Radiation Grafting of PVDF Track-Etched Membranes: A Study for Nanoscale Pore Functionalization

Functionalization of nanoporous membranes poses a substantial challenge in the development of advanced materials for selective transport applications. The primary objective of this study is to optimize the grafting process to ensure the functionalization is localized onto nanopore walls. Poly(vinylidene fluoride) (PVDF) foils were irradiated with Xe ions (1.2 MeV/u) followed by subsequent etching under optimized conditions to create nanoporous membranes. Radiation grafting of acrylic acid (AA) monomer was performed through the residual radical sites in post-etched pore walls of ion-irradiated PVDF. Radical concentrations after irradiation were quantified using EPR spectroscopy. Examination of reaction parameters including inhibitor concentration, temperature, monomer concentration, and reaction kinetics was conducted to achieve selective grafting within the nanopores. FT-IR and XPS analyses confirmed the successful covalent attachment of poly(acrylic acid) (PAA) to the PVDF TMs. Structural transformations of the PVDF matrix throughout the functionalization process were revealed by DSC analysis. The versatility of the approach was further demonstrated by grafting of pH-responsive poly(4-vinylpyridine), enabling modulation of nanopore surface charge, as evidenced by zeta-potential measurements. The spatial localization of the grafted polymer was confirmed by confocal fluorescence microscopy, demonstrating the potential for creating advanced functional membranes for separation and sensing applications.