Synergism of Surfactant Mixture in Lowering Vapor-Liquid Interfacial Tension

CS Chen and HG Zhang and XR Zhang, LANGMUIR, 39, 11828-11838 (2023).

DOI: 10.1021/acs.langmuir.3c01565

Through employing molecular dynamics, in this work, westudy howa two- component surfactant mixture cooperatively reduces the interfacialtension of a flat vapor-liquid interface. Our simulation resultsshow that in the presence of a given insoluble surfactant, addinga secondary surfactant would either further reduce interfacial tension,indicating a positive synergistic effect, or increase the interfacialtension instead, indicating a negative synergistic effect. The synergismof the surfactant mixture in lowering surface tension is found todepend strongly on the structure complementary effect between differentsurfactant components. The synergistic mechanisms are then interpretedwith minimization of the bending free energy of the composite surfactantmonolayer via cooperatively changing the monolayer spontaneous curvature.By roughly describing the monolayer spontaneous curvature with thebalanced distribution of surfactant heads and tails, we confirm thatthe positive synergistic effect in lowering surface tension is featuredwith the increasingly symmetric head-tail distributions, whilethe negative synergistic effect is featured with the increasinglyasymmetric head-tail distributions. Furthermore, our simulationresults indicate that minimal interfacial tension can only be observedwhen the spontaneous curvature is nearly zero.

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