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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Statistical Paradigm for Organic Optoelectronic Devices : Normal Force Testing for Adhesion of Organic Photovoltaics and Organic Light-Emitting Diodes
Vasilak, Lindsay ; Tanu Halim, Silvie M. ; Gupta, Hrishikesh Das; Yang, Juan ; Kamperman, Marleen ; Turak, Ayse - \ 2017
ACS Applied Materials and Interfaces 9 (2017)15. - ISSN 1944-8244 - p. 13347 - 13356.
adhesion testing - degradation - interfaces - metal contact delamination - organic electronics - Weibull statistics

In this study, we assess the utility of a normal force (pull-test) approach to measuring adhesion in organic solar cells and organic light-emitting diodes. This approach is a simple and practical method of monitoring the impact of systematic changes in materials, processing conditions, or environmental exposure on interfacial strength and electrode delamination. The ease of measurement enables a statistical description with numerous samples, variant geometry, and minimal preparation. After examining over 70 samples, using the Weibull modulus and the characteristic breaking strength as metrics, we were able to successfully differentiate the adhesion values between 8-tris(hydroxyquinoline aluminum) (Alq3) and poly(3-hexyl-thiophene) and [6,6]-phenyl C61-butyric acid methyl ester (P3HT:PCBM) interfaces with Al and between two annealing times for the bulk heterojunction polymer blends. Additionally, the Weibull modulus, a relative measure of the range of flaw sizes at the fracture plane, can be correlated with the roughness of the organic surface. Finite element modeling of the delamination process suggests that the out-of-plane elastic modulus for Alq3 is lower than the reported in-plane elastic values. We suggest a statistical treatment of a large volume of tests be part of the standard protocol for investigating adhesion to accommodate the unavoidable variability in morphology and interfacial structure found in most organic devices.

Coalescence, cracking, and crack healing in drying dispersion
Kooij, H.M. van der; Kool, R.H.M. de; Gucht, J. van der; Sprakel, J.H.B. - \ 2015
Langmuir 31 (2015)15. - ISSN 0743-7463 - p. 4419 - 4428.
latex film formation - glass-transition temperature - polymer diffusion - deformation - polystyrene - interfaces - coatings - surface - modes - bulk
The formation of a uniform film from a polymer dispersion is a complex phenomenon involving the interplay of many processes: evaporation and resulting fluid flows through confined geometries, particle packing and deformation, coalescence, and cracking. Understanding this multidimensional problem has proven challenging, precluding a clear understanding of film formation to date. This is especially true for drying dispersion droplets, where the particular geometry introduces additional complexity such as lateral flow toward the droplet periphery. We study the drying of these droplets using a simplified approach in which we systematically vary a single parameter: the glass transition temperature (Tg) of the polymer. We combine optical with scanning electron microscopy to elucidate these processes from the macroscopic down to the single-particle level, both qualitatively and quantitatively, over times ranging from seconds to days. Our results indicate that the polymer Tg has a marked influence on the time evolution of particle deformation and coalescence, giving rise to a distinct and sudden cracking transition. Moreover, in cracked droplets it affects the frequently overlooked time scale of crack healing, giving rise to a second transition from self-healing to permanently cracked droplets. These findings are in line with the classical Routh–Russel model for film formation yet extend its scope from particle-level dynamics to long-range polymer flow.
Ion adsorption-induced wetting transition in oil-water-mineral systems
Mugele, F. ; Bera, B. ; Cavalli, A. ; Siretanu, I. ; Maestro, A. ; Duits, M. ; Cohen Stuart, M.A. ; Ende, D. van den - \ 2015
Scientific Reports 5 (2015). - ISSN 2045-2322 - 8 p.
hydration forces - surfaces - recovery - wettability - interfaces - membranes - charge - layer
The relative wettability of oil and water on solid surfaces is generally governed by a complex competition of molecular interaction forces acting in such three-phase systems. Herein, we experimentally demonstrate how the adsorption of in nature abundant divalent Ca2+ cations to solid-liquid interfaces induces a macroscopic wetting transition from finite contact angles (˜10°) with to near-zero contact angles without divalent cations. We developed a quantitative model based on DLVO theory to demonstrate that this transition, which is observed on model clay surfaces, mica, but not on silica surfaces nor for monovalent K+ and Na+ cations is driven by charge reversal of the solid-liquid interface. Small amounts of a polar hydrocarbon, stearic acid, added to the ambient decane synergistically enhance the effect and lead to water contact angles up to 70° in the presence of Ca2+. Our results imply that it is the removal of divalent cations that makes reservoir rocks more hydrophilic, suggesting a generalizable strategy to control wettability and an explanation for the success of so-called low salinity water flooding, a recent enhanced oil recovery technology.
Colloidal liquid crystals in rectangular confinement: theory and experiment
Lewis, A.H. ; Garlea, I. ; Alvarado, J. ; Dammone, O.J. ; Howell, P.D. ; Majumdar, A. ; Mulder, B. ; Lettinga, M.P. ; Koenderink, G.H. ; Aarts, D.G.A.L. - \ 2014
Soft Matter 10 (2014)39. - ISSN 1744-683X - p. 7865 - 7873.
cell-sized confinement - de-gennes theory - alignment - phases - interfaces - surfaces - defects
We theoretically and experimentally study nematic liquid crystal equilibria within shallow rectangular wells. We model the wells within a two-dimensional Oseen-Frank framework, with strong tangent anchoring, and obtain explicit analytical expressions for the director fields and energies of the 'diagonal' and 'rotated' solutions reported in the literature. These expressions separate the leading-order defect energies from the bulk distortion energy for both families of solutions. The continuum Oseen-Frank study is complemented by a microscopic mean-field approach. We numerically minimize the mean-field functional, including the effects of weak anchoring, variable order and random initial conditions. In particular, these simulations suggest the existence of higher-energy metastable states with internal defects. We compare our theoretical results to experimental director profiles, obtained using two types of filamentous virus particles, wild-type fd-virus and a modified stiffer variant (Y21M), which display nematic ordering in rectangular chambers, as found by confocal scanning laser microscopy. We combine our analytical energy expressions with experimentally recorded frequencies of the different equilibrium states to obtain explicit estimates for the extrapolation length, defined to be the ratio of the nematic elastic constant to the anchoring coefficient, of the fd-virus.
The Landau free energy of hard ellipses obtained from microscopic simulations
Luo, A.M. ; Sagis, L.M.C. ; Ilg, P. - \ 2014
Journal of Chemical Physics 140 (2014). - ISSN 0021-9606 - 7 p.
isotropic-nematic transition - interfaces - crystals
Systems of two-dimensional hard ellipses of varying aspect ratios and packing fractions are studied by Monte Carlo simulations in the generalised canonical ensemble. From this microscopic model, we extract a coarse-grained macroscopic Landau-de Gennes free energy as a function of packing fraction and orientational order parameter. We separate the free energy into the ideal orientational entropy of non-interacting two-dimensional spins and an excess free energy associated with excluded volume interactions.We further explore the isotropic-nematic phase transition using our empirical expression for the free energy and find that the nature of the phase transition is continuous for the aspect ratios we studied.
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.
Effect of Glycation on the Flocculation Behavior of Protein-Stabilized Oil-in-Water Emulsions
Delahaije, R.J.B.M. ; Gruppen, H. ; Nieuwenhuijzen, N.H. van; Giuseppin, M.L.F. ; Wierenga, P.A. - \ 2013
Langmuir 29 (2013)49. - ISSN 0743-7463 - p. 15201 - 15208.
bovine serum-albumin - beta-lactoglobulin - physicochemical properties - adsorption dynamics - disjoining pressure - alpha-lactalbumin - interfaces - particles - thickness - size
Glycation of proteins by the Maillard reaction is often considered as a method to prevent flocculation of protein-stabilized oil-in-water emulsions. The effect has been suggested, but not proven, to be the result of steric stabilization, and to depend on the molecular mass of the carbohydrate moiety. To test this, the stabilities of emulsions of patatin glycated to the same extent with different mono- and oligosaccharides (xylose, glucose, maltotriose, and maltopentaose) were compared under different conditions (pH and electrolyte concentration). The emulsions with non-modified patatin flocculate under conditions in which the zeta potential is decreased (around the iso-electric point and at high ionic strength). The attachment of monosaccharides (i.e., glucose) did not affect the flocculation behavior. Attachment of maltotriose and maltopentaose (Mw > 500 Da), on the other hand, provided stability against flocculation at the iso-electric point. Since the zeta potential and the interfacial properties of the emulsion droplets are not affected by the attachment of the carbohydrate moieties, this is attributed to steric stabilization. Experimentally, a critical thickness of the adsorbed layer required for steric stabilization against flocculation was found to be 2.29–3.90 nm. The theoretical determination based on the DLVO interactions with an additional steric interaction coincides with the experimental data. Hence, it can be concluded that the differences in stability against pH-induced flocculation are caused by steric interactions.
Protein Concentration and Protein-Exposed Hydrophobicity as Dominant Parameters Determining the Flocculation of Protein-Stabilized Oil-in-Water Emulsions
Delahaije, R.J.B.M. ; Wierenga, P.A. ; Nieuwenhuijzen, N.H. van; Giuseppin, M.L.F. ; Gruppen, H. - \ 2013
Langmuir 29 (2013)37. - ISSN 0743-7463 - p. 11567 - 11574.
diffusing wave spectroscopy - beta-lactoglobulin - coalescence stability - disjoining pressure - drop size - adsorption - films - ph - interfaces - ovalbumin
DLVO theory is often considered to be applicable to the description of flocculation of protein-stabilized oil-in-water emulsions. To test this, emulsions made with different globular proteins (ß-lactoglobulin, ovalbumin, patatin, and two variants of ovalbumin) were compared under different conditions (pH and electrolyte concentration). As expected, flocculation was observed under conditions in which the zeta potential is decreased (around the isoelectric point and at high ionic strength). However, the extent of flocculation at higher ionic strength (>50 mM NaCl) decreased with increasing protein-exposed hydrophobicity. A higher exposed hydrophobicity resulted in a higher zeta potential of the emulsion droplets and consequently increased stability against flocculation. Furthermore, the addition of excess protein strongly increased the stability against salt-induced flocculation, which is not described by DLVO theory. In the protein-poor regime, emulsions showed flocculation at high ionic strength (>100 mM NaCl), whereas emulsions were stable against flocculation if excess protein was present. This research shows that the exposed hydrophobicity of the proteins and the presence of excess protein affect the flocculation behavior.
Solvated protein-protein docking using Kyte-Doolittle-based water preferences
Kastritis, P.L. ; Visscher, K.M. ; Dijk, A.D.J. van; Bonvin, A.M.J.J. - \ 2013
Proteins : Structure, Function, and Bioinformatics 81 (2013)3. - ISSN 0887-3585 - p. 510 - 518.
ligand docking - biomolecular complexes - globular-proteins - drug design - molecules - recognition - interfaces - solvent - haddock - challenges
HADDOCK is one of the few docking programs that can explicitly account for water molecules in the docking process. Its solvated docking protocol starts from hydrated molecules and a fraction of the resulting interfacial waters is subsequently removed in a biased Monte Carlo procedure based on water-mediated contact probabilities. The latter were derived from an analysis of water contact frequencies from high-resolution crystal structures. Here, we introduce a simple water mediated amino acid - amino acid contact probability scale derived from the Kyte-Doolittle hydrophobicity scale and assess its performance on the largest high-resolution dataset developed to date for solvated docking. Both scales yield high-quality docking results. The novel and simple hydrophobicity scale, which should reflect better the physico-chemical principles underlying contact propensities, leads to a performance improvement of around 10% in ranking, cluster quality and water recovery at the interface compared to the statistics-based original solvated docking protocol.
In vitro lipid digestion of chitin nanocrystal stabilized o/w emulsions
Tzoumaki, M.V. ; Moschakis, T. ; Scholten, E. ; Biliaderis, C.G. - \ 2013
Food & Function 4 (2013)1. - ISSN 2042-6496 - p. 121 - 129.
beta-lactoglobulin - cholesterol absorption - emulsified lipids - pancreatic lipase - fat digestion - chitosan - dispersions - interfaces - droplets - delivery
Chitin nanocrystals (ChN) have been shown to form stable Pickering emulsions. These oil-in-water emulsions were compared with conventional milk (whey protein isolate, WPI, and sodium caseinate, SCn) protein-stabilized emulsions in terms of their lipid digestion kinetics using an in vitro enzymatic protocol. The kinetics of fatty acid release were evaluated as well as the change in oil droplet size of the respective emulsions during lipid digestion. The interfacial pressure was measured by addition of the duodenal components using drop tensiometry and the electrical charge of the oil droplets was also assessed, in an attempt to relate the interfacial properties with the stability of the emulsions towards lipolysis. Lipid hydrolysis in the ChN-stabilized emulsion was appreciably slower and the plateau values of the total concentration of fatty acids released were much lower, compared to the WPI- and SCn-stabilized emulsions. Moreover, the ChN-stabilized emulsions were relatively stable to coalescence during lipid digestion, whereas the WPI- and SCn-stabilized emulsions exhibited a significant increase in their droplet size. On the other hand, no major differences were shown among the different emulsion samples in terms of their interfacial properties. The increased stability of the ChN-stabilized emulsions towards lipolysis could be attributed to several underlying mechanisms: (i) strong and irreversible adsorption of the chitin nanocrystals at the interface that might inhibit an extensive displacement of the solid particles by bile salts and lipase, (ii) network formation by the nanocrystals in the bulk (continuous) phase that may reduce lipid digestion kinetics, and (iii) the ability of chitin, and consequently of ChNs, to impair pancreatic lipase activity. The finding that ChNs can be used to impede lipid digestion may have important implications for the design and fabrication of structured emulsions with controlled lipid digestibility that could provide the basis for the development of novel products that may promote satiety, reduce caloric intake and combat obesity.
Biomimetic mineralization of calcium phosphate on a functionalizaed porous silicon carbide biomaterial
Dey, A. ; Hoogen, C.J. van de; Rosso, M. ; Lousberg, N.J.H.G.M. ; Hendrix, M.M.R.M. ; Friedrich, H. ; Ramirez Rico, J. ; Zuilhof, H. ; With, G. de; Sommerdijk, N.A.J.M. - \ 2012
ChemPlusChem 77 (2012)8. - ISSN 2192-6506 - p. 694 - 699.
octacalcium phosphate - biomedical applications - bioactive glass - in-vitro - hydroxyapatite - bone - transformation - ceramics - crystallization - interfaces
Porous biomorphic silicon carbide (bioSiC) is a structurally realistic, high-strength, and biocompatible material which is promising for application in load-bearing implants. The deposition of an osteoconductive coating is essential for further improvement of its integration with the surrounding tissue. A new strategy towards biomimetic calcium phosphate coatings on bioSiC is described. X-ray photoelectron spectroscopy (XPS) analysis shows that using 10-undecenoic acid methyl ester a covalently bound monolayer can be synthesized on the surface of the bioSiC. After hydrolysis it exposes carboxylic acid groups that promote the selective nucleation and growth of a very well-defined crystalline layer of calcium phosphate. The resulting calcium phosphate coating is characterized by X-ray diffraction and electron microscopy techniques. Further, ion beam imaging is employed to quantify the mineral deposition meanwhile, three-dimensional dual-beam imaging (FIB/SEM) is used to visualize the bioSiC/mineral interface. The monolayer is show to actively induce the nucleation of a well-defined and highly crystalline mixed octacalcium phosphate/hydroxyapatite (OCP/HAP) coating on implantable bioSiC substrates with complex geometry. The mild biomimetic procedure, in principle, allows for the inclusion of bioactive compounds that aid in tissue regeneration. Moreover, the mixed OCP/HAP phase will have a higher solubility compared to HAP, which, in combination with its porous structure, is expected to render the coating more reabsorbable than standard HAP coatings.
Hybrids of Organic Molecules and Flat, Oxide-Free Silicon: High-Density Monolayers, Electronic Properties, and Functionalization
Li, Y. ; Calder, S.A. ; Yaffe, O. ; Cahen, D. ; Haick, H. ; Kronik, L. ; Zuilhof, H. - \ 2012
Langmuir 28 (2012)26. - ISSN 0743-7463 - p. 9920 - 9929.
hydrogen-terminated si(111) - mixed methyl/allyl monolayers - alkyl monolayers - porous silicon - si surfaces - carrier lifetime - label-free - interfaces - hydrosilylation - passivation
Since the first report of Si–C bound organic monolayers on oxide-free Si almost two decades ago, a substantial amount of research has focused on studying the fundamental mechanical and electronic properties of these Si/molecule surfaces and interfaces. This feature article covers three closely related topics, including recent advances in achieving high-density organic monolayers (i.e., atomic coverage >55%) on oxide-free Si(111) substrates, an overview of progress in the fundamental understanding of the energetics and electronic properties of hybrid Si/molecule systems, and a brief summary of recent examples of subsequent functionalization on these high-density monolayers, which can significantly expand the range of applicability. Taken together, these topics provide an overview of the present status of this active area of research.
Properties of emulsions stabilised by sodium caseinate–chitosan complexes
Zinoviadou, K. ; Scholten, E. ; Moschakis, T. ; Biliaderis, C.G. - \ 2012
International Dairy Journal 26 (2012)1. - ISSN 0958-6946 - p. 94 - 101.
in-water emulsions - whey-protein isolate - beta-lactoglobulin-pectin - high-methoxyl pectin - polysaccharide interactions - bioactive components - particle tracking - dextran sulfate - o/w emulsions - interfaces
Oil-in-water emulsions (10%, w/w, oil) were prepared at pH 5.7 by using electrostatically formed complexes of 0.5% (w/w) sodium caseinate (Na-CAS) and 0–0.6% (w/w) chitosan. Emulsions stabilized by complexes with increased levels of chitosan (>0.2% w/w) had a smaller average droplet size and exhibited greater stability during storage. All chitosan containing emulsions exhibited a slight shear thinning behaviour with increased high-shear-rate viscosity at higher chitosan levels. Even though complexing of Na-CAS with chitosan resulted in a delay of the adsorption of the surface active components at the oil/water interface, the presence of chitosan did not significantly influence the rheological properties of the formed interfaces. Acid-induced aggregation was observed only for the emulsion that was stabilized solely by Na-CAS when the pH dropped close to the isoelectric point of the protein component, resulting in flocculation and large increase in the storage modulus.
Interactome-Wide Prediction of Protein-Protein Binding Sites Reveals Effects of Protein Sequence Variation in Arabidopsis thaliana
Valentim, F.L. ; Neven, F. ; Boyen, P. ; Dijk, A.D.J. van - \ 2012
PLoS ONE 7 (2012)10. - ISSN 1932-6203
interaction networks - hot-spots - conservation - interfaces - database - topless - motifs - growth - roles - gene
The specificity of protein-protein interactions is encoded in those parts of the sequence that compose the binding interface. Therefore, understanding how changes in protein sequence influence interaction specificity, and possibly the phenotype, requires knowing the location of binding sites in those sequences. However, large-scale detection of protein interfaces remains a challenge. Here, we present a sequence- and interactome-based approach to mine interaction motifs from the recently published Arabidopsis thaliana interactome. The resultant proteome-wide predictions are available via www.ab.wur.nl/sliderbio and set the stage for further investigations of protein-protein binding sites. To assess our method, we first show that, by using a priori information calculated from protein sequences, such as evolutionary conservation and residue surface accessibility, we improve the performance of interface prediction compared to using only interactome data. Next, we present evidence for the functional importance of the predicted sites, which are under stronger selective pressure than the rest of protein sequence. We also observe a tendency for compensatory mutations in the binding sites of interacting proteins. Subsequently, we interrogated the interactome data to formulate testable hypotheses for the molecular mechanisms underlying effects of protein sequence mutations. Examples include proteins relevant for various developmental processes. Finally, we observed, by analysing pairs of paralogs, a correlation between functional divergence and sequence divergence in interaction sites. This analysis suggests that large-scale prediction of binding sites can cast light on evolutionary processes that shape protein-protein interaction networks
An extended rational thermodynamics model for surface excess fluxes
Sagis, L.M.C. - \ 2012
Physica A 391 (2012)4. - ISSN 0378-4371 - p. 979 - 990.
irreversible thermodynamics - general formalism - complex fluids - kinetic-theory - dynamics - fluctuations - interfaces - rheology - bilayers
In this paper, we derive constitutive equations for the surface excess fluxes in multiphase systems, in the context of an extended rational thermodynamics formalism. This formalism allows us to derive Maxwell–Cattaneo type constitutive laws for the surface extra stress tensor, the surface thermal energy flux vector, and the surface mass flux vector, which incorporate a direct coupling to their corresponding bulk fluxes in the adjacent bulk phases. These constitutive laws also incorporate contributions to the time evolution of the surface excess fluxes from spatial inhomogeneities in these flux fields. These phenomenological equations can be used to model the dynamic behavior of complex viscoelastic interfaces in multiphase systems, in the small deformation limit.
Pluronic-lysozyme conjugates as anti-adhesive and antibacterial bifunctional polymers for surface coating
Muszanska, A.K. ; Busscher, H.J. ; Herrmann, A. ; Mei, H.C. van der; Norde, W. - \ 2011
Biomaterials 32 (2011)26. - ISSN 0142-9612 - p. 6333 - 6341.
egg-white lysozyme - protein adsorption - bacterial adhesion - block-copolymers - hydrophobic surfaces - grafting density - biomaterials - brushes - temperature - interfaces
This paper describes the preparation and characterization of polymer protein conjugates composed of a synthetic triblock copolymer with a central polypropylene oxide (PPO) block and two terminal polyethylene oxide (PEO) segments, Pluronic F-127, and the antibacterial enzyme lysozyme attached to the telechelic groups of the PEO chains. Covalent conjugation of lysozyme proceeded via reductive amination of aldehyde functionalized PEO blocks (CHO-Pluronic) and the amine groups of the lysine residues in the protein. SDS-PAGE gel electrophoresis together with MALDI-TOF mass spectrometry analysis revealed formation of conjugates of one or two lysozyme molecules per Pluronic polymer chain. The conjugated lysozyme showed antibacterial activity towards Bacillus subtilis. Analysis with a quartz crystal microbalance with dissipation revealed that Pluronic lysozyme conjugates adsorb in a brush conformation on a hydrophobic gold-coated quartz surface. X-ray photoelectron spectroscopy indicated surface coverage of 32% by lysozyme when adsorbed from a mixture of unconjugated Pluronic and Pluronic lysozyme conjugate (ratio 99:1) and of 47% after adsorption of 100% Pluronic-lysozyme conjugates. Thus, bifunctional brushes were created, possessing both anti-adhesive activity due to the polymer brush, combined with the antibacterial activity of lysozyme. The coating having a lower degree of lysozyme coverage proved to be more bactericidal.
Jatropha seed protein functional properties for technical applications
Lestari, D. ; Mulder, W.J. ; Sanders, J.P.M. - \ 2011
Biochemical Engineering Journal 53 (2011)3. - ISSN 1369-703X - p. 297 - 304.
soy protein - antinutritional factors - curcas - films - concentrate - interfaces - extraction - oilseed - plant - foams
Jatropha press cake, by-product after oil expression from Jatropha seeds, contains 24–28% protein on dry basis. Objectives of this research were to investigate functional properties, such as solubility, emulsifying, foaming, film forming, and adhesive properties, of Jatropha press cake proteins and compared those with relevant industrial proteins. From our study, we found that protein extracted from press cake proteins had a solubility of about 90% above pH 9. Emulsifying properties of press cake protein were comparable to sodium caseinates and reached the highest value at pH 9–10. Jatropha proteins formed films with tensile strength of 0.4–1.8 MPa with 10–75% elongation, which were below soy protein or wheat-gluten. Further oil removal from press cake decreased emulsifying properties, while increased foaming and adhesive properties of the extracted proteins. Protein extracted from de-oiled press cake showed better foaming properties than sodium caseinate at pH 10, but lower than egg white protein at all pH. Furthermore, press cake protein showed better adhesive properties than casein adhesives at the same dry matter content. Based on these results, Jatropha press cake protein showed most promising results on adhesive and emulsifying properties, which indicate the potential of Jatropha press cake protein as emulsifier or paper adhesive.
Modified Capillary Cell for Foam Film Studies Allowing Exchange of the Film-Forming Liquidwie
Wierenga, P.A. ; Basheva, E.S. ; Denkov, N.D. - \ 2009
Langmuir 25 (2009)11. - ISSN 0743-7463 - p. 6035 - 6039.
anionic surfactant solutions - continuous-flow tensiometry - coalescence stability - protein adsorption - ionic-strength - drop size - emulsions - interfaces - forces - ph
Many of the macroscopic properties of foams and emulsions are controlled by the mesoscopic properties of the thin films separating the bubbles or droplets. The properties of these films depend on contributions (1) from the adsorbed surface layers and (2) from the liquid that separates these adsorbed layers. To separate in the experimental studies the effects of these two contributions, we developed a new modified version of the capillary cell for foam film studies (originally developed by Scheludko and Exerowa (Scheludko, A.; Exerowa, D. Kolloid Z. 1959, 165, 148-151), which allows exchange of the film-forming liquid between the air-water surfaces. This modified cell allows one to distinguish between the role of the adsorbed species (e.g., proteins, particles, or long-chain synthetic polymers) and the species present in the film interior (e.g., particles, electrolytes, or surfactants). The film properties that can be studied in this way include film stability, rate of film thinning, and surface forces stabilizing the film. These properties are of significant interest in understanding and controlling the stability of dispersed systems. The experimental procedure and the capabilities of the modified cell are demonstrated in several examples.
Metal Flux in ligand mixtures. 2. Flux enhancement due to kinetic interplay: Comparison of the reaction layer approximation with a rigorous approach
Zhang, Z. ; Buffle, J. ; Town, R.M. ; Puy, J. ; Leeuwen, H.P. van - \ 2009
The Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment, & General Theory 113 (2009)24. - ISSN 1089-5639 - p. 6572 - 6580.
reaction-diffusion processes - complex-systems - dynamic speciation - alga chlamydomonas - phytoplankton - interfaces - lability - code
The revisited reaction layer approximation (RLA) of metal flux at consuming interfaces in ligand mixtures, discussed in the previous paper (part 1 of this series15) is systematically validated by comparison with the results of rigorous numerical simulations. The current paper focuses on conditions under which the total metal flux is enhanced in the ligand (and complex) mixture compared to the case where the individual fluxes of metal complexes are independent of each other. Such an effect is exhibited only in ligand mixtures and results from the kinetic interplay between the various complexes with different labilities. It is exemplified by the Cu/NTA/N-(2-carboxyphenyl)glycine system (see part 1 paper), in which we show that the flux due to the less labile complex (CuNTA) is increased in the presence of a ligand (2-carboxyphenyl)glycine) that forms labile Cu complexes, even when the latter is in negligible proportion in the bulk solution. This paper first explains how the so-called composite and equivalent reaction layer thicknesses computed by RLA can be determined graphically from the concentration profiles of free metal and its complexes, as obtained by rigorous calculations. This approach allows comparison between the latter and RLA predictions. Comparison between these reaction layer thicknesses is then done using the chemical system mentioned above. The mechanism of flux enhancement with this system is studied in detail by following the change of the concentration profiles and reaction layer thicknesses with the increase of concentration of the ligand forming labile complexes. The mechanism of flux enhancement is well explained by the RLA and is validated by the concentration profiles obtained by rigorous numerical simulations. Based on this validation, the RLA is used to predict the conditions of the individual complex labilities and degree of complexation required to get flux enhancement in a two-ligand system. Due to compensation effects between kinetic and thermodynamic factors, a maximum flux enhancement is observed in a specific range of ratios of the lability indices of the two complexes. Flux enhancement might play a significant role in metal uptake in environmental or biological systems and should be considered in data interpretation
New ends to the tale of tails: adsorption of comb polymers and the effect on colloid stability
Charlaganov, M. ; Kosovan, P. ; Leermakers, F.A.M. - \ 2009
Soft Matter 5 (2009)7. - ISSN 1744-683X - p. 1448 - 1459.
interacting chain molecules - statistical-theory - field theory - interfaces - surface - layers - macromolecules - weight
In this paper we consider the classical problem of homopolymer adsorption at the solid–liquid interface and discuss its implications for colloidal stability. More specifically, our focus is on comb-like homopolymers in the strong adsorption limit. A self-consistent field analysis shows that for relatively long side chains but still much longer backbones, the adsorbed layer is dominated by the side chains near the surface, whereas at larger distances the layer has features that belong to the backbone. As a rule, homopolymer adsorption promotes flocculation of colloids. This is attributed to the long polymer chains that form bridges between the colloidal particles. However, the free ends of the chains do not participate in the bridging and thus contribute with a small repulsive term to the mainly attractive pair interaction. For comb polymers, the free ends of the side chains amplify the repulsion dramatically. As a result, in contrast to linear adsorbed homopolymers, comb polymers typically prevent flocculation
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