Study on CO2-based plasmas for surface modification of polytetrafluoroethylene and the wettability effects

Surface modification of polymers is an attractive way to endow them with new interfacial properties while maintaining desirable bulk properties, thus expanding their possible applications. In the present work, CO2/N2 DBD plasma was applied for the surface modification of polytetrafluoroethylene (PTFE) membranes by using acrylic acid as the precursor. Systematic experiments has been carried out to investigate the influence of the plasma gas composition and the plasma exposure time to the composition, morphology, and wettability performance of the PTFE membranes. It is shown that acrylic acid has been successfully grafted on the surface of PTFE to form carboxylic functional groups by the plasma technique, leading to improved hydrophilicity. The increase of the CO2 content in CO2/N2 mixtures results in enhanced generation of CO, CO, and CC species, suggesting CO2 has been converted to functional groups on the surface of PTFE membranes. Moreover, at plasma exposure time of 0˜60 s, the hydrophilicity of the PTFE membranes can be improved, while longer plasma exposure time would lead to the degradation of the formed coating, leading to reduced hydrophilicity. This is also demonstrated by the quality of printed text on the corresponding PTFE membranes. The CO2-based plasma method was further extend to the surface modification of substrates like polyethylene (PE), polyvinylidene fluoride (PVDF), and plexiglass, suggesting high versatility of the process to alter their wettability performance. This study provides useful insight for the utilization and conversion of CO2 into value-added carboxylic groups on polymers via plasma technique.