Dual wettability on diarylethene microcrystalline surface mimicking a termite wing

Ryo Nishimura,Satoshi Yokojima,Kingo Uchida,Hiroyuki Mayama,Shinichiro Nakamura,Kengo Hyodo

doi:10.1038/s42004-019-0192-6

Abstract

The termite wing has a specific property of wetting in contact with a water droplet: it adsorbs water mist, whereas larger water droplets are bounced on the surface. This is owing to the survival strategy of termites. Here, we reproduce the termite wing’s dual wettability by a photoinduced crystal growth technique. Upon UV irradiation to a microcrystalline surface of a mixture of two diarylethenes, two types of needle-shaped crystals of distinctly different sizes are observed to grow. The surface shows behavior akin to the termite wing’s dual wettability. The bouncing ability of a water droplet is attributed to the smaller-sized needle crystals, whereas the adhesive property is owing to the larger-sized ones, explaining the microstructures of the termite wing. Considering dissipation energy and adhesion energy, the bouncing ability and dual wettability can be explained theoretically. The surface could potentially be used in water harvesting applications.

Highlights

The termite wing has a specific property of wetting in contact with a water droplet: it adsorbs water mist, whereas larger water droplets are bounced on the surface
The surface was irradiated for 5 min with 313-nm light followed by storage at 30 °C, which is higher than the Tg of both 1o and 2o crystals, as crystal growths of 1c and 2c were observed on a softened surface above Tg (Supplementary Fig. 9c)[26]
By comparing the scanning electron microscope (SEM) images of three types of surfaces, the larger needle-shaped crystals grown on the mixed microcrystalline surface are crystals of 1c, and their lengths and widths are about 16 and 1.5 μm, respectively, whereas the smaller ones are crystals of 2c with lengths and widths of ~ 1.9 and 0.2 μm, respectively (Supplementary Fig. 7)

Summary

Introduction

The termite wing has a specific property of wetting in contact with a water droplet: it adsorbs water mist, whereas larger water droplets are bounced on the surface. The bouncing ability of a water droplet is attributed to the smaller-sized needle crystals, whereas the adhesive property is owing to the larger-sized ones, explaining the microstructures of the termite wing. The unique micro- and nanostructures on such surfaces can be seen in the self-cleaning effect of lotus leaves[1], the superhydrophobic forces exerted by a water strider’s leg[2], the attachment mechanism of geckos[3], the structure colors of the peacock[4], or morpho butterfly[5,6], and many other natural phenomena[7,8,9,10,11,12]. We believe that better understanding the structure of termite wings would provide great hints for material design as an essential component of humidity management in human society We took advantage of this difference in the current study

Methods

Results

Conclusion