The impact of line tension on the contact angle of nanodroplets

The line tension for a Lennard-Jones (LJ) fluid on a (9, 3) solid of varying strength was calculated using Monte Carlo simulations. A new perturbation method was used to determine the interfacial tension between liquid-vapour, solid-liquid and solid-vapour phases for this system to determine the Young's equation contact angle. Cylindrical and spherical nanodroplets were simulated for comparison. The contact angles from the cylindrical drops and Young's equation agree very well over the range of surface strengths and cylindrical drop sizes, except on a very weak surface. Tolman length effects were not observable for cylindrical drops. This shows that quite small systems can reproduce macroscopic contact angles. For spherical droplets, a deviation between the contact angle of spherical droplets and Young's equation was evident, but decreased with increasing interaction strengths to be negligible for contact angles less than 90 degrees. Linear fitting of the contact angle data for varying droplet sizes showed no clear effect by line tension on contact angle. All calculated line tension values have a magnitude less than 4 x 10(-12) J/m with both negative and positive signs. The best estimate of line tension for this system of LJ droplets was 1 x 10(-13) J/m, which is smaller than the reported estimations in the literature, and is too small to be conclusively positive or negative in value.