Micelle growth of cationic gemini surfactants studied by NMR and by time-resolved fluorescence quenching

• Micelle growth of a series of stable and ester-containing cationic gemini surfactants has been studied.
• The spacer length is of importance for the development of micelle growth on increasing the surfactant concentration.
• The presence of ester bond in alkyl tail and a hydroxyl group in the spacer unit does not affect the micelle growth.

The micelle growth of a series of five cationic gemini surfactants has been investigated by time-resolved fluorescence quenching (TRFQ) and by two NMR techniques, line width analysis and diffusometry. The surfactant series was designed such that the effect of a number of variables could be assessed: length of the spacer unit, presence of ester bonds in the tails close to the head groups, and presence of a hydroxyl group in the spacer. For the gemini with long spacer, the micelles remained relatively small in size upon an increase of the concentration. The gemini surfactants with short spacer, on the other hand, showed a considerable micellar growth as the concentration was raised. It is of particular interest that the relatively simple line width analysis of one dimensional 1H NMR spectra gave qualitatively the same results as the more sophisticated TRFQ and NMR diffusometry techniques.

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