Adsorption layer characteristics of mixed sodium dodecyl sulfate/C(n)EO(m) solutions 1. Dynamic and equilibrium surface tension.

Bubble profile analysis tensiometry is used to study the dynamic and equilibrium surface tensions of mixed sodium dodecyl sulfate (SDS)/C(12)EO(5) and SDS/C(14)EO(8) solutions. For the data analysis, a new theoretical model was employed, which assumes different adsorption mechanisms for each type of surfactants. In particular, the adsorption behavior of oxyethylated surfactants was described by the so-called reorientation model, which assumes two states of surfactant molecules with different molar areas in the surface layer, and additionally an intrinsic compressibility of the adsorbed layer. For the anionic surfactant SDS, a modified Frumkin adsorption model was assumed, which also accounts for the intrinsic compressibility. For the theoretical analysis of the dynamic surface tensions, the theoretical model was based on the numerical solution of Fick's diffusion equation for a spherical geometry of the bubble. The proposed set of theoretical models describes accurately and consistently the experimental results of the equilibrium and dynamic surface tensions of the studied mixed solutions.