Measurement of the surface dilational viscoelasticity of adsorbed layers with a capillary pressure tensiometer

A capillary pressure tensiometer has been set up to measure the dilational surface viscoelasticity in liquid-air and liquid-liquid surfactant systems, according to the oscillating drop/bubble technique. A specific model which allows the dilational surface viscoelasticity to be inferred from the acquired pressure data is proposed and the critical points concerning the experimental procedure and the data interpretation are discussed. In order to optimize the method, side measurements utilizing the same tensiometer to evaluate equilibrium interfacial tensions and the system compressibility are coupled to this technique. Some nonionic surfactants, polyoxyethylene glycol ethers (C(i)EO(j)) and alkyl dimethyl phosphine oxide (C(12)DMPO), at water-air and water-hexane interfaces have been investigated by this technique. The measured dynamic dilational viscoelasticities are compared with the predictions of theoretical models which consider different adsorption mechanisms.