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A new approach to the analysis of nonlinear surface dilational rheological properties was developed with the aim to enlarge the accessible range of surface pressures. The dilational surface elasticity of spread monolayers of DPPC, cholesterol, DMEA and their mixtures was determined in the region of low surface tensions (less than 10 mN/m) corresponding to the state of pulmonary surfactants at the lung interface. The dilational surface elasticity of pure DPPC monolayer proved to be high (∼200 mN/m) up to the collapse. The addition of cholesterol, DMEA or their mixture to the DPPC monolayer increased the dynamic surface elasticity, but could decrease significantly the surface pressure of the monolayer collapse if the concentration of additions exceeds an optimal value. [ABSTRACT FROM AUTHOR]

Measurements of the dilational dynamic surface elasticity allow determination of some distinctions between the properties of monolayers of charged polystyrene nano- and microparticles at the water/air and water/oil interfaces. For example, the surface elasticity at the water/oil interface is lower and does not depend on the solution’s ionic strength unlike the case of water/air interface. The obtained results at relatively low surface pressures (<15 mN/m) and homogeneous surface compression agree with a recent theory taking into account the residual charges at the particle/oil interfaces. At higher surface pressures, the behavior has some similarities with the properties of the monolayers of silica nanoparticles but differs strongly from the behavior of monolayers of soft microgel particles. [ABSTRACT FROM AUTHOR]

This short review is devoted to recent achievements in studies of the dilational surface rheological properties of the systems containing complexes of silica nanoparticles with conventional surfactants. It is shown that there is a surfactant concentration range where the dynamic surface elasticity reaches extremely high values up to 1000 mN/m. This result can explain the formation of very stable foams and emulsions containing nanoparticles. In some surfactant concentration ranges the adsorption layer is characterized by a non-linear response to small compressions or expansions of the liquid surface. Possible causes of this behavior and the mechanism of main relaxation processes are briefly discussed. [ABSTRACT FROM AUTHOR]

The present analysis shows that the introduction of intrinsic two-dimensional compressibility of a surfactant adsorption layer allows a much better interpretation of experimental data on the limiting (high-frequency) elasticity and characteristic frequency of diffusional relaxation than models using Frumkin''s or other adsorption isotherms. The proposed model describes experimental data on surface dilational elasticity, as well as on surface pressure, sufficiently well at low and high surfactant concentrations, assuming the Lucassen and van den Tempel model of surface dilational elasticity is realized. [Copyright &y& Elsevier]

The non-monotonic concentration and kinetic dependencies of the dynamic dilational surface elasticity of mixed poly(diallyldimethylammonium chloride)/sodium dodecyl sulfate(SDS)/NaCl solutions indicate the formation of micro-aggregates in the surface layer. The increase of the solution's ionic strength results in strong changes of the surface dilational rheological properties and thereby of the interfacial layer structure at lower SDS concentrations due to the large increase of the adsorption rate. Close to the charge match point of the components, however, the rheological properties are influenced by the presence of micro-aggregates embedded in the adsorption layer. In this case, effects of changing the sample history on the rheological behavior and heterogeneity of the interface were further investigated. [ABSTRACT FROM AUTHOR]

The dynamic dilatational surface elasticity of mixed solutions of globular proteins (β-lactoglobulin (BLG) and bovine serum albumin (BSA)) with cationic (dodecyltrimethylammonium bromide (DTAB)) and anionic (sodium dodecyl sulfate (SDS)) surfactants was measured as a function of the surfactant concentration and surface age. If the cationic surfactant concentration exceeds a certain critical value, the kinetic dependencies of the dynamic surface elasticity of BLG/DTAB and BSA/DTAB solutions become nonmonotonous and resemble those of mixed solutions of proteins with guanidine hydrochloride. This result indicates not only the destruction of the protein tertiary structure in the surface layer of mixed solution but also a strong perturbation of the secondary structure. The corresponding kinetic dependencies for protein solutions with added anionic surfactants are always monotonous, thereby revealing a different mechanism of the adsorption layer formation. One can assume that the secondary structure is destroyed to a lesser extent in the latter case and hinders the formation of loops and tails at the interface. The increase of the solution’s ionic strength by the addition of sodium chloride results in stronger changes of the protein conformations in the surface layer and the appearance of a local maximum in the kinetic dependencies of the dynamic surface elasticity in a relatively narrow range of SDS concentration. [ABSTRACT FROM AUTHOR]

Abstract: Oscillating bubble and drop methods were applied to aqueous solutions of poly(dimethyldiallylammonium chloride) and copolymers of sodium 2-acrylamido-2-methyl-1-propansulfonate with acryl amide and N-isopropylacrylamide at various concentrations and ionic strengths. The dynamic surface elasticity was measured as a function of the surface age and non-monotonic kinetic dependencies were observed for some systems. Although solutions of different polyelectrolytes displayed various types of the surface viscoelastic behavior, they all differed strongly from the surface dilational viscoelasticity of non-ionic polymer solutions. At the same time some distinctions with the surface dilational viscoelasticity of sodium poly(styrenesulfonate) solutions were discovered too. They are a consequence of the specific structure of the PSS adsorption films as it had been assumed earlier (B.A. Noskov, S.N. Nuzhnov, G. Loglio, R. Miller, Macromolecules 37 (2004) 2519). [Copyright &y& Elsevier]

The experimental data on the surface rheological characteristics of dodecyl dimethyl phosphine oxide solutions obtained in a fully automatic oscillating bubble device under microgravity conditions in the frequency range 0.01–100 Hz are presented. The complex surface elasticity modulus is obtained form the amplitude- and phase-frequency characteristics of established pressure oscillations in a closed cell without calibration experiments by direct calculation of the necessary coefficients. The characteristics of the adsorption layers obtained from the elasticity modulus are in good agreement with adsorption isotherms and equations of state accounting for the intrinsic (2D) monolayer compressibility. [Copyright &y& Elsevier]