Investigation on surface wettability and surface structure of PTFE after remote oxygen plasma treatment

Summary form only given. In this paper, the surface wettability and surface structure of poly(tetrafluoroethylene) (PTFE) treated with remote oxygen plasma are studied. The contact angles of the samples are measured and the critical surface tensions (gamma_c) are determined on the basis of the Zisman´s plots. Then the variation of contact angle to water (thetas_H2O) and the gamma_c are as the functions of the sample positions, which are at the different distance from the center of oxygen plasma active discharge zone. Since the better surface wettability can be obtained at 0 cm and 40 cm from the center of oxygen plasma active discharge zone, respectively, the variation of thetas_H2O and are farther as the functions of the plasma treatment time. Furthermore, the values of dispersion force gamma_s ^d, dipole force gamma_s ^pand hydrogen bonding force gamma_s ^h to the surface free energy gamma_s of treated PTFE are evaluated by the extended Fowkes equation. The analysis is carried out between the distribution of reactive species in remote oxygen plasma and the surface free energy as well as surface wettability. All the results show that the surface wettability of PTFE treated with oxygen plasma is only determined by the value of polar force (gamma_s ^p + gamma_s ^h), especially the gamma_s ^h. A mixed atmosphere constituted by all reactive species or super pure and high free radicals concentration in remote oxygen plasma are both propitious to the increasing of polar force (gamma_s ^p + gamma_s ^h), but the surface free energy is influenced mainly by the concentration of charged particles. X-ray photoelectron spectroscopy (XPS) indicates that the C-F bonds on the PTFE surface are broken by the oxygen plasma treatment, and then the polar functional groups of C-- and C=0 are introduced effectively, the surface wettability increases.