Surface Modification of Rigid Gas Permeable Contact Lens Treated by Using a Low-Temperature Plasma in Air

Rigid gas permeable (RGP) contact lenses, based on fluorosilicone acrylate, were treated by using a plasma in air to improve surface wettability. As a function of the plasma exposure time, the wetting angles were estimated, the chemical compositions were analyzed by using X-ray photoelectron spectroscopy (XPS), and the surface morphology was observed by using atomic force microscopy (AFM). As the contact lenses were treated by the plasma, the wetting angle decreased significantly in the initial stage and decreased to 40 % of the wetting angle of the untreated lenses. The C, F, and N contents decreased significantly below 20 %, and the 0 and Si contents increased above 200 % on the surface. The rate of decrease of carbon was similar to the decrease in wetting angle. The number of oxygen-containing hydrophilic radicals (C-O and O-C=O) decreased because the carbons on the surface were oxidized and volatilized. The silica-like structure (SiOx, x = 1.5 similar to 2.0) increased greatly (above 50 %), and the surface became hydrophilic. The surface roughness R. decreased from 7 nm to about 4 nm, and the wetting angles decreased. The improved wettability of the contact lenses treated by using a plasma in air was affected more by the formation of a hydrophilic silica-like structure than by the change in surface morphology.