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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    Film Formation of High Tg Latex Using Hydroplasticization: Explanations from NMR Relaxometry
    Voogt, Benjamin ; Huinink, Hendrik P. ; Erich, Sebastiaan J.F. ; Scheerder, Jurgen ; Venema, Paul ; Keddie, Joseph L. ; Adan, Olaf C.G. - \ 2019
    Langmuir 35 (2019)38. - ISSN 0743-7463 - p. 12418 - 12427.

    The film formation of acrylic latex dispersions, containing different amounts of carboxylic acid functional groups by the incorporation of methacrylic acid (MAA), was studied with GARField 1H NMR at various relative humidities (RH). Polymer particles with glass-transition temperatures in the range from 26 to 50 °C formed films at room temperature because of hydroplasticization. It was found that with an increased drying rate due to lower RH, the evaporation flux of water was limited by the latex polymer. Only in the second stage of drying this phenomenon was more obvious with increasing MAA content. 1H NMR relaxometry was used to study the change of hydrogen mobilities during film formation and hardening of the films. This showed that the drying rate itself had no impact on the hydrogen mobility in the latex films as measured via the T2 relaxation time. Hydrogen mobilities of water and the mobile polymer phase only significantly decrease after most water has evaporated. This implies that the rigidity of the polymers increases with the evaporation of water that otherwise plasticizes the polymer through hydrogen bonding with the carboxylic acid groups. This hardening of the polymer phase is essential for applications in a coating. The hydrogen mobilities were affected by the MAA concentration. Densities of mobile hydrogens increase with increasing MAA content. This is expected if the mobile protons are contained in the MAA groups. The result thus confirms the role of carboxylic acid groups in hydrogen bonding and plasticization of the copolymers. Hydrogen mobilities, however, decrease with increasing MAA content, which is hypothesized to be caused by the formation of dimers of carboxylic acid groups that still hold water. They still enable short-range polymer hydrogen mobility due to hydroplasticization but limit long-range polymer mobility due to interaction between the carboxylic acid groups.

    Surface characterization of drying acrylic latex dispersions with variable methacrylic acid content using surface dilatational rheology
    Voogt, Benjamin ; Venema, Paul ; Sagis, Leonard ; Huinink, Henk ; Erich, Bart ; Scheerder, Jurgen ; Adan, Olaf - \ 2019
    Journal of Colloid and Interface Science 556 (2019). - ISSN 0021-9797 - p. 584 - 591.
    Dilatational rheology - Drying - Interface - Latex - Methacrylic acid

    Hypothesis: Drying of latex dispersions often results in particle gradients at the latex-air interface. We expect that, by increasing the carboxylic acid content of latex particles, inter-particle interactions at the interface change. With dilatational rheology one could detect particle-particle interactions in an early stage of the drying process and elucidate the nature of these interactions. Experiments: Acrylic latex dispersions were prepared with different amounts of methacrylic acid (MAA), ranging from 2 to 10 wt% on dry mass. Dilatational rheology studies during drying at different relative humidities RH were performed using profile analysis tensiometry. Visco-elastic properties of latex surfaces were used to identify inter-particle interactions at the surfaces depending on the drying rate and particle composition. Findings: Drying at 85% RH did not show significant changes of the mechanical properties of the latex surfaces. Drying at 65 and 53% RH resulted in a change of the mechanical properties, ultimately showing non-linear visco-elastic behavior. This indicates that capillary and/or Van der Waals forces were operating between particles at the surface. With increasing MAA content the viscous contribution decreased, possibly due to the formation of more gel-like structures at the particle surface due to higher solubility of polymer segments near to the surface.

    Hydroplasticization of latex films with varying methacrylic acid content
    Voogt, Benjamin ; Huinink, Henk ; Kamp-Scheerder, Loes van der; Erich, Bart ; Scheerder, Jurgen ; Venema, P. ; Adana, Olaf - \ 2019
    Polymer 166 (2019). - ISSN 0032-3861 - p. 206 - 214.
    Hydroplasticization - Coating - Polymer mobility
    The hydroplasticization of coatings of acrylic copolymers with different amounts of methacrylic acid (MAA) was investigated to clarify the role of carboxylic acid functionalities on the change in polymer mobility due to water uptake. The coating Tg as a function of water uptake was studied using dynamic mechanical analysis. The Tg’s decreased with increasing water content, confirming the plasticizing effect of water on the coatings. At relative humidities between 0 and 60% the coating Tg shows a sharper decrease than at higher , an effect that increases with increasing MAA content. This behavior is attributed to the presence of dimers of carboxylic acid in the coatings, which is also observed with FTIR-ATR analyses. Due to water uptake, the dimers are disrupted and form “open” dimers where carboxylic acid groups remain in close proximity and are connected through water molecules. With 1H NMR relaxometry, two T2 relaxation times are found, representing two hydrogen pools with different mobilities. Both mobilities increase with increasing water content, indicating the presence of polymer domains with different hardness. Correlating the T2 relaxation times with the coating Tg’s shows that at higher MAA content the proton mobility as a function of Tg of the soft domains increases with increasing MAA content. Since the polymer proton mobility, and hence the polymer mobility, is expected to scale with the polymer Tg, it is hypothesized that harder domains are present in the coatings, which are not visible in the Ostroff-Waugh decays due to the fast relaxation behavior of these protons.
    Water mobility during drying of hard and soft type latex : Systematic GARField 1H NMR relaxometry studies
    Voogt, Benjamin ; Huinink, Henk ; Erich, Bart ; Scheerder, Jurgen ; Venema, Paul ; Adan, Olaf - \ 2018
    Progress in Organic Coatings 123 (2018). - ISSN 0300-9440 - p. 111 - 119.
    GARField H NMR - Latex drying - Relaxometry - T - Water mobility

    GARField 1H NMR relaxometry experiments were done to study the drying process of two latices with different polymer Tg and to elucidate water mobility behavior during this process. It was found that the hard type latex, with a polymer Tg above room temperature, dries faster than the soft type latex, with a polymer Tg below room temperature. Diffusion measurements by means of echo time variations at different moments in the drying process show that water auto-diffusion decreases with increasing solid content of the latex independent of particle Tg. Two pools of protons with different mobilities were observed based on transversal relaxation T2. Determination of the long T2,long's and short T2,short's of both latex dispersions and their respective proton densities during drying at 80% RH showed evidence of particle deformation for the soft type latex and the absence thereof for the hard type latex. Additional drying of the resulting coatings with anhydrous CaCl2 showed a higher porosity for the hard type coating based on the proton distribution profile width. Moreover, two domains with different polymer proton mobilities are found for both coatings that are both plasticized by water at 80% RH. This is more apparent for the hard type coating, suggesting that a more hydrophilic polymer gives a higher degree of plasticization.

    Coating formation during drying of ß-lactoglobulin: Gradual and sudden changes
    Bouman, J. ; Vries, R.J. de; Venema, P. ; Belton, P. ; Baukh, V. ; Huinink, H. ; Linden, E. van der - \ 2015
    Biomacromolecules 16 (2015)1. - ISSN 1525-7797 - p. 76 - 86.
    diffusing-wave spectroscopy - concentrated colloidal suspensions - water-vapor sorption - mechanical-properties - film formation - protein films - wheat gluten - hydration - dynamics - solids
    The drying dynamics of protein coatings is of importance for many applications. The main focus of research so far was to investigate macroscopic properties of protein coatings, leaving drying dynamics virtually unexplored. A unique combination of techniques is used to monitor drying of a coating containing the protein ß-lactoglobulin. The techniques used cover both macroscopic and microscopic aspects of the drying process. For all water fractions amenable to diffusing wave spectroscopy analysis (xw > 0.2 w/w), the tracer particles diffuse in the coating as in a Newtonian viscous medium. Magnetic resonance imaging shows both protein and water are distributed homogeneously over the coating during drying, up to water fractions above 0.2 w/w. When drying continues to lower water fractions, sudden transitions in drying behavior are observed by both dynamic vapor sorption and IR spectroscopy, which we suggest are due to changes in molecular interactions caused by dehydration of the protein backbone.
    Meer water met regelbare drainage?
    Stuyt, L.C.P.M. ; Bolt, F.J.E. van der; Snellen, W.B. ; Groenendijk, P. ; Schipper, P.N.M. ; Harmsen, J. ; Bakel, P.J.T. van; Ruijtenberg, R. ; Jonkers, D.A. ; Peerboom, J.M.P.M. ; Buck, A.J. de; Huinink, M. ; Rijken, M. ; Straat, A.A. van der; Talsma, M.J.G. - \ 2012
    Amersfoort : Stowa (Rapport / STOWA 2012-33) - ISBN 9789057735707 - 60
    drainage - grondwaterstand - agrarische bedrijfsvoering - peilbeheer - drainage - groundwater level - farm management - water level management
    Dit rapport geeft aan de hand van resultaten van vijf Nederlandse praktijkproeven inzicht in de mogelijkheden van regelbare of peilgestuurde drainage. Deze vorm van drainage - waarbij boeren de grondwaterstand op hun percelen flexibel kunnen regelen - houdt in tegenstelling tot conventionele drainage veel beter rekening met de uiteenlopende wensen en behoeften vanuit de landbouw, natuur, milieu en waterbeheer. Dit kan de realisatie van waterkwaliteits- en waterkwantiteitsdoelstellingen door waterschappen bevorderen en tegelijkertijd de bedrijfsvoering van agrariërs verbeteren.
    NHI Toetsing, Ontwikkeling en toepassing van methode voor toetsing van NHI 2.1 inclusief vergelijking met NHI 2.0.
    Hoogewoud, J. ; Veldhuizen, A.A. ; Prinsen, G. ; Kuijper, M.J.M. ; Huinink, J. ; Lourens, A. ; Vernimmen, R. - \ 2011
    Delft : Deltares - 156
    hydrologie - grondwater - oppervlaktewater - informatiesystemen - hydrology - groundwater - surface water - information systems
    Dit rapport beschrijft de achtergrond van de methode om NHI2.1 te toetsen aan de criteria die opgesteld zijn door Rijkswaterstaat Waterdienst geldend voor 2010 en bevat de resultaten van die toetsing en de vergelijking met resultaten van NHI2.0. Volgens de criteria is de berekende aan en afvoer van oppervlakte water verbeterd. Op enkele belangrijke meetpunten van de oppervlaktewaterverdeling zijn signifinante verbeteringen te zien.
    Ultraslow microdialysis and microfiltration for in-line, on-line and off-line monitoring
    Korf, J. ; Huinink, K.D. ; Posthuma-Trumpie, G.A. - \ 2010
    Trends in Biotechnology 28 (2010)3. - ISSN 0167-7799 - p. 150 - 158.
    mass-spectrometric proteomics - ultrafiltration probes - quantitative microdialysis - protein-adsorption - inflammatory response - blood compatibility - vivo microdialysis - adipose-tissue - hollow-fiber - lactate
    In medicine and biotechnology, close monitoring of molecular processes might assist to optimise therapeutic interventions and production of biochemicals, respectively. Here, we summarize the current status of two automatic and continuous sampling technologies, microdialysis and microfiltration, which facilitate both in vivo and in vitro monitoring of nearly any analyte, because they can be combined easily with many analytical techniques. Conventional microdialysis and microfiltration, which require collecting relatively large samples, are however often impractical and semi-quantitative; hence, we focus on ultraslow sampling to circumvent such limitations. Ultraslow microdialysis and microfiltration already have been used successfully for quantitative pharmacokinetics, glucose metabolism (e.g. of the brain), cytokines and proteomics (e.g. tumour secretomes), both in vivo and in vitro.
    Microfiltration sampling in rats and in cows: toward a portable device for continuous glucocorticoid hormone sampling
    Huinink, K.D. ; Lambooij, E. ; Jansen-van Zelm, K. ; Cremers, T.I.F.H. ; Oeveren, W. van; Bakker, P.L. ; Venema, K. ; Westerink, B.H.C. ; Korf, J. - \ 2010
    The Analyst 135 (2010). - ISSN 0003-2654 - p. 390 - 396.
    mass-spectrometric proteomics - capillary ultrafiltration probes - in-vivo - interstitial fluid - microdialysis - lactate - glucose - proteins - brain - pharmacokinetics
    To monitor temporal patterns of glucocorticoids hormones in living animals, most often blood samples are collected. Blood sampling is invasive and subjects may find it – in particular – unpleasant when multiple samples are collected. We have developed a microfiltration collection device (MCD) sampling continuously, pulse-free, over a selected period of time, with minimum invasiveness as the device is inserted with only one venipuncture. The MCD consists of a hollow fiber membrane (probe), capillary collection coil and flow creator. Three biocompatible hollow fiber membranes were assessed on flow rate in rats, by placing the probe intraperitoneally, subcutaneously, or intravascularly and with or without heparin coating. The probe made from polyethylene coated with ethylene vinyl alcohol–heparin conveyed the best results and had the most benefit of the heparin coating. Consequently this probe was built into a collection device and tested in cows, sampling blood microfiltrate. Cortisol (protein-bound and -free) could be monitored in cows over a period of 7 hours. This device has several major advantages compared to manual blood collection: minor stress is induced by the application of the device; it has a low weight and can therefore be used in freely active subjects being in their own surroundings. The device can be sterilized and manufactured as a disposable tool, and the filled MCD can be shipped by regular mail to a specialized laboratory facility for analysis.
    De verbreding van de HELP-tabellen
    Bakel, J. van; Prak, H. ; Huinink, J. ; Talsma, M. - \ 2006
    H2O : tijdschrift voor watervoorziening en afvalwaterbehandeling 39 (2006)1. - ISSN 0166-8439 - p. 33 - 34.
    bodemwater - waterbeheer - modellen - grondwaterspiegel - agrarische bedrijfsvoering - grondwaterstand - regulatie - opbrengsten - nederland - waterstand - soil water - water management - models - water table - farm management - groundwater level - regulation - yields - netherlands - water level
    De HELP-tabellen dateren uit 1987 en geven de opbrengst weer van landbouwgewassen in afhankelijkheid van grondsoort en grondwatertrap. De vraag 'Is de HELP-tabel aan vervanging toe?' is in een eerder artikel bevestigend beantwoord. Een structurele herziening waarbij de effecten van verschillende ontwikkelingen in de landbouw worden meegenomen, is een project dat jaren zal vergen. Zolang moeten we verder werken met de HELP-tabellen. Deze zijn in opdracht van Stowa ten behoeve van het Waternoodinstrumentarium op een aantal punten uitgebreid en geschikt gemaakt voor gebruik in het Waternoodinstrumentarium. Het resultaat - de HELP-2005-tabellen - is inmiddels beschikbaar. Het vervangt de voorgaande versies
    HELP-2005, uitbreiding en actualisering van de HELP-tabellen ten behoeve van het Waternood-instrumentarium
    Bakel, J. van; Huinink, J. ; Prak, H. ; Bolt, F.J.E. van der - \ 2005
    Utrecht : Stowa (Rapport / STOWA 2005 16) - ISBN 9789057732973 - 50
    waterbeheer - modellen - grondwaterspiegel - agrarische bedrijfsvoering - grondwaterstand - regulatie - opbrengsten - nederland - bodemwater - waterstand - soil water - water management - models - water table - farm management - groundwater level - regulation - yields - netherlands - water level
    Hoofdstuk 1 schetst de aanleiding, de probleem- en doelstelling en de plaats van het onderzoek binnen het onderzoeksprogramma Waternood. In hoofdstuk 2 wordt een kort, historisch overzicht gegeven van het onderzoek naar de relatie tussen grondwaterstand en landbouwkundige oporengsten. De totstandkoming van de tabellen die ten grondslag liggen aan de HELP-2005-tabellen (de HELP-tabel uit 1987 en de zogenoemde HB-tabel) worden in hoofdstuk 3 beschreven. De werkwijze om te komen tot de HELP-2005-tabellen wordt beschreven in hoofdstuk 4. Hoofdstuk 5 geeft enige resultaten weer van de uitbreiding van de HELP-tabellen. In hoofdstuk 6 worden aanwijzingen en beperkingen gegeven voor praktisch gebruik voor de HELP-tabellen in het algemeen en de HELP-2005-tabellen in het bijzonder. Hoofdstuk 7 geeft conclusies en aanbevelingen
    Effecten van peilbeheer in de polders Zegveld en Oud-Kamerik op de nat- en droogteschade in de landbouw
    Vos, J.A. de; Hoving, I.E. ; Bakel, P.J.T. van; Wolf, J. ; Conijn, J.G. ; Holshof, G. - \ 2004
    Wageningen : Alterra (Alterra-rapport 987) - 77
    waterbeheer - modellen - grondwaterspiegel - agrarische bedrijfsvoering - regulatie - polders - oppervlaktewater - melkveehouderij - proefbedrijven - waterstand - utrecht - veenweiden - peilbeheer - water management - models - water table - farm management - regulation - polders - surface water - dairy farming - pilot farms - water level - utrecht - peat grasslands - water level management
    Voor een toekomstgericht melkveebedrijf in het veenweidegebied is met het nieuwe Waterpas-BBPR-model berekend wat de bedrijfeconomische gevolgen zijn van een oppervlaktewaterpeilverhoging. Modelresultaten voor hydrologie en graslandgebruik komen goed overeen met meetgegevens en praktijkgegevens voor het proefbedrijf Zegveld. Opvallend is dat een gemiddelde infiltratie vanuit het oppervlaktewater van 140 mm/jaar wordt berekend, wat wordt bevestigd door eerdere experimenten. Bij een slootwaterpeilverhoging van 60 naar 40 cm ¿mv neemt volgens het Waterpas-BBPR-model het netto bedrijfsresultaat af met 222 euro/ha/jaar. De HELP-tabel (Brouwer-Huinink-versie) geeft 186 euro/ha/jaar opbrengstderving en benadert daarmee financieel gezien de modelberekeningen redelijk. Echter bij vergelijking met melkveebedrijven op kleigrond blijkt de HELP-tabel minder opbrengstderving te berekenen dan het Waterpas-BBPR-model. De resultaten van het integrale Waterpas-BBPR-model laten zien dat een analyse op bedrijfsschaal noodzakelijk is en dat meer transparante, realistische resultaten worden verkregen dan met de HELP-systematiek.
    Opbrengstdervingpercentages voor combinaties van bodemtypen en grondwatertrappen; geactualiseerde help-tabellen en opbrengstdepressiekaarten
    Brouwer, F. ; Huinink, J.T.M. - \ 2002
    Wageningen : Alterra (Alterra-rapport 429) - 38
    bodemwater - grondwaterspiegel - oogstverliezen - bodemkarteringen - kaarten - graslanden - bouwland - bedrijfseconomie - bodemgebruik - bodemgeschiktheid - grondwaterstand - landbouw - opbrengstderving - soil water - water table - soil surveys - maps - yield losses - grasslands - arable land
    In 1983 heeft de Dienst Landelijk Gebied (voormalige Landinrichtingsdienst) de eerste HELP-tabellen samengesteld. Deze tabellen geven voor combinaties van bodemtypen en grondwatertrappen de opbrengstdervingspercentages voor akkerbouw en melkveehouderij. In 1987, 1993 en 1998 zijn de tabellen geactualiseerd en/of aangevuld voor andere landbouwkundige gebruiksvormen. In 2001 heeft het Expertisecentrum LNV de HELP-tabellen opnieuw aangepast, waarbij met name voor grasland wijzigingen zijn doorgevoerd. Deze aangepaste HELP-tabellen zijn gekoppeld aan de Bodemkaart van Nederland, schaal 1 : 50 000. Hieruit zijn voor vijf bodemgebruiksvormen opbrengstdepressiekaarten gemaakt: voor grasland, bouwland, (zomer)groente, fruitteelt (groot en klein) en boomteelt.
    Surfactants, interfaces and pores : a theoretical study
    Huinink, H. - \ 1998
    Agricultural University. Promotor(en): J. Lyklema; A. de Keizer. - S.l. : Huinink - ISBN 9789054857921 - 122
    oppervlaktespanningsverlagende stoffen - grensvlak - chemische structuur - chemische samenstelling - surfactants - interface - chemical structure - chemical composition

    The aim of this study was to investigate the behavior of surfactants in porous media by theoretical means. The influence of curvature of a surface on the adsorption has been studied with a mean field lattice (MFL) model, as developed by Scheutjens and Fleer. An analytical theory has been developed to interpret the MFL results. The chapters three and four, which form the core of this thesis, have been devoted to the background and the outcomes of both theories. These theories contain various approximations and therefore limitations. In the flanking chapters two and five attempts to overcome two of these approximations have been described. First, the MFL theory considers water as built up from isotropic monomers. As a consequence, the theory cannot predict the characteristic behavior of water. An alternative model could be the Besseling theory, which is based on the quasi- chemical approach. Some elaborations of this water model have been reported in chapter two. Second, the MFL theory, as used in the chapters three and four, always assumes homogeneous surfactant layers, which is inherent to its mean field approximation. However, it is well known that adsorption layers of surfactants often consist of discrete aggregates. The Herzfeld model has been chosen to study the discrete nature of the adsorbed layer. The theory and its outcomes, dealing with aggregation and ordering behavior of surfactant aggregates at interfaces, have been described in the last chapter.

    In chapter two a lattice model for water, developed by Besseling, has been extended by incorporation of the electrostatic interactions of the water molecules with each other and with an external electrostatic field. This could have been the first step towards a better description of water near charged interfaces or in charged pores and electrosorption phenomena. The waterwater and water-field interactions have been treated with the reaction field approach of Onsager. Expressions have been obtained for the dielectric constant of the water in an external field.

    At low field strengths, the predicted permittivity is close to the experimental one. The temperature dependence has also been reproduced. The dipolar correlation factor has been obtained by using the Clausius-Mossoti equation for the refractive index and the Kirkwood-Fröhlich expression for the dielectric constant. The predicted correlation factor and its temperature
    dependence agree well with experimental data. However, the field strength behavior of the model is unexpected. Before saturation the predicted permittivity passes through a maximum. By modifying the hydrogen-bond interaction the saturation could be manipulated. However, this latter procedure does not have a sound physical origin. Somehow, if water molecules orient in large amounts, their interactions change. Therefore, investigations with this theory were not continued and much more simple models for water had to be chosen to study surfactant adsorption.

    An analytical theory for nonionic surfactants in hydrophilic cylindrical pores has been developed in chapter three. The adsorption has been approximated with a phase transition model. Above a certain surfactant concentration a monolayer of isolated molecules converts into a bilayer. With the help the thermodynamics of phase transitions, the surfactant chemical potential at phase transition could be related to the curvature of the pore. The shift in this chemical potential due to the curvature is in first approximation proportional to the curvature constant of the bilayer. A molecular model, mean field type has been used to interpret this curvature energy. Both the curvature energy and the surface tension can be calculated from the excess grand potential density profile. The curvature constant has been calculated from the profile of a flat layer, which is allowed as long as this profile is not very sensitive to the curvature. An equation, which relates the chemical potential at phase transition, the curvature, the structure of the layer and the affinity, has been derived.

    Our model predicts that the chemical potential of phase transition decreases with decreasing pore radius. The adsorbed bilayer becomes more stable when the pore - radius decreases. Experiments confirmed these trends. If the affinity of the adsorbed layer for the surface increases, the curvature influence on the chemical potential of phase transition increases.

    To test the analytical theory and to obtain generic knowledge about the influence of curvature on surfactant adsorption, MFL calculations have been performed, which have been described in chapter four. Contrary to the analytical model, the MFL theory allows changes in the structure of the adsorbed layer with curvature.

    The position of the phase transition in a curved system has been calculated as a function of the adsorption energy and the size of the tails and the headgroups. No matter what parameters were used, the MFL calculations always predicted that the surfactant chemical potential of phase transition decreases with decreasing pore radius, which confirmed the outcome of the analytical model. Especially the adsorption energy turned out to have a strong influence on the sensitivity of phase transition for the curvature. The shift in the chemical potential of the phase transition becomes stronger with increasing adsorption energy, as has also been predicted with the analytical theory.

    The most important approximation of the analytical theory, which has been tested with MFL calculations, is the curvature independency of the structure of the adsorbed layer. The surface tension of an adsorbed bilayer has been calculated as a function of the curvature for different chemical potentials. The curvature constant has been obtained as a function of the chemical potential by fitting these curves and calculating it from the excess grand potential density profile of a flat layer. It turned out that the last procedure, which is also used in the analytical theory, underestimates the value of the curvature constant. As long as this constant has a considerable value, the error made by this procedure does not effect the essential physics. Therefore it may be concluded that the analytical theory still captures the important physics despite its severe assumptions.

    Both the analytical theory and the MFL model neglect the existence of discrete surfactant aggregates at the surface. To remedy this shortcoming, in chapter 5 the Herzfeld model has been applied to the adsorption of rod-like aggregates at a solid- water interface. The adsorbed layer was represented as a collection of rod-like polydisperse particles embedded in a monolayer of surfactants. An equilibrium condition has been derived, stating that the intrinsic excess grand potential of a rod of a given length plus its hard rod chemical potential has to be zero. The intrinsic excess grand potential has been divided into cap and body contributions, which are in principle the only two input parameters of the model. To calculate the hard rod chemical potential, the Herzfeld lattice model has been used. Rods are represented as rectangles. These rectangles have been placed on a square lattice. As a consequence the number of possible orientations of a rod is two.

    By combining the Herzfeld model and the equilibrium condition, expressions for the length distributions in both directions have been obtained. With these distributions expressions were derived for the total number of rods, the average aspect ratio and the standard deviation of this aspect ratio, all in both directions. The distributions have exponential forms, with decay parameters equal to the average aspect ratio minus one and the standard deviation of the aspect ratio. The close relationship between the average aspect ratio and its standard deviation has made clear that size fluctuations are very important in systems with large rods.

    Calculations have been performed on isotropic systems. Adsorption isotherms have been calculated for different cap Helmholtz energies. These isotherms show that the surfactants already adsorb in large amounts when the aggregates as such are not stable. However the collection of aggregates is stabilized by the translational entropy. If the caps become more unfavorable the co-operativity of the adsorption increases, because the length of the adsorbed aggregates increases. Adsorption isotherms have also been obtained for systems, which are allowed to order. It has been shown that at a certain surfactant chemical potential a second order isotropic- nematic phase transition occurs. After this transition the growth of the aggregates is promoted in the direction of alignment and inhibited in the direction perpendicular to that.

    The isotropic-nematic transition line has been calculated. It turned out that ordering can take place at much lower surface densities of rods when the average aspect ratio increases. The cap fraction is inversely proportional to the average aspect ratio minus one to the power two at the transition line. Although this expression could not be derived, the close resemblance with an equation, derived for monodisperse rods, confirmed that it is an exact outcome of the model. With the formula found, a relation between surface density at the transition line and the Helmholtz energy of the end caps has been derived, which showed that the nernatic ordering takes place at lower rod densities when the caps become more unfavorable.

    In the end of my study it has become more and more evident that the phase behavior of surfactants at interfaces should be at least as rich as in solution. As experimental techniques to investigate the structure of micelles at a surface are becoming available (e.g. AFM), we expect that the possible morphologies will become known to us in increasing detail in the near future. This thesis may assist the explorations, directed to fill the gaps in our knowledge of the behavior of surfactants at the solid-water interface, and thus allows us to use surfactants more effective in its applications.

    L'Micellization at surfaces: theory of polydisperse rodlike micelles.
    Huinink, H.P. ; Keizer, A. de; Leermakers, F.A.M. ; Lyklema, J. - \ 1998
    Langmuir 14 (1998). - ISSN 0743-7463 - p. 2693 - 2701.
    Nonionic surfactants in cylindrical hydrophylic pores.
    Huinink, H.P. ; Keizer, A. de; Leermakers, F.A.M. ; Lyklema, J. - \ 1997
    Progress in Colloid and Polymer Science 105 (1997). - ISSN 0340-255X - p. 91 - 95.
    The adsorption of nonionic surfactants in hydrophilic cylindrical pores. 1. A thermodynamic analysis.
    Huinink, H.P. ; Keizer, A. de; Leermakers, F.A.M. ; Lyklema, J. - \ 1997
    Langmuir 13 (1997). - ISSN 0743-7463 - p. 6452 - 6460.
    The adsorption of nonionic surfactants in hydrophilic cylindrical pores. 2. Mean field lattice calculations.
    Huinink, H.P. ; Keizer, A. de; Leermakers, F.A.M. ; Lyklema, J. - \ 1997
    Langmuir 13 (1997). - ISSN 0743-7463 - p. 6618 - 6625.
    Depletion and exclusion of polymers from porous particles.
    Keizer, A. de; Moerkens, D. ; Huinink, H.P. - \ 1996
    In: Abstract 7th Conf. on Colloid Chemistry, Szeged (H), Hungarian Chemical Soc., Budapest (1996) L-33
    Adsorption behavior of surfactant molecules in pores, a theoretical study.
    Huinink, H.P. ; Keizer, A. de; Leermakers, F.A.M. ; Lyklema, J. - \ 1996
    In: Abstract 10th Conf. European Colloid and Interface Society, Åbo (Finland), ECIS (1996) p-V.23
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