A critical assessment of the line tension determined by the modified Young's equation

Although the modified Young's equation is frequently applied to evaluate the line tension of droplets, debate concerning the value and even the sign of the line tension is ongoing. The reason for this is that the line tension defined in the modified Young's equation is not a pure line tension but an apparent line tension, which includes the effects of the Tolman length and the stiffness coefficients. In this paper, we employ molecular dynamics (MD) to simulate three-dimensional water nanodroplets on platinum surfaces and determine their apparent line tensions by applying a linear fit to the relation of the cosine of the contact angle to the curvature of the contact line. The effects of the Tolman length and the position of the solid-liquid dividing interface on the measured line tension are investigated. On the one hand, our results elucidate the reason why MD results for line tensions are so scattered and also lend numerical support to Schimmele et al.'s theoretical predictions ["Conceptual aspects of line tensions," J. Chem. Phys. 127, 164715 (2007)]. On the other hand, our MD simulation results demonstrate that the modified Young's equation is a useful tool to predict the macroscopic contact angle based on a linear fit of the measured contact angles at the nanoscale. The apparent line tension is, however, sensitive to the chosen position of the solid-liquid dividing interface. (C) 2018 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license.