Search

The adsorption of proteins (β-lactoglobulin, β-casein) and the oxyethylated non-ionic surfactants C 10 EO 8 and C 14 EO 8 at the aqueous solution/air interface is strongly enhanced and accelerated by the presence of hexane vapour in the air phase caused by the co-adsorption of hexane molecules. Due to this hexane co-adsorption, the dependence of dilational visco-elasticity modulus on surface pressure is shifted towards larger surface pressure values. The adsorption kinetics of the studied non-ionic surfactants shows the same picture as that observed for the two proteins. In contrast, the desorption process of the hexane molecules from a pre-adsorbed mixed adsorption layer is very slow. This decelerated desorption is explained by a rather large desorption energy required by the hexane molecules. The experimental data are compared with several theoretical models developed earlier. The results allow estimating the activation energy for the hexane desorption from adsorption layers of the two studied non-ionic surfactants. [ABSTRACT FROM AUTHOR]

The drop profile method is used to study the influence of hexane vapor in the air atmosphere on the surface tension of water. It was shown that the results depend essentially on the air humidity. At the interface with dry air a fast and strong decrease of surface tension was observed. In humid air and in a measurement cell filled with water, the process is slower and the resulting surface tension is higher. The experimental conditions are defined at which stable results can be measured. A new theoretical model is developed to describe the influence of alkane vapor in the gas phase on the surface tension of aqueous solutions of the reorientable surfactant C 10 EO 8 . This model assumes that a first interfacial layer is composed by surfactants mixed with alkane, and a second layer which is formed by alkane only. The experimental equilibrium surface tension data for the studied C 10 EO 8 solutions agree very well with those calculated from the given model. [ABSTRACT FROM AUTHOR]

The equations of state, adsorption isotherms and functions of the distribution of protein molecules in liquid interfacial layers with respect to molar area and the equations for their viscoelastic behavior are presented. This theory was used to determine the adsorption characteristics of β-casein and β-lactoglobulin at water/oil interfaces. The experimental results are shown to be describable quite adequately by the proposed theory with consistent model parameters. The data analysis demonstrated that the β-casein molecule adsorbed at equilibrium conditions is more unfolded as compared with dynamic conditions, and this fact causes the significant increase of the adsorption equilibrium constant. The theory assumes the adsorption of protein molecules from the aqueous solution and a competitive adsorption of alkane molecules from the alkane phase. The comparison of the experimental equilibrium interfacial tension isotherms for β-lactoglobulin at the solution/hexane interface with data calculated using the proposed theoretical model demonstrates that the assumption of a competitive adsorption is essential, and the influence of the hexane molecules on the shape of the adsorption isotherm does in fact exist. [ABSTRACT FROM AUTHOR]

Bubble profile analysis tensiometry was used to study the surface tension and dilational visco-elasticity of individual and mixed solutions of β-casein (BCS) and β-lactoglobulin (BLG) at various mixing ratios of the components. The results for the individual protein solutions were analysed based on a new theory, which is applicable in the pre-critical and post-critical concentration range of the surface tension isotherm. It is shown that these proteins are capable of displacing each other from the adsorption layer, which affects the surface tension and visco-elasticity modulus of the adsorbed layers. The model developed for protein mixtures agrees well with the experimental data and the calculated dependencies of the surface properties on the solution composition confirm the mutual influence of added proteins. Image 1 • A model for mixed adsorption layers is applied successfully to protein mixtures. • The theory predicts the equations of state for mixed BLG/BCS adsorption layers. • For the mixed protein layers the dilational visco-elasticity is correctly obtained. • At short times the mixed adsorption layers are dominated by the random coil BCS. • At longer adsorption times the globular protein BLG replaces the random coil BCS. [ABSTRACT FROM AUTHOR]

• Cooperative effects on the adsorption of alkane and surfactant molecules at very low concentrations are studied. • Quantum chemical PM3 simulations support the thermodynamic results for the alkane : surfactant ratios at the interface. • There are several principles of alkane and surfactant co-adsorption at the aqueous solution/alkane interface. • Results give a completely new picture of adsorption layers at the water/oil interface. A thermodynamic model is used to analyse the adsorbed layers of C n DMPO (n = 12, 13), C n TAB (n = 10, 12, 14, 16) and SDS at the aqueous solution/hexane and aqueous solution/dodecane interfaces. The combined model assumes that the adsorption of alkane from the oil phase is governed by the Frumkin model, and the adsorption of the surfactant molecules from the solution obeys the reorientation model. We are able to show that at low surfactant concentrations a remarkable decrease of interfacial tension occurs due to a cooperative formation of a mixed adsorption layers by surfactant and alkane molecules. By a quantum chemical semi-empiric (PM3) simulation we analyse the orientation of oil and surfactant molecules in the interfacial layer, and calculate the relative amounts of adsorbed surfactant and alkane. The values obtained from the thermodynamic models agree well with those results calculated via the PM3 simulation. The results show, that at the interface the short-chain hexane molecules can form bi-layers with the long-chain surfactants, while the dodecane and surfactant molecules having commensurable chain lengths are mainly forming mixed monolayer. [ABSTRACT FROM AUTHOR]

The adsorption of surfactants from aqueous solution at the water/air interface is changed when the air phase contains hexane vapor. This co-adsorption of surfactant and hexane depends on the hexane vapor pressure. A thermodynamic model developed for the adsorption of surfactant mixtures can be adapted to the present situation. The surfactants studied were SDS, C 12 TAB and C 12 DMPO, and the dependence of their adsorption characteristics on the partial hexane vapor pressure was determined. The co-adsorption of hexane from the vapor phase increases the surface activity of the adsorbing surfactants. [ABSTRACT FROM AUTHOR]

Highlights: [•] Hexane molecules adsorb from the vapour phase at the surfactant solution surface. [•] The presence of hexane enhances the C n TAB adsorption. [•] High C n TAB concentration, hexane molecules are removed from the adsorption layer. [•] Good theoretical fitting with a model for competitive adsorption of two components. [Copyright &y& Elsevier]