Adsorption layer characteristics of Tritons surfactants: 3. Dilational visco-elasticity

The dilational rheology of adsorption layers of four Tritons (TX45, TX100, TX165 and TX405) was studied by using the oscillating drop and bubble profile methods at frequencies between 0.005 Hz and 0.2 Hz. It is shown that the visco-elasticity modulus |E| for TX45 solutions can be excellently described by a rigorous reorientation model. For the description of the dilational rheology of TX100 adsorption layers an additional compressibility of the adsorbed molecules at high surface pressure has to be considered. Also the phase angle ϕ as a function of concentration can be described quantitatively for the two Tritons. For TX165 and TX405, having a much larger number of ethylene oxide units, the models is not in good agreement with the experimental data. For these molecules, obviously the presence of homologues in the surfactant samples play a larger role and the dependencies of |E|(c) and ϕ(c) show features as common for surfactant mixtures.