Effect of linking groups and hydrophobic groups on properties of sulfate Gemini surfactants

Abstract

From the perspective of molecular design, a series of sulfate Gemini surfactants with different hydrophobic chains and linking groups were synthesized by etherification, ring opening and sulfation. The structures of the products were characterized by IR and 1H NMR. The synthesized sulfate Gemini surfactants had good heat resistance, especially the surfactants with rigid linking groups, measured by thermogravimetric analysis. The synthetic surfactants had low Krafft points, wherein the Krafft points of the surfactants with a carbon chain of 12 were <0 °C. With increasing hydrophobic carbon chain length or decreasing methylene number of linker, their CMC and γcmc first decreased and then increased. The γcmc of surfactants with rigid linking groups were higher and their CMCs were lower. It is analyzed by the calculated surface activity parameters (pC20, Γmax, Amin) that with increasing hydrophobic chain length, the surface activity of synthetic surfactants increased first and then decreased, and the surfactant with hydrophobic carbon chain C14 had the best surface activity. The influences of the length of the linking group and the hydrophobic group on the emulsifying capacity, wetting property, calcium soap dispersion and foam property of the surfactants were also analyzed. It was an attempt to explore and design excellent Gemini surfactants.