Lotus leaf-inspired thermal insulation and anti-icing topography

Abstract

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.

Fig. 1. Surface and interlayer structure of the lotus leaf. (a) The lotus leaf in nature that we photographed ourselves. (b) Sketch of lotus leaf surface and interlayer structure.

Fig. 2. Preparation process of the micro–nano cone array surface and porous gradient sandwich foam structure.

Fig. 3. (a) Sketch of the sample topography. (b and c) SEM images of the surface topography. Nano-rods with a length and diameter of 3 μm and 100 nm were observed. (d) Superhydrophobic state of the droplet on the surface. (e) Back details of the sample. (f) Delay in the icing process. The water content of the prepared samples was 1.96%.

Fig. 4. (a–g) Temperature of the upper surface of the sample with water contents of 0%, 1.12%, 1.41%, 1.69%, 1.96%, 2.23%, 2.51% after 20 minutes. (h) Average upper surface temperature of different samples. (i) Comparison of the average temperature of the CS and NCS with a water content of 1.96% (sample) after 25 minutes. Simulation data of NCS (j–l) and CS (m–o).

Fig. 5. (a) Compression testing under varying water content conditions; (b) localized magnification view of the box area in (a).

Fig. 6. (a) Maximum tensile stress with different water contents. (b) The mass of the same volume with different water contents.

Fig. 7. (a) Comparison of the compressive mechanical properties. (b) Comparison of the tensile mechanical properties. (c) Fatigue resistance of repeated compression. (d–f) Top view, bottom view, and side view of the simulation of the structure without cone–pits at the bottom, respectively. (g–i) Simulation of the distribution of the NCS and CS.