A nuclear magnetic resonance investigation of the micellar properties of aseries of sodium cyclohexylalkanoates

The micellar properties of a family of surfactants, the sodium cyclohexylal kanoates, have been investigated in aqueous solution using multinuclear NMR spectroscopy. 0-13 chemical shift measurements have been used to determine both the cmc values and the micellar aggregation numbers (N-s values) of t hese surfactant. The cmc values and the degrees of counterion binding were estimated from Na-23 chemical shift measurements. The critical micelle conc entrations (cmc's) and the aggregation numbers determined from the NMR expe riments indicate that these amphiphiles have high cmc's and low aggregation numbers when compared to other single-headed surfactants (most notably the sodium alkanoates). The conformational changes incurred by the carbon atom s upon micelle formation have been deduced from the C-13 chemical shift dif ferences (delta(surf, mic) - delta(surf, aq)). These results are used to di scuss the formation of the aggregates of the sodium cyclohexylalkanoate sur factants as a function of the length of the alkanoate side chain.