Surface tension, interfacial tension and emulsification of sodium dodecyl sulfate extended surfactant

• The IFT between C12PmS solution and decane all reaches ultralow value at optimum NaCl concentration.
• Ultralow IFT between C12P8S and crude oil could be reached in wide range of CaCl2 concentrations without alkaline.
• Ultralow IFT between C12P8E2S and crude oil could be reached without alkaline in wide range of surfactant concentrations.
• Crude oil could be emulsified by C12PmS solutions in a wide range of CaCl2 concentrations.

surface tension, interfacial tension and emulsification of extended surfactants, sodium dodecyl polypropylene oxide sulfate (C12PmS, m = 4, 8 and 12) and sodium dodecyl polypropylene oxide–polyethylene oxide sulfate (C12P8E2S), were investigated. The influence factors such as propylene oxide (PO) number, calcium chloride (CaCl2) concentration, and surfactant concentration were studied in detail. It was found that surface activity of C12PmS increases with the increase of number of PO units. The interfacial tension (IFT) between C12PmS solution and decane all reaches ultralow range (<10−2 mN/m) at optimum NaCl concentration. Ultralow IFT between C12P8S solution and Shengli crude oil could be reached in a wide range of CaCl2 concentrations without alkali. IFT between C12P8E2S solution and crude oil could reach ultralow value without alkali in a wide range of CaCl2 concentrations and surfactant concentrations. For C12P8S and C12P8E2S, oil drop during the measurement of IFT was lengthened and broken in which IFT was below 10−4 mN/m. Emulsion between crude oil and C12PmS solution could form in a wide range of CaCl2 concentrations. Low IFT is not related to emulsion formation. However, ultralow IFT helps to increase the emulsion stability.

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