Interfacial Engineering with Amphiphilic Cationic Polymers: Role of Alkyl Chain Length in Biofilm Suppression and Corrosion Protection

Abstract Biofilm formation promotes microbiologically influenced corrosion (MIC) in marine environments, demanding coatings that can resist bacterial adhesion and corrosion simultaneously. Herein, we report amphiphilic cationic polymer coatings based on quaternized poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) with varying alkyl chain lengths (C4–C12) deposited over an inherently antimicrobial tannic acid–Cu (TA–Cu) interfacial layer on stainless steel. Increasing the alkyl chain length gives rise to noticeable surfactant-like action, resulting in improved hydrophobicity and reduced surface free energy of the coatings. Specifically, the dodecyl-functionalized polymer has the lowest surface free energy which effectively reduces bacterial adhesion and inhibits the formation of biofilm of Pseudomonas aeruginosa. The electrochemical tests show a significant drop in corrosion current density and rise in impedance with increasing chain length. The PC12 coating exhibits diffusion-limited corrosion behavior, which indicates a dense and impermeable barrier. In contrast, shorter chain counterparts provide only limited protection as these have less affinity to create a dense coating. The long-chain quaternized PDMAEMA coatings proved efficient multifunctional surfaces to reduce MIC in marine environments owing to their combined effects of decreased surface free energy, improved hydrophobicity, and cationic nature.