On the Formation and Dynamics of Micro Dew Droplets on Grass: the Role of Epicuticular Wax.

Abstract

Though ubiquitous in everyday life, the formation of dew on grass arises from a precise balance of environmental conditions and surface microstructure. While condensation requires sufficient atmospheric moisture availability and cooling below the dew point, the formation of stable, spherical droplets is dependent on specialized surface architectures that promote nucleation and resist total wetting. Here, a closer look at the formation, growth, and dynamics of microscale dew droplets on the surface of wheatgrass leaves, investigating the role of epicuticular wax, is provided. The wheatgrass leaf exhibits biphilic properties emerging from the hydrophilic lamina covered by hydrophobic wax microsculptures, therefore, dew formation and dynamics are largely governed by the arrangement and density of epicuticular wax. Drop-wise condensation is observed, resulting in discrete, highly mobile dew droplets on the superhydrophobic adaxial side, while the abaxial surfaces, characterised by reduced wax coverage, yield significant flooding and film-wise condensation. Frequent coalescence of multiple droplets of 5-20 µm diameter on the adaxial side results in self-propelled departure events, creating free potential sites for new nucleation. This dynamic regime of jumping dew droplets may provide a source of fresh water to surfaces and organisms in the vicinity of low grasses, considering their quasi-vertical orientation.