An investigation of some aqueous solution properites of dodecylammonium, N, N-dimethyldodecylammonium, and N, N, N-trimethyldodecylammonium chlorides

MacNeil, Joseph Mark (1982) An investigation of some aqueous solution properites of dodecylammonium, N, N-dimethyldodecylammonium, and N, N, N-trimethyldodecylammonium chlorides. Masters thesis, Memorial University of Newfoundland.

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Abstract

Some aqueous micellar solutions of dodecylammonium chloride (DAC), dimethyldodeclyammonium chloride (DMDAC) and trimethyldodecylammonium chloride (TMDAC) have been characterized by the methods of analytic equilibrium ultracentrifugation and variable shear viscometry in the presence of simple salt. In solutions of DAC the micelles become large and anisotropic with increasing concentration and ionic strength. Equilibrium centrifugation in 0.1 M NaC1 shows that the micelles formed at the CMC are aggregates of only about 100 monomers but grow rapidly with increasing surfactant concentration until a larger micelle of about 350 monomers is formed. The size of the large micelles is extreamly sensitive to deprotonation and ionic strength but shows limited concentration dependence. The rheological characteristics of solutions of large micelles include a Newtonian region at low shear rates followed by an anomalous region in which the viscosity increases with increasing rate of shear. Shear thinning is observed at high shear rates. In contrast, a constant aggregation number of 100±10 has been obtained over a wide range of concentrations in solutions of DMDAC, TMDAC and some DAC-TMDAC mixtures at ionic strengths as high as 0.2 M. The same value is obtained in solutions of DAC at ionic strengths less than about 0.2 M. This remarkable result follows from an analysis of the non-ideal behavior of these solutions in the centrifuge. The theory is based on a detailed description of the charge and salt effects, pair interactions and the macroscopic electric field which developes in the cell. Theoretical fit of the data also provides an estimate of an effective charge parameter which varies with ionic strength and head group in the order TMDAC>DMDAC>DAC. Intermediate values are obtained in mixed DAC-TMDAC solutions. Comparison of an estimated fractional surface charge, obtained by making Henry's correction to the charge parameter, with the values obtained from electrochemical measurements on solutions of large DAC micelles indicates that a critical value, above which large micelles will not form, is 0.25.

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