Colloidal particles derived from a complex of phosphotungstic acid and ethoxylated surfactants

Abstract

Stable, colloidal sols of submicron size were prepared by titration of aqueous solutions of alkylene oxide surfactants with phosphotungstic acid, H3PW12O40 (PTA), followed by neutralization with ammonium or potassium hydroxide. The stoichiometry of the complex between phosphotungstic acid and the ethoxylated surfactant was determined by 1H and 31P NMR and was dependent upon the degree of ethoxylation. For example, in the ethoxylated octylphenol having 9–10 ethylene oxide units, Triton X-100, the mole ratio of surfactant to PTA was 4.5. In the ethoxylated octylphenol having 70 ethylene oxide units, Triton X-705, the mole ratio of surfactant to PTA was 1. Prior to nucleation of particles, phosphotungstic acid forms an apparent yellow charge transfer complex with ethoxylated alkylphenol surfactants, typified by Triton X-405. This complex is characterized by an absorption spectrum that is the sum of the spectra of Triton X-405 and PTA with a very weak shoulder at 400–500 nm. Particles were nearly monodisperse and their size was dependent on the nonionic surfactant employed, the heteropolyacid, and the rate of addition of heteropolyacid solution.