Effect of surface wettability on transparency in different water conditions

Abstract

Water droplets or films which are formed according to surface wettability show different effects on surface transparency. The effects of surface wettability on transparency in different water conditions are worth investigating because the surface usually suffers from the variable environmental water conditions. Herein, superhydrophobic and superhydrophilic surfaces, with negligible differences of physical structure but great differences of chemical composition, are used to investigate for the first time the relationship between surface wettability and transparency in four water conditions, including ambient condition, liquid water, boiling water steam, and ambient conditions after freezing at −4°C for 1 week. The transparency of the superhydrophobic surface is only about 5% lower in 550 nm light wavelength than that of the superhydrophilic surface in ambient conditions, but it is about 24% lower than that of the superhydrophilic surface in liquid water. When the surfaces are exposed to boiling water steam and ambient conditions after freezing at −4°C for 1 week, the superhydrophobic surface also shows lower transparency than the superhydrophilic surface because of increased fogging. However, the transparency shows little difference when the fog evaporates completely. The relationship revealed between surface wettability and transparency in different water conditions will be beneficial in choosing suitable wettability surfaces to satisfy the needed transparency in actual applications. The effect of surface wettability on transparency has been quantitatively studied with a commercial UV–Vis spectrometer in ambient conditions (a, air) and in liquid water (a, water), and qualitatively studied with the fogging phenomenon in boiling water steam (b) and in ambient conditions after freezing at −4°C for 1 week (c) for hydrophilic glass substrates (left in b and c), superhydrophobic surfaces (middle in b and c), and superhydrophilic surfaces (right in b and c).