Photochromic and super anti-wetting coatings based on natural nanoclays

Abstract

Photochromic materials are of great interest in academic and industrial areas, but their applications are hindered by low stability and slow color switching. Here, inspired by Maya Blue and the lotus leaf, we report the preparation of photochromic and super anti-wetting coatings by the combination of amorphous tungsten oxide (WO₃) modified palygorskite (PAL) nanorods and polysiloxane. The WO₃ nanoparticles 5–10 nm in size uniformly and firmly attached on the PAL nanorods, which enhanced the specific surface area and utilization efficiency of the WO₃ nanoparticles. Consequently, the PAL/WO₃ coatings show rapid and highly reversible switching between the colored and discolored states upon UV irradiation and heat-erased process. In addition, the photochromic coatings can be easily prepared using different nanoclays, e.g., PAL, kaolinite, halloysite and sepiolite, via the same approach. The polysiloxane layers not only enhanced the discoloration speed by acting as electron donors but also made the coatings superhydrophobic or superamphiphobic. Consequently, the coatings show good self-cleaning properties and high stability under various conditions, making them superior to conventional photochromic materials. The photochromic and super anti-wetting coatings show great potential in various fields such as sensors, security printing ink, waterproof posters, etc.