Abstract

The ability of six humic acids (HAs) to form pseudomicellar structures in aqueous solution was evaluated by five techniques: size exclusion chromatography; pyrene fluorescence enhancement; the pyreneI₁/I₃ ratio; the cloud point of dilute HA solutions; and the fluorescence anisotropy of HAs. Soil HAs were found to aggregate most easily, both on microscopic and macroscopic scales. The formation of amphiphilic structures was chiefly related to HA–solvent interactions: highly solvated HAs aggregated poorly, while a lignite derived material underwent intermolecular, rather than intramolecular, rearrangements. A newly discovered algal HA was found to have minimal aggregative properties.