Synthesis and physicochemical properties of nonionic Gemini surfactants with a sulfonate spacer

We have prepared a series of novel nonionic Gemini surfactants, featuring sulfonate spacers, from maleic anhydride (MA), polyethylene glycol (PEG400), sodium hydrogen sulfite, and various fatty acids (C8–C18). We measured the surface activities of these compounds in terms of the critical micelle concentration (CMC), the surface tension at the CMC (γcmc), the surface excess concentration (Γcmc), the surface area occupied per molecule (Acmc), and the standard free energy of micellization per mole of monomer unit (ΔG°m). We used pyrene fluorescence spectroscopy to characterize the hydrophobicity of the aggregates of nonionic Gemini surfactants. We measured the CMCs from the intensity ratio of the emission of pyrene in the nonionic Gemini surfactant solutions. In addition, we studied the surface activity in terms of the emulsification of 10% (w/w) olive oil in nonionic Gemini surfactant solutions. Shorter hydrophobic chains provided more-stable emulsions.