Effect of electrolytes on the interfacial rheological behaviors of N-cocoyl glycinate

Abstract

Amino acid surfactants have been applied to numerous areas of science and are often used in the presence of electrolytes. In this study, the interfacial rheological behaviors of potassium N-cocoyl glycinate (KCGl), an amino acid surfactant, with three kinds of electrolytes (KCl, CaCl₂ and tetrabutylammonium bromide (TBABr)) have been investigated using the oscillating drop method. The interfacial tensions (IFTs) and dilational rheological parameters show that KCGl in conjunction with electrolytes has enhanced interfacial activity and stronger intermolecular interaction than pure KCGl, indicating that electrolytes contribute to denser molecular packing at the oil–aqueous interface. Interestingly, the butyl groups of TBA⁺ hinder closer arrangement of molecules at the interface, hindering KCGl ability to form a tightly packed layer compared with K⁺ and Ca²⁺ electrolytes. The relaxation processes, such as diffusion exchange of surfactant molecules between the aqueous phase and interface, are more probable to occur. Therefore, more viscoelastic films are formed in the presence of TBABr.

Graphical Abstract

Keywords:

• Amino acid surfactant
• interface
• interfacial dilational rheology
• interfacial tension
• interfacial viscoelasticity

Additional information

Funding

This work was financially supported by the Beijing Natural Science Foundation of China [2204076], National Key R&D Program of China [2017YFB0308700], Beijing Outstanding Talent Training Fundation [Young Backbone Project, 2018000020124G036], the National Natural Science Foundation of China [21676003, 21902004],  Science and Technology Plan of Beijing Municipal Education Commission [KM202010011003] and Youth Foundation of Beijing Technology and Business University [PXM2019_014213_000007].