Debbarma Rousan, Malani Ateeque
Department of Chemical Engineering, Indian Institute of Technology Bombay , Mumbai, India.
Langmuir. 2016 Feb 2;32(4):1034-46. doi: 10.1021/acs.langmuir.5b04131. Epub 2016 Jan 19.
Clay minerals are used in variety of applications ranging from composites to electronic devices. For their efficient use in such areas, understanding the effect of surface-active agents on interfacial properties is essential. We investigated the role of surface ions in the adsorption of water molecules by using a muscovite mica surface populated with two different, H(+) and K(+), surface ions. A series of grand canonical Monte Carlo (GCMC) simulations at various relative vapor pressures (p/p0) were performed to obtain the water structure and adsorption isotherm on the H(+)-exposed mica (H-mica) surface. The obtained results were compared to the recent simulation data of water adsorption on the K(+)-exposed mica (K-mica) surface reported by Malani and Ayyappa (Malani, A.; Ayappa, K. G. J. Phys. Chem. B 2009, 113, 1058-1067). Water molecules formed two prominent layers adjacent to the H-mica surface, whereas molecular layering was observed adjacent to the K-mica surface. The adsorption isotherm of water on the K-mica surface was characterized by three stages that corresponded to rapid adsorption in the initial regime below p/p0 = 0.1, followed by a linear development regime for p/p0 = 0.1-0.7 and rapid film thickening for p/p0 ≥ 0.7, whereas only latter two regimes were observed in the H-mica system. In addition, the film thickness of adsorbed water molecules for p/p0 < 0.7 was lower as compared to that for the K-mica surface and comparable beyond. The film thickness obtained from the MC simulations was in excellent agreement with the interferometry experimental data of Balmer et al. (Balmer, T. E.; Christenson, H. K.; Spencer, N. D.; Heuberger, M. Langmuir 2008, 24, 1566-1569). It was observed that the hydration behaviors of the two ions were completely different and depended on the size of their hydration shell and their ability to form hydrogen bonds. The behavior of water adsorption between these two cases was illustrated using the water density distribution, orientational distributions, hydrogen bonding, and isosteric heats of adsorption.
黏土矿物被用于从复合材料到电子设备等各种应用领域。为了在这些领域中高效使用它们，了解表面活性剂对界面性质的影响至关重要。我们通过使用具有两种不同表面离子H(+)和K(+)的白云母表面，研究了表面离子在水分子吸附中的作用。进行了一系列在各种相对蒸气压(p/p0)下的巨正则蒙特卡罗(GCMC)模拟，以获得在暴露H(+)的云母(H-云母)表面上的水结构和吸附等温线。将所得结果与Malani和Ayyappa报道的最近关于暴露K(+)的云母(K-云母)表面上水吸附的模拟数据(Malani, A.; Ayappa, K. G. J. Phys. Chem. B 2009, 113, 1058 - 1067)进行了比较。水分子在H-云母表面附近形成了两个显著的层，而在K-云母表面附近观察到了分子分层。水在K-云母表面的吸附等温线具有三个阶段，分别对应于p/p0 < 0.1初始阶段的快速吸附、p/p0 = 0.1 - 0.7时的线性发展阶段以及p/p0≥0.7时的快速膜增厚阶段，而在H-云母体系中仅观察到后两个阶段。此外，与K-云母表面相比，p/p0 < 0.7时吸附水分子的膜厚度更低，而在p/p0≥0.7时两者相当。从蒙特卡罗模拟获得的膜厚度与Balmer等人的干涉测量实验数据(Balmer, T. E.; Christenson, H. K.; Spencer, N. D.; Heuberger, M. Langmuir 2008, 24, 1566 - 1569)非常吻合。观察到这两种离子的水合行为完全不同，并且取决于它们水合壳的大小以及形成氢键的能力。利用水密度分布、取向分布、氢键和吸附等量热说明了这两种情况下水吸附的行为。
