Aggregation Behavior Of Gemini Surfactants In Aqueous And Nonaqueous Solution Studied By Molecular Spectroscopy

The order structural aggregate of surfactants plays an important role in life sciences, materials science and other advanced technological regions. Gemini surfactant is a novel amphiphilic molecule which is paid close attention because of its complicated aggregation behavior and delicate aggregation structure. In view of the importance of understanding the order molecular aggregate as well as the complicated aggregation of surfactant, it is necessary to develop the molecular spectroscopic technique to study the aggregation of surfactant. In this dissertation, we established three methods to investigate the aggregation behavior of gemini surfactants and their mixtures with other surfactants in aqueous or nonaqueous solution by molecular spectroscopic technique.1. The intrinsic fluorescence quenching technique was first developed for the determination of micellar aggregation number, which as well as the intrinsic absorption spectrum technique for the determination of cmc of aqueous surfactant solutions was based on the chromophore residue of gemini surfactant C11pPHCNa.The aggregation number N of gemini surfactant is considerably small due to its superior surface-activity. An extrinsic probe will cause significant perturbation in measurement of aggregation number. The disadvantage can be overcome by intrinsic fluorescence quenching technique, especially for the small micelles formed by gemini surfactants.2. 1-naphthylamine (1-NA)was developed as the better fluorescence probe than the generally used Pyrene to well characterize the transformation of the micelle structure over the region close to cmc. Two inflection points crossing about one order of magnitude in concentration appeared in the semilogarithmic plot ofλversus surfactant concentration C, which combining with the results of micellar aggregation number measurements showed the first inflection point corresponded to the critical micelle concentration (cmc) and the second one (Ccm) addressed the critical point of the micelle reaching dense structure.The transformation of micelles over the concentration range close to cmc characterized by 1-NA is of great help to understanding the relationship between the molecular structure and the self-assembly of surfactants, which, however, was not revealed before because the aggregation number N was generally examined at concentration several times of cmc.