Evaporating droplets on inclined plant leaves and synthetic surfaces: Experiments and mathematical models

Hypothesis: Evaporation of surfactant droplets on leaves is complicated due to the complex physical and chemical properties of the leaf surfaces. However, for certain leaf surfaces for which the evaporation pro-cess appears to follow the standard constant-contact-radius or constant-contact-angle modes, it should be possible to mimic the droplet evaporation with both a well-chosen synthetic surface and a relatively simple mathematical model.Experiments: Surfactant droplet evaporation experiments were performed on two commercial crop spe-cies, wheat and capsicum, along with two synthetic surfaces, up to a 90 degrees incline. The time-dependence of the droplets' contact angles, height, volume and contact radius was measured throughout the evapora-tion experiments. Mathematical models were developed to simulate the experiments.Findings: With one clear exception, for all combinations of surfaces, surfactant concentrations and angles, the experiments appear to follow the standard evaporation modes and are well described by the math-ematical models (modified Popov and Young-Laplace-Popov). The exception is wheat with a high surfac-tant concentration, for which droplet evaporation appears nonstandard and deviates from the diffusion limited models, perhaps due to additional mechanisms such as the adsorption of surfactant, stomatal density or an elongated shape in the direction of the grooves in the wheat surface. (c) 2021 Elsevier Inc. All rights reserved.