Antireflection and Superhydrophobicity of nanostructured polymeric films

초록

Antireflection films have been used to reduce the surface reflectivity as well as to enhance the transmittance of the visible light. By decreasing the surface reflectivity, various display panels can be clearer and the eye fatigue can be reduced. Furthermore, the increased transmittance can be utilized to increase the power conversion efficiency of a solar cell. One plausible way to secure antireflection effect of the polymer film is to modify the surface structure by forming various nanostructure. Similar method has been tried to have superhydrophobicity of the film. Fig1. 1 shows the SEM image of corneal nipple arrays in the moth-eye.1 The main purpose of the regular nanostructure in the moth-eye is to reduce the light reflectivity in other to make itself invisible to various predators in nature and to enhance the transmittance for the better viewing especially at night. In this study, we have developed a new technique for fabricating the various nanostructures on the polymeric surfaces using nanoporous metal template. The technique can be quite useful to modify various types of polymeric surface to tailor the surface properties for specialized purposes such as antireflection, superhydrophobicity, and super adhesion and other surface properties. Fig.2 is the SEM image of the PMMA surface we fabricated by forming nanodot structures. The diameter of the nanodot is about 50nm and the height of the nanodot is about 200nm. It is clear that the surface nanostructure of Fig.2 resembles the one in Fig.1. The surface reflectivity of general polymer film is about 4-5%. It was found that by forming the nanostructure on the PMMA film in Fig.2 the reflectivity can be almost completely reduced. Therefore, it seems to be possible to make almost transparent film by forming the nanostructure on both surfaces (front and back surfaces) of a film. The hydrophobicity of the nanostructured film was also tested by measuring the contact angle of the water droplet.