Fabrication of honeycomb films by the breath figure technique and their applications

The breath figure method, which is used to form porous films from water droplet templates, has attracted considerable interest because it is simple and applicable to a wide variety of materials. Research on breath figures took off after the 2000s, accompanied by new polymer synthesis methods, fabrication methods, and a wide variety of applications. There are several comprehensive reviews of the applications of the porous films, which are usually called ‘honeycomb films’ because their hexagonally packed porous structure resembles honeycombs. However, new materials, progress in preparation technologies for controlling nano- and microstructures, and large-area fabrication are still areas that require further research. Furthermore, new applications of honeycomb films have emerged. In this review, the recent development of honeycomb films prepared by the breath figure techniques and their numerous applications are summarized. The production of honeycomb films can be performed on an industrial scale, greatly broadening their possible applications in areas such as optics, photonics, surface science, biotechnology, and regenerative medicine. Present problems and future perspectives are also discussed.