A critical review on robust self-cleaning properties of lotus leaf

Lotus leaf-inspired thermal insulation and anti-icing topography

Porous sandwich-like structures with surface roughness possess the capacity to sustain droplets, diminish the area of contact between solids and liquids, and augment heat conductivity, and thus delay ice formation when the temperature drops below the freezing point. The prevalence of this combination of surface roughness and a hollow sandwich structure has been observed in several organisms, such as lotus leaves, which have developed these features as a result of environmental adaptation. This study introduces a new design for a surface consisting of a micro-nano conical array and a foam structure with a gradient of pores. The primary components of this design were isocyanate and polyether. The hollow gradient sandwich structure was created by manipulating the water content to increase the porosity, resulting in the formation of a conical-pit morphology on the underside of the specimen. This configuration significantly decreased the amount of heat lost and the modulus of elasticity of the sample. Additionally, the micro-nano hydrophobic structure on the upper surface hindered the transmission of temperature and delayed the formation of ice. This concept, inspired by natural structures, has significant potential applications in the areas of anti-icing, energy conservation, and environmental preservation.

Anti-Environmental Aging Passive Daytime Radiative Cooling

Passive daytime radiative cooling technology presents a sustainable solution for combating global warming and accompanying extreme weather, with great potential for diverse applications. The key characteristics of this cooling technology are the ability to reflect most sunlight and radiate heat through the atmospheric transparency window. However, the required high solar reflectance is easily affected by environmental aging, rendering the cooling ineffective. In recent years, significant advancements have been made in understanding the failure mechanisms, design strategies, and manufacturing technologies of daytime radiative cooling. Herein, a critical review on anti-environmental aging passive daytime radiative cooling with the goal of advancing their commercial applications is presented. It is first introduced the optical mechanisms and optimization principles of radiative cooling, which serve as a basis for further endowing environmental durability. Then the environmental aging conditions of passive daytime radiative cooling, mainly focusing on UV exposure, thermal aging, surface contamination and chemical corrosion are discussed. Furthermore, the developments of anti-environmental aging passive daytime radiative cooling materials, including design strategies, fabrication techniques, structures, and performances, are reviewed and classified for the first time. Last but not the least, the remaining open challenges and the insights are presented for the further promotion of the commercialization progress.

Dynamic Anti-Icing Performance of Flexible Hybrid Superhydropohobic Surfaces

Normal superhydrophobic surfaces with a rough topography provide pocketed air at the solid-liquid interface, which guides the droplet to easily detach from the surface at room temperature. However, at low temperatures, this function attenuates obviously. In this research, a flexible hybrid topography with submillimeter (sub-mm) and microcone arrays is designed to adjust the impacting behavior of the droplet. The sub-mm cone could provide rigid support to limit deformation, leading to reduced energy consumption during impact processes. However, the microcone could maintain surface superhydrophobicity under different conditions, preventing droplet breakage and the change of the droplet contact state during impact processes by providing multiple contact points. Under the synergistic effect, such a hybrid structure could provide much more pocket air at the solid-liquid interface to limit the spreading of liquid droplets and reduce the energy loss during the impact process. At a low temperature (-5 °C), even if the impact height is reduced to 1 cm, the droplets still could be bound off, and the hybrid superhydrophobic surface presents excellent dynamic anti-icing ability. The special flexible hybrid superhydropohobic surface has potential application in fast self-cleaning and anti-icing fields.