Hierarchical Nano-Porous Layer with Persistent Superhydrophilicity and High Transparency Etched onto Silicate Glass

We have developed a hierarchical nano-porous layer (HNL) on a silicate glass by simple alkaline etching method. The HNL has a three-dimensionally-continuous sponge-like structure with a pore size of a few tens of nm at its apparent surface. The pore size gradually decreases from the apparent surface to the interface of the porous layer and the bulk substrate. This HNL gives two significant properties to glass: (1) higher optical transparency than untreated glass by 7% for all over the visible light. (2) long persistent superhydrophilicity with a water contact angle of 5 degree for more than 140 days. The superhydrophilicity also realizes anti-fogging and anti-fouling functionalities.