Influence of the interfacial molecular structures of quaternary ammonium-type poly(ionic liquid) brushes on their antibacterial properties

Abstract

Tethering a quaternary ammonium (QA)-based poly(ionic liquid) (PIL) onto substrate surfaces appears to be an attractive strategy for the development of antibacterial surfaces. In this work, N-alkyl QA-type PIL brushes were prepared via surface-initiated atom transfer radical polymerization, and their antibacterial activities against E. coli and S. aureus were investigated in detail. In particular, the interfacial molecular structures of these PIL brushes in bacterial PBS solution were detected in situ by SFG vibrational spectroscopy in order to explore the antibacterial process occurring at the interfaces between the PIL brushes and PBS solution. It was shown that for PIL brushes with shorter alkyl chains, both QA groups and alkyl chains dominated the PIL brush/PBS interfaces, which facilitates the adsorption of bacteria and the insertion of alkyl chains into cell membranes. In contrast, longer alkyl chains tended to fold back at the interfaces, which made their access to bacteria difficult, leading to lower antibacterial efficacies and slower bactericidal behavior. Furthermore, the antibacterial potency was improved with the increase of grafting density, which was closely related to the molecular structures at the PIL brush/PBS interfaces. Our results indicate that the surface molecular structures should be considered for antibacterial property optimization, and they provide in-depth guidance for the design and fabrication of antibacterial surfaces.