Atomistic Insights into Hydrogen-Bonding-Driven Competitive Adsorption of Acetone-Chloroform Binary Mixtures
N Kumar and S Singla and MC Wilson and S Kaur and S Bekele and M Tsige and A Dhinojwala, JOURNAL OF PHYSICAL CHEMISTRY C, 123, 29729-29738 (2019).
The competitive adsorption of molecules on a surface has both beneficial and detrimental effects for technological applications, such as chromatography (material separation) and protein adsorption on medical implants. A comprehensive understanding of adsorption can aid in the design of surfaces with desired functional properties. Molecular dynamics (MD) simulations serve as a direct approach to quantify interfacial behavior. In this study, we use MD simulations to gain insights into the adsorption of acetone-chloroform mixtures on a solid sapphire substrate. Acetone segregates preferentially to the sapphire surface because of hydrogen bonding between the oxygen atom of the acetone molecules and the sapphire surface hydroxyl groups. Both acetone and chloroform possess two probable orientations next to sapphire. Orientation analysis reveals that the presence of chloroform alters the way acetone interacts with the surface, and vice versa. Two analysis methods were developed and utilized to calculate the surface segregation: radial-cut and Z-cut. By comparing the results from the two MD simulation analysis methods, we gain insights into hydrogen-bonding- driven surface segregation and illustrate challenges in defining the surface phase. The surface segregation calculated using the radial-cut method matches with the Defay-Prigogine adsorption model with the differences in interfacial energies of individual components calculated using the Badger-Bauer and Dupre-Fowkes formalism. In addition, the surface segregation from the radial-cut method is found to correlate well with previously reported sum-frequency generation spectroscopy results. The current study paves the way for the overall understanding of adsorption, which can help in designing new surfaces for controlling adsorption.
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