Counterion-coupled gemini surfactants based on propoxylated hexamethylenediamine and fatty acids: Theory and application

Novel cocogem surfactants are synthesized from N, N′-di-(propane-2-olyl)-1,6-hexanediamine and six different fatty acids (capric, lauric, myristic, palmitic, stearic, oleic). N,N′-di-(propane-2-olyl)-1,6-hexanediamine is the product of the reaction between hexamethylenediamine and propylene oxide in 1:2 mol ratio. Important surface activity parameters, such as critical micelle concentration (CMC), negative logarithm of the concentration required for 20 mN/m reduction in surface tension (pC₂₀), surface pressure (π_CMC), surface excess concentration (Γ_max) of the synthesized surfactants are determined. Application properties such as foamability, foam stability, and emulsion stability of cocogem surfactants are measured. Absorption and micellization Gibbs energies are calculated. Surfactants having palmitic and stearic tails display quite high foam and emulsion stability. Viscosity measurement data are utilized to explain the high foam persistence and emulsion stability of these surfactants. The cocogem surfactant based on myristic acid is able to show surface tension reduction performance comparable to that of commercial fluorinated surfactants. Computational studies are performed in density functional theory (DFT) B3LYP functional and 6-31G* basis set for optimizing the synthesized surfactant structures and determining their formation free energies.