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Measurements of the surface tension, density and viscosity of sodium dodecyl sulfate (SDS) and rhamnolipid (RL) mixtures were carried out in aqueous solution. From the obtained results, composition of mixed surface layer at the water–air interface, mixed micelles, parameter of intermolecular interactions, activity of SDS and RL in the surface layer and micelles, Gibbs standard free energy of adsorption and micellization as well as Gibbs free energy of SDS and RL mixing in the surface layer and micelles were established. These parameters were discussed in the light of independent adsorption of SDS and RL and the size of their molecules as well as the area in contact with water molecules. A correlation between the number of water molecules in contact with those of SDS and RL and standard free energy of adsorption as well as micellization of these surfactants was observed. A correlation between the apparent and partial molar volumes of RL and SDS in their mixture and size of surfactant molecules as well as the average distance between molecules was also found. The parameter of intermolecular interactions indicates that there is a synergetic effect in the reduction of water surface tension and micelle formation.Electronic supplementary materialThe online version of this article (doi:10.1007/s11743-016-1916-6) contains supplementary material, which is available to authorized users.

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From year to year natural surfactants are gaining ever growing awareness because of their valuable properties (in the absence of negative impact on the environment, as with the use of synthetic surface active agents). In the group of surfactants of natural origin there are surface active agents produced by microorganisms (biosurfactants) or compounds having a natural part (hydrophilic head and/or hydrophobic tail) [1]. This review includes the short characteristic of surfactants with sugar-head group in their structure called sugar-based surfactants. The structure, properties and some applications of these surfactants are described in this paper.