Molecular Insights into the Effect of Crystal Planes on Droplet Wetting

Abstract

Dynamic wetting by liquids on solid surfaces depends on several aspects such as surface energy, roughness, and interfacial tension, among many others. Copper (Cu), gold (Au), aluminum (Al), and silicon (Si) are a few of the most important metals that are used extensively as substrates in various industrial and biomedical applications. Metals are etched frequently on different crystal planes for fabrication purposes. Etching exposes distinct crystal planes that may come in contact with the liquids when used for different applications. The interaction of the crystal planes with the liquid that comes in contact with the solid dictates the wetting behavior of the surface. This necessitates the importance of understanding how various crystal planes of the same metals behave under similar conditions. Herein, three specific crystal planes, namely, (1 0 0), (1 1 0), and (1 1 1), are investigated at a molecular scale for the above-mentioned metals. The dynamic contact angle and contact diameter trends revealed that the relatively hydrophobic surfaces (Cu, Si) tend to reach their equilibrium contact angle faster compared to the hydrophilic substrates (Al, Au). Molecular kinetic theory is used to estimate the three-phase contact line friction which is found to be higher for (1 1 1) planes. Further, a consistent potential energy distribution variation is observed for the crystal lattice of (1 0 0), (1 1 0), and (1 1 1). These findings can be used as a guideline to determine the factors needed to completely describe a dynamic wetting phenomenon of the droplet over the different crystal planes. The understanding will be of great use in deciding experimental strategies where fabricated different crystal planes would be required to have a liquid contact.

A Review of Nano and Microscale Heat Transfer: An Experimental and Molecular Dynamics Perspective

“…Figure 7a,b depicts the water droplet on a Cu (1 0 0) surface [73] and the density plot to calculate the water droplet interface, which is further analyzed to calculate the contact angle and contact diameter using traditional curve-fitting methodologies. The droplet tends to modify its shape until it reaches an equilibrium shape.…”

“…The TPCL friction force is molecular in nature, and MD research is considered an obvious choice for understanding the impacts of crystal planes on analogous wetting parameters at an atomic level. Molecular Kinetic Theory [78,79] (MKT) is a model that is commonly used in conjunction with AMD simulations for the improved understanding of water-spreading dynamics on hydrophobic surfaces [77], droplet motion on gradient surfaces [80], contact line movement in electrowetting [81,82], different crystal planes [73], and various other similar studies.…”