Fluorocarbon versus hydrocarbon organosilicon surfactants for wettability alteration: A molecular dynamics approach
I Moncayo-Riascos and BA Hoyos, JOURNAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY, 88, 224-232 (2020).
This paper presents a theoretical model based on molecular dynamics to represent and explain the experimental measurements of water droplet contact angles on fluorocarbon and hydrocarbon organosilicon surfactants of different chain lengths. In addition to the contact angles, we evaluated the distribution of the surfactants on the surface (surface density, packing degree, density profile, and coating thickness) and the interaction energies (surfactant-surfactant, surfactant-water, and water-water) to better understand the effect generated by the differences in the molecular structure of the surfactants. We found that the surface densities of the fluorocarbon surfactants were lower than those of hydrocarbon surfactants. This is because fluorocarbon chains are more rigid and because the attractive interaction energy between CF chains is less than that between CH chains because the fluorine-fluorine repulsive electrostatic interactions are stronger than the corresponding hydrogen-hydrogen interactions. The wettability alteration resulted from the modified surface-water interactions. The initial state was hydrophilic (water angle contact of 24 degrees), produced by the high interaction energy between water and the silica surface. Upon application of surfactant, the surface-water interaction energies were considerably lowered, generating hydrophobic surfaces, with water angles contact between 87 degrees and 99 degrees. (C) 2020 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
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