Department of Chemical and Biomolecular Engineering, Rice University, 6100 S. Main, Houston, Texas 77005, USA.
J Chem Phys. 2013 Sep 21;139(11):114706. doi: 10.1063/1.4821604.
Aqueous solutions of alcohols are interesting because of their anomalous behavior that is believed to be due to the molecular structuring of water and alcohol around each other in solution. The interfacial structuring and properties are significant for application in alcohol purification processes and biomolecular structure. Here we study aqueous mixtures of short alcohols (methanol, ethanol, 1-propanol, and 2-propanol) at a hydrophobic surface using interfacial statistical associating fluid theory which is a perturbation density functional theory. The addition of a small amount of alcohol decreases the interfacial tension of water drastically. This trend in interfacial tension can be explained by the structure of water and alcohol next to the surface. The hydrophobic group of an added alcohol preferentially goes to the surface preserving the structure of water in the bulk. For a given bulk alcohol concentration, water mixed with the different alcohols has different interfacial tensions with propanol having a lower interfacial tension than methanol and ethanol. 2-propanol is not as effective in decreasing the interfacial tension as 1-propanol because it partitions poorly to the surface due to its larger excluded volume. But for a given surface alcohol mole fraction, all the alcohol mixtures give similar values for interfacial tension. For separation of alcohol from water, methods that take advantage of the high surface mole fraction of alcohol have advantages compared to separation using the vapor in equilibrium with a water-alcohol liquid.
醇的水溶液因其异常行为而引人注目，据信这种异常行为是由于水和醇在溶液中彼此分子结构造成的。界面结构和性质对于醇的净化过程和生物分子结构的应用具有重要意义。在这里，我们使用界面统计关联流体理论（一种微扰密度泛函理论）研究了疏水表面上短醇（甲醇、乙醇、1-丙醇和 2-丙醇）的水溶液混合物。少量醇的加入会大大降低水的界面张力。这种界面张力的趋势可以通过靠近表面的水和醇的结构来解释。加入醇的疏水分子基团优先进入表面，从而保持了主体中的水结构。对于给定的醇本体浓度，与甲醇和乙醇相比，与不同醇混合的水具有不同的界面张力，丙醇的界面张力较低。2-丙醇降低界面张力的效果不如 1-丙醇，因为由于其较大的排斥体积，它在表面上的分配较差。但是对于给定的表面醇摩尔分数，所有醇混合物的界面张力都具有相似的值。对于从水中分离醇，利用醇的高表面摩尔分数的方法与使用与水-醇液体平衡的蒸汽相比具有优势。
