Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Langmuir monolayers of non-ionic polymers: Equilibrium of metastability? Case study of PEO and its PPO-PEO diblock copolymers
    Deschenes, L. ; Saint-Germain, F. ; Lyklema, J. - \ 2015
    Journal of Colloid and Interface Science 449 (2015). - ISSN 0021-9797 - p. 494 - 505.
    air-water-interface - poly(ethylene oxide) monolayers - interacting chain molecules - air/water interface - scaling description - statistical-theory - block-copolymers - liquid-films - surface - layers
    Stability and reorganization in Langmuir films of PEO in PEO homopolymers and PPO–PEO block copolymers were investigated using film balance measurements. The apparent fractional losses of EO segments transferred into the subphase resulting from successive compression–expansion cycles have been estimated. The apparent loss is mainly Gmax, Mn and time-dependent. At surface concentrations G ¿ 0.32 mg/m2, PEO films are in equilibrium. For 0.32 ¿ G ¿ 0.7 mg/m2, the losses remain modest. Further compression leads to densification of the monolayer, requiring the interplay of thermodynamics and kinetic factors In the plateau regime, the loss is higher and constant for 1 ¿ Gmax ¿ 2 mg/m2 upon maintaining the achieved surface area for 15 min. Similar losses were obtained for PEO homopolymers of high Mn and PPO353–PEO2295. It suggests that the PEO remains anchored in a metastable state at the air–water interface at surface concentration well above the onset of the plateau. Additional losses are incurred for PEO homopolymers for monolayers kept compressed in the plateau for 2 h. For the interpretation of these phenomena a combination of elements from self-consistent field theory and scaling is desirable with as a trend an increasing contribution of the latter with increasing surface concentration.
    Hard and soft colloids at fluid interfaces: Adsorption, interactions, assembly and rheology
    Deshmukh, O.S. ; Ende, D. van den; Cohen Stuart, M.A. ; Mugele, F. ; Duits, M. - \ 2015
    Advances in Colloid and Interface Science 222 (2015). - ISSN 0001-8686 - p. 215 - 227.
    air-water-interface - particle-stabilized emulsions - sensitive microgel suspensions - angle neutron-scattering - undulated contact line - wave light-scattering - liquid interfaces - pickering emulsions - electrostatic interactions - laden interfaces
    Soft microgel particles inherently possess qualities of both polymers as well as particles. We review the similarities and differences between soft microgel particles and stiff colloids at fluid–fluid interfaces. We compare two fundamental aspects of particle-laden interfaces namely the adsorption kinetics and the interactions between adsorbed particles. Although it is well established that the transport of both hard particles and microgels to the interface is driven by diffusion, the analysis of the adsorption kinetics needs reconsideration and a proper equation of state relating the surface pressure to the adsorbed mass should be used. We review the theoretical and experimental investigations into the interactions of particles at the interface. The rheology of the interfacial layers is intimately related to the interactions, and the differences between hard particles and microgels become pronounced. The assembly of particles into the layer is another distinguishing factor that separates hard particles from soft microgel particles. Microgels deform substantially upon adsorption and the stability of a microgel-stabilized emulsion depends on the conformational changes triggered by external stimuli.
    Enhanced adhesion of bioinspired nanopatterned elastomets via colloidal surface assembly
    Akerboom, S. ; Appel, J. ; Labonte, D. ; Federle, W. ; Sprakel, J.H.B. ; Kamperman, M.M.G. - \ 2015
    Journal of the Royal Society, Interface 12 (2015). - ISSN 1742-5689 - 12 p.
    elastic wavy surface - air-water-interface - gecko foot-hair - large-area - rapid fabrication - dry adhesives - monolayers - crystals - solids - soft
    We describe a scalable method to fabricate nanopatterned bioinspired dry adhesives using colloidal lithography. Close-packed monolayers of polystyrene particles were formed at the air/water interface, on which polydimethylsiloxane (PDMS) was applied. The order of the colloidal monolayer and the immersion depth of the particles were tuned by altering the pH and ionic strength of the water. Initially, PDMS completely wetted the air/water interface outside the monolayer, thereby compressing the monolayer as in a Langmuir trough; further application of PDMS subsequently covered the colloidal monolayers. PDMS curing and particle extraction resulted in elastomers patterned with nanodimples. Adhesion and friction of these nanopatterned surfaces with varying dimple depth were studied using a spherical probe as a counter-surface. Compared with smooth surfaces, adhesion of nanopatterned surfaces was enhanced, which is attributed to an energy-dissipating mechanism during pull-off. All nanopatterned surfaces showed a significant decrease in friction compared with smooth surfaces.
    Competitive adsorption of the protein hydrophobin and an ionic surfactant: Parallel vs sequential adsorption and dilatational rheology
    Stanimirova, R. ; Marinova, K.G. ; Danov, K.D. ; Kralchevsky, P.A. ; Basheva, E.S. ; Stoyanov, S.D. ; Pelan, E.G. - \ 2014
    Colloids and Surfaces. A: Physicochemical and Engineering Aspects 457 (2014). - ISSN 0927-7757 - p. 307 - 317.
    air-water-interface - sodium dodecyl-sulfate - beta-casein - air/water interface - fluid interfaces - layers - hfbii - elasticity - stability - mixtures
    The competitive adsorption of the protein HFBII hydrophobin and the anionic surfactant sodium dodecyl sulfate (SDS) is investigated in experiments on parallel and sequential adsorption of the two components. The dynamic surface tension and the surface storage and loss dilatational moduli are determined by the oscillating bubble method. A new procedure for data processing is proposed, which allows one to collect data from many different runs on a single master curve and to determine more accurately the dependence of the dilatational elasticity on the surface pressure. Experiments on sequential adsorption are performed by exchanging the HFBII solution around the bubble with an SDS solution. Experiments with separate thin foam films bring additional information on the effect of added SDS. The results indicate that if HFBII has first adsorbed at the air/water interface, it cannot be displaced by SDS at any concentration, both below and above the critical micellization concentration (CMC). In the case of parallel adsorption, there is a considerable difference between the cases below and above the CMC. In the former case, SDS cannot prevent the adsorption of HFBII at the interface, whereas in the latter case adsorption of HFBII is absent, which can be explained with hydrophilization of the hydrophobin aggregates by the SDS in the bulk. The surface dilatational elasticity of the HFBII adsorption layers markedly decreases in the presence of SDS, but it recovers after washing out the SDS. With respect to their dilatational rheology, the investigated HFBII layers exhibit purely elastic behavior, the effect of dilatational viscosity being negligible. As a function of surface tension, the elasticity of the investigated interfacial layers exhibits a high maximum, which could be explained with the occurrence of a phase transition in the protein adsorption layer.
    Nonlinear rheology of complex fluid-fluid interfaces
    Sagis, L.M.C. ; Fischer, P. - \ 2014
    Current Opinion in Colloid and Interface Science 19 (2014)6. - ISSN 1359-0294 - p. 520 - 529.
    fourier-transform rheology - air-water-interface - extended irreversible thermodynamics - adsorbed protein layers - surface shear rheology - langmuir monolayers - liquid interfaces - adsorption layers - amyloid fibrils - nonequilibrium thermodynamics
    Fluid–fluid interfaces stabilized by proteins, protein aggregates, polymers, or colloidal particles, tend to have a complex microstructure. Their response to an applied deformation is often highly nonlinear, even at small deformation (rates). The nonlinearity of the response is a result of changes in the interfacial microstructure. Most of the studies on interfacial rheology of complex interfaces currently available in the scientific literature, focus on the linear response regime. Since multiphase systems such as emulsions or foam are routinely exposed to large and fast deformations, characterization of the nonlinear response of complex interfaces is highly relevant. In this paper we review the recent work on nonlinear rheology of complex interfaces, both in shear and dilatational deformations. We also discuss several methods currently available for analyzing nonlinear interfacial rheology data, and recent progress in modeling nonlinear interfacial rheology, using nonequilibrium thermodynamic frameworks.
    Quantitative description of the parameters affecting the adsorption behaviour of globular proteins
    Delahaije, R.J.B.M. ; Gruppen, H. ; Giuseppin, M.L.F. ; Wierenga, P.A. - \ 2014
    Colloids and Surfaces. B: Biointerfaces 123 (2014). - ISSN 0927-7765 - p. 199 - 206.
    air-water-interface - bovine serum-albumin - beta-lactoglobulin - rheological properties - air/water interface - surface rheology - kinetics - ovalbumin - charge - denaturation
    The adsorption behaviour of proteins depends significantly on their molecular properties and system conditions. To study this relation, the effect of relative exposed hydrophobicity, protein concentration and ionic strength on the adsorption rate and adsorbed amount is studied using ß-lactoglobulin, ovalbumin and lysozyme. The curves of surface elastic modulus versus surface pressure of all three proteins, under different conditions (i.e. concentration and ionic strength) superimposed. This showed that the interactions between the adsorbed proteins are similar and that the adsorbed proteins retain their native state. In addition, the adsorption rate (kadsorb) was shown to scale with the relative hydrophobicity and ionic strength. Moreover, the adsorbed amount was shown to be dependent on the protein charge and the ionic strength. Based on these results, a model is proposed to predict the maximum adsorbed amount (Gmax). The model approximates the adsorbed amount as a close-packed monolayer using a hard-sphere approximation with an effective protein radius which depends on the electrostatic repulsion. The theoretical adsorbed amount was in agreement with experimental Gmax (±10%).
    Nonlinear stress deformation behavior of interfaces stabilized by food-based ingredients
    Sagis, L.M.C. ; Humblet-Hua, K.N.P. ; Kempen, S.E.H.J. van - \ 2014
    Journal of Physics-Condensed Matter 26 (2014). - ISSN 0953-8984 - 9 p.
    air-water-interface - fatty-acid esters - surface rheological properties - beta-lactoglobulin fibrils - liquid interfaces - amyloid fibrils - dilatational rheology - air/water interfaces - protein adsorption - bending rigidity
    Interfaces stabilized by food-based ingredients, such as proteins or glycolipids, often display nonlinear behavior when subjected to oscillatory dilatational deformations, even at the lowest deformation amplitudes which can currently be applied experimentally. Here we show that classical approaches to extract dilatational properties, based on the Young–Laplace equation, may not always be suitable to analyze data. We discuss a number of examples of foodingredient stabilized interfaces (interfaces stabilized by protein fibrils, protein–polysaccharide complexes and oligosaccharide–fatty aid conjugates) and show how an analysis of the dynamic surface tension signal using Lissajous plots and a protocol which includes deformation amplitude and droplet size variations, can be used to obtain a more detailed and accurate description of their nonlinear dilatational behavior.
    Molecular assembly, interfacial rheology and foaming properties of oligofructose fatty acid esters
    Kempen, S.E.H.J. van; Schols, H.A. ; Linden, E. van der; Sagis, L.M.C. - \ 2014
    Food & Function 5 (2014)1. - ISSN 2042-6496 - p. 111 - 122.
    lipase-catalyzed synthesis - surface-active properties - solid-phase synthesis - air-water-interface - enzymatic-synthesis - beta-lactoglobulin - chain-length - sugar esters - dilatational rheology - candida-antarctica
    Two major types of food-grade surfactants used to stabilize foams are proteins and low molecular weight (LMW) surfactants. Proteins lower the surface tension of interfaces and tend to unfold and stabilize the interface by the formation of a visco-elastic network, which leads to high surface moduli. In contrast, LMW surfactants lower the surface tension more than proteins, but do not form interfaces with a high modulus. Instead, they stabilize the interface through the Gibbs-Marangoni mechanism that relies on rapid diffusion of surfactants, when surface tension gradients develop as a result of deformations of the interface. A molecule than can lower the surface tension considerably, like a LMW surfactant, but also provide the interface with a high modulus, like a protein, would be an excellent foam stabilizer. In this article we will discuss molecules with those properties: oligofructose fatty acid esters, both in pure and mixed systems. First, we will address the synthesis and structural characterization of the esters. Next, we will address self-assembly and rheological properties of air/water interfaces stabilized by the esters. Subsequently, this paper will deal with mixed systems of mono-esters with either di-esters and lauric acid, or proteins. Then, the foaming functionality of the esters is discussed.
    Non-linear surface dilatational rheology as a tool for understanding microstructures of air/water interfaces stabilized by oligofructose fatty acid esters
    Kempen, S.E.H.J. van; Schols, H.A. ; Linden, E. van der; Sagis, L.M.C. - \ 2013
    Soft Matter 9 (2013)40. - ISSN 1744-683X - p. 9579 - 9592.
    air-water-interface - monolayers - layers - shear - viscoelasticity - adsorption - systems - foams
    In this paper, the rheological response of air/water interfaces, stabilized by various oligofructose fatty acid esters, to oscillatory dilatational deformations was studied and compared to the response of interfaces stabilized by sucrose esters. We have followed a traditional approach to surface rheology, where the development of the modulus as a function of time is studied as well as the frequency dependence of the modulus. We also adopted a different approach where we investigate in detail the amplitude dependence of the modulus. Finally, we studied the temperature dependence. We show that for an accurate characterization of the dilatational rheology of fluid-fluid interfaces with a complex microstructure, a protocol should be used that not only involves variations of surface pressure, frequency, and temperature, but also establishes amplitude dependence. We show that Lissajous plots of surface pressure versus deformation can be useful tools to help interpret surface dilatational behavior in terms of interfacial microstructure. The rheological response of interfaces stabilized by oligofructose esters differed significantly from the response of those stabilized by sucrose esters. Sucrose esters behaved like typical low molecular weight surfactants, and gave interfaces with relatively low moduli, a frequency scaling of the dilatational modulus with an exponent close to 0.5, and displayed no asymmetries in Lissajous plots. In contrast, the oligofructose esters gave, depending on the fatty acid tail, relatively high moduli, almost independent of frequency. Significant asymmetries were observed in the Lissajous plots, with strain hardening during compression and strain softening during extension. Our results suggest that the unusual rheological properties of interfaces stabilized by oligofructose esters may be the result of the formation of a two-dimensional soft glass phase by the oligofructose part of the ester.
    Dynamic surface tension of complex fluid-fluid interfaces: A useful concept, or not?
    Sagis, L.M.C. - \ 2013
    The European Physical Journal. Special Topics 222 (2013)1. - ISSN 1951-6355 - p. 39 - 46.
    scanning angle reflectometry - air-water-interface - neutron reflectivity - 2-dimensional suspensions - air/water interface - bending rigidity - latex-particles - beta-casein - systems - equilibrium
    Dilatational moduli are typically determined by subjecting interfaces to oscillatory area deformations, and are often defined in terms of the difference between the dynamic or transient surface tension of the interface (the surface tension in its deformed state), and the surface tension of the interface in its non-deformed state. Here we will discuss the usefulness of the dynamic surface tension concept in the characterization of dilatational properties of complex fluid-fluid interfaces. Complex fluid-fluid interfaces are interfaces stabilized by components which form mesophases (two-dimensionional gels, glasses, or (liquid) crystalline phases), as a result of in-plane interactions between the components. We will show that for such interfaces dilatational properties are not exclusively determined by the exchange of surface active components between interface and adjoining bulk phases, but also by in-plane viscoelastic stresses. The separation of these contributions remains a challenging problem which remains to be solved.
    Colloids in Flatland: a perspective on 2D phase-separated systems, characterisation methods, and lineactant.
    Bernardini, C. ; Stoyanov, S.D. ; Arnaudov, L.N. ; Cohen Stuart, M.A. - \ 2013
    Chemical Society Reviews 42 (2013)5. - ISSN 0306-0012 - p. 2100 - 2129.
    langmuir-blodgett-films - air-water-interface - perfluorinated carboxylic-acids - field optical microscopy - hydrogenated hybrid amphiphiles - fluorinated comb copolymers - brewster-angle microscopy - organized molecular films - atomic-force microscopy - mixed lan
    In 1861 Thomas Graham gave birth to a new field of science, today known as colloid science. Nowadays, the notion “colloid” is often used referring to systems consisting of two immiscible phases, one of which is finely dispersed into the other. Research on colloids deals mostly with sols (solids dispersed in a liquid), emulsions (liquids dispersed in liquid), and foams (gas dispersed in a liquid). Because the dispersed particles are small, there is a lot of interface per unit mass. Not surprisingly, therefore, the properties of the interface have often a decisive effect on the behaviour of colloids. Water–air interfaces have a special relevance in this field: many water-insoluble molecules can be spread on water and, given the right spreading conditions and enough available surface area, their spreading proceeds until a monolayer (a one-molecule thick layer) eventually remains. Several 2D phases have been identified for such monolayers, like “gas”, “liquid expanded”, “liquid condensed”, and “solid”. The central question of this review is whether these 2D phases can also exist as colloidal systems, and what stabilizes the dispersed state in such systems. We shall present several systems capable of yielding 2D phase separation, from those based on either natural or fluorinated amphiphiles, to polymer-based ones. We shall seek for analogies in 3D and we shall try to clarify if the lines between these 2D objects play a similar role as the interfaces between 3D colloidal systems. In particular, we shall consider the special role of molecules that tend to accumulate at the phase boundaries, that is, at the contact lines, which will therefore be denoted “line-actants” (molecules that adsorb at a 1D interface, separating two 2D colloidal entities), by analogy to the term “surfactant” (which indicates a molecule that adsorbs at a 2D interface separating two 3D colloidal entities).
    Interfacial properties of air/water interfaces stabilized by oligofructose palmitic acid esters in the presence of whey protein isolate
    Kempen, S.E.H.J. van; Maas, K. ; Schols, H.A. ; Linden, E. van der; Sagis, L.M.C. - \ 2013
    Food Hydrocolloids 32 (2013)1. - ISSN 0268-005X - p. 162 - 171.
    air-water-interface - beta-lactoglobulin - competitive adsorption - rheological properties - surfactant systems - dynamic properties - foaming properties - liquid interfaces - mixed films - displacement
    To study the applicability of oligofructose palmitic acid esters (OF-C16) as novel surfactants in food systems, the functional properties of OF-C16 were studied in the presence of whey protein isolate (WPI). Surface tension measurements, surface dilatational rheology, foam stability tests and Brewster Angle Microscopy were used to study the competitive adsorption of WPI and OF-C16 and the displacement of WPI by OF-C16. Pure WPI stabilized interfaces had a moderate surface tension (48 mN/m) and a dilatational modulus of 90 mN/m, while pure OF-C16 stabilized interfaces had a low surface tension (30 mN/m) and a dilatational modulus of 50 mN/m. The stabilization mechanisms of WPI (elastic network formation) and of OF-C16 (surface solidification) are very different, and the combined adsorption of these two components led to a structure with a much lower dilatational modulus. At the lowest WPI concentrations (0.5% and 1%), the equilibrium surface tension was similar to a pure OF-C16 stabilized interface, pointing to a low WPI surface concentration. However, apparently still sufficient WPI had adsorbed either at or just below the interface, to prevent the OF-C16 from solidifying. Despite the low moduli, the foam stability for the mixed systems was high. The interfaces were probably stabilized by the Gibbs-Marangoni mechanism. In contrast, at the highest WPI concentration (2%), the equilibrium surface concentration of WPI was sufficiently high to decrease the interfacial mobility of OF-C16, which decreased the Gibbs-Marangoni effect and resulted in decreased foam stability. Finally, OF-C16 could also displace a fully developed WPI network from the interface.
    Surface shear rheology of hydrophobin adsorption layers: laws of viscoelastic behaviour with applications to long-term foam stability
    Danov, K.D. ; Radulova, G.M. ; Kralchevsky, P.A. ; Golemanov, K. ; Stoyanov, S.D. - \ 2012
    Faraday Discussions 158 (2012). - ISSN 1359-6640 - p. 195 - 221.
    class-ii hydrophobins - air-water-interface - hfbii hydrophobin - liquid interfaces - protein layers - beta-casein - films - elasticity - monolayers - viscosity
    The long-term stabilization of foams by proteins for food applications is related to the ability of proteins to form dense and mechanically strong adsorption layers that cover the bubbles in the foams. The hydrophobins represent a class of proteins that form adsorption layers of extraordinary high shear elasticity and mechanical strength, much higher than that of the common milk and egg proteins. Our investigation of pure and mixed (with added beta-casein) hydrophobin layers revealed that their rheological behavior obeys a compound rheological model, which represents a combination of the Maxwell and Herschel-Bulkley laws. It is remarkable that the combined law is obeyed not only in the simplest regime of constant shear rate (angle ramp), but also in the regime of oscillatory shear strain. The surface shear elasticity and viscosity, E-sh and eta(sh), are determined as functions of the shear rate by processing the data for the storage and loss moduli, G' and G ''. At greater strain amplitudes, the spectrum of the stress contains not only the first Fourier mode, but also the third one. The method is extended to this non-linear regime, where the rheological parameters are determined by theoretical fit of the experimental Lissajous plot. The addition of beta-casein to the hydrophobin leads to softer adsorption layers, as indicated by their lower shear elasticity and viscosity. The developed approach to the rheological characterization of interfacial layers allows optimization and control of the performance of mixed protein adsorption layers with applications in food foams.
    Surface Shear Rheology of Saponin Adsorption Layers
    Golemanov, K. ; Tcholakova, S. ; Denkov, N. ; Pelan, E. ; Stoyanov, S.D. - \ 2012
    Langmuir 28 (2012)33. - ISSN 0743-7463 - p. 12071 - 12084.
    physico-chemical properties - quillaja bark saponin - air-water-interface - thin liquid-films - plant saponins - chromatographic determination - phospholipid monolayers - yucca-schidigera - acid saponins - cholesterol
    Saponins are a wide class of natural surfactants, with molecules containing a rigid hydrophobic group (triterpenoid or steroid), connected via glycoside bonds to hydrophilic oligosaccharide chains. These surfactants are very good foam stabiliziers and emulsifiers, and show a range of nontrivial biological activities. The molecular mechanisms behind these unusual properties are unknown, and, therefore, the saponins have attracted significant research interest in recent years. In our previous study (Stanimirova et al. Langmuir 2011, 27, 12486-12498), we showed that the triterpenoid saponins extracted from Quillaja saponaria plant (Quillaja saponins) formed adsorption layers with unusually high surface dilatational elasticity, 280 +/- 30 mN/m. In this Article, we study the shear rheological properties of the adsorption layers of Quillaja saponins. In addition, we study the surface shear rheological properties of Yucca saponins, which are of steroid type. The experimental results show that the adsorption layers of Yucca saponins exhibit purely viscous rheological response, even at the lowest shear stress applied, whereas the adsorption layers of Quillaja saponins behave like a viscoelastic two-dimensional body. For Quillaja saponins, a single master curve describes the data for the viscoelastic creep compliance versus deformation time, up to a certain critical value of the applied shear stress. Above this value, the layer compliance increases, and the adsorption layers eventually transform into viscous ones. The experimental creep recovery curves for the viscoelastic layers are fitted very well by compound Voigt rheological model. The obtained results are discussed from the viewpoint of the layer structure and the possible molecular mechanisms, governing the rheological response of the saponin adsorption layers.
    Interfacial layers from the protein HFBII hydrophobin: Dynamic surface tension, dilatational elasticity and relaxation times
    Alexandrov, N.A. ; Marinova, K.G. ; Gurkov, T.D. ; Danov, K.D. ; Kralchevsky, P.A. ; Stoyanov, S.D. ; Blijdenstein, T.B.J. ; Arnaudov, L.N. ; Pelan, E.G. ; Lips, A. - \ 2012
    Journal of Colloid and Interface Science 376 (2012). - ISSN 0021-9797 - p. 296 - 306.
    class-ii hydrophobins - air-water-interface - trichoderma-reesei - structural-analysis - crystal-structures - curved interfaces - latex-particles - beta-casein - adsorption - rheology
    The pendant-drop method (with drop-shape analysis) and Langmuir trough are applied to investigate the characteristic relaxation times and elasticity of interfacial layers from the protein HFBII hydrophobin. Such layers undergo a transition from fluid to elastic solid films. The transition is detected as an increase in the error of the fit of the pendant-drop profile by means of the Laplace equation of capillarity. The relaxation of surface tension after interfacial expansion follows an exponential-decay law, which indicates adsorption kinetics under barrier control. The experimental data for the relaxation time suggest that the adsorption rate is determined by the balance of two opposing factors: (i) the barrier to detachment of protein molecules from bulk aggregates and (ii) the attraction of the detached molecules by the adsorption layer due to the hydrophobic surface force. The hydrophobic attraction can explain why a greater surface coverage leads to a faster adsorption. The relaxation of surface tension after interfacial compression follows a different, square-root law. Such behavior can be attributed to surface diffusion of adsorbed protein molecules that are condensing at the periphery of interfacial protein aggregates. The surface dilatational elasticity, E, is determined in experiments on quick expansion or compression of the interfacial protein layers. At lower surface pressures (
    Dynamic properties of interfaces in soft matter: Experiments and theory
    Sagis, L.M.C. - \ 2011
    Reviews of Modern Physics 83 (2011)4. - ISSN 0034-6861 - p. 1367 - 1403.
    air-water-interface - surface light-scattering - liquid-vapor interface - fluid-fluid interface - fourier-transform rheology - common line motion - extended irreversible thermodynamics - hydroxypropyl-methyl-cellulose - molecular-weight dependence - globulin adsor
    The dynamic properties of interfaces often play a crucial role in the macroscopic dynamics of multiphase soft condensed matter systems. These properties affect the dynamics of emulsions, of dispersions of vesicles, of biological fluids, of coatings, of free surface flows, of immiscible polymer blends, and of many other complex systems. The study of interfacial dynamic properties, surface rheology, is therefore a relevant discipline for many branches of physics, chemistry, engineering, and life sciences. In the past three to four decades a vast amount of literature has been produced dealing with the rheological properties of interfaces stabilized by low molecular weight surfactants, proteins, (bio)polymers, lipids, colloidal particles, and various mixtures of these surface active components. In this paper recent experiments are reviewed in the field of surface rheology, with particular emphasis on the models used to analyze surface rheological data. Most of the models currently used are straightforward generalizations of models developed for the analysis of rheological data of bulk phases. In general the limits on the validity of these generalizations are not discussed. Not much use is being made of recent advances in nonequilibrium thermodynamic formalisms for multiphase systems, to construct admissible models for the stress-deformation behavior of interfaces. These formalisms are ideally suited to construct thermodynamically admissible constitutive equations for rheological behavior that include the often relevant couplings to other fluxes in the interface (heat and mass), and couplings to the transfer of mass from the bulk phase to the interface. In this review recent advances in the application of classical irreversible thermodynamics, extended irreversible thermodynamics, rational thermodynamics, extended rational thermodynamics, and the general equation for the nonequilibrium reversible-irreversible coupling formalism to multiphase systems are also discussed, and shown how these formalisms can be used to generate a wide range of thermodynamically admissible constitutive models for the surface stress tensor. Some of the generalizations currently in use are shown to have only limited validity. The aim of this review is to stimulate new developments in the fields of experimental surface rheology and constitutive modeling of multiphase systems using nonequilibrium thermodynamic formalisms and to promote a closer integration of these disciplines
    PMMA highlights the layering transition of PDMS in Langmuir films
    Bernardini, C. ; Stoyanov, S.D. ; Cohen Stuart, M.A. ; Arnaudov, L.N. ; Leermakers, F.A.M. - \ 2011
    Langmuir 27 (2011)6. - ISSN 0743-7463 - p. 2501 - 2508.
    air-water-interface - molecular layers - polymer-films - surface - poly(dimethylsiloxane) - methacrylate - ellipsometry - behavior - spread
    We report a system consisting of a mixed Langmuir monolayer, made of water-insoluble, spreadable, fluid-like polymers polydimethylsiloxane (PDMS) and polymethylmethacrylate (PMMA) with a minority P(DMS-b-MMA) copolymer. We have performed both Langmuir trough pressure/area isotherm measurements and Brewster angle microscopy (BAM) observations and complement the experiments with molecularly detailed self-consistent field (SCF) calculations. PDMS undergoes a layering transition that is difficult to detect by BAM. Addition of PMMA gives contrast in BAM, now showing a two-phase system: if this would consist of separate two-dimensional (2D) PMMA and PDMS phases, a PDMS-PMMA diblock should accumulate at the phase boundary. However, the diblock copolymer of PDMS-PMMA failed to show the expected “lineactant” behavior, i.e., failed to accumulate at the phase boundary. The calculations point to a nontrivial arrangement of the polymer chains at the interface: in mixtures of the two homopolymers, in a rather wide composition ratio, we find a vertical (with respect to the air/water interfacial plane) configuration, with PMMA sitting preferably at the PDMS/water interface of the thicker PDMS film, during the PDMS layering phase transition. This also explains why the diblock copolymer is not a lineactant. Both PMMA and P(DMS-b-MMA) are depleted from the thin-thick PDMS film interface, and the line tension between the phases is, consequently, increased, in the binary mixtures as well as in the ternary ones
    Improvement of foaming properties of cuttlefish skin gelatin by modification with N-hydroxysuccinimide esters of fatty acid
    Aewsiri, T. ; Benjakul, S. ; Visessanguan, W. ; Wierenga, P.A. ; Gruppen, H. - \ 2011
    Food Hydrocolloids 25 (2011)5. - ISSN 0268-005X - p. 1277 - 1284.
    air-water-interface - proteins - proteolysis - adsorption - surfactant - ovalbumin - charge
    Conformation and foaming properties of cuttlefish skin gelatin modified by N-hydroxysuccinimide esters of different saturated fatty acids including capric acid (C10:0), lauric acid (C12:0) and myristic acid (C14:0) at different molar ratios (0.25, 0.50, 1.00 and 2.00) were investigated. Covalent attachment of fatty acids into gelatin was observed as evidenced by the decrease in amino groups. Fourier transform infrared spectroscopic study indicated the presence of alkyl group of modified gelatin. The higher increase in surface activity with coincidental increase in surface hydrophobicity was observed in gelatin modified with fatty acid ester having a longer chain, especially at the higher molar ratio. The increase in foam expansion was related with the improved surface activity mediated by the modification by N-hydroxysuccinimide esters of fatty acid.
    New views on foams from protein solutions
    Wierenga, P.A. ; Gruppen, H. - \ 2010
    Current Opinion in Colloid and Interface Science 15 (2010)5. - ISSN 1359-0294 - p. 365 - 373.
    air-water-interface - beta-lactoglobulin - air/water interface - rheological properties - liquid interfaces - adsorption-kinetics - shear rheology - whey-protein - structural conformation - orogenic displacement
    The stabilization of foam by proteins has been mostly studied in relation to the food industry. The main aim of the research is to understand the relation between proteins used and the product properties. The molecular properties of proteins and their foam forming and stabilizing properties are typically linked to the adsorption kinetics and the interfacial properties. Additionally, the properties of thin liquid films formed between neighboring air bubbles are considered. While there are several rules of thumb describing the relations between the different parameters and processes it seems that there is not yet a ‘unifying’ theory on protein stabilized foams. If the different processes could be described by quantitative parameters the applications of traditional proteins and the use of proteins from novel sources could be optimized. However, even for simple protein systems there is a lack of such quantitative rules, and as a result the advancement in the understanding of protein foam seems to progress slowly. This is attributed to the complexity of the system by some authors, but by viewing the literature it also becomes apparent that certain ideas seem to resist change. There are some interesting articles that offer a different point of view. In this article we aim to provide an insight in the different ways in which proteins and their role in foamed systems are described. Based on recent results, it seems that protein adsorption and subsequent changes in interfacial properties could be described in colloidal terms such as the net charge, exposed hydrophobicity and size of the proteins. Such a description can help to understand the behavior of single-component systems, but can also add to the understanding of the more complex systems that seem to attract more and more interest in recent years. An example of the value of using new viewpoints is the exchange of information between fields of food and non-food foams. Examples in this field are the use of particles to stabilize foams, or the production of very stable microbubbles.
    Structure of mixed Beta-lactoglobulin/pectin adsorbed layers at air/water interfaces; a spectroscopy study
    Ganzevles, R.A. ; Fokkink, R.G. ; Vliet, T. van; Cohen Stuart, M.A. ; Jongh, H.H.J. de - \ 2008
    Journal of Colloid and Interface Science 317 (2008)1. - ISSN 0021-9797 - p. 137 - 147.
    air-water-interface - o/w emulsions - neutron reflection - protein adsorption - pectin - casein - films - polysaccharides - complexes - membranes
    Based on earlier reported surface rheological behaviour two factors appeared to be important for the functional behaviour of mixed protein/polysaccharide adsorbed layers at air/water interfaces: (1) protein/polysaccharide mixing ratio and (2) formation history of the layers. In this study complexes of ß-lactoglobulin (positively charged at pH 4.5) and low methoxyl pectin (negatively charged) were formed at two mixing ratios, resulting in negatively charged and nearly neutral complexes. Neutron reflection showed that adsorption of negative complexes leads to more diffuse layers at the air/water interface than adsorption of neutral complexes. Besides (simultaneous) adsorption of protein/polysaccharide complexes, a mixed layer can also be formed by adsorption of (protein/)polysaccharide (complexes) to a pre-formed protein layer (sequential adsorption). Despite similar bulk concentrations, adsorbed layer density profiles of simultaneously and sequentially formed layers were persistently different, as illustrated by neutron reflection analysis. Time resolved fluorescence anisotropy showed that the mobility of protein molecules at an air/water interface is hampered by the presence of pectin. This hampered mobility of protein through a complex layer could account for differences observed in density profiles of simultaneously and sequentially formed layers. These insights substantiated the previously proposed organisations of the different adsorbed layers based on surface rheological data.
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