Sweeping by sessile drop coalescence★
Robert Frederick Smith School of Chemical and Biomolecular Engineering, Cornell University,
a e-mail: email@example.com
Accepted: 6 July 2020
Published online: 14 September 2020
During coalescence of liquid drops contacting a solid, the liquid sweeps wetted and solid-projected areas. The extent of sweeping dictates the performance of devices such as self-cleaning surfaces, anti-frost coatings, water harvesters, and dropwise condensers. For these applications, weakly- and non-wetting solid substrates are preferred as they enhance drop dynamical behavior. Accordingly, our coalescence studies here are restricted to drops with contact angle 90° ≤ θ0 ≤ 180°. Binary sessile drop coalescence is the focus, with volume of fluid simulations employed as the primary tool. The simulations, which incorporate a Kistler dynamic contact angle model, are first validated against three different experimental substrate systems and then used to study the influence of solid wettability on sweeping by modifying θ0. With increasing θ0 up to 150°, wetted and projected swept areas both increase as drop center of mass heightens. For θ0 ≥ 150°, coalescence-induced drop jumping occurs owing to the decreasing wettability of the substrate and a focusing of liquid momentum due to the symmetry-breaking solid. In this regime, projected swept area continues to increase with θ0 while wetted swept area reaches a maximum and then decreases. The sweeping results are interpreted using the mechanical energy balance from hydrodynamic theory and also compared to free drop coalescence.
Supplementary material in the form of one zip file available from the Journal web page at https://doi.org/10.1140/epjst/e2020-900265-5
© EDP Sciences, Springer-Verlag GmbH Germany, part of Springer Nature, 2020