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arXiv 1012.4636cond-mat.stat-mechcond-mat.mtrl-sci
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二元混合物固有结构与相分离机理的相关性

Correlation between inherent structures and phase separation mechanism in binary mixtures

Sarmistha Sarkar, Biman Bagchi

摘要:

已知二元混合物通过成核和亚稳分解两者进行相分离,这取决于初始组成和淬灭程度。在这里,我们开发了一个能源景观的相分离和非理想性的二元混合物,探索其势能景观(PEL)作为温度和组成的函数,通过采用分子模型,促进结构破坏能力的溶质-溶剂母二元液体在低温下。通过去除动能(包括分子间振动的动能)来获得提供系统的固有结构(IS)的PEL。固有结构能的宽分布表明熵在稳定结构破坏型二元混合物的母液中起较大的作用。在高温下,虽然母体结构是均匀的,但发现相应的固有结构总是相分离的,具有与固有结构的能量显著相关的密度图案。在较宽的中间固有结构能范围内,双连续相分离普遍存在,互穿条纹作为Spinodal分解的特征。在低的固有结构能,该结构主要是相分离的一个界面,在高的固有结构能,我们发现成核型生长。有趣的是,在低温下,平均固有结构能(<EIS>)随温度下降,这表明其中一个相中开始结晶,而另一个保持液态。粘度的非理想组成依赖性与平均固有结构能反相关。

英文摘要:

Binary mixtures are known to phase separate via both nucleation and spinodal decomposition, depending on the initial composition and extent of the quench. Here we develop an energy landscape view of phase separation and non-ideality in binary mixtures by exploring their potential energy landscape (PEL) as functions of temperature and composition, by employing a molecular model that promotes structure breaking abilities of the solute-solvent parent binary liquid at low temperatures. PEL that provides the inherent structure (IS) of a system is obtained by removing the kinetic energy (including that of intermolecular vibrations). Broad Distribution of inherent structure energy demonstrates the larger role of entropy in stabilizing the parent liquid of the structure breaking type of binary mixtures. At high temperature, although the parent structure is homogenous, the corresponding inherent structure is found to be always phase separated, with a density pattern that exhibits marked correlation with the energy of inherent structure. Over broad range of intermediate inherent structure energy, bicontinuous phase separation prevails with interpenetrating stripes as signatures of spinodal decomposition. At low inherent structure energy, the structure is largely phase separated with one interface where as at high inherent structure energy, we find nucleation type growth. Interestingly, at low temperature, the average inherent structure energy (<EIS>) exhibits a drop with temperature which signals onset of crystallization in one of the phases while the other remains in the liquid state. The non-ideal composition dependence of viscosity is anti-correlated with average inherent structure energy.

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