Calculation of contact angle via Young-Dupre equation with molecular dynamic simulation: Kaolinite as an example

YM Liu and YY Zheng and HJ Lin and PC Wei and QC Fan and GG Huang and D Meng, COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS, 697, 134469 (2024).

DOI: 10.1016/j.colsurfa.2024.134469

To explore the surface wettability, the contact angle was usually experimentally measured by sessile drop method, which is very sensible to the experimental conditions. Molecular Dynamics (MD) simulation method has been applied to study nanodroplets, but the contact angles were usually obtained via curve fittings of the droplets, which is subjective and the errors inevitable. In this work, Young-Dupre equation was applied to calculate the contact angle with the surface tension coefficient of water and the adhesion work of water/surface, which were achieved via MD simulations results. The wettability of layered kaolinite was studied as an example. The computed contact angle of water on the Al-O octahedral surface of kaolinite was 0 degrees, and those on the Si-O tetrahedral surface were roughly 92 degrees similar to 104 degrees, which agreed well with the results of curve fitting method, about 0 degrees for the Al-O octahedral surface and 106 degrees +/- 9 degrees on the Si-O tetrahedral surface. The dipole moment distribution, dipole angle distribution of water molecules, as well as the evolution of hydrogen bond number during the whole dripping process of water droplet on kaolinite surfaces were analyzed to reveal the mechanism of hydrophobic/hydrophilic of different surfaces of kaolinite.

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