Modification of substratum physicochemistry by material adsorbed from groundwater—analysis by contact angles and relevance to microbial adhesion

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Abstract
Stainless steel, polypropylene, shale, and andesite were coated with films derived from shallow (5–13 m) and deep (35–65 m) groundwaters representing a cross section through a fractured bedrock aquifer. Contact angles of water, formamide, and di‐iodomethane measured on clean and conditioned interfaces were used to calculate physicochemical surface properties by the Lifshitz‐van der Waals acid‐base approach. Interfacial parameters were also determined for the interaction of carbon‐limited cells of the Gram‐negative bacterium SW8 with these surfaces. The alteration of surface free energy attributable to conditioning films was generally moderate, as was their impact on the Lifshitz‐van der Waals component of surface free energy. Most coatings did, however, significantly modify the acid‐base components of surface free energy of both hydrophilic and hydrophobic substrata, and the substratum‐water and the bacterium‐water interfacial tensions, as well as the free energy of adhesion of bacteria to substrata. The number of carbon‐limited SW8 cells retained on clean and coated surfaces did not correlate with any of the physicochemical parameters investigated. Contact angles provided a sensitive means for analysis of interfaces conditioned with material from aquifers. Caution needs to be applied, however, when using contact‐angle‐derived physicochemical data to predict attachment of bacteria to conditioned substrata.

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