Adsorption and Aggregation Activity of Sodium Dodecyl Sulfate and Rhamnolipid Mixture

Diana Mańko,Anna Zdziennicka,Bronisław Jańczuk

doi:10.1007/s11743-016-1916-6

Diana Mańko, Anna Zdziennicka + Show 1 more

Open Access

https://doi.org/10.1007/s11743-016-1916-6

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Abstract

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.

Highlights

Surfactants are amphiphilic compounds which have very wide application due to their ability to reduce surface tension, increase solubility of many substances connected with micelle formation or detergency power [1, 2]
It appeared that both isotherms of surface tension calculated on the basis of independent adsorption of sodium dodecyl sulfate (SDS) and RL (Eq S2) as well as by using the Fainerman and Miller equation (Eq S3) [23, 24] are nearly the same as those measured if the concentration of one component of surfactant mixture is lower than that corresponding to its saturated monolayer at the water–air interface in the absence of another one
It is interesting to know the relation between the mole fraction of RL in the mixed monolayer calculated on the basis of the Gibbs surface excess concentration of particular components and that obtained on the basis of Hua, Rosen and Rubingh theory [1, 21, 22]. For this reason we considered the changes of the surface tension of aqueous solutions of SDS and RL mixture as a function of its concentration at mole fractions of RL in the mixture equal to 0.2, 0.5 and 0.8 (Fig. 5a)