title: Reversibility and irreversibility of adsorption of surfactants and proteins at liquid interfaces.
abstract: It is shown experimentally that the desorption of sodium decyl sulphate from the liquid/air interface is purely diffusion controlled, while the desorption of higher surface active surfactants such as the non-ionic surfactants Triton X-100 and tridecyl dimethyl phosphine oxide obeys a mixed mechanism. The desorption kinetics of beta-lactoglobulin (BLG) and beta-casein is, however, determined by a barrier mechanism. From the analysis of the BLG and beta-casein desorption kinetics at different temperatures the activation energy of desorption is calculated. The values obtained are rather close to the free energy of adsorption. The theoretical model of desorption kinetics predicts that these two energetic parameters are similar if the adsorption activation energy is low. This explains why substances with a higher adsorption activity have a lower desorption rate. Adsorption kinetics studies for beta-casein with and without forced convection show the same equilibrium surface tension values. This leads to the conclusion that the protein adsorption at liquid interfaces is thermodynamically reversible, although the slow desorption kinetics would allow to assume it to be an irreversible process.
authors.affiliation: Medical Physicochemical Centre, Donetsk Medical University, 16 Ilych Avenue, 83003 Donetsk, Ukraine.
authors.forename: V B
authors.initials: VB
authors.lastname: Fainerman
authors.forename: R
authors.initials: R
authors.lastname: Miller
authors.forename: J K
authors.initials: JK
authors.lastname: Ferri
authors.forename: H
authors.initials: H
authors.lastname: Watzke
authors.forename: M E
authors.initials: ME
authors.lastname: Leser
authors.forename: M
authors.initials: M
authors.lastname: Michel
mesh_terms: D000327:Adsorption; D001665:Binding Sites; D003198:Computer Simulation; D007700:Kinetics; D008956:Models, Chemical; D008958:Models, Molecular; D011485:Protein Binding; D011506:Proteins / Q000737:chemistry*; D012996:Solutions; D012997:Solvents / Q000737:chemistry*; D013499:Surface Properties; D013501:Surface-Active Agents / Q000737:chemistry*
chemical_list: D011506:Proteins; D012996:Solutions; D012997:Solvents; D013501:Surface-Active Agents