A series of anionic gemini surfactants with the same structure except the spacer nature have been studied. Their solution properties were characterized by the equilibrium surface tension and intrinsic fluorescence quenching method. The critical micelle concentrations (CMC), surface tension at cmc, C 20 , and the micelle aggregation number (N) were obtained. The surface tension measurements indicate that these gemini surfactants have much lower cmc values and great efficiency in lowering the surface tension of water compared with those of conventional monomeric surfactants. Furthermore, the standard free energy of micellization for anionic gemini surfactants was also determined. The results showed that the nature of the spacer has an important effect on the aggregation properties of gemini surfactants in aqueous solutions. The surfactant with a hydrophilic, flexible spacer was more readily able to form micelle compared with the surfactant with a hydrophobic, rigid spacer, which leads to a lower CMC value, larger N, more negative free energy of micellization, and a more closely packed micelle structure.
The interaction of dyes with a sulfonated Gemini surfactant was investigated in aqueous solution using Förster resonance energy transfer with acridine orange (AO) as a donor and rhodamine B (RhB) as an acceptor. Surface tension results showed that AO and RhB have different effects on the self-assembly of the Gemini surfactant, with AO giving a higher critical micelle concentration (cmc) and lower surface tension, while the opposite was observed for RhB. Energy transfer from AO to RhB was observed in the presence of the surfactant, and the energy transfer efficiency initially improved with increased surfactant concentration but then decreased significantly when the surfactant reached a higher concentration due to the formation of larger aggregates, which increased the average distance between AO and RhB. Dynamic light scattering demonstrated the existence of these large aggregates. Moreover, simulations using dissipative particle dynamics supported the experimental results.
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