Abstract: The intermolecular interactions and interfacial behaviours of the bio-based surfactant sophrolipid (SL) and three high interfacial activity surfactants (SA) with different alkyl chain lengths, dodecyl, tetradecyl and hexadecyl(C₁₂,C₁₄,C₁₆), in a mixed system were investigated from the aspects of surface tension, oil/water interfacial tension, contact angle and atomic force microscopy, respectively. The results showed that the intermolecular synergistic interactions of the mixed SL/SA systems were gradually enhanced with the increase of the alkyl chain length of the SA. The mixed SL/C₁₆SA systems can effectively reduce the oil/water interfacial tension between the system and the victorious thick oil when mixed with sophrolipid. With the increase of the molar fraction of C₁₆SA (X_C16SA), the turbidity of the mixed system was gradually reduced, the particle size of the aggregates formed by the surfactant in the water was gradually reduced, the wetting and inversion ability of the system on the oily surface was enhanced, and the penetration rate of the system on the porous oily substrate was faster. When X_C16SA>0.2 for the SL/C₁₆SA hybrid system,the micelle surface charge density decreases,the absolute value of the zeta potential decreases,and the size of the particles formed by deposition gradually increases, and when X_C16SA> 0.7, the SL/C₁₆SA hybrid system had the better interfacial activity, which can be used for oil field exploitation.

Key words: sophrolipid, surfactant, intermolecular interaction, interfacial behavior