Solar-driven interfacial evaporation of a hanging liquid marble

Abstract

A liquid marble is a droplet coated with hydrophobic particles. Due to the large capillary energy associated with particle adsorption, this particle-armed liquid normally sustains long-term stability rather than evaporation under ambient condition. Conversely, we show here experimentally that liquid marbles coating with photothermal nanoparticles can significantly accelerate the liquid evaporation under solar irradiation. A series of experiment in solar evaporation of water drops, nanofluid drops as well as liquid marbles are conducted under controlled condition to verify this concept. It is found that the liquid marble exhibits the highest evaporation rate among the three cases. This high performance is attributed to the plasmon-coupling effect between neighboring nanoparticles along the drop surface, creating a high-temperature thermal boundary for intense evaporation of the interfacial liquid. While solar evaporation of nanofluid induces multiple scattering events among the nanoparticles that increases photon absorption within the drop domain, resulting in a collective heating to enhance the evaporation. Numerical modelling is further introduced to disclose the temperature distribution in these photothermic systems. Despite its diffusion nature, the temperature distribution can be engineered highly non-uniform and concentrated at the nanoscale using the particle assemblies in close proximity. A significant degree of nanoscale control over the individual temperatures of neighboring particles is demonstrated, depending on the interparticle gaps and dielectric surrounding media. Our findings open new possibilities for flexible control of photothermal processes and precisely heat delivery for solar vapor generation or local welding of textured nanomaterial.