On the aging of oxygen plasma-treated polydimethylsiloxane surfaces

Abstract Oxygen plasma-treated polydimethylsiloxane surfaces were aged in a low-energy (air) and in a high-energy (water) medium. Treated samples were characterized using a combination of surface-sensitive techniques: X-ray photoelectron spectroscopy, static secondary ion mass spectroscopy, and contact angle measurements. Plasma treatments cause large increases in surface tension of treated samples. When aged in air (low-surface-energy medium) the samples returned to a low-surface-tension situation. The mechanism was a combination of diffusive burial of polar groups in the bulk and condensation of silanol groups formed by plasma treatment and consequent crosslinking. When aging was performed in water, a high surface tension was maintained.