Alvarado Omar, Quezada Gonzalo R, Saavedra Jorge H, Rozas Roberto E, Toledo Pedro G
Departamento de Química, Facultad de Ciencias, Universidad del Bío-Bío, Av. Collao 1202, Concepción 4030000, Chile.
Departamento de Ingeniería Química, Universidad de Concepción, Concepción 4030000, Chile.
Polymers (Basel). 2022 May 12;14(10):1967. doi: 10.3390/polym14101967.
Methyl isobutyl carbinol (MIBC) is a high-performance surfactant with unusual interfacial properties much appreciated in industrial applications, particularly in mineral flotation. In this study, the structure of air-liquid interfaces of aqueous solutions of MIBC-NaCl is determined by using molecular dynamics simulations employing polarizable and nonpolarizable force fields. Density profiles at the interfaces and surface tension for a wide range of MIBC concentrations reveal the key role of polarizability in determining the surface solvation of Cl ions and the expulsion of non-polarizable Na ions from the interface to the liquid bulk, in agreement with spectroscopic experiments. The orientation of MIBC molecules at the water liquid-vapor interface changes as the concentration of MIBC increases, from parallel to the interface to perpendicular, leading to a well-packed monolayer. Surface tension curves of fresh water and aqueous NaCl solutions in the presence of MIBC intersect at a reproducible surfactant concentration for a wide range of salt concentrations. The simulation results for a 1 M NaCl aqueous solution with polarizable water and ions closely capture the MIBC concentration at the intercept. The increase in surface tension of the aqueous MIBC/NaCl mixture below the concentration of MIBC at the intersection seems to originate in a disturbance of the interfacial hydrogen bonding structure of the surface liquid water caused by Na ions acting at a distance and not by its presence on the interface.
甲基异丁基甲醇（MIBC）是一种高性能表面活性剂，具有独特的界面性质，在工业应用中备受青睐，尤其是在矿物浮选方面。在本研究中，通过使用采用可极化和不可极化力场的分子动力学模拟，确定了MIBC-NaCl水溶液的气液界面结构。在广泛的MIBC浓度范围内，界面处的密度分布和表面张力揭示了极化率在决定Cl离子的表面溶剂化以及将不可极化的Na离子从界面排斥到液体本体中的关键作用，这与光谱实验结果一致。随着MIBC浓度的增加，MIBC分子在水液-气界面的取向从平行于界面变为垂直，形成紧密堆积的单分子层。在广泛的盐浓度范围内，在MIBC存在下，淡水和NaCl水溶液的表面张力曲线在可重复的表面活性剂浓度处相交。使用可极化水和离子的1M NaCl水溶液的模拟结果在截距处紧密捕捉到了MIBC浓度。在交点处MIBC浓度以下的MIBC/NaCl混合水溶液表面张力的增加似乎源于远距离作用的Na离子对表面液态水界面氢键结构的干扰，而非其在界面上的存在。
