Surface-oriented fluorinated pyridinium silicone with enhanced antibacterial activity on cotton via supercritical impregnation

Most research efforts focus on synthesis of new biocides. This study shows that orientating biocidal groups on top surface with the help of a low-surface-tension constituent also imparts enhanced antibacterial ability. A CO 2 -philic biocidal silicone with pyridinium pendants was synthesized by hydrosilylation reaction of (45% methylhydrosiloxane)–dimethylsiloxane random copolymer (P(MHS–DMS)) and 4-vinylpyridine and subsequent quaternization of pyridine groups with 6-perfluorooctyl-1-bromohexane. The fluorinated pyridinium silicone was impregnated into cotton yarns in supercritical CO 2 to form a 50 nm thickness biocidal layer at 24 MPa and 50 °C. Pyridinium groups preferentially segregated to the top surface with the aid of low-surface-tension perfluorooctyl segments and provided higher biocidal efficacy against Staphylococcus aureus and Escherichia coli compared to their counterparts that were quaternized with 1-bromohexane at similar total pyridinium content of about 4.65 × 10 16 /cm 2 . The synthesis and coating results were characterized by FTIR, SEM, and XPS. The stabilities of fluorinated pyridinium silicone layer toward washing cycles, UV irradiation, and storage were good. The presented strategy uses environmentally benign CO 2 as solvent and affords a general method to functionalize polymers for improved biocidal capability due to the surface orientation of pyridinium groups.