Surface Properties of Aqueous Solutions of Mixtures of Sodium Dodecyl Sulphate and Linalool under Equilibrium and Dynamic Conditions

The effect of the concentration and of the composition of mixtures of a traditional surfactant sodium dodecyl sulphate (SDS) and of linalool (LL), a volatile fragrance with surface-active properties, on the surface tension of their aqueous solutions has been studied. Surface tension was measured both under equilibrium and under dynamic conditions of the surface formation (in a time range of 20 ms to 20 s), as well as during evaporation of solutions. It has been shown that under equilibrium conditions the individual surfactants and their mixtures exhibit similar surface activity. On the contrary, under dynamic conditions LL decreases surface tension faster in comparison to SDS, so that the surface tension of mixed solutions is determined by adsorption of LL. A synergetic effect on the decreasing of the surface tension at high surfactants concentration is observed both under dynamic and under equilibrium conditions. Upon evaporation of droplets of mixed solutions at a time interval of about minutes, the composition of the adsorption layer changes as a result of desorption of LL into the gas phase, so that the surface tension is determined by the adsorption of the second component—SDS.