Droplet motion over a chemical step*

Controlling and understanding the mechanisms of droplet motion on physically and chemically structured substrates is relevant to application in microfluidics. 

 

In this work, we present multi-phase simulations of a water droplet rolling over a chemical step (i.e. a sudden change in the wettability of a flat surface). We implement a high-density ratio and focus on droplet deformation near the step. The chemical step is incorporated by adapting the wetting condition in the lattice Boltzmann equation. We investigate the influence of the surface tilt angle, the equilibrium contact angle, and the droplet viscosity on the maximum droplet height, elongation, and the advancing and receding contact angles once the chemical step has been passed. 

Our research elucidates the physical mechanisms of droplet deformation as they approach a chemical step, contributing to the development of predictive models for droplet behaviour on heterogeneous substrates while addressing challenges of high-density ratios and stability in multi-phase flow simulations.