Foam films from mixed solutions of bovine serum albumin and n-dodecyl-β- d-maltoside

Abstract

New data for foam films from mixed aqueous solutions of important components non-ionic surfactant “ n-dodecyl-β- d-maltoside” (C 12G 2) and globular protein “bovine serum albumin” (BSA) are presented. Based on the equilibrium surface tension isotherm of mixed aqueous solutions of BSA (10 −6 M) with C 12G 2, obtained by Wilhelmy method it is found that protein–surfactant complexes are formed at concentration region from 3 × 10 −6 to 1.5 × 10 −5 M C 12G 2. Thinning of the films stabilized by mixtures with a composition corresponding to the special points of the isotherm is recorded and compared with this of the individual components. It is found that the films from mixed protein–surfactant solutions, exhibit irregular thinning behaviour and thickness nonhomogeneity. The critical and equilibrium thickness of stable films is measured interferometrically and discussed based on the specificity of interactions between the components. Films from pure BSA solutions are thinnest (11 nm) and their thickness corresponds to Newton black (NB). It is found that the thickness of mixed films is larger (17 nm) than that of films from pure BSA and corresponds to thickness of common black films, irrespectively that they visually look like Newton film (NF). The larger value of these thicknesses is explained with an increase in the thickness of adsorption layers due to the bigger hydrodynamic radius of complexes or reorientation of BSA molecule to the volume face during its displacement by C 12G 2 domains.