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.

Emulsification properties of the average droplet diameter increased from 1000 to 3200 nm after 6 h. For product (I), the droplet diameter was more stable relative to those of the other. Thus, the alkyl chain length affected the stability. From the adsorption isotherms, it appears that the emulsions prepared using 10% (w/w) of the various Gemini surfactants were formed under conditions that led to full coverage of each droplet's surface. Nevertheless, the stability was strongly dependent on the alkyl chain length.Figure optionsDownload as PowerPoint slideHighlights
► The IR spectrum displayed the adsorption band at 2854 cm−1 and 2924 cm−1 increased upon increasing the alkyl chain length.
► Fluorescence Properties of the product I results indicate that aggregates formed in solution, leading to the decrease in the value of I1/I3.
► Using conductometry to measure the CMC of novel nonionic Gemini surfactants. An inflection point which it corresponds to the CMC.
► A decrease in the alkyl chain length resulted in an increase in the emulsifying ability in the average initial droplet diameter.
► The droplet diameter was more stable and an increase in the sharpness of the particle size distribution.