Soft Condensed Matter, Debye Institute for NanoMaterials Science, Utrecht University, Princetonplein 5, 3584 CC Utrecht, The Netherlands.
J Chem Phys. 2010 Jun 14;132(22):224907. doi: 10.1063/1.3432864.
We study the layer-to-layer diffusion in smectic-A liquid crystals of colloidal hard rods with different length-to-diameter ratios using computer simulations. The layered arrangement of the smectic phase yields a hopping-type diffusion due to the presence of permanent barriers and transient cages. Remarkably, we detect stringlike clusters composed of interlayer rods moving cooperatively along the nematic director. Furthermore, we find that the structural relaxation in equilibrium smectic phases shows interesting similarities with that of out-of-equilibrium supercooled liquids, although there the particles are kinetically trapped in transient rather than permanent cages. Additionally, at fixed packing fraction we find that the barrier height increases with increasing particle anisotropy, and hence the dynamics is more heterogeneous and non-Gaussian for longer rods, yielding a lower diffusion coefficient along the nematic director and smaller clusters of interlayer particles that move less cooperatively. At fixed barrier height, the dynamics becomes more non-Gaussian and heterogeneous for longer rods that move more collectively giving rise to a higher diffusion coefficient along the nematic director.
我们使用计算机模拟研究了具有不同长径比的胶体硬棒状近晶 A 液晶中的层间扩散。近晶相的层状排列由于存在永久障碍和瞬态笼而产生跳跃式扩散。值得注意的是，我们检测到由层间棒组成的串状团簇，它们沿着向列序协同移动。此外，我们发现平衡近晶相中的结构弛豫与非平衡过冷液体有有趣的相似之处，尽管在过冷液体中，粒子由于瞬态而不是永久笼而被动力学捕获。此外，在固定堆积分数下，我们发现随着粒子各向异性的增加，势垒高度增加，因此对于较长的棒，动力学更加非均匀和非高斯，导致沿着向列序的扩散系数更低，层间粒子的团簇移动得不太协同。在固定势垒高度下，对于更集体移动的较长棒，动力学变得更加非高斯和非均匀，从而导致沿着向列序的扩散系数更高。
