Effects of Spacers on Surface Activities and Aggregation Properties of Anionic Gemini Surfactants

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Abstract
This present article employs four anionic Gemini surfactants with different spacer groups and investigates their physicochemical and aggregation properties. The critical micelle concentration (CMC), surface tension at CMC (γCMC) and C20 of these surfactants have been investigated using the du Nouy ring method. The aggregation number (N) was determined with intrinsic fluorescence quenching method using pyrene as a fluorescence probe and benzophenone as a quencher. Results show that these anionic Gemini surfactants have lower CMC and C20 values compared with those conventional ones and show higher surface activity. As expected, the spacer plays an important role in the aggregation properties of Gemini surfactants. Under experimental conditions, Gemini B–D with an alkoxylated group as spacer has a lower CMC and a higher aggregation number than Gemini A with methylene as spacer. For Gemini B–D, the CMC and aggregation number values decrease with the increasing flexible spacer length. The micropolarity also affects the aggregation of the present anionic Gemini surfactants. The micropolarity of micelle becomes low when the concentration of surfactants increases. Aggregation numbers of surfactants increase and fluorescence intensities decrease with the increasing concentration of NaCl. These results will help us to understand the relationship between the architectures of Gemini surfactants and their various properties in aqueous solution.

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