Variations in surface and electrical properties of polytetrafluoroethylene film after plasma-induced grafting of acrylic acid

Polytetrafluoroethylene (PTFE) film was graft-polymerized with acrylic acid (AAc) via a low-temperature plasma technique. The effect of plasma treatment parameters (radio-frequency power and treatment time) on the spin number of free radicals in PTFE film was examined. Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy were employed to characterize the chemical structure, surface composition, and microstructure of the original PTFE and PTFE-g-PAAc films, respectively, in order to verify the successful graft polymerization of AAc onto a PTFE film surface. Thermogravimetric analysis illustrated that the thermal stability of bulk PTFE film remains unchanged after graft modification. Water contact angle measurements confirmed that the hydrophilicity of PTFE-g-PAAc film was effectively improved as compared to the original PTFE film. The dielectric constant (ε_r) of PTFE-g-PAAc (GD = 218 μg/cm²) film remained invariable, compared to that of the unmodified PTFE film. Nevertheless, the dielectric loss (tanδ) of PTFE film increased considerably, from 0.0002 (GD = 0 μg/cm²) to 0.0073 (GD = 218 μg/cm²), which might be due to the increase in surface polarity and moisture resulting from AAc graft modification. In addition, the surface electrical resistance (R_s) of PTFE film decreased slightly, from 131.89 (GD = 0 μg/cm²) to 110.28 Ω cm² (GD = 218 μg/cm²) after surface modification, but still retained its inherent high impedance. (authors)