Surface dilational viscoelasticity of C14EO8 micellar solution studied by bubble profile analysis tensiometry

The experimental dependences of viscoelasticity modulus and phase angle as a function of frequency for various C14EO8 concentrations at the critical micelle concentration (cmc) of 7 mu mol/L and far above the cmc (up to 70 x cmc) were studied using the buoyant bubble profile analysis method. With increasing C14EO8 concentration the viscoelasticity modulus decreases and the phase angle increases. At the highest surfactant concentrations, the phase angle was more than 45 degrees. For the theoretical description of the equilibrium surface tension isotherm and the limiting elasticity modulus, a combined theoretical model was used considering surface reorientation and molecular compression. To analyze the experimental dependencies of the viscoelasticity modulus and phase angle on frequency, a model proposed by Joos for fast micellar kinetics was applied. This theory agrees well with the experimental data of the viscoelasticity modulus obtained for all concentrations of the studied nonionic surfactant C14EO8.