Effects of protonation on the thermodynamic properties of alkyl dimethylamine oxides

The effects of protonation on alkyldimethyl amine oxide micelles are review ed, mainly with regard to dodecyl and tetradecyl homologs. The topics discu ssed are hydrogen ion titration properties, critical micelle concentration (CMC), area per surfactant and micelle aggregation number. A hydrogen bond hypothesis is proposed to interpret the several characteristic results asso ciated with protonation: between two cationic species as well as between th e non-ionic-cationic pair. The dipole-dipole interaction of the non-ionic m icelle is discussed in relation to both: (a) the unusually high CMC values of the non-ionic micelles compared with other non-ionic surfactants with th e same hydrocarbon chain; and (b) the reversal of the stability of the non- ionic and the cationic micelles at high ionic strengths. Two different appr oaches of the salting out effect on the ionic micelles are compared, the Ch an-Mukerjee approach and ours, in relation to the non-linear Corrin-Harkins relation. The obtained salting out constants of the surfactants carrying a dodecyl chain decreased as the head group becomes more polar. Infrared and C-13-NMR spectra data are examined from the point of the specific interact ion claimed by the hydrogen bond model. Mixed surfactant systems including amine oxides and the solid state phase behavior of amine oxides are both br iefly reviewed. (C) 2000 Elsevier Science B.V. All rights reserved.