Multiscale Simulation Method for Quantitative Prediction of Surface

5 days ago - Using this approach, we simulate the surface wettability of a graphene and graphite surface, resulting in a reliable contact angle value ...
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Surfaces, Interfaces, and Catalysis; Physical Properties of Nanomaterials and Materials

Multiscale Simulation Method for Quantitative Prediction of Surface Wettability at the Atomistic Level Suji Gim, Hyung-Kyu Lim, and Hyungjun Kim J. Phys. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.jpclett.8b00466 • Publication Date (Web): 20 Mar 2018 Downloaded from http://pubs.acs.org on March 21, 2018

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The Journal of Physical Chemistry Letters

Multiscale Simulation Method for Quantitative Prediction of Surface Wettability at the Atomistic Level Suji Gim1, Hyung-Kyu Lim2,*, and Hyungjun Kim1,*

1

Department of Chemistry and Graduate School of EEWS, Korea Advanced Institute of

Science and Technology (KAIST), Yuseong-gu, Daejeon 34141, Korea 2

Department of Chemical Engineering, Kangwon National University, Chuncheon,

Gangwon-do 24341, Korea

*

Correspondence to H.-K. L. ([email protected]) and H.K. ([email protected]) 1

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The Journal of Physical Chemistry Letters

TOC GRAPHICS

KEYWORDS wettability, work of adhesion, contact angle, QM/MM, graphene wetting

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Abstract The solid-liquid interface is of great interest because of its highly heterogeneous character and its ubiquity in various applications. The most fundamental physical variable determining the strength of the solid-liquid interface is the solid-liquid interfacial tension, which is usually measured according to the contact angle. However, an accurate experimental measurement and a reliable theoretical prediction of the contact angle remain lacking because of many practical issues. Here, we propose a first principles-based simulation approach to quantitatively predict the contact angle of an ideally clean surface using our recently developed multiscale simulation method of density functional theory in classical explicit solvents (DFT-CES). Using this approach, we simulate the surface wettability of a graphene and graphite surface, resulting in a reliable contact angle value that is comparable to the experimental data. From our simulation results, we find that the surface wettability is dominantly affected by the strength of the solid-liquid van der Waal’s interaction. However, we further elucidate that there exists a secondary contribution from the change of water-water interaction, which is manifested by the change of liquid structure and dynamics of interfacial water layer. We expect that our proposed method can be used to quantitatively predict and understand the intriguing wetting phenomena at an atomistic level and can eventually be utilized to design a surface with a controlled hydrophobic(philic)ity.

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Introduction The concept of wettability, i.e., the degree of spreading water over the solid surface, has been applied to regulate various chemo-physical reactions in the fields of water harvesting [1], self-cleaning [2], corrosion [3], filtration [4], heterogeneous catalytic reaction [5,6], etc. Despite its critical importance in a number of practical applications, fundamental characterizations and understanding on the wetting phenomena at the molecular level remain lacking. Moreover, an accurate measurement of the contact angle ( ) is often difficult to accomplish because of defects [7], airborne contaminants [8], and oxide layer formation [9] on the surface. In case of thin film systems, their intrinsic surface corrugation adds more complications because the surface geometry is another influential element on the surface energy. Even for a graphite surface that is chemically much more inert than other surfaces, e.g., metals, experimental measurement on the water contact angle substantially varies. In 1940, Fowkes et al. reported the  of 86° that is measured using the tilting plate method [10]. Using the rising meniscus method, Morcos reported the similar value of 86° in 1972 [11]. However, Tadros et al. measured a rather low value of 60-80° using the captive bubble method in 1974. [12]. An even lower value of 42±7° was estimated by Schrader in 1980 [7], and