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Line tension of water nanodroplets on self assembled monolayers
  • burbol laila
burbol laila
Freie Universität Berlin

Corresponding Author:[email protected]

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Abstract

The line tension acts at the three-phase contact line of droplets on solid surfaces. It is often determined indirectly through the contact angle. The line tension is only significant in nanoscopic systems, but there is not a consensus about its sign and order of magnitude. The position of the solid-liquid interface is considered non-decisive in its determination. We investigated whether different positions would lead to different contact angles and line tensions by performing MD simulations of differently sized nanodroplets placed on rigid self assembled monolayers with varying polarities. Analyzing the radial density profiles, the contact angle of the equilibrated droplets was determined. A line tension was obtained for each polarity by fitting the modified Young’s equation to the contact angles and base radii. Three positions of the solid-liquid interface were tested, including the Gibbs dividing surface. We found that the sign of the line tension and the microscopic characteristics of the droplet (contact angle, base radius, etc.) change depending on the interface definition used, but not the macroscopic contact angle. This may explain in some cases the inconsistencies of the line tension sign, and also shows the necessity of a reviewed convention for the solid-liquid interface position at the molecular scale.

There is not a consensus about the sign and the order of magnitude of the line tension. It acts at the three-phase contact line of droplets on solid surfaces, but it is only significant in nanoscopic systems. Often, it is determined indirectly through the contact angle, for which the position of the solid-liquid interface is considered non-decisive.

There is not a consensus about the sign and the order of magnitude of the line tension. Furthermore, it is difficult to measure experimentally because it is only significant in nanoscopic systems. For droplets on solid surfaces it is measured indirectly through the contact angle, for which the position of the solid-liquid interface is considered non-decisive.

We investigated whether different positions of the solid-liquid interface would lead to different contact angles and line tension in nanoscopic systems. We performed MD simulations of differently sized nanodroplets on rigid self assembled monolayers with varying polarities. Analyzing the radial density profiles, the shape and contact angle of the equilibrated droplets were determined, which were used to calculate the line tension. Three positions of the solid-liquid interface were tested, including the Gibbs dividing surface. We found that the sign of the line tension and the microscopic properties of the droplet (contact angle, base radius, etc.) change depending on the interface definition used, but not the macroscopic contact angle. This may explain in some cases the inconsistencies of the line tension sign, and also shows the necessity of a reviewed convention for the solid-liquid interface position at the molecular scale.