title: Influence of charge exchange in acidic aqueous and alcoholic titania dispersions on viscosity.
abstract: Charging effects resulting from adsorption of acid, acid anions, and protons on titania (anatase) surfaces in anhydrous or mixed alcohol-water dispersions is summarized. The suddenly enhanced conductivity as compared to titania-free solutions has previously been modeled and explained as surface-induced electrolytic dissociation (SIED) of weak acids. This model and recently published results identifying concurrent surface-induced liquid (solvent) dissociation (SILD) are evaluated with experimentally determined conductivity and pH of solutions, zeta-potential of particles, and viscosity of dispersions. Titania (0-25wt%)-alcohol (methanol, ethanol, and propanol) dispersions mixed with (0-100wt%) water were acidified with oxalic, phosphoric, and sulfuric acids. It was found that the experimental results could in many cases be condensed to master curves representing extensive experimental results. These curves reveal that major properties of the systems appear within three concentration regions were different mechanisms (SILD, surface-induced liquid dissociation; SIAD, surface-induced acid dissociation) and charge rearrangement were found to be simultaneously active. In particular, zeta-potential - pH and viscosity - pH curves are in acidified non-polar solvents mirror images to those dependencies observed in aqueous dispersions to which hydroxyl is added. The results suggest that multiple dispersion and adsorption equilibria should be considered in order to characterize the presented exceptionally extensive and complex experimental results.
authors.affiliation: Laboratory of Physical Chemistry, Center of Excellence for Functional Materials, Åbo Akademi University, FIN 20500 Åbo (Turku), Finland. Electronic address: Jarl.Rosenholm@abo.fi.
authors.forename: Jarl B
authors.initials: JB
authors.lastname: Rosenholm
authors.affiliation: Laboratory of Physical Chemistry, Center of Excellence for Functional Materials, Åbo Akademi University, FIN 20500 Åbo (Turku), Finland.
authors.forename: Per
authors.initials: P
authors.lastname: Dahlsten
keywords: Charge exchange; Dispersion stability; Solvent/acid adsorption; Solvent/acid dissociation; Surface-induced dissociation (SIED, SILD, SIAD)