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.

    The effect of adhesives and solvents on the capture and specimen quality of pest thrips on coloured traps
    Davidson, M.M. ; Nielsen, M.C. ; Butler, R.C. ; Vellekoop, R. ; George, S. ; Gunawardana, D. ; Muir, C.A. ; Teulon, D.A.J. - \ 2015
    Crop Protection 72 (2015). - ISSN 0261-2194 - p. 108 - 111.
    frankliniella-occidentalis pergande - sticky traps - thysanoptera - palmi - eradication - surfaces - diptera - crop
    The present study compared different adhesives for trapping efficacy, ease of removing specimens and the subsequent quality of specimens for identification of thrips pests captured on blue plastic boards in a commercial capsicum glasshouse. The mean total number of thrips caught on sticky boards differed significantly with different adhesives. Blue boards covered with a water-based adhesive caught the least total number of thrips in the two experiments (56 thrips per trap, experiment 1; 4 thrips per trap, experiment 2). Traps covered with Stikem Special® caught the greatest number of total thrips (299 per trap, experiment 1; 32 per trap, experiment 2). De-Solv-it® was the most effective solvent to remove thrips from sticky boards compared with water and mineral oil, with all thrips detached from boards for all adhesive treatments within 150 min. Damage to or absence of key morphological features due to removal of specimens with De-Solv-it that would prevent species identification was recorded in only 10 of the 720 specimens removed from traps across all adhesives. The majority of thrips (70–92%) identified were Thrips tabaci Lindeman or Frankliniella occidentalis (Pergande). The type of adhesive used is an important factor to consider when developing traps for insect pest monitoring and management.
    Ion adsorption-induced wetting transition in oil-water-mineral systems
    Mugele, F. ; Bera, B. ; Cavalli, A. ; Siretanu, I. ; Maestro, A. ; Duits, M. ; Cohen Stuart, M.A. ; Ende, D. van den - \ 2015
    Scientific Reports 5 (2015). - ISSN 2045-2322 - 8 p.
    hydration forces - surfaces - recovery - wettability - interfaces - membranes - charge - layer
    The relative wettability of oil and water on solid surfaces is generally governed by a complex competition of molecular interaction forces acting in such three-phase systems. Herein, we experimentally demonstrate how the adsorption of in nature abundant divalent Ca2+ cations to solid-liquid interfaces induces a macroscopic wetting transition from finite contact angles (˜10°) with to near-zero contact angles without divalent cations. We developed a quantitative model based on DLVO theory to demonstrate that this transition, which is observed on model clay surfaces, mica, but not on silica surfaces nor for monovalent K+ and Na+ cations is driven by charge reversal of the solid-liquid interface. Small amounts of a polar hydrocarbon, stearic acid, added to the ambient decane synergistically enhance the effect and lead to water contact angles up to 70° in the presence of Ca2+. Our results imply that it is the removal of divalent cations that makes reservoir rocks more hydrophilic, suggesting a generalizable strategy to control wettability and an explanation for the success of so-called low salinity water flooding, a recent enhanced oil recovery technology.
    The effect of molecular composition and crosslinking on adhesion of a bio-inspired adhesive
    Yang, J. ; Keijsers, J. ; Heek, M. van; Stuiver, A. ; Cohen Stuart, M.A. ; Kamperman, M.M.G. - \ 2015
    Polymer Chemistry 6 (2015). - ISSN 1759-9954 - p. 3121 - 3130.
    polychaete phragmatopoma-californica - density-functional theory - mussel - protein - dopa - mechanisms - surfaces - catechol - glue
    In this article, catechol-functionalized polymers are synthesized by free radical polymerization of dopamine methacrylamide (DMA) and 2-methoxyethyl methacrylate (MEA) at 60 °C in DMF. By varying the DMA content in the polymer, it is found that during free radical polymerization, the catechol groups in DMA react with the propagating radicals, resulting in the formation of a crosslinked structure. We systematically study the effect of DMA content and crosslinking on the adhesion properties of the polymers. Under both dry and wet conditions, maximum adhesion is obtained for a polymer composed of 5 mol% DMA. This polymer exhibits an optimum balance between the catechol content to strengthen the interface, compliance to ensure good contact formation and cohesive strength to resist separation. An increase in the crosslinking degree of the polymer resulted in reduced dry adhesion.
    Controlling the dopant dose in silicon by mixed-monolayer doping
    Ye, L. ; Pujari, S.P. ; Zuilhof, H. ; Kudernac, T. ; Jong, M.P. de; Wiel, W.G. van der; Huskens, J. - \ 2015
    ACS Applied Materials and Interfaces 7 (2015)5. - ISSN 1944-8244 - p. 3231 - 3236.
    organic monolayers - surfaces
    Molecular monolayer doping (MLD) presents an alternative to achieve doping of silicon in a nondestructive way and holds potential for realizing ultrashallow junctions and doping of nonplanar surfaces. Here, we report the mixing of dopant-containing alkenes with alkenes that lack this functionality at various ratios to control the dopant concentration in the resulting monolayer and concomitantly the dopant dose in the silicon substrate. The mixed monolayers were grafted onto hydrogen-terminated silicon using well-established hydrosilylation chemistry. Contact angle measurements, X-ray photon spectroscopy (XPS) on the boron-containing monolayers, and Auger electron spectroscopy on the phosphorus-containing monolayers show clear trends as a function of the dopant-containing alkene concentration. Dynamic secondary-ion mass spectroscopy (D-SIMS) and Van der Pauw resistance measurements on the in-diffused samples show an effective tuning of the doping concentration in silicon.
    Volatilisation of pesticides after application in vegetable greenhouses
    Doan Ngoc, K. ; Berg, F. van den; Houbraken, M. ; Spanoghe, P. - \ 2015
    Science of the Total Environment 505 (2015). - ISSN 0048-9697 - p. 670 - 679.
    fungicide fenpropimorph - potato crop - plants - soil - air - surfaces - reentry - tunnel
    Background Volatilisation of pesticides after application to the soil or the crop is an important source of emission into the atmosphere. As a result, workers, residents and bystanders are potentially at risk when exposed to these volatilised substances. Nonetheless, data on measured concentrations are quite scarce, especially in greenhouses. The objective of this work is to present the results of volatilisation experiments performed in greenhouses. Results The results indicate that the concentrations are highest in the hours after application and rapidly decline during the days following application. Conclusion Greenhouse temperature, ventilation rate, the substance vapour pressure and the rate of competing processes were identified as important factors influencing volatilisation in greenhouses. The results from this study contribute to a better understanding of volatilisation in greenhouses and may help to improve the recent PEARL model for volatilisation in greenhouses.
    Influence of Pluronic F127 on the distribution and functionality of inkjet-printed biomolecules in porous nitrocellulose substrates
    Mujawar, L.H. ; Amerongen, A. van; Norde, W. - \ 2015
    Talanta 131 (2015). - ISSN 0039-9140 - p. 541 - 547.
    protein microarrays - spot morphology - block-copolymer - antibody - surfaces - additives - membrane - flow - hydrophobicities - orientation
    The distribution of inkjet-printed biomolecules in porous nitrocellulose substrates often results in a non-homogeneous spot morphology commonly referred to as 'doughnut-shaped' spots. We have studied the influence of Pluronic F127 (an amphiphilic surfactant) on the functionality of inkjet-printed primary antibody molecules and on the final assay result by performing a one-step antibody binding assay in the nitrocellulose substrate. The primary antibody was printed with and without Pluronic, followed by the addition of double-labelled amplicons as antigen molecules and a fluorophore-labelled streptavidin as detection conjugate. The distribution of the fluorescence intensity down into the nitrocellulose substrate was investigated by confocal laser scanning microscopy in 'Z' stacking mode. Each horizontal slice was further analysed by applying a concentric ring format and the fluorescence intensity in each slice was represented in a colour-coded way. The mean and total fluorescence intensity of the antibody binding assay (fluorescent streptavidin) showed a peak at 0.2% (w/v) Pluronic F127. In addition, an improved spot morphology was observed also peaking at the same Pluronic concentration. Subsequently, we investigated the direct influence of Pluronic F127 on the location of the primary antibody molecules by labelling these molecules with the fluorophore Alexa-488. Our results show that upon increasing the concentration of Pluronic F127 in the printing buffer, the spot diameter increased and the number of primary antibody molecules bound in the spot area gradually decreased. This was confirmed by analysing the distribution of fluorescently labelled primary antibody molecules down into the membrane layers. We conclude that a particular ratio between primary antibody and Pluronic F127 molecules in combination with available substrate binding capacity results in an optimal orientation, that is Fab-UP, of the primary antibody molecules. Consequently, an increased number of antigen molecules (in our case the labelled amplicons) and of the fluorescent detection conjugate (streptavidin) will give an optimal signal. Moreover, distribution of the primary antibody molecules was more homogeneous at the optimal Pluronic F127 concentration, contributing to the better spot morphology observed.
    Colloidal liquid crystals in rectangular confinement: theory and experiment
    Lewis, A.H. ; Garlea, I. ; Alvarado, J. ; Dammone, O.J. ; Howell, P.D. ; Majumdar, A. ; Mulder, B. ; Lettinga, M.P. ; Koenderink, G.H. ; Aarts, D.G.A.L. - \ 2014
    Soft Matter 10 (2014)39. - ISSN 1744-683X - p. 7865 - 7873.
    cell-sized confinement - de-gennes theory - alignment - phases - interfaces - surfaces - defects
    We theoretically and experimentally study nematic liquid crystal equilibria within shallow rectangular wells. We model the wells within a two-dimensional Oseen-Frank framework, with strong tangent anchoring, and obtain explicit analytical expressions for the director fields and energies of the 'diagonal' and 'rotated' solutions reported in the literature. These expressions separate the leading-order defect energies from the bulk distortion energy for both families of solutions. The continuum Oseen-Frank study is complemented by a microscopic mean-field approach. We numerically minimize the mean-field functional, including the effects of weak anchoring, variable order and random initial conditions. In particular, these simulations suggest the existence of higher-energy metastable states with internal defects. We compare our theoretical results to experimental director profiles, obtained using two types of filamentous virus particles, wild-type fd-virus and a modified stiffer variant (Y21M), which display nematic ordering in rectangular chambers, as found by confocal scanning laser microscopy. We combine our analytical energy expressions with experimentally recorded frequencies of the different equilibrium states to obtain explicit estimates for the extrapolation length, defined to be the ratio of the nematic elastic constant to the anchoring coefficient, of the fd-virus.
    Electrokinetics as an alternative to neutron reflectivity for evaluation of segment density distribution in PEO brushes
    Zimmermann, R. ; Romeis, D. ; Bihannic, I. ; Cohen Stuart, M.A. ; Sommer, J.U. ; Werner, C. ; Duval, J.F.L. - \ 2014
    Soft Matter 10 (2014)39. - ISSN 1744-683X - p. 7804 - 7809.
    poly(ethylene oxide) brushes - diffuse soft interfaces - grafted polymer brush - streaming current - aqueous-solution - behavior - films - water - thin - surfaces
    Unravelling details of charge, structure and molecular interactions of functional polymer coatings defines an important analytical challenge that requires the extension of current methodologies. In this article we demonstrate how streaming current measurements interpreted with combined self consistent field (SCF) and soft surface electrokinetic theories allow the evaluation of the segment distribution within poly(ethylene oxide) (PEO) brushes beyond the resolution limits of neutron reflectivity technique.
    Influence of the relative humidity on the morphology of inkjet printed spots of IgG on a non-porous substrate.
    Mujawar, L.H. ; Kuerten, J.G.M. ; Siregar, D.P. ; Amerongen, A. van; Norde, W. - \ 2014
    RSC Advances : An international journal to further the chemical sciences 4 (2014)37. - ISSN 2046-2069 - p. 19380 - 19388.
    experimental-verification - protein microarrays - dna microarrays - contact-angle - evaporation - surfaces - drops - performance - fabrication - adsorption
    During the drying of inkjet printed droplets, the solute particles (IgG-Alexa-635 molecules) in the drop may distribute unevenly on the substrate, resulting in a “coffee-stain” spot morphology. In our study, we investigated the influence of the relative humidity on the distribution of inkjet printed fluorophore labeled IgG molecules on a polystyrene substrate. A theoretical model for an evaporating droplet was developed in order to predict the changes in the spot diameter, height and volume of a drying droplet. An experiment was performed where a sessile droplet was monitored using a CCD camera installed on a goniometer and good agreement was found between the experimental results and simulation data. We also compared the predicted morphology for an inkjet-printed microarray spot with the experimental results where IgG molecules were printed for various relative humidities. The spot morphology of the dried spots was analyzed by a confocal laser microscopy. At a lower relative humidity (i.e.,
    The ratio of the lateral correlation length and particle radius determines the density profile of spherical molecules near a fluctuating membrane
    Córdoba-Valdés, F. ; Castañeda-Priego, R. ; Timmer, J. ; Fleck, C. - \ 2014
    Soft Matter 10 (2014). - ISSN 1744-683X - p. 8475 - 8481.
    depletion forces - fluid membranes - lipid bilayers - vesicles - surfaces - colloids - contact - regime
    Interactions between membranes and molecules are important for many biological processes, e.g., transport of molecules across cell membranes. However, the detailed physical description of the membrane–biomolecule system remains a challenge and simplified schemes allow capturing its main intrinsic features. In this work, by means of Monte Carlo computer simulations, we systematically study the distribution of uncharged spherical molecules in contact with a flexible surface. Our results show that the distribution for finite size particles has the same simple functional form as the one obtained for point-like particles and depends only on the ratio of the lateral correlation length of the membrane and the radius of the molecules.
    Stability of (Bio)Functionalized Porous Aluminum Oxide
    Debrassi, A. ; Ribbera, A. ; Vos, W.M. de; Wennekes, T. ; Zuilhof, H. - \ 2014
    Langmuir 30 (2014). - ISSN 0743-7463 - p. 1311 - 1320.
    self-assembled monolayers - lactic-acid bacteria - lactobacillus-plantarum - nanoporous alumina - click chemistry - anodic alumina - surfaces - adsorption - membrane - carbohydrate
    Porous aluminum oxide (PAO), a nanostructured support for, among others, culturing microorganisms, was chemically modified in order to attach biomolecules that can selectively interact with target bacteria. We present the first comprehensive study of monolayer-modified PAO using conditions that are relevant to microbial growth with a range of functional groups (carboxylic acid, a-hydroxycarboxylic acid, alkyne, alkene, phosphonic acid, and silane). Their stability was initially assessed in phosphate-buffered saline (pH 7.0) at room temperature. The most stable combination (PAO with phosphonic acids) was further studied over a range of physiological pHs (4–8) and temperatures (up to 80 °C). Varying the pH had no significant effect on the stability, but it gradually decreased with increasing temperature. The stability of phosphonic acid-modified PAO surfaces was shown to depend strongly on the other terminal group of the monolayer structure: in general, hydrophilic monolayers were less stable than hydrophobic monolayers. Finally, an alkyne-terminated PAO surface was reacted with an azide-linked mannose derivative. The resulting mannose-presenting PAO surface showed the clearly increased adherence of a mannose-binding bacterium, Lactobacillus plantarum, and also allowed for bacterial outgrowth.
    An exploratory study on the use of digital sculpting in conceptual product design
    Alcaide-Marzal, J. ; Diego-Más, J.A. ; Asensio-Cuesta, S. ; Piqueras Fiszman, B. - \ 2013
    Design Studies 34 (2013)2. - ISSN 0142-694X - p. 264 - 284.
    freehand sketches - cad tools - 3d - reconstruction - discovery - surfaces - features
    The product design process involves intensive manipulation of graphical data, from pencil sketches to CAD files. The use of graphic software is common among professionals in this field. Despite this, the conceptual design stage remains intensive in paper and pencil work, as CAD systems are still too rigid to allow a creative production of concepts. In this paper the use of digital sculpting software is proposed as a way of producing 3D sketches in the early stages of the process. An experiment is conducted to determine to which extent 3D sculpt sketches can be considered as a suitable tool for conceptual design. The results show a better performance of 2D drawings, but support the complementary use of digital sculpting.
    The Condensation of Water on Adsorbed Viruses
    Alonso Carnicero, J.M. ; Tatti, F. ; Chuvilin, A. ; Mam, K. ; Ondarcuhu, T. ; Bittner, A.M. - \ 2013
    Langmuir 29 (2013)47. - ISSN 0743-7463 - p. 14580 - 14587.
    scanning-electron-microscopy - surfaces - wet - morphologies - diffraction - droplets - dynamics - liquids
    The wetting and dewetting behavior of biological nanostructures and to a greater degree single molecules is not well-known even though their contact with water is the basis for all biology. Here, we show that environmental electron microscopy (EM) can be applied as a means of imaging the condensation of water onto viruses. We captured the formation of submicrometer water droplets and filaments on single viral particles by environmental EM and by environmental transmission EM. The condensate structures are compatible with capillary condensation between adsorbed virus particles and with known droplet shapes on patterned surfaces. Our results confirm that such droplets exist down to
    Tribology and Stability of Organic Monolayers on CrN: A Comparison among Silane, Phosphate, Alkene, and Alkyne Chemistries
    Pujari, S.P. ; Li, F. ; Regeling, R. ; Zuilhof, H. - \ 2013
    Langmuir 29 (2013)33. - ISSN 0743-7463 - p. 10405 - 10415.
    self-assembled monolayers - indium-tin oxide - chain-length - nanotribological properties - silicon-carbide - high-pressure - phase state - surfaces - adhesion - titanium
    The fabrication of chemically and mechanically stable monolayers on the surfaces of various inorganic hard materials is crucial to the development of biomedical/electronic devices. In this Article, monolayers based on the reactivity of silane, phosphonate, 1-alkene, and 1-alkyne moieties were obtained on the hydroxyl-terminated chromium nitride surface. Their chemical stability and tribology were systematically investigated. The chemical stability of the modified CrN surfaces was tested in aqueous media at 60 °C at pH 3, 7, and 11 and monitored by static water contact angle measurements, X-ray photoelectron spectroscopy (XPS), ellipsometry, and Fourier transform infrared reflection absorption spectroscopy (FT-IRRAS). The tribological properties of the resulting organic monolayers with different end groups (fluorinated or nonfluorinated) were studied using atomic force microscopy (AFM). It was found that the fluorinated monolayers exhibit a dramatic reduction of adhesion and friction force as well as excellent wear resistance compared to those of nonfluorinated coatings and bare CrN substrates. The combination of remarkable chemical stability and superior tribological properties makes these fluorinated monolayers promising candidates for the development of robust high-performance devices.
    Diversity assessment of Listeria monocytogenes biofilm formation: Impact of growth condition, serotype and strain origin
    Kadam, S.R. ; Besten, H.M.W. den; Veen, S. van der; Zwietering, M.H. ; Moezelaar, R. ; Abee, T. - \ 2013
    International Journal of Food Microbiology 165 (2013)3. - ISSN 0168-1605 - p. 259 - 264.
    4b strains - temperature - motility - surfaces - chloride - 1/2a
    The foodborne pathogen Listeria monocytogenes has the ability to produce biofilms in food-processing environments and then contaminate food products, which is a major concern for food safety. The biofilm forming behavior of 143 L. monocytogenes strains was determined in four different media that were rich, moderate or poor in nutrients at 12°C, 20°C, 30°C and 37°C. The biofilm formation was mostly influenced by temperature, resulting in decreased biofilm formation with decreasing temperature. Biofilm formation was enhanced in nutrient-poor medium rather than in nutrient-rich medium, and especially in nutrient-poor medium significantly enhanced biofilm production was observed early in biofilm maturation underlining the effect of medium on biofilm formation rate. Also serotype had a significant effect on biofilm formation and was influenced by medium used because strains from both serotype 1/2b and 1/2a formed more biofilm than serotype 4b strains in nutrient-rich medium at 20°C, 30°C and 37°C, whereas in nutrient-poor medium the biofilm production levels of serotype 1/2a and 4b strains were rather similar and lower than serotype 1/2b strains. The strains used originated from various origins, including dairy, meat, industrial environment, human and animal, and the level of biofilm formation was not significantly affected by the origin of isolation, irrespective of medium used and temperature tested. A linear model was used to correlate crystal violet staining of biofilm production to the number of viable cells within the biofilm. This showed that crystal violet staining was poorly correlated to the number of viable cells in nutrient-poor medium, and LIVE/DEAD staining and DNase I treatment revealed that this could be attributed to the presence of non-viable cells and extracellular DNA in the biofilm matrix. The significant impact of intrinsic and extrinsic factors on biofilm production of L. monocytogenes underlined that niche-specific features determine the levels of biofilm produced, and insights in biofilm formation characteristics will allow us to further optimize strategies to control the biofilm formation of L. monocytogenes
    On the collapse transition of a polymer brush: the case of lateral mobility
    Leermakers, F.A.M. ; Egorov, S.A. - \ 2013
    Soft Matter 9 (2013)12. - ISSN 1744-683X - p. 3341 - 3348.
    terminally attached chains - consistent field-theory - poor solvents - molecular-dynamics - tethered polymers - model - adsorption - interface - surfaces - layers
    We consider a polymer brush composed of end-grafted polymer chains. Classical theory advocates that a worsening of the solvent quality results in a smooth decrease of the brush height from a swollen to a dense brush. We report that a homogeneous brush under poor solvent conditions can have a negative surface pressure, indicating an instability in favour of lateral segregation. Also by using a two-gradient version of the self-consistent field (SCF) theory we show that, in contradiction to the classical result, but in line with the negative pressure, the collapse transition for laterally mobile chains has a first-order character, exemplified by the presence of a compact brush that coexists with a dilute gas of end-grafted chains. The dense brush assumes a pancake shape wherein the chains balance the stretching entropy against surface energies. The height of the pancake scales sub-linearly with the chain length because the local grafting density decreases with increasing chain length. In analogy with wetting studies we discuss how the spreading parameter has an influence on the pancake structure. Accordingly, the height increases with worsening of the solvent quality and decreases with increased affinity for the substrate. The two-phase state is expected in many practical situations
    Interfacial tension and wettability in water-carbon dioxide systems: Experiments and self-consistent field modeling
    Banerjee, S. ; Hassenklover, E. ; Kleijn, J.M. ; Cohen Stuart, M.A. ; Leermakers, F.A.M. - \ 2013
    The Journal of Physical Chemistry Part B: Condensed Matter, Materials, Surfaces, Interfaces & Biophysical 117 (2013)28. - ISSN 1520-6106 - p. 8524 - 8535.
    block copolymer adsorption - statistical thermodynamics - elevated pressures - mixtures - co2 - temperature - surfaces - density - mpa
    This paper presents experimental and modeling results on water–CO2 interfacial tension (IFT) together with wettability studies of water on both hydrophilic and hydrophobic surfaces immersed in CO2. CO2–water interfacial tension (IFT) measurements showed that the IFT decreased with increasing pressure and the negative slopes of IFT–pressure isotherms decreased with increasing temperature. Water contact angle on a cellulose surface (hydrophilic) immersed in CO2 increased with pressure, whereas the water contact angle on a hydrophobic surface such as hexamethyl disilazane (HMDS) coated silicon surface was almost independent of pressure. These experimental findings were augmented by modeling using the self-consistent field theory. The theory applies the lattice discretization scheme of Scheutjens and Fleer, with a discretization length close to the size of the molecules. In line with this we have implemented a primitive molecular model, with just small variations in the molar volume. The theory makes use of the Bragg-Williams approximation and has binary Flory–Huggins interaction parameters (FH) between CO2, water, and free volume. Using this model, we generated the complete IFT–pressure isotherms at various temperatures, which coincided well with the trends reported in literature, that is, the water–CO2 interfacial tension decreased with increasing pressure for pressures =100 bar and became independent of pressure >100 bar. The transition point occurred at higher pressures with increasing temperature. At three-phase coexistence (water–CO2–free volume) and at the water–vapor interface (water–free volume), we always found the CO2 phase in between the water-rich and free volume-rich phases. This means that for the conditions studied, the water–vapor interface is always wet by CO2 and there are no signs of a nearby wetting transition. Calculation of the water contact angle on a solid surface was based on the computed adsorption isotherms of water from a vapor or from a pressurized CO2-rich phase and analysis of surface pressures at water–vapor or water–CO2 coexistence. The results matched reasonably well with the experimental contact angle data. Besides, we also computed the volume fraction profiles of the CO2, H2O, and the V phase, from which the preferential adsorption of CO2 near the hydrophilic surface was deduced.
    Distribution of biomolecules in porous nitrocellulose membrane pads using confocal laser scanning microscopy and high-speed cameras
    Mujawar, L.H. ; Maan, A.A. ; Khan, M.K.I. ; Norde, W. ; Amerongen, A. van - \ 2013
    Analytical Chemistry 85 (2013)7. - ISSN 0003-2700 - p. 3723 - 3729.
    printed protein molecules - antibody microarrays - spot morphology - liquid-drops - additives - surfaces - flow
    The main focus of our research was to study the distribution of inkjet printed biomolecules in porous nitrocellulose membrane pads of different brands. We produced microarrays of fluorophore-labeled IgG and bovine serum albumin (BSA) on FAST, Unisart, and Oncyte-Avid slides and compared the spot morphology of the inkjet printed biomolecules. The distribution of these biomolecules within the spot embedded in the nitrocellulose membrane was analyzed by confocal laser scanning microscopy in the “Z” stack mode. By applying a “concentric ring” format, the distribution profile of the fluorescence intensity in each horizontal slice was measured and represented in a graphical color-coded way. Furthermore, a one-step diagnostic antibody assay was performed with a primary antibody, double-labeled amplicons, and fluorophore-labeled streptavidin in order to study the functionality and distribution of the immune complex in the nitrocellulose membrane slides. Under the conditions applied, the spot morphology and distribution of the primary labeled biomolecules was nonhomogenous and doughnut-like on the FAST and Unisart nitrocellulose slides, whereas a better spot morphology with more homogeneously distributed biomolecules was observed on the Oncyte-Avid slide. Similar morphologies and distribution patterns were observed when the diagnostic one-step nucleic acid microarray immunoassay was performed on these nitrocellulose slides. We also investigated possible reasons for the differences in the observed spot morphology by monitoring the dynamic behavior of a liquid droplet on and in these nitrocellulose slides. Using high speed cameras, we analyzed the wettability and fluid flow dynamics of a droplet on the various nitrocellulose substrates. The spreading of the liquid droplet was comparable for the FAST and Unisart slides but different, i.e., slower, for the Oncyte-Avid slide. The results of the spreading of the droplet and the penetration behavior of the liquid in the nitrocellulose membrane may (partly) explain the distribution of the biomolecules in the different slides. To our knowledge, this is the first time that fluid dynamics in diagnostic membranes have been analyzed by the use of high-speed cameras.
    Preload-responsive adhesion: effects of aspect ratio, tip shape and alignment
    Paretkar, D. ; Kamperman, M.M.G. ; Martina, D. ; Zhao, J. ; Creton, C. ; Lindner, A. ; Jagota, A. ; McMeeking, R. ; Arzt, E. - \ 2013
    Journal of the Royal Society, Interface 10 (2013)83. - ISSN 1742-5689 - 13 p.
    fibrillar interfaces - switchable adhesion - contact - surfaces - microstructure - design
    We tested the adhesive response of polymer surfaces structured with arrays of cylindrical fibrils having diameters of 10–20 µm and aspect ratios 1–2.4. Fibrils had two different tip shapes of end-flaps and round edges. A preload-induced mechanical buckling instability of the fibrils was used to switch between the states of adhesion and non-adhesion. Non-adhesion in fibrils with round edges was reached at preloads that caused fibril buckling, whereas fibrils with end-flaps showed adhesion loss only at very high preloads. The round edge acted as a circumferential flaw prohibiting smooth tip contact recovery leading to an adhesion loss. In situ observations showed that, after reversal of buckling, the end-flaps unfold and re-form contact under prevailing compressive stress, retaining adhesion in spite of buckling. At very high preloads, however, end-flaps are unable to re-form contact resulting in adhesion loss. Additionally, the end-flaps showed varying contact adaptability as a function of the fibril–probe alignment, which further affects the preload for adhesion loss. The combined influence of preload, tip shape and alignment on adhesion can be used to switch adhesion in bioinspired fibrillar arrays
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