Effect of counterions on anionic fluorocarbon surfactant micelles by dielectric spectroscopy

Abstract

The dielectric spectra of sodium perfluorooctanoate (NaPFO), ammonium perfluorooctanoate (APFO) and tetraalkylammonium perfluorooctanoate (C₇F₁₅COON(C_nH_2n+1)₄, n = 1, 2, 3, 4, namely, TMPFO, TEPFO, TPPFO and TBPFO) were studied in the frequency range from 40 Hz to 110 MHz. An obvious dielectric relaxation was observed in each aqueous system whose low-frequency limit of relative permittivity (ε_l) was divided into two groups based on their dependence on concentration, except there were two relaxations for TBPFO. Furthermore, their relaxation mechanism was analyzed and attributed to the radial diffusion of the free counterions in the diffuse layer. What's more, combined with the average radius of these micelles obtained on the basis of the Grosse's model, the difference between these two groups and their structural information were speculated. It was proved that the type of counterion has an important influence on the structure and properties of fluorocarbon surfactants.