Shape evolution of drops on surfaces of different wettability gradients

Passive droplet manipulation on open surfaces can be achieved by creating a wettability gradient on surfaces, which is essential in the fabrication of low cost biological and biochemical chips. We performed 3D numerical simulations to analyze the droplet motion on a broad range of wettability gradient surfaces. We found that the droplet shape evolves with time to maintain a minimum energy state, and the surface energy of the droplet is identical at a particular non-dimensional time (r) for different wettability gradient surfaces. Although the droplet is at various locations at a fixed t*, the shape of the droplet is found to be identical. The physics behind this interesting phenomenon of identical droplet shape formation is explored. A co-relation for t* is proposed to get the dependency of t* on various geometrical parameters and fluid properties. Three distinct regimes of the droplet identical shape on different wettability gradient surfaces are shown using a regime plot. Along with the identical droplet shape phenomena, the detailed understanding of the dynamics of the droplet shape evolution on different wettability gradient surfaces gives an insight for better open surface passive manipulation. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

Passive droplet manipulation can be achieved by creating a wettability gradient on surfaces, and 3D numerical simulations were performed to analyze droplet motion on a broad range of wettability gradient surfaces. The droplet shape at a particular non-dimensional time was found to be identical on different surfaces, despite being at various locations at a fixed time. Further exploration into the physics behind this identical droplet shape formation is proposed, along with a correlation for the dependence of this phenomenon on various geometrical parameters and fluid properties.