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Abstract

BACKGROUND The amphiphilic character and surface activity endows silk fibroin the ability to reside at fluid interfaces and effectively stabilize emulsions. However, the influence factors and their actual effects for the interfacial viscoelasticity and stability of silk fibroin at the oil/water interface were less reported. In this paper, effect of ionic strength on the interfacial viscoelasticity, emulsification effectiveness and stability of silk fibroin at the oil/water interface was investigated in detail. RESULTS Higher ion concentration facilitates greater adsorption, stronger molecular interaction and faster structure reorganization of silk fibroin at the oil/water interface, thus causing quicker interfacial saturation adsorption, greater interfacial strength and lower interfacial structural fracture at large deformation. However, the presence of concentrated ions screens charges in silk fibroin molecules, and zeta potential decreases due to the electrostatic screening and ion binding effects, which may result in emulsion droplet coalescence and decrease of emulsion stability. CONCLUSION The positively charged ions significantly affect the interfacial elasticity and stability of silk fibroin layers at the oil/water interface due to the strong electrostatic interactions between counterions and negatively charged groups of silk fibroin.