Enhancement of visible light absorbance and hydrophobicity by sputter-coating of PTFE onto fine protrusions formed by sputter-etching of steels

Abstract

Argon ion sputter-etching was applied to type 316 stainless steel and AISI M2 (JIS SKH 51) steel, and the sputter-coating of polytetrafluoroethylene (PTFE) film was carried out onto the sputter-etched surface. The sputter-etching of the steels formed fine and dense ridge- or column-shaped protrusions with a diameter of 100 nm to 1 μ m on the surface. The protrusions of as-sputter-etched type 316 and M2 steels specimens showed low re flectance of visible light smaller than 8.5 % and 4.4 % respectively, and the sputter-coating of PTFE film reduced the refl ectance further to 5.3% and 2.8 % as long as the thickness of the fi lm is thin. In addition, the protrusions of both steels sputter-coated with PTFE films showed superhydrophobicity with a contact angle of a water droplet of more than 165°. The superhydrophobicity of the type 316 specimen was still preserved after an ultrasonic vibration test of 3.6 ks in water.