliferation regime, the defects may be partially annealed by slowly decreasing the applied shear rate; this causes marked memory effects, and history-dependent rheology. Simulations in three dimensions show instead shear-induced ordering even at the highest shear rates studied here. This suggests that c shifts markedly upward on increasing dimensionality. This may in part reflect the reduced constraints on defect motion, allowing them to find and annihilate each other more easily. Residual edge defects in the 3D aligned state mostly point along the flow velocity, an orientation impossible in two dimensions.