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Influence of the ion size on the stability of the smectic phase of ionic liquid crystals.
Soft Matter ( IF 2.9 ) Pub Date : 2019-11-26 , DOI: 10.1039/c9sm02115a Wudi Cao 1 , Beeran Senthilkumar , Valerio Causin , Vincent P Swamy , Yanting Wang , Giacomo Saielli
Soft Matter ( IF 2.9 ) Pub Date : 2019-11-26 , DOI: 10.1039/c9sm02115a Wudi Cao 1 , Beeran Senthilkumar , Valerio Causin , Vincent P Swamy , Yanting Wang , Giacomo Saielli
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The thermotropic phase behavior of ionic liquids and ionic liquid crystals based on novel N-alkyl-3-methylpyridinium halides, trihalides and dichloroiodates was experimentally studied by polarized optical spectroscopy (POM) and differential scanning calorimetry (DSC) as well as by molecular dynamics (MD) simulation. In the experiments, the existence and thermal range of stability of the smectic phase of these ionic liquid crystals are found to strongly depend on the volume ratio between the cation and anion, that is their relative size. Only compounds with a relatively large volume ratio of the cation to anion, i.e., those with longer cationic alkyl chains and monoatomic halide anions, have a stable smectic A phase. Both melting points and clearing points increase with such a ratio. The MD simulation results qualitatively agree very well with the experimental data and provide molecular details which can explain the experimentally observed phenomena: the stronger van der Waals interactions from the longer alkyl chains and the stronger electrostatic interactions from the smaller anions with a higher charge density increase the stability of both the crystal phase and the smectic phase; this also prevents the ionic layers from easily mixing with the hydrophobic regions, a mechanism that ultimately leads to a nanosegregated isotropic liquid phase.
中文翻译：
离子尺寸对离子液晶近晶相稳定性的影响。
通过偏光光谱（POM）和差示扫描量热法（DSC）以及分子动力学研究了基于新型N-烷基-3-甲基吡啶鎓卤化物，三卤化物和二氯碘酸盐的离子液体和离子液晶的热致相行为。MD）模拟。在实验中，发现这些离子液晶的近晶相的稳定性的存在和热范围在很大程度上取决于阳离子和阴离子之间的体积比，即它们的相对大小。仅化合物具有相对较大的阳离子与阴离子的体积比，即那些具有较长阳离子烷基链和单原子卤化物阴离子的化合物具有稳定的近晶A相。熔点和透明点均以该比例增加。MD模拟结果在质量上与实验数据非常吻合，并提供了可以解释实验观察到的现象的分子细节：更长的烷基链产生的Van der Waals相互作用更强，而较小的阴离子产生的静电相互作用更强，电荷密度越高晶相和近晶相的稳定性；这也防止了离子层容易与疏水区域混合，这种机制最终导致了纳米分离的各向同性液相。
更新日期：2019-11-26
中文翻译：
离子尺寸对离子液晶近晶相稳定性的影响。
通过偏光光谱（POM）和差示扫描量热法（DSC）以及分子动力学研究了基于新型N-烷基-3-甲基吡啶鎓卤化物，三卤化物和二氯碘酸盐的离子液体和离子液晶的热致相行为。MD）模拟。在实验中，发现这些离子液晶的近晶相的稳定性的存在和热范围在很大程度上取决于阳离子和阴离子之间的体积比，即它们的相对大小。仅化合物具有相对较大的阳离子与阴离子的体积比，即那些具有较长阳离子烷基链和单原子卤化物阴离子的化合物具有稳定的近晶A相。熔点和透明点均以该比例增加。MD模拟结果在质量上与实验数据非常吻合，并提供了可以解释实验观察到的现象的分子细节：更长的烷基链产生的Van der Waals相互作用更强，而较小的阴离子产生的静电相互作用更强，电荷密度越高晶相和近晶相的稳定性；这也防止了离子层容易与疏水区域混合，这种机制最终导致了纳米分离的各向同性液相。
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