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Author Notes:

Fredric M. Menger, Department of Chemistry, Emory University, Atlanta, GA 30322, USA, Email: menger@emory.edu


Research Funding:

The authors appreciate the support by the National Institutes of Health.

Electrostatic Binding among Equilibrating 2-D and 3-D Self-Assemblies


Journal Title:

Journal of the American Chemical Society


Volume 131, Number 19


, Pages 6672-6673

Type of Work:

Article | Post-print: After Peer Review


Six organic additives, each bearing a different number of anionic charges, were added to a large excess of cationic surfactant (dodecyltrimethylammonium bromide, DTAB). The surface-tension vs. log [DTAB] plot for solutions containing DTAB/trianion = 15:1 showed an abrupt break (routinely taken as the critical micelle concentration, CMC) at 2.9 mM. This constitutes a 5-fold decrease compared with a CMC of 15 mM for pure aqueous DTAB. There is a 10-fold decrease in the break-point concentration caused by a mere 3 mol-% of hexanion. Corresponding CMC values from DTAB/trianion mixtures, measured by both conductivity and diffusion-NMR, gave normal values of 14 mM. The unusual discrepancy between the CMC based on surface tension and on the two “bulk” methods was attributed to saturation of the air/water interface by a DTAB/trianion complex far below the concentration at which the micelles form. Thus, the sharp break seen in surface-tension “CMC plots” need not in fact attest to actual micelle formation as is almost universally assumed in colloid chemistry.

Copyright information:

© 2009 American Chemical Society

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