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 ( γ s) and its components ( γ s p = polar and γ s d = apolar components in GME as well as γ s lw, γ s − and γ s + = Lifschitz-van der Waals, electron-donor and electron-acceptor components in LWAB) in addition to solid-liquid interfacial tension ( γ SL), particle-solid interfacial tension ( γ SP) and free energy of adhesion of particle to substrata ( ΔF adh). The Gram-negative bacterium SW8 grown under carbon-limited conditions was used as a model particle. On high-energy surfaces, γ s was highest in approaches with water whereas on synthetic medium-energy materials all approaches produced similar estimates for γ s. On many mineral surfaces, however, approaches with α-br provided significantly larger γ s than those with di. On low-energy surfaces, apolar liquids generally provided higher estimates for γ s than polar liquids. The generally similar trends for γ s in approaches with polar liquids differed from those observed in approaches with apolar liquids. In GME, the values of γ s d correlated only between pairs with the same apolar liquid. The trends for γ s lw and γ s d were similar in approaches with di. γ s p determined with polar liquids generally correlated with each other and the trends were similar to those of γ s −, but not γ s + · γ s − was practically identical with γ s p calculated with the GME pair f/w, as were γ s calculated with di or α-br in ES and γ s lw obtained in triplets with the respective apolar liquid. The trends of γ s-ES of water and formamide were similar to those of γ s − and of γ s p in GME pairs involving polar liquids. γ SL, γ SP and ΔF adh of approaches involving water contact angles differed considerably; however, similar trends were obtained with all approaches for γ SL and with four approaches for ΔF adh. Every approach produced a unique trend for γ SP. 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.