Methane at the gas/water interface: Molecular simulations of surface adsorption and second surface virial coefficients
Methane at the gas/water interface: Molecular simulations of surface adsorption and second surface virial coefficients
复制标题
气/水界面处的甲烷：表面吸附和第二表面维里系数的分子模拟
DOI：
10.1016/j.colsurfa.2022.129725
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发表时间：
2022
期刊：
影响因子：
--
通讯作者：
Ashbaugh, Henry S.
中科院分区：
文献类型：
--
作者：
Wang, Yang;Allen, Olivia;Collins, Eboni;Ashbaugh, Henry S.
液体的表面张力是由表面活性剂和气体在界面处的吸附来调节的。为了解开竞争的极性和非极性相互作用，反对/有利于吸附在气/水界面，并获得分子的洞察力，调节表面张力的溶质间相互作用的作用，我们在这里报告纯非极性甲烷吸附到水表面在宽范围的温度（0-50 °C）和大气压（高达~750巴）的分子模拟。正如预期的那样，界面处的正甲烷吸附随着压力的增加显着降低了表面张力，尽管这种效应并非没有限制，因为在500 bar附近观察到表面张力的平台/最小值。从模拟中直接观察到的甲烷的过量表面吸附与根据Gibbs吸附等温线从表面张力确定的那些定量地一致，从而在模拟结果的热力学一致性和Gibbs对溶质吸附效果的解释中给予信心。从模拟结果，我们能够评估表面吸附系数和第二表面维里系数甲烷的坐在界面上。从模拟确定的第二维里系数被发现是稍微更有吸引力的比从二维气体的统计热力学积分预测，这表明水可以帮助驱动甲烷在界面上的相互作用。将第二表面维里系数的统计热力学积分推广到被限制在伪二维狭缝中的气体，然而，观察到与模拟结果的近定量一致，表明水有效地起不到任何作用。与实验的模拟结果的比较一般是有利的，虽然模拟出现下预测净吸附可能是由于忽略甲烷极化相互作用。
Liquid surface tensions are moderated by the adsorption of species like surfactants and gases at interfaces. In order to disentangle the competing polar and nonpolar interactions that oppose/favor adsorption at a gas/water interface and gain molecular insights into the role of inter-solute interactions on moderating the surface tension, we report here molecular simulations of purely nonpolar methane adsorption onto aqueous surfaces over a broad range of temperatures (0–50 °C) and bulk gas pressures (up to ~750 bar). As expected, positive methane adsorption at the interface significantly lowers the surface tension with increasing pressure, although this effect is not without bound as plateaus/minima in the surface tension are observed near 500 bar. The excess surface adsorption of methane directly observed from simulation agrees quantitatively with those determined from the surface tension following Gibbs adsorption isotherm, giving confidence in the thermodynamic consistency of the simulation results and Gibbs’ interpretation of the effect of solute adsorption. From the simulation results we were able to evaluate surface adsorption coefficients and second surface virial coefficients for methane’s sitting at the interface. The second virial coefficients determined from simulation were found to be slightly more attractive than those predicted from statistical thermodynamic integrals for two-dimensional gases, suggesting water could help drive methane interactions in the interface. Generalizing the statistical thermodynamic integral for the second surface virial coefficient to that for a gas confined to a pseudo-two-dimensional slit, however, near quantitative agreement with the simulation results is observed, indicating water plays effectively no role. Comparisons of the simulation results with experiment are generally favorable, although the simulations appear to under predict net adsorption likely as a result of the neglect of methane polarization interactions.