Tensiometry and dilational rheology of mixed beta-lactoglobulin/ionic surfactant adsorption layers at water/air and water/hexane interfaces

摘要

Oscillating drop tensiometry was applied to study adsorbed interfacial layers at water/air and water/hexane interfaces formed from mixed solutions of p-lactoglobulin (BLG, 1 mu M in 10 mM buffer, pH 7 - negative net charge) and the anionic surfactant SDS or the cationic DoTAB. The interfacial pressure Pi and the dilational viscoelasticity modulus vertical bar E vertical bar of the mixed layers were measured for mixtures of varying surfactant concentrations. The double capillary technique was employed which enables exchange of the protein solution in the drop bulk by surfactant solution (sequential adsorption) or by pure buffer (washing out). The first protocol allows probing the influence of the surfactant on a pre-adsorbed protein layer thus studying the protein/surfactant interactions at the interface. The second protocol gives access to the residual values of Pi and vertical bar E vertical bar measured after the washing out procedure thus bringing information about the process of protein desorption.