Systematic investigation of ionic liquid-type gemini surfactants and their abnormal salt effects on the interfacial tension of a water/model oil system.

Ionic liquid-type gemini surfactants have the advantages of both a gemini surfactant and a surface active ionic liquid and have been widely applied in multiple fields. A series of ionic liquid-type gemini imidazolium surfactants with a four-methylene spacer group (CnD, n = 8, 10, 12) was introduced for chemical enhanced oil recovery. The CnD had great effects on the interfacial tension (IFT) between water and a model oil (toluene and n-decane, v:v = 1:1), which appears to be closely related to the hydrocarbon chain length. Interestingly, the addition of NaCl caused abnormal variations in the IFT values. Based on the phase behaviour of the surfactants in solution, we proposed a mechanism to explain the relationship between the salt effects and the surfactant concentration, which was verified by measuring the IFT values between the surfactant solutions and a homologous series of alkanes with different alkane carbon numbers. The temperature effects were also evaluated to further explore the effects of the CnD molecular structures on the IFT. [ABSTRACT FROM AUTHOR]