title: Tensiometry and dilational rheology of mixed β-lactoglobulin/ionic surfactant adsorption layers at water/air and water/hexane interfaces.
abstract: Oscillating drop tensiometry was applied to study adsorbed interfacial layers at water/air and water/hexane interfaces formed from mixed solutions of β-lactoglobulin (BLG, 1 μM in 10 mM buffer, pH 7 - negative net charge) and the anionic surfactant SDS or the cationic DoTAB. The interfacial pressure Π and the dilational viscoelasticity modulus |E| 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 Π and |E| measured after the washing out procedure thus bringing information about the process of protein desorption. The DoTAB/BLG complexes exhibit higher surface activity and higher resistance to desorption in comparison with those for the SDS/BLG complexes due to hydrophobization via electrostatic binding of surfactant molecules. The neutral DoTAB/BLG complexes achieve maximum elastic response of the mixed layer. Mixed BLG/surfactant layers at the water/oil interface are found to reach higher surface pressure and lower maximum dilational elasticity than those at the water/air surface. The sequential adsorption mode experiments and the desorption study reveal that binding of DoTAB to pre-adsorbed BLG globules is somehow restricted at the water/air surface in comparison with the case of complex formation in the solution bulk and subsequently adsorbed at the water/air surface. Maximum elasticity is achieved with washed out layers obtained after simultaneous adsorption, i.e. isolation of the most surface active DoTAB/BLG complex. These specific effects are much less pronounced at the W/H interface.
authors: Max-Planck-Institute for Colloid and Interface Science, 14476 Potsdam/Golm, Germany.
authors: Abhijit
authors: A
authors: Dan
authors: Max-Planck-Institute for Colloid and Interface Science, 14476 Potsdam/Golm, Germany; Institute of Physical Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria. Electronic address: gochev@mpikg.mpg.de.
authors: Georgi
authors: G
authors: Gochev
authors: Max-Planck-Institute for Colloid and Interface Science, 14476 Potsdam/Golm, Germany.
authors: Reinhard
authors: R
authors: Miller
mesh_terms: D000327:Adsorption; D004548:Elasticity; D006586:Hexanes / Q000737:chemistry; D007782:Lactoglobulins / Q000737:chemistry*; D012212:Rheology; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry; D013499:Surface Properties; D013501:Surface-Active Agents / Q000737:chemistry*; D014783:Viscosity; D014867:Water / Q000737:chemistry
chemical_list: D006586:Hexanes; D007782:Lactoglobulins; D013501:Surface-Active Agents; D014867:Water; C026385:n-hexane; D012967:Sodium Dodecyl Sulfate
keywords: Dilational visco-elasticity; Double capillary; Drop bulk exchange; Drop profile analysis tensiometry; Oscillating drops; Sequential vs. simultaneous adsorption; Water/air surface; Water/oil interface; β-Lactoglobulin–DoTAB interactions; β-Lactoglobulin–SDS interactions