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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    Bioinspired nanopatterned surfaces via colloidal templating; a pathway for tuning wetting and adhesion
    Akerboom, Sabine - \ 2016
    Wageningen University. Promotor(en): Frans Leermakers, co-promotor(en): Marleen Kamperman. - Wageningen : Wageningen University - ISBN 9789462578470 - 198
    surface chemistry - surfaces - particles - water - nanotechnology - unimolecular films - adhesion - colloidal properties - oppervlaktechemie - oppervlakten - deeltjes - water - nanotechnologie - unimoleculaire films - adhesie - colloïdale eigenschappen

    We can learn from nature that, next to chemistry, surface structures can be used for tuning different functions of surfaces. In this thesis we present a novel fabrication method using colloidal templating on the air/water interface. Two distinct ways to obtain nanopatterned surfaces are described, namely (i) addition of PDMS on top of the colloidal monolayer and (ii) synthesis of polypyrrole around the particles of the monolayer. An increase in adhesion is found for the nanopatterned PDMS surfaces, and the contact angle of water on the nanopatterned polypyrrole surface is increased.

    Oriented antibodies as versatile detection element in biosensors
    Trilling, A.K. - \ 2013
    Wageningen University. Promotor(en): Han Zuilhof, co-promotor(en): Jules Beekwilder. - S.l. : s.n. - ISBN 9789461735683 - 168
    biosensoren - oppervlakten - oppervlaktechemie - oriëntatie - antilichamen - lama's - antistoftesten - mycobacterium tuberculosis - unimoleculaire films - immobilisatie - biosensors - surfaces - surface chemistry - orientation - antibodies - llamas - antibody testing - mycobacterium tuberculosis - unimolecular films - immobilization

    The aim of this thesis is to explore orientation of detection elements on biosensor

    surfaces. To this end, different strategies were combined such as surface chemistry and protein functionalization, with the aim to generate a platform for oriented immobilization of antibodies

    in biosensors. Chapter 2 investigates the formation of organic monolayers on

    oxide-free copper. Detailed studies were performed to characterize the monolayers

    and proof its quality. Apart from being the first oxide-free monolayers on copper

    reported thus far, further functionalization was successfully investigated.

    Chapter 3 gives an overview about approaches used to orient antibodies on surfaces.

    It also summarizes methods used to characterize the orientation of immobilized

    antibodies in a more direct manner.

    In chapter 4 a set of detection elements for tuberculosis bacteria is described. These

    are variable domains of llama heavy-chain antibodies, known as VHH proteins. A

    number of VHHs, selected by phage display, were expressed by Escherichia coli bacteria

    and characterized for binding towards Mycobacterium tuberculosis bacteria.

    Specificity of VHHs was investigated and the antigen was identified.

    In chapter 5 the impact of orientation on the analyte binding capacity was studied

    by SPR as model biosensor. Established techniques (NH2 coupling, biotyinylation)

    were used to immobilize VHHs, and a comparison between oriented and random

    immobilized VHHs was made. The effect of molecular weight, epitope number and

    affinity of the target analyte was investigated.

    In chapter 6, a novel coupling chemistry was used to immobilize VHHs, and in this case the same chemistry could be used for oriented and random immobilization. VHHs were engineered and functionalized with a non-natural amino acid to bear either one or five azide groups. Azide groups served as unique chemical handles on the VHHs and were used to click proteins onto a cyclooctyne-modified surface in an oriented and random approach. Spectacular effects on biosensor sensitivity were observed when VHHs were immobilized in an oriented manner.

    Finally, in chapter 7, the main results of this thesis are summarized and remaining

    problems as well as ideas for future research are discussed.

    Van eiwitten in platland tot bionanotechnologie in Wageningen
    Norde, W. - \ 2010
    Wageningen : Wageningen Universiteit - ISBN 9789085855767 - 28
    eiwitten - oppervlakten - grensvlak - nanotechnologie - bionanotechnologie - oppervlaktechemie - oppervlakteverschijnselen - proteins - surfaces - interface - nanotechnology - bionanotechnology - surface chemistry - surface phenomena
    Interfacial Transport Phenomena (Second edition)
    Slattery, J.C. ; Sagis, L.M.C. ; Oh, E.S. - \ 2007
    New York (US) : Springer - ISBN 9780387384382 - 830
    engineering - mechanica - materialen - thermodynamica - oppervlakten - grensvlak - engineering - mechanics - materials - thermodynamics - surfaces - interface
    Gives a presentation of transport phenomena or continuum mechanics focused on momentum, energy, and mass transfer at interfaces. This work includes a discussion of transport phenomena at common lines or three-phase lines of contact, and a theory for the extension of continuum mechanics to the nanoscale region immediately adjacent to the interface.
    Estimating input data for computations on the volatilisation of pesticides from plant canopies and competing processes
    Leistra, M. - \ 2005
    Wageningen : Alterra (Alterra-rapport 1256) - 79
    pesticiden - depositie - diffusie - vervluchtiging - emissie - oppervlakten - bladeren - opname (uptake) - gewassen - kroondak - kroondak penetratie - gebladerte - oppervlakkige afvoer - verontreiniging - pesticides - deposition - diffusion - volatilization - emission - surfaces - leaves - uptake - crops - canopy - canopy penetration - foliage - runoff - pollution
    Volatilisation of pesticides from the crop can be an important emission pathway to the environment. A computation module was developed for making estimates on this emission. However, various input data for this module are not measured directly in registration procedures, so they have to be estimated from theory or from a diversity of experimental data. Vapour pressure is the most important property in volatilisation, which needs a critical evaluation in case of conflicting data. Diffusion coefficients for transport in a laminar boundary layer are estimated from theory. Penetration of pesticides into the leaves is highly affected by substances in the formulation and by environmental conditions. Pesticide deposit is often vulnerable to washoff by rainfall. Often, no directly measured rates are available for photochemical transformation on plant surfaces, so these have to be estimated from a variety of experimental results. In critical cases, comprehensive experiments with micro-agro-ecosystems and/or in the field are needed.
    Interactions between metal ions and biogeo-surfaces in soil and water : basis for quantitative risk assessment
    Weng, L.P. - \ 2002
    Wageningen University. Promotor(en): W.H. van Riemsdijk; E.J.M. Temminghoff. - S.l. : S.n. - ISBN 9789058086075 - 193
    metaalionen - zware metalen - risicoschatting - oppervlakten - bodem - bodemoplossing - water - chemische speciatie - adsorptie - bodemwater - milieu - metal ions - heavy metals - risk assessment - surfaces - soil - soil solution - water - chemical speciation - adsorption - soil water - environment

    To provide the basis for an improved quantitative risk assessment of heavy metals in the environment, the interactions between the metal ions and the biogeo-surfaces in soil and water were studied using both experimental and modelling approaches.

    The Donnan membrane technique was developed and optimised for the measurement of metal speciation in soil solutions, in which a soil column was linked to the Donnan cell to provide buffering capacities. In acid natural waters and soils, aluminium is potentially a relatively strong competitor for the heavy metals to the binding on colloidal particles such as organic matter. Using the Donnan membrane technique, aluminium binding to purified humic acid and to the dissolved organic matter in soil solutions was measured. The ability of the NICA-Donnan model for the prediction of Al binding to humic substances was tested.

    A multi-surface model was developed for the prediction of metal speciation in soil and water. This model can also be used to estimate the relative contribution of the individual sorbents to the control of metal distribution. This multi-surface model considers soil as a set of independent sorption surfaces. Metal binding to soil organic matter (solid and dissolved), to clay mineral and to iron hydroxides was modelled using the NICA-Donnan, Donnan, DDL and CD-MUSIC models. This model approach was validated against the concentrations of total dissolved metal concentration and the activities of free metals in sandy soil samples measured using the Donnan membrane technique.

    The interactions between the metal ions and the natural organic matter are not only important for the metal distribution, but also for the solubility and mobility of organic matters. Using the NICA-Donnan model, the effects of the binding of protons and metal ions on the physico-chemical behaviour of humic acid was studied. It was found that the coagulation of humic acid started when the calculated electrostatic potential was less negative. The electrostatic potential of the dissolved organic matter in the soil solution of six forest soil profiles was calculated using the same model. The measured concentration of the dissolved organic matter also decreased in a soil profile, as the calculated potential became less negative. Humic and fulvic acids are the major components in the dissolved organic matter. The mobility and transport of humic and fulvic acids were studied in a column experiment. By comparing the breakthrough curves and the modelled physico-chemical behaviour, it was found that coagulation might be important in the control of the solubility and mobility of humic acid, while adsorption was more likely the mechanism that could explain the immobilisation of fulvic acid in this soil.

    The experimental and the modelling approaches developed are helpful in improving the quantitative risk assessment of the heavy metals. Pot experiments using three different soils and a solution culture experiment have been conducted to study the effects of pH and soil characteristics on the phytotoxicity of nickel. Using the model predictions the differences in the bioavailability of Ni in the three different soils could be explained. By comparing the toxicity of the free Ni 2+ion in the nutrient solution and in the soil solution, the toxicity of Ni in the soils could be predicted reasonably using the quantitative approach.

    The developedDonnan membrane technique is proved to be a useful analytical technique for the determination of metal speciation in soil and water samples. Further research is needed to improve the method to make it capable to measure lower concentrations. The multi-surface model approach proposed in this research is validated against the measurements of the samples from several different soils. Further validation and improvement of this model approach can be achieved after comparing the prediction with the measurement for more different soils, and by better understanding of the interactions between metal ions and the biogeo-surfaces.

    Kavelpad van kunststof op het Lagekostenbedrijf
    Dooren, H.J. van - \ 2000
    Praktijkonderzoek Rundvee, Schapen en Paarden. Praktijkonderzoek 13 (2000)1. - ISSN 1386-8470 - p. 4 - 5.
    bedrijfswegen - oppervlakten - bovenlagen - rundvee - bestrating - wegen - kosten - efficiëntie - agrarische bedrijfsvoering - belastingskenmerken (grond) - synthetische materialen - farm roads - surfaces - surface layers - cattle - pavements - roads - costs - efficiency - farm management - bearing characteristics - synthetic materials
    Om de kosten zo laag mogelijk te houden is op het lagekostenbedrijf een proef begonnen met kunststof grasplaten. Dit materiaal is goedkoper maar moet zijn bruikbaarheid in de landbouw nog bewijzen.
    Proteins and protein/surfactant mixtures at interfaces in motion
    Boerboom, F.J.G. - \ 2000
    Agricultural University. Promotor(en): A. Prins; M.A. Cohen Stuart. - S.l. : S.n. - ISBN 9789058082817 - 213
    eiwitten - oppervlakten - oppervlaktespanningsverlagende stoffen - eigenschappen - surfaces - surfactants - foaming - properties

    The research described in this thesis covers a number of aspects of the relation between surface properties and foaming properties of proteins, low molecular surfactants and mixtures thereof. This work is the result of a question of the industrial partners if it is possible to understand the foaming properties of protein hydrolysates. As there are many aspects of the surface properties that can be responsible for the foaming behaviour a number of problems were defined by which we can obtain a better understanding of the relation between surface properties and foam formation and stability in relation to the type of surface active substance.

    In this thesis an important question a priori has been: How can we understand the foaming properties from the properties of the surface active species. We presumed that the molecular properties cannot be translated forthwith to foaming properties but that a number of translation steps are necessary. First of all the molecular properties need to be translated into surface properties which manifest themselves in mechanical properties of surfaces and films. In addition there is a relation between these mechanical properties and the foaming properties.

    An important consideration a priori was that the way in which the surface is deformed is important for finding the relevant relation between the mechanical properties and the foaming properties. Here we made a distinction in two types of deformation being deformations caused by forces applied parallel and perpendicular to the surface. A force that is applied perpendicular to the surface (pressure) generally leads to a homogeneous deformation of the surface. The properties of the surface change with time or time scale but at the surface there are no differences with respect to surface tension. surface concentration or relative rate of expansion. Forces applied perpendicular to the surface generally lead solely to enlargement or reduction in surface area. Forces applied parallel to the surface (shear forces) can also lead to enlargement or reduction in surface area. These forces are generally due to viscous friction with the surface. In addition to a change in surface area these forces also cause a redistribution of surface active material over the surface. Hence the surface concentration. the surface tension as well as the relative rate of expansion vary over the surface. This leads to a surface tension gradient that is necessarily equal to the viscous drag at the surface. It is striking that in literature only homogeneous deformations are studied in detail. This fact can be attributed to the difficult experimental accessibility of surfaces subjected to shear forces. Nevertheless shear forces may play a role in the foaming properties such as in drainage and bubble break-up. An important part of this thesis will be devoted to the relation between viscous friction and surface motion.

    A device which enables the quantification of the relation between viscous drag and motion of the surface in relation to the surface properties is the overflowing cylinder. This device consists of an inner cylinder surrounded by an outer cylinder with a larger diameter. In this inner cylinder liquid is pumped up which flows over the rim into the space between the inner and outer cylinder. At the top surface we find a continuously expanding surface of which the relative expansion rate remains approximately constant over the surface in the vicinity of the centre of the cylinder. The expansion rate of the surface can be influenced by changing the length of the falling film. Hence within certain limits the expansion rate at the top surface c5n be varied. If we consider the falling film at the leading edge of the inner cylinder the falling motion of the liquid in the film causes the deformation of the surface parallel to the surface. If we would be able to measure the properties of the falling film we could learn how the surface properties vary with distance. However the surface of the falling film is experimentally not accessible. Therefore in this thesis the changes in surface properties of the falling film have been studied by measuring the surface tension of the top and bottom surface at a fixed place. This provides a reasonable measure of the surface tension difference over the falling film of the overflowing cylinder.

    In order to interpret this difference, the conditions at the falling film have been approximated by means of simple hydrodynamic theory. From this approximation we could conclude that there is a relation between the relative expansion rate, the length of the falling film and the surface tension difference. The surface of the falling film is propelled by the falling motion of the liquid which causes a surface tension gradient at the surface as a consequence of the viscous drag. If we compare the calculations with experimental data we can find that this approach is in agreement with the experiments. Hence the difference in surface tension over the falling film can be considered to be a measure of the resistance to deformation of the surface to forces applied parallel to the surface.

    The surface tension gradients which could be generated by means of different surface active species appeared to differ significantly from each other. Especially the difference between low molecular surfactants and proteins could be shown to be large. This can be ascribed to the sensitivity of the surface tension of these substances to expansion and compression of the surface. Adsorbed layers of proteins have a high surface tension in expansion. This can be explained by the time required for unfolding at a surface of these substances. In compression low surface tensions are found for proteins due to the slow desorption of proteins. The surface tension of low molecular surfactants is less sensitive to compression and expansion. In expansion the relatively short diffusion length causes the surface tension to deviate much less from the equilibrium surface tension. In compression these substances desorb easily causing the surface tension to be close to the equilibrium surface tension as well. Hence the surface tension gradient that can be generated by proteins is much larger the for low molecular surfactants. If mixtures of low molecular surfactants and proteins (Tween 20 andβ-casein) are considered it is found that in expansion the surface tension is influenced by both species. In compression however the surface tension is around the equilibrium surface tension of the low molecular surfactant. From this we can conclude that the low molecular surfactant determines the surface tension in compression. Most probably there the affinity of the surface active substance for the surface is important which causes the preferential desorption of proteins. This means that the surfaces of these mixtures have a low resistance to deformation by forces applied parallel to the surface.

    Unfolding behaviour of proteins at interfaces

    The most important class of surface active substances which have been studied in this thesis are proteins due to the similarities in structure and properties with protein hydrolysates. Proteins consist of 20 different amino acids which vary in residual group. Despite the similarity in the basic structure of these substances the difference in foaming properties between proteins is large. In literature this difference in foaming properties is ascribed to the difference in unfolding rate during adsorption at air/water interfaces of these polymers. There are no reliable data on the unfolding rate of proteins however. The overflowing cylinder technique can be used to determine the unfolding rates of proteins since the top surface is in a steady state while the relative expansion rate is finite. The relative expansion rate can be seen as a characteristic time scale of the surface.

    In order to measure the unfolding rate of the proteins, at the top surface, the surface tension, the relative rate of expansion and the surface concentration were determined using the Wilhelmy plate technique, laser Doppler anemometry and ellipsometry respectively. With these three parameters the surface can be characterised completely. The reasoning behind the characterisation is as follows: If proteins need time for the unfolding at an interface, the relative expansion rate determines the mean degree of unfolding of the proteins at the interface. As a function of the relative rate of expansion and at equal adsorbed amounts the surface tension will vary due to a difference in the mean degree of unfolding.

    If we would know the surface tension and surface concentration for different bulk concentrations as a function of the relative rate of unfolding then we would be able to establish the influence of the unfolding rate of the protein on the surface tension. Since this is difficult to determine on the basis of the raw date, a simple model was used to express this influence of unfolding in an unfolding and a refolding parameter. In this model the transport to and the unfolding at the top surface of an overflowing cylinder has been described. The unfolding and refolding has been described by means of a first order reaction. In essence we assume that the degree of unfolding can be seen as an average over many stages of unfolding over a large number of molecules. By dividing the interface into a large number of concentric rings and by carrying out the calculations for the transport and unfolding for each concentric ring the surface properties can be calculated as a function of the distance to the centre. By varying the relative rate of expansion as a function of the distance to the centre in the same way as takes place at the top surface of the overflowing cylinder also the surface tension gradient can be determined. Since there is a fixed relation between the surface tension gradient and the maximum relative rate of expansion, the maximum relative rate of expansion can be determined by means of iteration.

    In this thesis the unfolding behaviour of the proteins:β-casein,β-lactoglobulin, BSA and lysozyme has been determined experimentally. In literature these proteins have been characterised well with respect to adsorption and unfolding behaviour. The unfolding rates of these proteins differ several orders of magnitude.β-Casein andβ-lactoglobulin were shown to unfold most rapid. The characteristic time scales of unfolding of these proteins is in the order of a tenth forβ-casein to a few tenths forβ-lactoglobulin. Lysozyme hardly unfolds within the time scale of the experiment which indicates that the unfolding takes more than 100 seconds. The model was shown not to apply for BSA since the change in surface tension proceeds in two steps. Nevertheless it could be calculated that the unfolding of BSA takes place in a time scale in the order of 20 seconds.

    The model and the overflowing cylinder technique have also been applied to mixtures of proteins and low molecular surfactants. The systemβ-casein/Tween 20 was chosen because in this system no complications are known such as aggregation in he bulk phase, or electrostatic interactions at the surface. At expanding interfaces these systems were shown to behave in a more or less additive manner. The surface tension of the mixture appeared to be lower than the addition of the decrease in surface tension of each species individually. This can be attributed to the fact that both species occupy part of the space at the interface. In static conditions it was found in literature that low molecular surfactants can displace proteins from the interface. This difference in behaviour is caused by the fact that in expansion the surface tension is controlled mainly by transport to and unfolding at the surface while in equilibrium time scale is irrelevant and the affinity of the substances to the surface determines the behaviour. Despite certain deviations the measured properties were indicated to be consistent with the calculations by the model. Higher order effects such as the presence of the surfactants in micelles and preferential adsorption were shown to have little effect of these mixtures at expanding surfaces.

    Foam formation and foam stability

    In order to quantify the experimental values and techniques of this research for practical situations, foaming experiments have been performed for a number of relevant systems. In these experiments, the bubble size and the drainage rate of the foams have been determined. Subsequently the results of these experiments were related to mechanical surface properties.

    The experiments indicated that the surface tension difference over the falling film in the overflowing cylinder correlated with the bubble size and the rate of drainage. For the formation of foam this means that not only the amount of energy supplied is important for the bubble size but that also characteristic properties of the surface being the maximal viscous drag that can be transferred is important for the break-up of foam bubbles. The explanation that can be given for this is that the shear stress generated at the surface provides the deformation that leads to an unstable shape of the bubbles which finally leads to break-up. Surface active species that enable the generation of a high shear stress therefore promote the generation of small bubbles.

    In addition it was demonstrated that there is a relation between drainage and viscous friction at the bubble surface. The rate of drainage expressed in the decrease of the characteristic film thickness decreases when a higher surface tension difference between top and bottom surface in the overflowing cylinder is present at a rather arbitrarily chosen relative rate of expansion of 1 s -1 .

    In chapter 6 the foaming properties of protein hydrolysates were discussed. The most important reason that protein hydrolysates have good foaming properties is that in these systems the low molecular components do not displace high molecular components. This causes the surface tension difference between a compressed and expanded surface to be high. This supports the creation of small bubbles and the resistance to drainage. It is possible that the good foamability of protein hydrolysates compared to proteins is caused by the lower surface tension in equilibrium.

    In general it can be said that surface tension gradients play a larger role in foam formation and foam stability than the attention in literature would suggest. More attention for the properties which determine the resistance against deformation of surfaces, parallel to the surface would lead to a better insight in the reasons why different surface active substances exhibit different foaming behaviour.

    Verdamping van kale grond in de winter
    Dolman, A.J. ; Moors, E.J. ; Elbers, J.A. - \ 1999
    Stromingen : vakblad voor hydrologen 5 (1999)3. - ISSN 1382-6069 - p. 23 - 34.
    evaporatie - land - oppervlakten - modellen - winter - evaporation - land - surfaces - models - winter
    Traditioneel is door hydrologen en micrometeorologen aan verdamping in de zomer meer aandacht gegeven dan aan verdamping in de winter. Dit is te verklaren uit het grote belang dat de landbouw heeft bij het juist voorspellen van vochttekorten in de zomer in verband met mogelijke opbrengstdalingen. De winter is echter de belangrijkste periode voor aanvulling van grondwater. Bovendien bepaalt de hydrologische balans van de winter in hoge mate de voorjaarsgrondwaterstand, die weer grote invloed heeft op het mogelijke voorkomen van plantensoorten in de natuur. Daarnaast geven berekeningen met regionale hydrologische modellen in de winter vaak een te hoge afvoer te zien. Een van de mogelijke redenen hiervoor is dat de verdamping tijdens de winterperiode onderschat wordt
    A remote sensing surface energy balance algorithm for land (SEBAL); 1 formulation
    Bastiaanssen, W.G.M. ; Menenti, M. ; Feddes, R.A. ; Holtslag, A.A.M. - \ 1998
    Journal of Hydrology 212/213 (1998)1/4. - ISSN 0022-1694 - p. 198 - 212.
    land - oppervlakten - energiebalans - evaporatie - remote sensing - algoritmen - land - surfaces - energy balance - evaporation - remote sensing - algorithms
    A remote sensing surface energy balance algorithm for land (SEBAL); 2 validation
    Bastiaanssen, W.G.M. ; Pelgrum, H. ; Wang, J. ; Ma, Y. ; Moreno, J.F. ; Roerink, G.J. ; Wal, T. van der - \ 1998
    Journal of Hydrology 212-213 (1998)1-4. - ISSN 0022-1694 - p. 213 - 229.
    land - oppervlakten - energiebalans - evaporatie - remote sensing - algoritmen - land - surfaces - energy balance - evaporation - remote sensing - algorithms
    Impact of floor surface on behaviour, locomotion and foot lesions in cattle
    Stefanowska, J. ; Smits, M.C.J. ; Braam, C.R. - \ 1998
    Wageningen : IMAG-DLO - ISBN 9789054061717 - 68
    rundvee - huisvesting van koeien - vloeren - vloertypen - oppervlakten - diergedrag - voortbeweging - laesies - impact - mankheid - bewegingsstoornissen - leg weakness - cattle - cow housing - floors - floor type - surfaces - animal behaviour - locomotion - lesions - impact - lameness - movement disorders - leg weakness
    Electrodynamics of colloids
    Minor, M. - \ 1998
    Agricultural University. Promotor(en): J. Lyklema; H.P. van Leeuwen. - S.l. : Minor - ISBN 9789054858010 - 145
    colloïden - adsorptie - oppervlakten - oppervlaktechemie - elektrodynamica - colloids - adsorption - surfaces - surface chemistry - electrodynamics - cum laude

    The goal of the present study is to deepen the insight into the non-equilibrium properties of the electric double layer of colloidal systems. Of basic interest are the ionic mobilities in the different regions of the electric double layer as well as the potential at the plane of shear, i.e., the electrokinetic potential (ζ-potential). These parameters determine the colloidal behaviour under non-equilibrium conditions when the double layer is perturbed, for instance if external fields are applied and in particle-particle interaction during coagulation.

    One of the experimental methods utilized in this study is the measurement of the conductivity and the streaming potential of close-packed plugs of particles. From the resulting data we retrieved the dzeta.gif -potential, the surface conductivity, and the mobility of the counterions behind the plane of shear. The results are well comparable to those from the experimental low-frequency (LF) dielectric response of dilute dispersions of latex particles.

    The electrodynamic parameters can be influenced by adsorbing neutral polymer onto the surface

    It is shown that the ζ-potential as well as the mobilities of the ions behind the plane of shear are decreased by the polymer film.

    The data in the above studies were successfully interpreted under the assumption of local equilibrium between the (complete) electric double layer and the adjacent electrolyte. However, there are double-layer conditions where this assumption is violated. In order to study these, we theoretically investigated the influence of relaxation of the compact part of the double layer (occupied inner-Helmholtz Stern layer) on the LF dielectric response and electrophoretic mobility. Possible relaxation mechanisms are retarded adsorption/desorption and ion migration along the surface. Along the same lines, the stability of the sol against coagulation was expressed in terms of the relaxation characteristics of the Stem layer.

    Chapter 2 dealt with the determination of plug conductivities and streaming potentials of a close-packed porous plug of latex particles for a number of indifferent electrolytes and ionic strengths. From these, the dzeta.gif -potentials and surface conductivities were computed. Monodisperse sulphate latex is an ideal model system since the surface charge consists of strong acidic groups so that a constant surface charge density is maintained throughout all the experiments. It was shown that the surface conductivity is insensitive to the ionic strength and that a large part of the countercharge is situated behind the shear plane. Furthermore, it was demonstrated that the ions in the double layer have a mobility close to the bulk mobility.<

    In chapter 3 practical expressions were developed for the low-frequency (LF) dielectric response of dilute dispersions of spherical particles suspended in a binary electrolyte. The LF dielectric response of dilute sulphate latex dispersions was experimentally determined in the frequency range of 500 Hz to 500 kHz as a function of the ionic strength of suspending KCI. The resulting surface conductivities are insensitive to the ionic strength and practically identical to the values obtained by steady state methods (chapter 2). It was proposed that counterion motion can be retarded by specific interaction with the surface and by neutral polymer hairs present on the surface. In order to test the latter effect, the influence of the adsorption of uncharged polymer poly(ethylene) oxide onto the latex surface was investigated by means of LF spectroscopy, plug conductivities and streaming potentials of plugs in chapter 4. It was found that the polymer film on the surface reduces the surface conductivity. The drag on the ions in the polymer film can be described by considering the polymer layer as an inhomogeneous Brinkman fluid, characterised by a Darcy permeability which depends on the local polymer volume fraction. The polymer and counterion distributions were calculated from statistical self-consistent field lattice models.<

    In order to investigate the influence of the surface charge density on the streaming potential and static conductivity, plugs of monodisperse spherical Stöber-silica particles were studied in chapter 5. Contrary to the latex, the surface charge density of silica can be controlled by pH. The high-charge silica plug showed more surface conduction than the low-charge plug since more mobile counterions are present in the double layer of the former. Stöber-silica particles are highly porous. For the relatively large particles under consideration, the major part of the countercharge is situated in the micropores of the particles. It was shown that these counterions do not contribute to the plug conductivity because of their low mobility.

    Chapter 6 analysed the dynamic aspects of particle electrophoresis. It was shown theoretically as well as experimentally that colloidal particles respond to an applied electric field much faster than does the liquid inside a measuring capillary. Therefore, it is possible to apply an alternating electric field with such a frequency that unwanted electroosmosis, induced by charge on the capillary wall, is suppressed, whereas the particles are still able to follow the field according to their dc mobility. This study illustrates that knowledge of the dynamics and the corresponding relaxation times is not only of purely scientific interest, but that it also offers solutions to very practical problems.

    In chapter 7 the influence of polarization of surface charge (or charge in an inner-Helmholtz layer) on the particle mobility, static conductivity, and low-frequency dielectric response was studied within the framework of the thin double-layer theory. It was shown that the characteristic times of relaxation processes in the Stern layer are accessible from dielectric spectroscopy. The relaxation phenomena under consideration are Stern-layer polarization via retarded adsorption/desorption and polarization via lateral transport in the Stem layer. The two processes may occur simultaneously. Since these relaxation processes are also relevant for particle-particle interaction, chapter 8 considered the implications for colloidal stability. In the situation of small transient disequilibrations of the surface charge, the stability could be expressed in terms of the characteristic times of surface charge relaxation. This allows the use of electrodynamic data obtained by dielectric spectroscopy in the interpretation of colloidal stability. On an even more rigorous level, the free energy of particle-particle interaction was also considered in the space of the two variables surface charge and separation. This formalism opens the way to investigate coagulation far from equilibrium.

    Ongewapend beton in de landbouw
    Braam, C.R. - \ 1997
    Agrabeton 7 (1997)2. - ISSN 0167-3246 - p. 13 - 15.
    bindmiddelen - bakstenen - cement - beton - betonwegen - landbouwbedrijfsgebouwen - industrie - bestrating - wegen - oppervlakten - erven - landbouwbedrijven - binding agents - bricks - cement - concrete - concrete roads - farm buildings - industry - pavements - roads - surfaces - yards - farms
    Een vraaggesprek met J.W. Frenay, specialist op het gebied van betonverhardingen en betonwegen
    Gevraagd: een verbeterd ontwerp
    Guldemond, J.L. - \ 1997
    Groen : vakblad voor groen in stad en landschap 53 (1997)3. - ISSN 0166-3534 - p. 20 - 24.
    ontwerp - onderhoud - bedrijfsvoering - bestrating - wegen - oppervlakten - theorie - design - maintenance - management - pavements - roads - surfaces - theory
    Selective treatment of weeds on hard surfaces
    Timmermans, A.J.M. ; Visser, R. - \ 1997
    Tuin en Park Techniek 4 (1997)5. - ISSN 1380-3212 - p. 28 - 29.
    roadsides - weed control - ultralow volume sprayers - controlled droplet application - roads - management - maintenance - pavements - surfaces - wegbermen - onkruidbestrijding - fijnnevelspuiten - controlled droplet application - wegen - bedrijfsvoering - onderhoud - bestrating - oppervlakten
    AT-DLO heeft in 2 jaar samen met andere bedrijven een machine ontwikkeld voor selectief onkruidbestrijden op verhardingen. Uitleg volgt van de werking van deze machine, die een aantal sensoren voor onkruiddetectie bezitten
    The influence of spreading particles on the stability of thin liquid films
    Bisperink, C.G.J. - \ 1997
    Agricultural University. Promotor(en): A. Prins; H.J. Bos. - S.l. : Bisperink - ISBN 9789054857174 - 214
    oppervlakten - grensvlak - dispersie - gassen - schuim - oppervlakteverschijnselen - surfaces - interface - dispersion - gases - foams - surface phenomena

    The influence of spreading particles on the stability of thin liquid films was investigated. Due to the spreading of a particle, i.e. an oil droplet, over a surface of a thin liquid film the latter becomes thinner and may rupture. The following steps in the whole process were distinguished: 1) transport of the particle to the film surface, 2) dewetting of the particle ensuring physical contact between the particle surface and the film surface, 3) spreading of the particle over the film surface and 4) movement of the film bulk liquid induced by the surface movement due to spreading material.

    An attempt was made to develop a theory that describes the spreading process quantitatively. It describes the film thinning process as a result of the liquid drag due to the surface motion initiated by the spreading material by using the parameters film thickness, droplet radius, liquid bulk viscosity, liquid bulk density and the surface rheological properties of the oil droplet and the film liquid.

    Model systems of foaming liquid and lipid material were used to study this spreading process. The latter was done on a relative macroscopic scale over bulk surfaces which is different compared to the dimensions and conditions which are valid for spreading particles on a foam film. It was assumed that the developed theory could be applied to both dimensions. The experimental results pointed in this direction. This was verified by the experimental results of introducing small spreading emulsion droplets on thin liquid films. A clear correlation between the above mentioned parameters and film rupture initiated by the spreading droplets was found.

    Zacht, groen, nat & mooi: kolloidkunde in Wagenings perspectief.
    Cohen Stuart, M.A. - \ 1997
    Wageningen : Landbouwuniversiteit Wageningen - 19
    chemie - colloïden - adsorptie - oppervlakten - fysica - colleges (hoorcolleges) - oppervlaktechemie - macromoleculen - chemistry - colloids - adsorption - surfaces - physics - lectures - surface chemistry - macromolecules
    Heat and water transfer in bare topsoil and the lower atmosphere
    Berge, H.F.M. ten - \ 1996
    Wageningen : Pudoc (Simulation monographs 33) - ISBN 9789022009611 - 207
    luchttemperatuur - analogen - atmosfeer - computersimulatie - energiebalans - milieu - evaporatie - fluctuaties - hydrologie - land - methodologie - modellen - onderzoek - simulatie - simulatiemodellen - bodem - bodemtemperatuur - thermische bodemeigenschappen - bodemwater - oppervlakten - thermische geleiding - grenslaag - aardoppervlak - air temperature - analogues - atmosphere - computer simulation - energy balance - environment - evaporation - fluctuations - hydrology - land - methodology - models - research - simulation - simulation models - soil - soil temperature - soil thermal properties - soil water - surfaces - thermal conductivity - boundary layer - land surface
    This book describes an analysis of processes and factors that affect the energy balance of bare soil, and the associated exchange of heat and moisture at the surface. After a brief treatment of basic transport theory, the processes of soil-atmosphere interaction are expressed in a simulation algorithm. This algorithm provides an instrument to study the 'conditioning' effect of soil on the lower atmosphere, and vice versa. Examples of sensitivity analysis are presented, with emphasis on the behaviour of surface temperature. In remote sensing practice, surface temperature is estimated from thermal imagery; simulation algorithms can assist in its interpretation. Field data of fluxes, state variables and soil properties are extensively discussed and are used to validate appropriate sections of the model
    Regionalization and parameterization of exchange processes at the land surface-atmosphere interface
    Kabat, P. ; Dolman, A.J. ; Bastiaanssen, W.G.M. ; Ogink-Hendriks, M.J. ; Elbers, J.A. - \ 1995
    In: Climate change research : evaluation and policy implications : proceedings of the international climate change research conference, Maastricht, The Netherlands, 6 - 9 December 1994 / Zwerver, S., - p. 421 - 424.
    toepassingen - evaporatie - land - remote sensing - bodem - oppervlakten - applications - evaporation - land - remote sensing - soil - surfaces
    Regionalization of local-scale modelling concepts is of paramount importance to realistically predicting climate by global climate models and to improving accuracy in regional hydrological modelling. A series of land surface experiments provides a methodology and a unique data set to develop and test regionalization algorithms. Most of these data are successfully used in analysis of local-scale phenomena and the physical interpretation of remote sensing data. SC-DLO integrates these results into regional atmospheric and hydrological models.
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