New class of cocogem surfactants based on hexamethylenediamine, propylene oxide, and long chain carboxylic acids: Theory and application

Six cocogem surfactants were synthesized from N,N,Nʹ,Nʹ-tetra-(propane-2-olyl)-1,6-hexanediamine and higher monocarboxylic acids: capric, lauric, myristic, palmitic, stearic and oleic. N,N,Nʹ,Nʹ-tetra-(propane-2-olyl)-1,6-hexanediamine was synthesized from hexamethylenediamine and propylene oxide at room temperature, without utilizing any catalyst or solvent. Surface tension, conductivity, foaming ability, foam stability, emulsion stability, viscosity and density measurements were performed on aqueous solutions of all cocogem surfactants. Their surface activity and colloidal-chemical parameters such as critical micelle concentration (CMC), surface pressure at CMC (π_CMC), surface tension at CMC (γ_CMC), surface excess (Γ_max), concentration required for 20 mN/m reduction of surface tension (C₂₀), Gibbs energies of adsorption and micellization (ΔG_ad and ΔG_mic) were recorded and variation of these parameters based on hydrophobic chain length and structure was investigated experimentally and computationally. Synthesized surfactants with myristic, palmitic, and stearic tail continued to decrease surface tension even above CMC. The possible reason of this unusual behavior was determined based on computational studies. Surface activity parameters of cocogem surfactant with oleic tail disobeyed the general tendency established by other cocogems with saturated tail group. Palmitic and stearic acid based cocogem surfactants had good foam stability and the reason of this high foam stability was rationalized with high viscosity of their solutions.