Foaming and dynamic surface tension of aqueous polymer/surfactants solutions 1: ethyl(hydroxyethyl) cellulose and sodium dodecyl sulphate

Foaming (in a column) and dynamic surface tension behaviour of aqueous solutions of sodium dodecyl sulphate (SDS), and ethyl (hydroxy ethyl) cellulose/sodium dodecyl sulphate (EHEC/SDS) mixtures was determined. The results indicated a synergism in foaming and surface activity for the EHEC/SDS mixtures over a specific concentration range. For the SDS solution, the maximum value in Marangoni elasticity (Emmax), as determined from dynamic surface tension data, was reached within a surface age of 0.05 s and it could be suggested that in this case Emmax was relevant to foam stability. However, for the EHEC (nonfoaming solutions), Emmax was reached after longer surface ageing periods (0.05–0.1 s). For the EHEC/SDS solutions, Emmax occurred over a range of surface ageing periods depending on the polymer/surfactant ratio and no correlation was obtained between Emmax and foaming. The Emmax time lag for the polymer and polymer/surfactant mixtures was explained by the slower diffusion from solution to the new surface. For the EHEC/SDS, the enhanced the foaming behaviour was explained by the adsorption of surface active polymer/surfactant (clusters) species at the air/solution interface. It was suggested that this could lead to coherent (gelatinous) interfacial layers in the thin film lamella which reduce drainage.