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Interaction of a biosurfactant, Surfactin with a cationic Gemini surfactant in aqueous solution

Jin, Lei, Garamus, Vasil M., Liu, Fang, Xiao, Jingwen, Eckerlebe, Helmut, Willumeit-Römer, Regine, Mu, Bozhong, Zou, Aihua
Journal of colloid and interface science 2016 v.481 pp. 201-209
aqueous solutions, biosurfactants, bromides, light scattering, micelles, neutron diffraction, phosphates, surface tension, surfactin, synergism, turbidity
The interaction between biosurfactant Surfactin and cationic Gemini surfactant ethanediyl-1,3-bis(dodecyldimethylammonium bromide) (abbreviated as 12-3-12) was investigated using turbidity, surface tension, dynamic light scattering (DLS) and small angle neutron scattering (SANS). Analysis of critical micelle concentration (CMC) values in Surfactin/12-3-12 mixture indicates that there is synergism in formation of mixed Surfactin/12-3-12 micelles. Although Surfactin and 12-3-12 are oppositely charged in phosphate buffer solution (PBS, pH7.4), there are no precipitates observed at the concentrations below the CMC of Surfactin/12-3-12 system. However, at the concentration above CMC value, the Surfactin/12-3-12 mixture is severely turbid with high 12-3-12 content. DLS and SANS measurements follow the size and shape changes of mixed Surfactin/12-3-12 aggregates from small spherical micelles via elongated aggregates to large bulk complexes with increasing fraction of Gemini surfactant.