LAUSR

Abstract Stimulus-responsive surfactant is becoming a hot research topic with high controllability and excellent emulsifying properties. In this work, an amidine naphthenate surfactant was synthesized for the first time by the reaction between alkyl amidine and naphthenic acid. Surface activity and emulsion performance of this novel surfactant in oil/water emulsion were investigated. Compared with the previously synthesized amidine bicarbonate surfactants, amidine naphthenate surfactants exhibited a superior emulsification performance above 60 °C due to their lower critical micelle concentration (CMC) and interfacial tension (IFT). The presence of two long alkyl groups is recognized as the main reason for its superior properties than amidine bicarbonate having only one long alkyl group. Increased hydrophobic interactions between the long alkyl chains and electrostatic interactions between the ionic head groups lead to the easier formation of micelles. Notably, the amidine naphthenate has a characteristic of CO2-responsive property. The amidine naphthenate emulsion can be demulsified by CO2 bubbling which destroys the chemical structure of amidine naphthenate, accompanied by the formation of amidine cations and naphthenic acids. Then, the emulsion was completely demulsified due to the demulsification effect of naphthenic acid. Therefore, the synthesized amidine naphthenate surfactant possesses not only high interface activity but also CO2 responsive property, which endows it an extensive application prospect for enhanced oil recovery (EOR) operations in the oil industry.