Role of molecular interactions between biosurfactant surfactin and alkylbenzenesulfonate

Abstract

Interaction between biosurfactant, [Glu1,Asp5]-iso-surfactin, and widely used synthetic surfactant, alkylbenzenesulfonate, will offer instructions for the applications of their binary systems. Physicochemical properties of mixed monolayers and mixed micelles, and their dependence on mixing ratios were explored by using of surface tension measurements, dynamic light scattering, and thermodynamic calculations. Results showed that synergism occurred when the mole ratio of surfactin to alkylbenzenesulfonate absorbed at air/water interface tends to be 1:1. Antagonism between surfactin and alkylbenzenesulfonate appeared when the air/water interface was covered nearly by one kind of surfactants. Surfactin constitutes predominant part both at air/water interface and in mixed micelles when its hydrophobicity is much higher than alkyl benzenesulfonate. Steric structure shows greater impact than the length of alkyl chain on the interaction between surfactin and alkylzbenzenesulfonate. With temperature increasing, the fraction of surfactin in the mixed monolayer decreased. While in mixed micelles, interaction between surfactin and alkyl benzenesulfonate didn’t show direct correlation with constitution of individual surfactant components, but largely with molecule structure, micelle size, and steric hindrance.

Graphical Abstract

Keywords:

• Biosurfactant
• surfactin
• alkylbenzenesulfonate
• molecular interactions
• aggregation behavior
• mixing ratio

Disclosure statement

The authors declare that they have no conflict of interest.

Additional information

Funding

This research was supported by National Natural Science Foundation of China (Grant No. 51574125, 21203063) and the 863 program (Grant No. 2013AA064403), and the Fundamental Research Funds for the Central Universities of China.