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The development of next-generation surface coatings benefits from surfactant systems whose interfacial and bulk properties can be tuned to achieve targeted functionalities. In this work, we examine the influence of tetrabromometallate counterions, MBr₄²⁻ (M = Co, Ni, Cu, Zn), on the rheological, wetting, and antibacterial properties of dimeric metallosurfactants derived from bis(N,N-dimethyl-N-dodecyl)ethylene-1,2-diammonium dibromide (12-2-12). Dissociation of the complex counterions increases ionic strength and promotes micellar transitions from spherical to cylindrical to wormlike aggregates. This results in a pronounced increase in viscosity and viscoelasticity in the low millimolar concentration range, without added salts or co-surfactants.Similarly, at the stainless steel interface, electrostatic screening reduces repulsion between quaternary ammonium headgroups, enabling tighter interfacial packing and improved wetting compared with the metal-free precursor.Antibacterial assays demonstrate potent activity in the low micromolar range against both Gram-positive and Gram-negative bacteria. Antibacterial performance is primarily governed by the amphiphilic dication (12-2-12)²⁺, as evidenced by comparable minimum inhibitory (MIC) and minimum bactericidal (MBC) concentrations across the metallosurfactants and parent surfactant. For all tested species, minimum biofilm eradication concentrations (MBEC) exceed biofilm prevention concentrations (BPC), highlighting the increased resilience of established biofilms while confirming antibiofilm efficacy at micromolar levels.This combination of viscoelasticity, surface wettability, and antibacterial performance is relevant to coating applications through its impact on film retention, thickness control, and bioprotective functionality. The limited influence of the metal ion on these properties allows metal selection to introduce additional functionalities without compromising the fundamental performance of the surfactant.
Ivančić et al. (Fri,) studied this question.