Carbon Tetrafluoride, Oxygen, and Air RF Plasma Modified Low-Density Polyethylene and Polydimethylsiloxane

Low-density polyethylene (LDPE) and polydimethylsiloxane (silicone or PDMS) were exposed to low-pressure air, oxygen (O2), and carbon tetrafluoride (CF4) plasma to modify their surfaces. Plasma power and irradiation time were varied to determine the optimal yield for the water contact angle (θ). For both polymers, the CF4 plasma treatment resulted in the fluorination of the surfaces corroborated by FT-IR and XPS analysis, while small changes in the corresponding θ could be observed. For the O2 and air plasma treatment, the θ values of LDPE were reduced from 100° to around 60°. The changes in surface free energies (SFE) were compared for pre- and post-plasma gas treatment for both polymers and their stability under different aging conditions e.g., air, vacuum, and in water were investigated. The SFE of silicone was increased with the O2 plasma treatment from 10 to 75 mN/m and remained stable in water. Whereas the SFE of LDPE was indifferent to all storing conditions and stable up to 168 h. Also, while the SFE for the CF4 plasma-treated silicone remained almost unchanged, for the LDPE it was decreased to 15 from 35 mN/m. The wettability studies under different conditions e.g., different pH, NaCl, and BSA concentrations affirmed that they can be potentially used for biomedical applications. Finally, the multiple successive gas plasma treatment of LDPE and silicone were done up to 6 times to attain the θ values in the desired range e.g., about 120° to 30° for LDPE and 120° to 13° for silicone.