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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    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.
    Dynamics of multiphase systems with complex microstructure. I. Development of the governing equations through nonequilibrium thermodynamics
    Sagis, L.M.C. ; Öttinger, H.C. - \ 2013
    Physical Review. E, Statistical nonlinear, and soft matter physics 88 (2013)2. - ISSN 1539-3755 - 13 p.
    scanning angle reflectometry - in-water emulsions - superficial viscosity - general formalism - bending rigidity - lipid-bilayers - interfaces - surface - fluid - rheology
    In this paper we present a general model for the dynamic behavior of multiphase systems in which the bulk phases and interfaces have a complex microstructure (for example, immiscible polymer blends with added compatibilizers, or polymer stabilized emulsions with thickening agents dispersed in the continuous phase). The model is developed in the context of the GENERIC framework (general equation for the nonequilibrium reversible irreversible coupling). We incorporate scalar and tensorial structural variables in the set of independent bulk and surface excess variables, and these structural variables allow us to link the highly nonlinear rheological response typically observed in complex multiphase systems, directly to the time evolution of the microstructure of the bulk phases and phase interfaces. We present a general form of the Poisson and dissipative brackets for the chosen set of bulk and surface excess variables, and show that to satisfy the entropy degeneracy property, we need to add several contributions to the moving interface normal transfer term, involving the tensorial bulk and interfacial structural variables. We present the full set of balance equations, constitutive equations, and boundary conditions for the calculation of the time evolution of the bulk and interfacial variables, and this general set of equations can be used to develop specific models for a wide range of complex multiphase systems.
    Dynamics of multiphase systems with complex microstructure. II. Particle-stabilized interfaces
    Sagis, L.M.C. - \ 2013
    Physical Review. E, Statistical nonlinear, and soft matter physics 88 (2013)2. - ISSN 1539-3755 - 9 p.
    fourier-transform rheology - in-water emulsions - superficial viscosity - bending rigidity - surface - liquid - viscoelasticity - liquid/liquid - fluid - gas/liquid
    In this paper we use the GENERIC (general equation for nonequilibrium reversible-irreversible coupling) nonequilibrium thermodynamics framework to derive constitutive equations for the surface extra stress tensor of an interface stabilized by a two-dimensional suspension of anisotropic colloidal particles. The dependence of the surface stress tensor on the microstructure of the interface is incorporated through a dependence on a single tensorial structural variable, characterizing the average orientation of the particles. The constitutive equation for the stress tensor is combined with a time-evolution equation describing the changes in the orientation tensor as a result of the applied deformation field. We examine the predictions of the model in in-plane steady shear flow, in-plane oscillatory shear flow, and oscillatory dilatational flow. The model is able to predict the experimentally observed shear thinning behavior in surface shear flow, and also the experimentally observed emergence of even harmonics in the frequency spectrum of the surface stress in oscillatory dilatational flow. Our results show that the highly nonlinear stress-deformation behavior of interfaces with a complex microstructure can be modeled well using simple structural models like the one presented here.
    Normal stresses in surface shear experiments
    Sagis, L.M.C. - \ 2013
    The European Physical Journal. Special Topics 222 (2013)1. - ISSN 1951-6355 - p. 99 - 103.
    in-water emulsions - interfacial permeability - general formalism - bending rigidity - complex fluids - dynamics - viscoelasticity - thermodynamics - liquid/liquid - gas/liquid
    When viscoelastic bulk phases are sheared, the deformation of the sample induces not only shear stresses, but also normal stresses. This is a well known and well understood effect, that leads to phenomena such as rod climbing, when such phases are stirred with an overhead stirrer, or to die swell in extrusion. Viscoelastic interfaces share many commonalities with viscoelastic bulk phases, with respect to their response to deformations. There is however little experimental evidence that shear deformations of interfaces can induce in-plane normal stresses (not to be confused with stresses normal to the interface). Theoretical models for the stress-deformation behavior of complex fluid-fluid interfaces subjected to shear, predict the existence of in-plane normal stresses. In this paper we suggest methods to confirm the existence of such stresses experimentally.
    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.
    Editorial: Dynamics of complex fluid-fluid interfaces
    Sagis, L.M.C. ; Fischer, P. ; Anderson, P.D. - \ 2013
    The European Physical Journal. Special Topics 222 (2013)1. - ISSN 1951-6355 - p. 1 - 5.
    in-water emulsions - liquid interfaces - bending rigidity - rheology - fibrils - viscoelasticity - permeability - particles - mixtures - behavior
    Generalized surface momentum balances for the analysis of surface dilatational data
    Sagis, L.M.C. - \ 2013
    The European Physical Journal. Special Topics 222 (2013)1. - ISSN 1951-6355 - p. 31 - 38.
    in-water emulsions - interfacial permeability - superficial viscosity - bending rigidity - lipid-bilayers - fluid - dynamics - liquid - microbubbles - mixtures
    Dilatational rheological properties of interfaces are often determined using drop tensiometers, in which the interface of the droplet is subjected to oscillatory area changes. A dynamic surface tension is determined either by image analysis of the droplet profile or by measuring the capillary pressure. Both analysis modes tend to use the Young-Laplace equation for determining the dynamic surface tension. For complex fluid-fluid interfaces there is experimental evidence that this equation does not describe the response of the interface to deformations adequately. Generalizations of this equation are available, and in this comment we will discuss these generalizations, and the conditions for which they reduce to the Young-Laplace equation.
    Surface rheological properties of liquid-liquid interfaces stabilized by protein fibrillar aggregates and protein-polysaccharide complexes
    Humblet-Hua, K.N.P. ; Linden, E. van der; Sagis, L.M.C. - \ 2013
    Soft Matter 9 (2013)7. - ISSN 1744-683X - p. 2154 - 2165.
    in-water emulsions - egg-white lysozyme - air/water interface - beta-lactoglobulin - amyloid fibrils - oil/water interface - bending rigidity - sodium caseinate - dextran sulfate - food systems
    In this study we have investigated the surface rheological properties of oil-water interfaces stabilized by fibrils from lysozyme (long and semi-flexible and short and rigid ones), fibrils from ovalbumin (short and semi-flexible), lysozyme-pectin complexes, or ovalbumin-pectin complexes. We have compared these properties with those of interfaces stabilized by the native proteins. The surface dilatational and surface shear moduli were determined using an automated drop tensiometer and a stress controlled rheometer with biconical disk geometry. Results show that interfaces stabilized by complexes of these proteins with high-methoxyl pectin have higher surface shear and dilatational moduli than interfaces stabilized by the native proteins only. The interfaces stabilized by ovalbumin and lysozyme complexes have comparable shear and dilatational moduli though ovalbumin-pectin complexes are twice as large in radius as lysozyme-pectin complexes. Under most of the experimental conditions, interfaces stabilized by fibrils have the highest surface rheological moduli. The difference between long semi-flexible lysozyme fibrils or short rigid lysozyme fibrils is not pronounced in interfacial dilation rheology but significant in interfacial shear rheology. The complex surface shear moduli of interfaces stabilized by long semi-flexible fibrils are about 10 times higher than those of interfaces stabilized by short rigid fibrils, over a range of bulk concentrations. Interfaces stabilized by short and more flexible ovalbumin fibrils have a significantly higher surface shear modulus than those stabilized by longer and more rigid lysozyme fibrils. This study has shown that the use of such supra-molecular structural building blocks creates a wider range of microstructural features of the interface, with higher surface shear and dilatational moduli and a more complex dependence on strain.
    On the curvature energy of a thin membrane decorated by polymer brushes
    Birshtein, T.M. ; Iakovlev, P.A. ; Arnoskov, V.M. ; Leermakers, F.A.M. ; Zhulina, E.B. ; Borisov, O.V. - \ 2008
    Macromolecules 41 (2008)2. - ISSN 0024-9297 - p. 478 - 488.
    molecular bottle-brushes - interacting chain molecules - repulsive interactions - cylindrical brushes - lyotropic behavior - statistical-theory - elastic properties - grafted polymers - bending rigidity - lipid-membranes
    In this work, we present approximate analytical predictions for the contribution to the free energy of curvature of a thin (flexible) membrane rising from a polymer brush, which is grafted to both sides of the membrane. The influence of the approximations is revealed by a detailed comparison with numerically exact self-consistent field (SCF) calculations. We consider both the quenched case, i.e., when the grafting density is the same on both sides, and the annealed case, i.e., when the polymer chains can translocate upon bending from one side of the membrane to the other. It is found that the analytical predictions give the correct sign for the brush contribution to the free energy of curvature. Moreover, for spherically curved membranes, a reasonably accurate scaling with the grafting density ¿ and the chain length N is obtained. However, in the case of a cylindrical curvature, the analytical models overestimate the dependence on the polymer chain length. It is shown that the mean bending modulus is positive, which implies that the grafting of polymers onto membranes makes these stiffer. The Gaussian bending modulus is negative and scales with the chain length in the power three, whereas the mean bending modulus scales with the chain length with a power two. This is in contrast with the analytical predictions which point to the same power-law dependence of three. Our results imply that for sufficiently long polymers the flat conformation becomes unstable in favor of bending.
    Dynamics of controlled release systems based on water-in-water emulsions: A general theory
    Sagis, L.M.C. - \ 2008
    Journal of Controlled Release 131 (2008)1. - ISSN 0168-3659 - p. 5 - 13.
    common line motion - simple shear-flow - interfacial permeability - mechanical-properties - bending rigidity - surface-tension - lipid-bilayers - spinning drop - drug-release - vesicles
    Phase-separated biopolymer solutions, and aqueous dispersions of hydrogel beads, liposomes, polymersomes, aqueous polymer microcapsules, and colloidosomes are all examples of water-in-water emulsions. These systems can be used for encapsulation and controlled release purposes, in for example food or pharmaceutical applications. The stress-deformation behavior of the droplets in these systems is very complex, and affected by mass transfer across the interface. The relaxation time of a deformation of a droplet may depend on interfacial properties such as surface tension, bending rigidity, spontaneous curvature, permeability, and interfacial viscoelasticity. It also depends on bulk viscoelasticity and composition. A non-equilibrium thermodynamic model is developed for the dynamic behavior of these systems, which incorporates all these parameters, and is based on the interfacial transport phenomena (ITP) formalism. The ITP formalism allows us to describe all water-in-water emulsions with one general theory. Phase-separated biopolymer solutions, and dispersions of hydrogel beads, liposomes, polymersomes, polymer microcapsules, and colloidosomes are basically limiting cases of this general theory with respect to bulk and interfacial rheological behavior.
    Fluctuations of Permeable Interfaces in Water-in-Water Emulsions
    Sagis, L.M.C. - \ 2007
    Physical Review Letters 98 (2007). - ISSN 0031-9007 - 4 p.
    bending rigidity - biopolymer - mixtures
    The fluctuations of highly permeable interfaces, encountered in phase-separated biopolymer solutions, liposomes, polymersomes, or colloidosomes, are investigated. An expression for the power spectrum of the height correlation function is derived for a multicomponent system, incorporating the effects of mass transfer across the interface, using nonequilibrium thermodynamics. We also derive an expression for the relaxation time of the height correlation function, and calculate the relaxation time for a phase-separated gelatin-dextran-water system. Comparing our expression with the expression for an impermeable interface shows that mass transfer has a significant impact on the relaxation time of the interface
    Nonequilibrium Thermodynamic Model of Water-in-Water Emulsions
    Sagis, L.M.C. - \ 2007
    The Journal of Physical Chemistry Part C: Nanomaterials and Interfaces 111 (2007)7. - ISSN 1932-7447 - p. 3139 - 3145.
    interfacial permeability - bending rigidity - biopolymer - deformation - mixtures
    The dynamic behavior of highly permeable interfaces in phase-separated biopolymer solutions, liposomes, polymersomes, and colloidosomes is investigated. Using nonequilibrium thermodynamics, an expression for the correlation function of the height of a flat interface is derived for a multicomponent system, incorporating the effects of mass transfer across the interface. In addition, an expression is derived for the relaxation time of the height correlation function. This relaxation time is calculated for a phase-separated gelatin-dextran-water system. Comparing our expression with the expression for an impermeable interface shows that mass transfer has a significant impact on the fluctuations of the interface. At small values for the amplitude, the relaxation of fluctuations is completely dominated by the permeability of the interface. At high values for the amplitude, the relaxation is dominated by the viscosities and densities of the bulk phases. In this regime, the long-time limit of the height correlation function shows multiexponential decay. The existence of such a multiexponential response was confirmed by recent experiments (Biomacomolecules 2006, 7, 2224). The crossover length between permeability- and viscosity-dominated relaxation is in the range of 0.1-50 µm.
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