Microstructure and surface state of plasma-treated high-density polyethylene elucidated by energy-tunable positron annihilation and water contact angle measurements

抄録

Positron gamma ray spectroscopy coupled with an energy-tunable positron beam was utilized to the study of the microstructure in polyethylene (PE) modified by the radio-frequency (RF) plasma. The energy dependence of the line-shape S parameter, a measure of the Doppler broadening of the positron radiation, confirmed that the change in the hydrophilic state of the PE surface after plasma modification was due to the altered chemical structure in the near-surface region. Moreover, only a region at a depth shallower than 700 nm was influenced by the plasma modification. The recovery in the surface hydrophobicity after plasma modification was observed through contact angle measurements. The variation of the contact angle of water can be fitted by a two-factor decay model, suggesting that the surface recovery is caused by the diffusion of two different groups.