Flexible Optical Devices with Reversible Light Transmittance by Superhydrophobicity Regulation

Flexible optical devices with waterproof, antifouling, and light transmission properties have significant potential in various practical fields, such as solar cells, microelectronics, and aerospace. The common method for achieving water and stain resistance is to create superhydrophobic surfaces by constructing micro/nano hierarchical structures on hydrophobic substrate surfaces. However, rough superhydrophobic surfaces could lead to light scattering and therefore compromise light transmittance as ascribed to the Mie scattering. In this article, a method is proposed to reversibly regulate the superhydrophobicity and light transmittance of flexible optical devices. Utilizing hydrophobically treated nanoparticles to construct micro/nano hierarchical structures on the flexible substrate surface, a superhydrophobic flexible substrate was achieved. By adding a medium to alter the refractive index of the substrate surface, light scattering was reduced, thereby changing light transmittance. Reversible changes in light transmittance were achieved through the evaporation of the medium. Experimental results shown that the water contact angle of the superhydrophobic flexible substrate surface was 153.2°, and the sliding angle was 1.7°. Light transmittance could be increased from 16.0% to 79.3%. By shortening the distance between the optical power meter probe and the substrate, the light transmittance is further increased to 91.3%. The reversible change process took approximately 3 min. The substrate remained superhydrophobic after 300 cycles of bending and stretching. The proposed method has significant potential in the fields of optical imaging and sensors.