Ian Acworth

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

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 ...

Determination of physicochemical parameters of solids covered with conditioning films from groundwaters using contact angles. Comparative analysis of different thermodynamic approaches utilizing a range of diagnostic liquids

Abstract Contact angles of two polar [water (w) and formamide (f)] and two apolar diagnostic liquids [α-bromonaphthalene (α-br) and diiodomethane (di)] were measured on substrata (andesite, shale, stainless steel and polypropylene) either clean or coated with conditioning films from groundwaters collected from shallow and deep bores. The equation of state (ES), the Lifshitz-van der Waals acid-base approach (LWAB) and the geometric mean equation (GME) were evaluated for calculation of the following parameters: surface free energy (γs) and its components (γsp = polar and γsd = apolar components in GME as well as γslw, γs− and γs+ = Lifschitz-van der Waals, electron-donor and electron-acceptor components in LWAB) in addition to solid-liquid interfacial tension (γSL), particle-solid interfacial tension (γSP) and free energy of adhesion of particle to substrata (ΔFadh). The Gram-negative bacterium SW8 grown under carbon-limited conditions was used as a model particle. On high-energy surfaces, γs was highest in approaches with water whereas on synthetic medium-energy materials all approaches produced similar estimates for γs. On many mineral surfaces, however, approaches with α-br provided significantly larger γs than those with di. On low-energy surfaces, apolar liquids generally provided higher estimates for γs than polar liquids. The generally similar trends for γs in approaches with polar liquids differed from those observed in approaches with apolar liquids. In GME, the values of γsd correlated only between pairs with the same apolar liquid. The trends for γslw and γsd were similar in approaches with di. γsp determined with polar liquids generally correlated with each other and the trends were similar to those of γs−, but not γs+ · γs− was practically identical with γsp calculated with the GME pair f/w, as were γs calculated with di or α-br in ES and γslw obtained in triplets with the respective apolar liquid. The trends of γs-ES of water and formamide were similar to those of γs− and of γsp in GME pairs involving polar liquids. γSL, γSP and ΔFadh of approaches involving water contact angles differed considerably; however, similar trends were obtained with all approaches for γSL and with four approaches for ΔFadh. Every approach produced a unique trend for γSP. Results obtained with ES on most interfaces were not consistent with fundamental premises of the equation of state theory and values for the dispersive component of surface free energy appeared to be generally underestimated in the GME approach. LWAB w/f/di was found to be the most suitable approach for surface analysis of the interfaces investigated in this work.