Effect of UV/ozone irradiation on the surface properties of electrospun webs and films prepared from polydimethylsiloxane–urea copolymers

Abstract

Highly hydrophobic surfaces of silicone–urea copolymers were transformed into hydrophilic ones upon UV/ozone treatment. The extent of surface modification was strongly dependent on the sample preparation method and the exposure time. The physical and chemical changes at the copolymer surfaces were analyzed by spectroscopic (XPS, ATR-FTIR), microscopic (SEM) techniques and static water contact angle measurements. ATR-FTIR spectra clearly showed the dramatic change in the strongly hydrogen bonded urea hard segments and the degradation of dimethylsiloxane units in silicone–urea copolymers. XPS results revealed the formation of SiOx on the surface, which gradually increased with exposure time. After 3h of UV/ozone exposure, Si(2p) binding energy shifted from 101.9 to 102.85eV, which is a clear indication of an increase in the oxidation state of silicon. The deterioration of microroughness of the electrospun webs upon UV/ozone exposure, which was revealed by SEM, resulted in a dramatic decrease in the static water contact angle values from 129 to 62°. These results clearly show that UV/ozone process is a very simple and facile method to transform hydrophobic silicone–urea copolymer surfaces into fairly hydrophilic ones.