Complete breakdown of the Debye model of rotational relaxation near the isotropic-nematic phase boundary: effects of intermolecular correlations in orientational dynamics.
Complete breakdown of the Debye model of rotational relaxation near the isotropic-nematic phase boundary: effects of intermolecular correlations in orientational dynamics.
复制标题
各向同性向列相边界附近旋转弛豫德拜模型的完全分解：取向动力学中分子间相关性的影响。
DOI：
10.1103/physreve.73.031705
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发表时间：
2005
期刊：
影响因子：
--
通讯作者：
B. Bagchi
中科院分区：
文献类型：
--
作者：
P. P. Jose;D. Chakrabarti;B. Bagchi
旋转扩散的Debye-Stokes-Einstein （DSE）模型预测，方向相关时间tau l变化为[l(l+1)]-1，其中l是方向时间相关函数的秩（用秩为l的Legendre多项式表示）。人们经常会发现这种预测在任何一个方向上都有明显的偏差。在过冷的分子液体中，tau 1/tau 2的比值大大低于3（德拜极限），人们通常调用跳跃扩散模型来解释tau 1/tau 2与统一的比值。在这里，我们通过对热致液晶标准模型系统的计算机模拟研究表明，当从各向同性一侧接近各向同性-向列相边界时，该比率远小于1。同时，液体剪切粘度的比值tau 2/eta在I-N跃迁附近变得比水动力值大得多。我们还分析了旋转扩散的Debye模型在高阶方向相关时间比下的分解。我们证明了DSE模型的崩溃是由于取向对相关的增长，并提供了一个模式耦合理论分析来解释结果。
The Debye-Stokes-Einstein (DSE) model of rotational diffusion predicts that the orientational correlation times tau l vary as [l(l+1)]-1, where l is the rank of the orientational time correlation function (given in terms of the Legendre polynomial of rank l). One often finds significant deviation from this prediction, in either direction. In supercooled molecular liquids where the ratio tau 1/tau 2 falls considerably below 3 (the Debye limit), one usually invokes a jump diffusion model to explain the approach of the ratio tau 1/tau 2 to unity. Here we show in a computer simulation study of a standard model system for thermotropic liquid crystals that this ratio becomes much less than unity as the isotropic-nematic phase boundary is approached from the isotropic side. Simultaneously, the ratio tau 2/eta, eta, being the shear viscosity of the liquid, becomes much larger than the hydrodynamic value near the I-N transition. We also analyze the breakdown of the Debye model of rotational diffusion in ratios of higher order orientational correlation times. We show that the breakdown of the DSE model is due to the growth of orientational pair correlation and provide a mode coupling theory analysis to explain the results.