Molecular-dynamics simulations on the mesophase transition induced by oscillatory shear in imidazolium-based ionic liquid crystals
Molecular-dynamics simulations on the mesophase transition induced by oscillatory shear in imidazolium-based ionic liquid crystals
复制标题
咪唑基离子液晶振荡剪切诱导中间相转变的分子动力学模拟
DOI：
10.1039/d0cp05677d
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发表时间：
2021
影响因子：
3.3
通讯作者：
Peng Hailong
中科院分区：
文献类型：
--
作者：
Liu Min;Shiba Hayato;Liu Huashan;Peng Hailong
采用分子动力学方法，在振荡剪切作用下对1-十二烷基-3-甲基咪唑六氟磷酸盐（[C12 mim][PF 6]）离子液晶（ILC）进行了模拟.我们发现，振荡剪切既可以加速，也可以抑制中间相的形成取决于剪切振幅。小振幅剪切可以加速中间相转变动力学，并导致比没有剪切时更有序的介晶结构，即，加速老化的影响。当剪切振幅足够大时，中间相不稳定，导致近晶A（SmA）向液体或近晶B（SmB）向SmA转变，其中中间相行为总结在非平衡相图中。在层平面内的中程六阶观察，与相关长度延伸到几个纳米的剪切诱导的SmA阶段。我们合理化的非平衡中间相的行为从各向同性液体的流变学，找到一个温度无关的临界弛豫时间的中间相转变的平移或旋转动力学。这一发现可以用来预测剪切的各向同性液体的流变学的液晶的中间相行为。
Molecular dynamics simulations were performed on a 1-dodecyl-3-methylimidazolium hexafluorophosphate ([C12mim][PF6]) ionic liquid crystal (ILC) with the application of an oscillatory shear. We found that the oscillatory shear can both accelerate and suppress mesophase formation depending on shear amplitude. A small amplitude shear can speed up the mesophase transition dynamics and result in a more ordered mesomorphic structure than that without shear, i.e., an effect of accelerated aging. The mesophase is destabilized when the shear amplitude is large enough, resulting in a smectic A (SmA) to liquid or a smectic B (SmB) to SmA transition, with the mesophase behaviour summarized in an out-of-equilibrium phase diagram. Inside the layer plane a medium-range hexatic order was observed, with the correlation length extending to several nanometres in the shear-induced SmA phase. We rationalize the nonequilibrium mesophase behaviour from the rheology of isotropic liquids, finding a temperature-independent critical relaxation time for the mesophase transition in the translational or rotational dynamics. This finding can be used to predict the mesophase behaviour in the sheared ILCs from the rheology of isotropic liquids.