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Experimental results on the dynamic dilational surface elasticity of protein solutions are analyzed and compared. Short reviews of the protein behavior at the liquid-gas interface and the dilational surface rheology precede the main sections of this work. The kinetic dependencies of the surface elasticity differ strongly for the solutions of globular and non-globular proteins. In the latter case these dependencies are similar to those for solutions of non-ionic amphiphilic polymers and have local maxima corresponding to the formation of the distal region of the surface layer (type I). In the former case the dynamic surface elasticity is much higher (>60 mN/m) and the kinetic dependencies are monotonical and similar to the data for aqueous dispersions of solid nanoparticles (type II). The addition of strong denaturants to solutions of bovine serum albumin and β-lactoglobulin results in an abrupt transition from the type II to type I dependencies if the denaturant concentration exceeds a certain critical value. These results give a strong argument in favor of the preservation of the protein globular structure in the course of adsorption without any denaturants. The addition of cationic surfactants also can lead to the non-monotonical kinetic dependencies of the dynamic surface elasticity indicating destruction of the protein tertiary and secondary structures. The addition of anionic surfactants gives similar results only for the protein solutions of high ionic strength. The influence of cationic surfactants on the local maxima of the kinetic dependencies of the dynamic surface elasticity for solutions of a non-globular protein (β-casein) differs from the influence of anionic surfactants due to the heterogeneity of the charge distribution along the protein chain. In this case one can use small admixtures of ionic surfactants as probes of the adsorption mechanism. The effect of polyelectrolytes on the kinetic dependencies of the dynamic surface elasticity of protein solutions is weaker than the effect of conventional surfactants but exceeds the error limits., (© 2013.)

Abstract: Recent application of the methods of surface dilational rheology to solutions of the complexes between synthetic polyelectrolytes and oppositely charged surfactants (PSC) gave a possibility to determine some steps of the adsorption layer formation and to discover an abrupt transition connected with the formation of microaggregates at the liquid surface. The kinetic dependencies of the dynamic surface elasticity are always monotonous at low surfactant concentrations but can have one or two local maxima in the range beyond the critical aggregation concentration. The first maximum is accompanied by the generation of higher harmonics of induced surface tension oscillations and caused by heterogeneities in the adsorption layer. The formation of a multilayered structure at the surface for some systems leads to the second maximum in the dynamic surface elasticity. The hydrophobicity and charge density of a polymer chain influence strongly the surface structure, resulting in a variety of dynamic surface properties of PSC solutions. Optical methods and atomic force microscopy give additional information for the systems under consideration. Experimental results and existing theoretical frameworks are reviewed with emphasis on the general features of all studied PSC systems. [Copyright &y& Elsevier]

Abstract: Recent studies show strong influence of the dilational surface rheological properties on the stability and dynamics of foam and emulsions. On the other hand, the dilational dynamic surface elasticity proved to be highly sensitive to conformational transitions of macromolecules at fluid–fluid interfaces and can be used to investigate the adsorption mechanism and aggregate formation in the surface layer. The intention of this review consists in the discussion of recent progress in the dialtional surface rheology of solutions of non-ionic homopolymers, block copolymers, polyelectrolytes, polyelectrolyte/surfactant and protein/surfactant complexes. [Copyright &y& Elsevier]