Anionic Gemini surfactants: Synthesis and aggregation properties in aqueous solutions

A series of anionic Gemini surfactants with the same structure except the spacer length of the polyethylene chain have been synthesized based on nonylphenol (NP). The critical micelle concentration (cmc) of the title surfactants in aqueous solutions has been investigated using drop volume method. Surface tension at cmc (γcmc) and C20 were also obtained. It was found that the cmc of Gemini surfactants has much lower values compared with those conventional monomeric ones and the value of cmc decreases with the increase of carbon atom numbers of the spacer. C20 values indicate that Gemini surfactants are more efficient at reducing the surface tension of water than conventional ionic ones. The aggregation number (N) was determined with intrinsic fluorescence quenching method using methylviologen (MV2+) as the quencher. N of the surfactant series all goes through a maximum upon the increase of the concentration of the Gemini surfactants for the appearance of new phase-formation of liquid crystal phase.