Droplet Mobility and Detachment on Inclined Substrates

We present numerical study of droplet motion driven by gravitational buoyancy on inclined substrates—a configuration of particular relevance to cleaning, decontamination, and surface transport applications. Our simulation results are compared against experiments on a model system of triacyl glycerol (common 'fat') sessile droplets and surfactants sodium dodecyl sulfate (SDS) and dodecyldimethylamine oxide (DDAO) in aqueous solution. Our investigation employs fully three-dimensional direct numerical simulations (DNS), incorporating a coupled model for soluble surfactant transport in the bulk fluid, at the interface, and along the substrate. A Generalized Navier Boundary Condition (GNBC), modified to account for surfactant presence and its effects, is used to accurately capture interfacial stress dynamics and slip behaviour. We also explore the influence of the substrate inclination angle and surfactant properties on droplet dynamics. Key flow metrics—including droplet detachment time, trailing distance, and dynamic contact area—are quantified to assess the interplay between surfactant effects and gravitational forces.