Interactions and stability of foam films from pentaethyleneglycol monodecyl ether

Foam films stabilized with the non-ionic surfactant pentaethylenglycol monodecyl ether C10E5 were studied. The film thickness, the contact angle between the film and the meniscus and the mean life time (a measure of film stability) of the films were measured. Films with a thickness of 78 nm were formed at low electrolyte concentrations. The film thickness decreased with increasing concentration of NaCl in the film forming solution. This proves the existence of an electrical double layer potential at the film surfaces even though the film was formed from a non-ionic surfactant. An electrostatic double layer potential of 39 mV was obtained from the data. Newton black films (NBF) with a constant thickness of about 6 nm were formed above an electrolyte concentration of 3 × 10−3 M, indicating that the electrostatic double layer repulsion component of the disjoining pressure was suppressed above this concentration. The measured contact angles of the NBFs (around 1°) and the specific film interaction free energy (around 0.01 mJ/m2) calculated from the contact angle values were small in comparison to foam films stabilized with other surfactants, and did not vary significantly with the surfactant-concentration. Formation of stable NBF was possible only at surfactant-concentrations of 3 × 10−4 M above which the film life time increases strongly. This behaviour was analyzed using the theory of the rupture of NBFs, which is based on the mechanism of nucleation of holes in the film. Satisfactory relation between the theory and the experiment was observed.