Effect of gamma radiation on the surface and bulk properties of poly(tetrafluoroethylene)

Abstract

The effect of gamma radiation on the contact angle θ, the work of adhesion γ _SL for polar and nonpolar liquids, disperse and polar components of the surface energy γ _S , the magnitude of bulk dielectric polarization P ₀, and the dielectric increment Δε for sintered and non-sintered poly(tetrafluoroethylene) (PTFE) of suspension polymerization are studied. Sintered PTFE exhibits anomalously high growth of the studied parameters with an absorbed dose up to 500 kGy: Δε by more than four orders of magnitude, the work of adhesion of the polar liquid $\gamma _{SL}^{{H_2}O}$ by a factor of 1.5, the polar component of the surface energy γ^pol _S by 20 times. The observed changes are found to be considerably larger than those expected from the viewpoint of the amplification of dipole–dipole and donor–acceptor molecular interactions with the participation of polar groups formed in poly(tetrafluoroethylene) upon irradiation. The similar behavior of Δε, $\gamma _{SL}^{{H_2}O}$, and γ^pol _S parameters depending on the exposed dose and subsequent annealing of the samples at 150°C is revealed. A unified mechanism for changes in the bulk polarization and surface properties caused by the formation in poly(tetrafluoroethylene) of long-lived electron–hole pairs is suggested.