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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    Microfluidic methods to study emulsion formation
    Muijlwijk, Kelly - \ 2017
    Wageningen University. Promotor(en): C.G.P.H. Schroën, co-promotor(en): C.C. Berton-Carabin. - Wageningen : Wageningen University - ISBN 9789463430715 - 169
    emulsions - microfluidics - food emulsions - droplets - adsorption - colloidal properties - emulsies - microfluidics - voedselemulsies - druppels - adsorptie - colloïdale eigenschappen

    Emulsions are dispersions of one liquid in another that are commonly used in various products, and methods such as high-pressure homogenisers and colloid mills are used to form emulsions. The size and size distribution of emulsion droplets are important for the final product properties and thus need to be controlled. Rapid coalescence of droplets during emulsification increases droplet size and widens the size distribution, and therefore needs to be prevented.

    To increase stability of emulsions, emulsifiers are added to adsorb at the oil-water interface before droplets collide. The time allowed for emulsifier adsorption is typically in the range of sub-milliseconds to seconds and to optimise emulsification processes, emulsifier adsorption and coalescence stability need to be measured in this time-scale, for which the microfluidic methods described in this thesis were developed.

    Chapter 2 provides an overview of existing literature on cross-flow microfluidic emulsification. The effects of various parameters such as microfluidic design, shear forces, and interfacial tension forces on droplet formation and the resulting droplet size are discussed, as well as the use of microfluidics to produce food-grade emulsions. Based on this evaluation, the methods to elucidate interfacial tension and coalescence stability are chosen, and these are presented in the next chapters.

    To measure emulsifier adsorption in the sub-millisecond time-scale, a tensiometric method was developed using a cross-flow microfluidic Y-junction, which is described in Chapter 3. This method is based on the relation between droplet size and interfacial tension at the moment of droplet formation, which is referred to as the acting interfacial tension. The acting interfacial tension of a system with hexadecane as the dispersed phase and sodium dodecylsulfate (SDS, a model surfactant) solutions as the continuous phase was successfully measured for droplet formation times ranging from 0.4 to 9.4 milliseconds and with high expansion rates (100-2000 s-1). Comparison of these results with data from a drop tensiometer (a conventional, static, and supra-second time-scale method) indicates that mass transport in the microfluidic Y-junction is fast and probably not limited by diffusion.

    Emulsifier mass transport conditions were further investigated in Chapter 4. The continuous phase viscosity and velocity were systematically varied and the effect on the acting interfacial tension in presence of water-soluble SDS was measured. We found that the acting interfacial tension was independent of the continuous phase viscosity, but was inversely dependent on continuous phase velocity. Both aspects led us to conclude that convective emulsifier transport in the continuous phase determines the acting interfacial tension in the Y-junction. When using oil-soluble surfactant Span 20 (dissolved in hexadecane), the acting interfacial tension also decreased with increasing continuous phase velocity, and we therefore concluded that convection also dominated mass transport of emulsifiers dissolved in the to-be-dispersed phase.

    The Y-junction method was used in Chapter 5 to elucidate the effect of the dispersed phase viscosity on adsorption of the food-grade emulsifiers Tween 20 (dissolved in the continuous water phase) and Span 20 (dissolved in the dispersed oil phase). A reduction in dispersed phase viscosity sped up adsorption of Tween 20, probably because the shorter hydrocarbon made intercalation of the hydrophobic surfactant tail at the interface easier. Dispersed phase viscosity had an even greater effect on adsorption of Span 20 because convective transport towards the interface was increased.

    Next to interfacial tension, also coalescence can be measured with microfluidics and a microfluidic collision channel was used in Chapter 6 to measure emulsion coalescence stability shortly after droplet formation under flow. Coalescence of emulsions stabilised with proteins was measured at various concentrations, pH values, and adsorption times. We found that protein concentrations just below the concentration needed for monolayer surface coverage may be used effectively. β-lactoglobulin-stabilised emulsions were most stable. Emulsions stabilised with whey protein isolate (with as main component β-lactoglobulin), were less stable and when these proteins were oxidised, this led to reduced stability, therewith indicating that also the oxidative state of proteins needs to be considered in emulsion formulation.

    The relevance of our work for microfluidic research and industrial emulsification processes is discussed in Chapter 7. Microfluidic devices can be used to study emulsion formation and stability under conditions relevant to industrial emulsification processes; at short time-scales and with convective mass transport. In this thesis we used various food-grade ingredients, and with that application in that field has come closer. We expect that the findings on emulsions can also be applied on foams. With the discussed microfluidic devices different aspects that are important for emulsion formation can be decoupled: for example interfacial tension during droplet formation and emulsion coalescence stability. Furthermore, microfluidic methods are available to for example gain insight in emulsion interface mobility and emulsion storage stability, and we envision that all these microfluidic methods will lead to faster ingredient screening, lower ingredient usage, and more energy efficient emulsion production.

    Core-shell particles at fluid interfaces : performance as interfacial stabilizers
    Buchcic, C. - \ 2016
    Wageningen University. Promotor(en): Martien Cohen Stuart, co-promotor(en): R.H. Tromp; Marcel Meinders. - Wageningen : Wageningen University - ISBN 9789462578968 - 140
    stabilization - stabilizers - particles - colloidal properties - adsorption - interface - fluids - stabilisatie - stabiliseermiddelen - deeltjes - colloïdale eigenschappen - adsorptie - grensvlak - vloeistoffen (fluids)

    There is a growing interest in the use of particles as stabilizers for foams and emulsions. Applying hard particles for stabilization of fluid interface is referred to as Pickering stabilization. By using hard particles instead of surfactants and polymers, fluid interfaces can be effectively stabilized against Ostwald ripening and coalescence. A drawback of the use of hard particles as interfacial stabilizers is that they often experience a pronounced energy barrier for interfacial adsorption and that hard particles are very specific with regard to the type of fluid interface they can adsorb to. Soft particles, on the other hand, are known as good stabilizers against coalescence and they spontaneously adsorb to a variety of different fluid interfaces.

    The aim of this thesis was to investigate core-shell particles comprising a hard core and soft shell with regard to their interfacial behaviour and their ability to act as sole stabilizers for foams and emulsions. We hypothesised that the presence of the soft shell allows for easier interfacial adsorption of core-shell particles compared to the hard core particles only. To test this hypothesis, we prepared core-shell particles comprising a solid polystyrene (PS) core and a soft poly-N-isopropylacrylamide (PNIPAM) shell. To ascertain the effect of shell thickness, we prepared a range of core-shell particles with different shell thicknesses, containing identical core particles. We found that core-shell particles are intrinsically surface active and can generate high surface pressures at the air-water interface and oil-water interfaces, whereas core particles seemed to experience a large energy barrier for interfacial adsorption and did not lower the surface tension. We also confirmed by microscopy that core-shell particles are actually adsorbing to the fluid interface and form densely packed interfacial layers. Further, we found that a certain critical thickness of the soft shell is necessary in order to ensure facile interfacial adsorption. If the PNIPAM shell on top of the core particles is well above 100nm thick, particle adsorption at the air-water interface was found to be diffusion limited.

    By gentle hand-shaking we were able to produce dispersion of air bubbles and emulsion droplets solely stabilized by core-shell particles. The resulting bubbles still underwent Ostwald ripening, albeit slowly. For oil-in-water emulsions of hexane and toluene, both of which have a relatively high solubility in the continuous phase, we found that core-shell particles can stop Ostwald ripening. The resulting emulsion droplets adopted pronounced non-spherical shapes, indicating a high elasticity of the interface. The high stability and the remarkable non-spherical shape of the emulsion droplets stabilized by core-shell particles were features we also observed for fluid dispersion stabilized by hard particles. This shows that in terms of emulsion stability core-shell particles behave similar to hard particles as interfacial stabilizer.

    As to why the differences between the stability of bubble and oil dispersions arise could not be finally answered. Yet, microscopic analysis of the interfacial configuration of core-shell particles at the air-water interface reveals some peculiar insights which may suggest that core-shell particles adsorb in a polymer-like fashion with the soft PNIPAM shells adsorbing to the air-water interface only, while the hard PS cores reside in the continuous phase.

    In summary, we showed that core-shell particles with a hard core and a soft shell can indeed combine the advantageous properties of hard and soft particles. The soft shell enables spontaneous adsorption to a variety of fluid interfaces. Despite their spontaneous adsorption, core-shell particles strongly anchor and do not spontaneously desorb from the fluid interface again. Further, the hard core provides enough rigidity to the core-shell particles to allow the establishment of a stress bearing interfacial particle network. This network eventually stops Ostwald ripening in oil-in-water emulsions. Our results therefore show that in the case of oil-water interfaces, core-shell particles can perform better than solely hard particles as interfacial stabilizers.

    Transformation by photolysis in water in the pesticide model TOXSWA : implementation report
    Beltman, W.H.J. ; Mulder, H.M. ; Horst, M.M.S. ter; Wipfler, E.L. - \ 2015
    Wageningen : Alterra (Alterra report 2649) - 47
    waterverontreiniging - pesticiden - fotolyse - biochemische omzettingen - waterbodems - adsorptie - ecotoxicologie - modellen - water pollution - pesticides - photolysis - biochemical pathways - water bottoms - adsorption - ecotoxicology - models
    The TOXSWA model has been extended with the functionality to simulate photolysis in water. TOXSWA simulates the fate of substances in water bodies to calculate exposure concentrations for aquatic organisms or sediment-dwelling organisms as part of the risk assessment of plant protection products (PPP). Photolysis is modelled as a first-order process, where transformation occurs in the water phase only. The transformation rate is considered to be linearly proportional to global radiation. Studies in outdoor surface water systems can in principle be used to derive the PPP transformation rates due to photolysis.
    Phosphorus leaching from soils: process description, risk assessment and mitigation
    Schoumans, O.F. - \ 2015
    Wageningen : Alterra, Wageningen-UR (Alterra scientific contributions 46) - ISBN 9789462573666 - 261
    nutrient leaching - leaching - soil chemistry - adsorption - phosphorus - phosphate leaching - risk assessment - water quality - eutrophication - nutriëntenuitspoeling - uitspoelen - bodemchemie - adsorptie - fosfor - fosfaatuitspoeling - risicoschatting - waterkwaliteit - eutrofiëring
    Leaching of plant protection products and their transformation products : proposals for improving the assessment of leaching to groundwater in the Netherlands : version 2
    Boesten, J.J.T.I. ; Linden, A.M.A. van der; Beltman, W.H.J. ; Pol, J.W. - \ 2015
    Wageningen : Alterra, Wageningen-UR (Alterra report 2630) - 105
    bodemchemie - adsorptie - pesticiden - uitspoelen - chemische afbraak - schatting - modellen - soil chemistry - adsorption - pesticides - leaching - chemical degradation - estimation - models
    Assessment of leaching of plant protection products to groundwater is an important aspect of the environmental risk assessment of these substances. Analysis of available Dutch groundwater monitoring data for these substances triggered a critical review of the current Dutch leaching assessment. As a result, proposals were developed for improving this assessment. These include: (i) a procedure for correcting systematic errors in measured sorption coefficients, (ii) a preliminary procedure for a quality check of Freundlich exponents, (iii) a flow chart for obtaining parameters describing the relationship between the organic-matter/water distribution coefficient, Kom, and the pH for weak acids, (iv) a procedure for obtaining a Kom endpoint from a population of Kom values including lower and upper limits, (v) a procedure for estimating the total amount of substance in soil from a concentration profile (needed for assessment of degradation half-lives from field experiments). This report is an update of the proposals reported in 2011 by the same authors based on testing the feasibility of the proposals to a few dossiers
    Phosphorus leaching from soils: process description, risk assessment and mitigation
    Schoumans, O.F. - \ 2015
    Wageningen University. Promotor(en): Sjoerd van der Zee, co-promotor(en): Wim Chardon. - Wageningen : Wageningen University - ISBN 9789462572997 - 261
    nutriëntenuitspoeling - uitspoelen - bodemchemie - adsorptie - fosfor - fosfaatuitspoeling - risicoschatting - waterkwaliteit - eutrofiëring - nutrient leaching - leaching - soil chemistry - adsorption - phosphorus - phosphate leaching - risk assessment - water quality - eutrophication
    Er zijn succesvolle management strategieën voor P nodig om de waterkwaliteit te verbeteren en daarvoor is allereerst kwantitatieve informatieve nodig over de ruimtelijke verdeling van de fosfaatbelasting van het oppervlaktewater vanuit landbouwgronden. In Nederland is een protocol fosfaatverzadigde gronden ontwikkeld om het potentiële risico van verhoogde fosfaatconcentraties in het bovenste grondwater (op termijn) te voorspellen voor kalkarme zandgronden, omdat in deze gebieden veel intensieve veehouderij voorkomt. Voor deze grondsoort zijn de parameters voor het protocol vastgesteld. Echter, voor de overige grondsoorten is geen informatie verzameld, waardoor er voor Nederland als geheel geen ruimtelijke beeld bestaat van de mate van fosfaatverzadiging en van het potentiële risico van verhoogde fosfaatconcentraties in het bovenste grondwater. Daarnaast is er behoefte aan eenvoudige methoden om het (huidige) actuele risico van de fosfaatbelasting van het oppervlaktewater in kaart te brengen, zodat inzichtelijk gemaakt kan worden welke gebieden nu al substantieel de oppervlaktewaterkwaliteit en de eutrofiestatus beïnvloeden.
    Afvangen van fosfaat uit bloembollensector met ijzerzand : Test van maatregelen die fosforemissie verminderen
    Chardon, W.J. ; Groenenberg, J.E. ; Jansen, S. ; Buijert, A. ; Talens, R. ; Krol, A.F. - \ 2014
    Bodem 24 (2014)6. - ISSN 0925-1650 - p. 20 - 22.
    vollegrondsteelt - bloembollen - bodemchemie - emissiereductie - fosfaten - adsorptie - ijzer - bollenstreek - outdoor cropping - ornamental bulbs - soil chemistry - emission reduction - phosphates - adsorption - iron - bollenstreek
    In het oppervlaktewater van de Bollenstreek is de fosfaatconcentratie veel hoger dan de norm van de Europese Kaderrichtlijn Water. Met ijzerzand, een nevenproduct van drinkwaterproductie, kan fosfaat worden afgevangen. Het hoogheemraadschap van Rijnland heeft drie maatregelen op basis van ijzerzand laten onderzoeken op hun effectiviteit. Welke was de beste?
    Technologieën voor verwijdering gewasbeschermingsmiddelen
    Beerling, E.A.M. - \ 2014
    gewasbescherming - chemische bestrijding - milieueffect - cost effective analysis - afvalverwerking - oxidatie - scheidingsapparaten - bioremediëring - adsorptie - plant protection - chemical control - environmental impact - cost effectiveness analysis - waste treatment - oxidation - separators - bioremediation - adsorption
    Mogelijk geschikte technieken om chemische gewasbeschermingsmiddelen te verwijderen zodat ze niet het milieu verontreiningen worden geïnventariseerd met behulp van onafhankelijke experts uit de watersector (o.a. KWR, Wetsus, Mannen van de Wit en Stowa)
    Gedrag van chloorprofam en 3-chlooraniline in de bodem : bepaling van adsorptie, omzetting en uitloging met tarragrond van aardappelen
    Beltman, W.H.J. ; Matser, A.M. ; Linden, A.M.A. van der; Brand, E. - \ 2014
    Wageningen : Alterra, Wageningen-UR (Alterra-rapport 2523) - 65
    aardappelopslagplaatsen - aardappelen - opslag - kiemremmers - adsorptie - uitspoelen - grondwaterverontreiniging - potato stores - potatoes - storage - germination inhibitors - adsorption - leaching - groundwater pollution
    Bij de bewaring van aardappelen wordt als kiemremmer de werkzame stof chloorprofam gebruikt. Na verwerking van de aardappelen in de fabriek blijft chloorprofam en haar omzettingsprodukt 3-chlooraniline in de resterende tarragrond aanwezig. De tarragrond wordt hergebruikt in grootschalige bodemtoepassingen. Omzetting, adsorptie en uitloging van chloorprofam en haar metaboliet 3-chlooraniline zijn onderzocht met tarragrond van aardappelen (onbelast en belast met chloorprofam) en met bouwvoorgrond. De omzettingssnelheid van chloorprofam en 3-chlooraniline is bepaald in bouwvoorgrond, in onverzadigde onbelaste tarragrond en in waterverzadigde onbelaste tarragrond. De adsorptieparameters van de Freundlich sorptie isotherm zijn bepaald voor 3-chlooraniline in onbelaste tarragrond en in bouwvoorgrond. De uitloogproeven zijn gedaan met onverzadigde belaste tarragrond en met waterverzadigde belaste tarragrond. De omzettingssnelheden en adsorptieparameters uit deze studie worden gebruikt voor het bepalen van het risico van uitspoeling van chloorprofam en 3-chlooraniline uit grote bodemtoepassingen naar het grondwater.
    Implications of nanoparticles in the aquatic environment
    Velzeboer, I. - \ 2014
    Wageningen University. Promotor(en): Bart Koelmans. - Wageningen : Wageningen University - ISBN 9789461739506 - 253
    microplastics - polychloorbifenylen - nanotechnologie - adsorptie - ecotoxicologie - aquatisch milieu - verontreinigde sedimenten - aquatische ecologie - microplastics - polychlorinated biphenyls - nanotechnology - adsorption - ecotoxicology - aquatic environment - contaminated sediments - aquatic ecology
    De productie en het gebruik van synthetische nanodeeltjes (ENPs) nemen toe en veroorzaken toenemende emissies naar het milieu. Dit proefschrift richt zich op de implicaties van ENPs in het aquatisch milieu, met de nadruk op het sediment, omdat er wordt verwacht dat ENPs hoofdzakelijk in het aquatisch sediment terecht zullen komen. ENPs kunnen directe effecten veroorzaken op organismen in het aquatisch milieu, indirecte effecten op het levensgemeenschap niveau en/of voedselweb en kunnen effecten op het gedrag en de risico’s van andere contaminanten hebben. Om de risico’s van ENPs vast te stellen, is niet alleen informatie nodig over het gevaar, oftewel de kans op een effect, maar ook over de kans op blootstelling.
    Sterke vermindering van fosfaatuitspoeling uit landbouwgronden met de fosfaatbindende drain
    Groenenberg, J.E. ; Chardon, W.J. ; Koopmans, G.F. - \ 2013
    draineerbuizen - drainagewater - ijzer - adsorptie - waterkwaliteit - fosfaten - veldproeven - drain pipes - drainage water - iron - adsorption - water quality - phosphates - field tests
    Voor gedraineerde landbouwgronden (meer dan 50% in Nederland) heeft Alterra de fosfaatbindende drain ontwikkeld. Dit is een normale buisdrain die is ingebed in ijzerzand. De omhulling met ijzerzand bindt het fosfaat uit het fosfaatrijke water voor het de drainbuis instroomt. Het schone water wordt afgevoerd naar het oppervlaktewater.
    Goede waterkwaliteit en meer kansen voor natuur : met immobilisatie van fosfaat door restmaterialen
    Chardon, W.J. ; Groenenberg, J.E. - \ 2013
    landbouwgrond - fosfaatuitspoeling - adsorptie - kaderrichtlijn water - natuurgebieden - agricultural land - phosphate leaching - adsorption - water framework directive - natural areas
    Hoge fosfaatgehalten in landbouwgronden kunnen eutrofiëring van het oppervlaktewater veroorzaken, waardoor overmatige groei van waterplanten en algen optreedt. Met alleen het mestbeleid lukt het niet om de doelstellingen van de Kaderrichtlijn Water (KRW) te bereiken, onder andere als gevolg van de voorraden fosfaat die in de bodem aanwezig zijn. Daarom zijn aanvullende maatregelen noodzakelijk.. Een mogelijke oplossing is de verwijdering van fosfaat in het naar het oppervlaktewater uitstromende water.
    Manual of PEARLNEQ v5
    Boesten, J.J.T.I. ; Horst, M.M.S. ter - \ 2012
    Wageningen : Wettelijke Onderzoekstaken Natuur & Milieu (WOt-werkdocument 304)
    bodemchemie - pesticiden - adsorptie - degradatie - modellen - soil chemistry - pesticides - adsorption - degradation - models
    This manual describes the PEARLNEQ v5 software package . This package can estimate long-term sorption parameters using results of aged-sorption studies with soil, using a submodel for sorption and transformation that is identical to the submodel used for that purpose in the FOCUS_PEARL v3.3.3. The submodel assumes two types of sorption sites: equilibrium sites and non-equilibrium sites. The sorption isotherms for both sites are described with Freundlich equations. The mathematical equations describing the submodel are solved via a FORTRAN programme. An additional FORTRAN programme generates the necessary input files for the PEST optimisation package. Instructions are given how to obtain optimized parameters using an example dataset and how to obtain parameters using your own data.
    Verwijdering van fosfaat uit bodemwater met ijzerzand : De omhulde drain
    Koopmans, G.F. ; Chardon, W.J. ; Belder, P. ; Groenenberg, B.J. - \ 2011
    H2O : tijdschrift voor watervoorziening en afvalwaterbehandeling 44 (2011)20. - ISSN 0166-8439 - p. 35 - 38.
    grondwaterkwaliteit - fosfaatuitspoeling - eutrofiëring - drainagewater - draineerbuizen - zand - ijzer - adsorptie - waterzuivering - ijzeroxiden - oppervlaktewaterkwaliteit - veldproeven - groundwater quality - phosphate leaching - eutrophication - drainage water - drain pipes - sand - iron - adsorption - water treatment - iron oxides - surface water quality - field tests
    In het Nederlandse oppervlaktewater zijn de fosfaatconcentraties vaak te hoog en vormt eutrofiëring een groot probleem. Fosfaatuitspoeling uit landbouwgronden draagt flink bij aan de totale fosfaatbelasting van het oppervlaktewater. Met brongerichte maatregelen, zoals evenwichtsbemesting, zal in sommige delen van het landelijk gebied de hoofddoelstelling van de Kaderrichtlijn Water niet worden gerealiseerd. Hiervoor zijn aanvullende maatregelen nodig, die kunnen bijdragen aan het verbeteren van de chemische waterkwaliteit. We hebben de effectiviteit getest van een drainagebuis omhuld met ijzerzand om fosfaatuitspoeling te verminderen. Deze veldproef is uitgevoerd op een duinzandgrond in het bloembollengebied. Het gemiddelde zuiveringsrendement van de omhulde drainagebuis bedraagt 94 procent. Het omhullen van drainagebuizen met ijzerzand lijkt een veelbelovende maatregel voor het verminderen van fosfaatuitspoeling
    Brushes and proteins
    Bosker, W.T.E. - \ 2011
    Wageningen University. Promotor(en): Martien Cohen Stuart, co-promotor(en): Willem Norde. - [S.l.] : S.n. - ISBN 9789085859178 - 142
    biofilms - eiwitten - adsorptie - aangroeiwerende middelen - fabricage - biomaterialen - biofilms - proteins - adsorption - antifouling agents - manufacture - biomaterials

    Brushes and Proteins

    Wouter T. E. Bosker

    Protein adsorption at solid surfaces can be prevented by applying a polymer brush at the surface. A polymer brush consists of polymer chains end-grafted to the surface at such a grafting density that the polymer chains stretch out into the solution. This is schematically shown in figure 1.

    Fig. 1. Cartoons of a polymer brush. Two ways of preparation: (a) chemical grafting and (b) grafting through adsorption of block copolymers, for instance by Langmuir-Blodgett deposition (LB).

    The main parameters determining the protein resistance of a brush are the grafting density (σ), the chain length (N) and the solvent quality. The thickness of the brush is a function of these parameters: H ~ N σ1/3.

    This research is related to biofouling: 'the undesirable accumulation of proteins and cells at a surface', which starts by adsorption of proteins at the surface. Prevention of biofouling is of vital interest in medicine, where bacterial adhesion may cause severe infections on biomaterials used for implants. Treatment with antibiotics has hardly any effect. The only promising remedy against infections in this case is the prevention of a bacterial film. Because protein adsorption is the first step in this process, the research in this thesis is focused on prevention of protein adsorption by polymer brushes.

    Numerous studies over the past decades revealed that neutral polymer brushes, especially from poly(ethylene oxide) (PEO), can minimize protein adsorption. Mindful of the parameters determining the adsorbed amount mentioned above, the following three mechanisms can be identified, displayed in figure 2. Primary adsorption occurs when the diameter of the protein is (much) smaller than the distance between the polymer chains. In case of secondary adsorption, the protein is (much) bigger than the distance between the polymer chains. Ternary adsorption results from an attraction between the proteins and the polymer chains in the brush and was first discovered by Currie et al. In 1999. For a considerable time researchers have assumed a repulsion between the proteins and the polymer chains, thereby neglecting the possible ternary adsorption. However, there is increasing evidence that this attraction occurs, especially with PEO brushes. This is highlighted in this research, by adsorption studies at bimodal PEO brushes, consisting of a dense PEO brush of short chains with a varying PEO brush of long chains.

    Figure 2.
    Different mechanisms for protein adsorption at polymer brushes:

    primary, secondary and ternary adsorption.

    The main objective of this research was to investigate whether polysaccharide brushes, in particular dextran brushes, could be prepared at a solid surface and to study their protein repellency. It was suggested that brushes from these natural polymers would be more successful to prepare nonfouling surfaces with. Dextran brushes were prepared using Langmuir-Blodgett deposition (LB) and PS-dextran diblock copolymers, illustrated in figure 1. With the LB method it is possible to control both σ and N. The synthesis of the PS-dextran diblock copolymers is described in the thesis as well as the interfacial behavior. Quasi-2D aggregation occurred at the air-water interface during preparation (compression of the PS-dextran monolayer, see figure 1), resulting in inhomogeneous dextran layers at low grafting density. At higher grafting density these aggregates were pushed together to form a homogeneous dextran brush, as illustrated by AFM images. This transition from inhomogeneous to homogeneous results in non-continuous adsorption behavior at dextran brushes, in contrast to PEO brushes, as demonstrated in figure 3.

    Figure 3. Normalized adsorption of BSA (Γ/ Γ0) at dextran brushes (■) and PEO brushes (○).

    In case of dextran brushes the adsorption of BSA is constant up to a specific σ, followed by a drastic decrease, while PEO brushes show a gradual reduction.Figure 3 also demonstrates that dextran brushes are as efficient as PEO brushes in preventing protein adsorption, at high σ. This is the main conclusion of this research. It is expected that at even higher σ dextran brushes will completely suppress protein adsorption.

    Surface complexation at mineral interfaces: Multisite and Charge Distribution approach
    Hiemstra, T. - \ 2010
    Wageningen University. Promotor(en): Willem van Riemsdijk. - S.l. : s.n. - ISBN 9789085857174 - 383
    bodemchemie - geochemie - adsorptie - fosfaten - ionen - organische stof - kleimineralen - kationenwisseling - soil chemistry - geochemistry - adsorption - phosphates - ions - organic matter - clay minerals - cation exchange - cum laude
    cum laude graduation (with distinction)
    Why low powdered activated carbon addition reduces membrane fouling in MBRs
    Remy, M.J.J. ; Potier, V. ; Temmink, B.G. ; Rulkens, W.H. - \ 2010
    Water Research 44 (2010)3. - ISSN 0043-1354 - p. 861 - 867.
    afvalwaterbehandeling - waterzuivering - actieve kool - adsorptie - membranen - biologische filtratie - filtreerbaarheid - uitvlokking - biodegradatie - zuiveringsinstallaties - waste water treatment - water treatment - activated carbon - adsorption - membranes - biological filtration - filterability - flocculation - biodegradation - purification plants - waste-water treatment - bioreactor mbr - sludge - flux - performance - filtration - bioflocculation - operation
    Previous research had demonstrated that powdered activated carbon (PAC), when applied at very low dosages and long SRTs, reduces membrane fouling in membrane bioreactor (MBRs). In this contribution several mechanisms to explain this beneficial effect of PAC were investigated, including enhanced scouring of the membrane surface by PAC particles, adsorption of membrane foulants by PAC and subsequent biodegradation and a positive effect of PAC on the strength of the sludge flocs. It was concluded that the latter mechanism best explains why low dosages of PAC significantly reduce membrane fouling. Cheaper alternatives for PAC may have a similar effect
    Karakterisatie van ijzerslib en -zand : een verkenning van de mogelijkheden van het gebruik van deze reststoffen om fosfaatverliezen vanuit landbouwgronden naar het oppervlaktewater te verminderen
    Koopmans, G.F. ; Chardon, W.J. ; Groenenberg, J.E. - \ 2010
    Wageningen : Alterra (Alterra-rapport 2047) - 52
    landbouwgronden - fosfaat - oppervlaktewater - ijzer - adsorptie - nederland - bodemchemie - intensieve veehouderij - fosfaatuitspoeling - maatregelen - agricultural soils - phosphate - surface water - iron - adsorption - netherlands - soil chemistry - intensive livestock farming - phosphate leaching - measures
    Het fosfaatgehalte van Nederlandse landbouwgronden in gebieden met (intensieve) veehouderij is vaak hoog. Dit leidt tot ongewenste fosfaatverliezen naar het oppervlaktewater. Perceelsgerichte maatregelen zijn noodzakelijk om deze verliezen te verminderen en de oppervlaktewaterkwaliteit te verbeteren. Een voorbeeld hiervan is het inwerken van fosfaatbindende materialen in ‘iron reactive barriers’ in de bodem of het toepassen van deze materialen in filters die aan het uiteinde van drainagebuizen kunnen worden gekoppeld. IJzerslib en ijzerzand kunnen worden gebruikt voor het binden van fosfaat.
    Reduction of protein adsorption on surfaces coated with Complex Coacercate Core Micelles
    Brzozowska, A.M. - \ 2010
    Wageningen University. Promotor(en): Martien Cohen Stuart; Willem Norde, co-promotor(en): Arie de Keizer. - [S.l. : S.n. - ISBN 9789085856832 - 246
    micellen - afdeklagen - eiwitten - adsorptie - oppervlaktechemie - micelles - coatings - proteins - adsorption - surface chemistry
    The structure and formation of Ionomer Complexes (ICs) consisting of linear polyelectrolytes
    (C3Ms) has been extensively studied in the past years. Recently, these structures were also
    considered for several applications. This thesis deals with the possible application of ICs as a
    surface coating suppressing protein adsorption independent of the properties of the native
    surface. To reach this goal it was crucial to understand the principles governing the adsorption
    and the stability of the IC layers on solid surfaces, as well as their interactions with proteins.
    Therefore, this research was limited to well defined model substrates: silica (model hydrophilic
    surface), polystyrene (model hydrophobic surface), and polysulfone (a surface mimicking
    polymeric membrane material), and model proteins: β-lactoglobulin, bovine serum albumin,
    fibrinogen, and lysozyme. The ultimate goal, however, was to apply the coating on surfaces of
    membranes used in water purification to suppress biofilm growth. We have observed that
    reduction of protein adsorption by coating formed by regular C3Ms is not satisfactory due to
    relatively low density of the polymer brushes formed on the coated surface. We increased the
    grafting density, and hence significantly improved the reduction of protein adsorption, by
    introducing grafted block and grafted copolymers into the micelles. In our work we discuss an
    influence of various factors, i.e. physical-chemical properties of the native surfaces, lengths of the
    charged blocks, distribution of the grafts along the backbone of the copolymer, salt concentration
    etc., on the performance of the formed coatings. In the final part we focus on the mechanical
    stability of the coatings formed with ICs, and discuss their applicability as a membrane surface
    Adsorptive removal of manganese, arsenic and iron from groundwater
    Buamah, R. - \ 2009
    Wageningen University. Promotor(en): J.C. Schippers, co-promotor(en): B. Petrusevski. - [S.l.] : S.n. - ISBN 9789085855262 - 183
    grondwater - grondwaterverontreiniging - waterbeheer - watervoorziening - volksgezondheid - adsorptie - waterzuivering - mangaan - arsenicum - ijzer - ghana - grondwaterkwaliteit - groundwater - groundwater pollution - water management - water supply - public health - adsorption - water treatment - manganese - arsenic - iron - ghana - groundwater quality
    To determine the scale of the problem of arsenic, iron and manganese contamination of groundwater in Ghana a survey was performed in the first phase of the research to provide in depth information with respect to these contaminants. Presence of these mentioned contaminants in groundwater is not peculiar to Ghana alone. Many countries in the world have similar problems with their groundwater. Establishing the existence of the problem also calls for the need to find remedies. Over the years much studies have been done in the Unesco-ihe on the adsorptive mechanisms and techniques for iron and arsenic removal from groundwater. Therefore in this study much emphasis is placed on the adsorptive removal of manganese from groundwater. This research has the following as it objectives: 1. The conduction of a survey for the arsenic, iron and manganese content in selected groundwater aquifers in Ghana. 2. Determination of the arsenic, manganese and iron adsorption capacities of different locally available filter media. 3. Determination of the effect of pH on adsorption capacities of the selected media for arsenic, manganese and iron. To determine the effect of iron (II), manganese (II) presence on arsenic adsorption capacity of selected media – (competition). 4. Studies on the rate of oxidation of Fe (II) and Mn (II) adsorbed onto one or more selected media under different conditions (e.g. dissolved oxygen, pH etc.). 5. Determination of the rate of adsorption of Mn (II) onto one or more selected media under different oxic conditions. 6. To develop a conceptual model that describes the processes involved in adsorptive arsenic, manganese and iron removal. To investigate to what extent these processes can be described in a quantitative way with one or more mathematical models . Generally the study has the following relevance: 1. Provide a base line data on the arsenic and manganese content of selected groundwater aquifers in Ghana. 2. Provide information on the adsorption capacities of locally available filter media for manganese. 3. Contribute to the knowledge on the kinetics and mechanisms of catalytic adsorptive iron, manganese removal. 4. Provide an efficient backwashing procedure for regeneration of adsorptive sites in iron-oxide coated filters operating in the oxidative adsorption mode.
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