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

Foaming tin a column) and dynamic surface tension behaviour of aqueous solu tions of sodium dodecyl sulphate (SDS), and ethyl (hydroxy ethyl) cellulose /sodium dodecyl sulphate (EHEC/SDS) mixtures was determined. The results in dicated a synergism in foaming and surface activity for the EHEC/SDS mixtur es over a specific concentration range. For the SDS solution, the maximum v alue in Marangoni elasticity (E-mmax), as determined from dynamic surface t ension data, was reached within a surface age of 0.05 s and it could be sug gested that in this case E-mmax was relevant to foam stability. However, fo r the EHEC (nonfoaming solutions), E-mmax was reached after longer surface ageing periods (0.05-0.1 s). For the EHEC/SDS solutions, E-mmax Occurred ov er a range of surface ageing periods depending on the polymer/surfactant ra tio and no correlation was obtained between E-mmax and foaming. The E-mmax time lag for the polymer and polymer/surfactant mixtures was explained by t he 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 polpmer/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. (C) 2001 Elsevier S cience B.V. All rights reserved.