van der Waals interactions in non-polar liquids
van der Waals interactions in non-polar liquids
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DOI：
10.1039/c2sc21666c
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发表时间：
2013-01-01
期刊：
影响因子：
8.4
通讯作者：
Hunter, Christopher A.
中科院分区：
文献类型：
--
作者：
Hunter, Christopher A.
液体的整体性质提供了关于非极性分子之间分子间相互作用的热力学性质的信息。本文分析了惰性气体、烷烃和全氟化碳的文献数据，研究了非极性分子间的货车范德华相互作用的大小与化学结构和分子结构的关系。基于零点空隙的概念，提出了液态的分子模型，每个分子的体积为5 A（3），表面积为19 A（2）。该空隙是每个分子独立交换分子间接触并因此在液体中移动所需的最小体积。三个假设的结构（零点固体，零点液体和理想液体）被用来分离的熔化，热膨胀和蒸发的过程。熔化是一个复杂的过程，受到固体结构变化、零点空隙形成和热膨胀的影响。蒸发涉及破坏分子与周围液体之间的所有分子间相互作用，因此提供了总货车德瓦耳斯相互作用的直接测量。蒸发过程焓垒的实验数据表明，总的货车德瓦尔斯相互作用近似是分子表面积的线性函数，对于非极性液体，值为0.3 kJ mol（-1）A（-2）。膨胀涉及破坏局部分子间接触，并且通常与显著较低的能垒相关，该能垒取决于分子表面上相互作用位点之间的耦合程度。膨胀过程与三相点和临界点处发生的相变密切相关，因此这些性质是分子结构的复杂函数。类似地，汽液平衡的自由能变化取决于分子结构。相反，液-液平衡的转移自由能数据表明，货车德瓦尔斯相互作用是一个简单的功能的分子表面积，独立的原子类型或分子结构。对于在液态内发生的过程，由于货车德瓦尔斯相互作用的交换而引起的自由能变化因此预计是小的。
The bulk properties of liquids provide information on the thermodynamic properties of intermolecular interactions between non-polar molecules. Literature data on noble gases, alkanes and perfluorocarbons have been analysed to investigate the relationship of the magnitude of van der Waals interactions between non-polar molecules with chemical structure and molecular architecture. A molecular model of the liquid state is proposed based on the concept of a zero point void, which has a volume of 5 A(3) and a surface area of 19 A(2) per molecule. This void is the minimum volume required for each molecule to independently exchange an intermolecular contact and hence move in the liquid. Three hypothetical constructs (the zero point solid, the zero point liquid and the ideal liquid) are used to separate the processes of melting, thermal expansion and evaporation. Melting is a complex process affected by contributions from changes in structure in the solid, formation of the zero point void and thermal expansion. Evaporation involves breaking all intermolecular interactions between a molecule and the surrounding liquid and therefore provides a straightforward measure of the total van der Waals interaction. Experimental data for the enthalpy barrier to the evaporation process indicate that the total van der Waals interaction is approximately a linear function of molecular surface area, worth 0.3 kJ mol(-1) A(-2) for non-polar liquids. Expansion involves breaking local intermolecular contacts and is generally associated with a substantially lower energy barrier that depends on the degree of coupling between interaction sites across the molecular surface. The expansion process is closely related to the phase changes that occur at the triple point and the critical point, and these properties are therefore a complex function of molecular architecture. Similarly, the free energy change for the vapour-liquid equilibrium depends on the molecular architecture. In contrast, transfer free energy data for liquid-liquid equilibria suggest that van der Waals interactions are a simple function of molecular surface area, independent of atom type or molecular architecture. For processes that take place within the liquid state, free energy changes due to exchange of van der Waals interactions are therefore expected to be small.