Staff Publications

Staff Publications

  • external user (warningwarning)
  • Log in as
  • language uk
  • About

    '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.

    We have a manual that explains all the features 

Current refinement(s):

Records 1 - 12 / 12

  • help
  • print

    Print search results

  • export

    Export search results

  • alert
    We will mail you new results for this query: keywords==hydrofobiciteit
Check title to add to marked list
Ionic liquid pre-treatment of microalgae and extraction of biomolecules
Desai, Rupali K. - \ 2016
Wageningen University. Promotor(en): Michel Eppink; Rene Wijffels. - Wageningen : Wageningen University - ISBN 9789462579804 - 126
salts - liquids - fractionation - extraction - hydrophobicity - algae - biomass production - zouten - vloeistoffen (liquids) - fractionering - extractie - hydrofobiciteit - algen - biomassa productie

Liquid-liquid extraction (LLE) techniques are widely used in separation primarily due to ease of scale up. Conventional (LLE) systems based on organic solvents are not suitable for extraction of fragile molecules such as proteins as it would result in denaturation. On the other hand aqueous biphasic system though suitable for extraction of proteins they are restricted by limited polarity range. Ionic liquids are salts which are liquid at room temperature. Ionic liquids have gained interest in extraction over the past years due to its non-volatility and tunable property. In this thesis we explored the feasibility of using two ionic liquid based systems for extraction: 1) Ionic liquid based aqueous two phase system for extraction of microalgae proteins and 2) ionic liquid based emulsions for separation of hydrophilic (e.g. proteins) and hydrophobic (e.g. pigments) components from complex biomass such as microalgae. Additionally the influence of IL pre-treatment on microalgae cell walls and subsequent fractionation of its components (e.g. proteins, pigments, lipids) was also investigated.

Biorefinery of proteins from rubber plantation residues
Widyarani, R. - \ 2016
Wageningen University. Promotor(en): Johan Sanders, co-promotor(en): Marieke Bruins; E. Ratnaningsih. - Wageningen : Wageningen University - ISBN 9789462576643 - 236 p.
biorefinery - biomass conversion - rubber - rubber plants - protein extraction - latex - hydrolysis - hydrophobicity - amino acids - wheat gluten - residual streams - biobased economy - bioraffinage - biomassaconversie - rubberplanten - eiwitextractie - hydrolyse - hydrofobiciteit - aminozuren - tarwegluten - reststromen

Biorefinery of rubber tree side streams could add economic value and income for farmers, who already grow the trees for latex production. The objective of this research was to design a process for the recovery of proteinaceous fractions from rubber tree. The aimed applications were expected to be suitable for local use, particularly in Indonesia, being one of the world’s largest rubber producers. Rubber seed was selected as a model biomass based on its availability (21-144 kg-protein/ha) and its oil content that enables the combination of protein and biodiesel productions within a biorefinery framework. Experimental works were focused on three parts: separation of protein and oil from rubber seed kernel, enzymatic hydrolysis of rubber seed protein into amino acids, and separation of amino acids from hydrolysate. Using alkaline extraction, up to 80% protein from the total original amount of protein in the kernel could be recovered in the extract, comparable to protein recoveries from other oilseeds and oilseed cakes. Seed type and pre-treatment had the most influence on protein recovery. Following protein extraction, the extracted proteins were recovered via isoelectric precipitation, resulting in rubber seed protein concentrate that can be used as such or can be processed further. Different protease combinations were used to hydrolyse rubber seed protein concentrate. After 24 h hydrolysis of rubber seed protein, up to 53% degree of hydrolysis and 35% protein recovery as free amino acids could be achieved. Combination of Pronase + Peptidase R resulted in the highest recovery and concentration of hydrophobic amino acids (phenylalanine, leucine, isoleucine, tyrosine, tryptophan, valine, methionine, and proline) in the hydrolysate. Some hydrophobic amino acids are essential in human and farm animal diets, therefore they can potentially be applied as a group in food and feed. Ethanol was used as an anti-solvent for selective precipitation of amino acids. Ethanol was able to selectively increase the hydrophobic amino acid fraction in rubber seed protein hydrolysate from 59% (mol/mol) in the starting material to 76% in the supernatant. Leucine and valine contributed most to this increase. The results of this study show that rubber seed proteins can be applied locally as animal feed or in industries for technical applications.

Drying and hydration of proteins at high concentration
Bouman, J. - \ 2015
Wageningen University. Promotor(en): Erik van der Linden, co-promotor(en): Renko de Vries. - Wageningen : Wageningen University - ISBN 9789462575509 - 161
eiwit - wei-eiwit - zeïne - drogen - droogmethoden - geneesmiddeltoedieningssystemen - hydratatie - hydrofobiciteit - ph - vacuolen - protein - whey protein - zein - drying - drying methods - drug delivery systems - hydration - hydrophobicity - vacuoles

Proteins are the building blocks of life and serve a wide range of essential functions in organisms. Many metabolic reactions in organisms are catalysed by enzymes, DNA is replicated by proteins and in cells proteins often facilitate active transport of e.g. glucose or ions. Proteins also serve an essential functionality in foods, pharmaceutics, bioplastics and even clothing. Recently, the use of proteins towards higher concentrations is of interest for food, pharmaceutical and medical applications. Nevertheless, the preparation of products with desired product properties can be challenging, when approaching higher protein concentrations. Therefore, in this thesis we investigate proteins at higher concentrations, especially focussing on their drying and hydration behaviour.

In part one of the thesis, the focus is on the dynamics of drying of proteins towards higher concentrations. Dense proteins systems have been scarcely studied compared to proteins at lower concentrations. We address drying behaviour where we focus on the use of whey protein isolate as a model system. In part two of the thesis we focus on the hydration properties of the corn protein zein, where we apply it as a drug excipient. In this part we also investigate the influence of hydration on the release behaviour of drugs into the hydration media.

The drying part (part one) contains two studies. The first study is more fundamental in nature, focussing on the drying of a protein coating. In previous studies mainly the macroscopic properties of protein coatings after drying are investigated, leaving the drying dynamics virtually unexplored. Here we investigate the drying behaviour of the model protein β-lactoglobulin on multiple length scales with an unique combination of in-line techniques. On the microscopic length scale we use dynamic vapour sorption and magnetic resonance imaging while on a smaller length scales, we apply diffusing wave spectroscopy and IR-spectroscopy to monitor the drying process. For all used techniques, the changes in the measured physical properties of the coating as a function of water weight fraction Xw from Xw = 0.8 down to Xw = 0.2 are gradual. However, using dynamic vapour sorption and IR-spectroscopy we measure a sharp change below water weight fractions of Xw = 0.2. We hypothesise that changes in the molecular interactions caused by dehydration of the protein results in a change in the drying kinetics of the film.

In the second study of part one, protein drying is approached on a more applied level, where we study the drying of a spherical droplet. We use single droplet drying as a methods that can model the spray drying process in a simplified and well-controlled way. Sessile droplets are subjected to varying drying conditions such as temperature, initial protein concentration, presence of airflow and droplet rotation. During these experiments the morphological development is monitored by a camera. After drying, scanning electron microscopy and X-ray tomography are used to examine the particles that are formed after complete drying. Irrespective of the conditions used, we observe an initial droplet shrinkage, followed by the nucleation of a hole in the droplet skin, which is followed by the formation of a vacuole. The drying conditions used, strongly influenced the location of the hole and the locking point prior to hole formation. We hypothesise that the location of the hole is caused by local inhomogeneities in protein concentration causing a the nucleation of the hole where the local skin modulus is lowest. Also the locking point of the droplet is found to be due to a inhomogeneity over the whole droplet caused by rapid evaporation. These results can be of importance to understand powder structure and functionality as obtained in spray drying.

In the hydration part (part 2), we investigate the potential of zein as a sole excipient in macroscale caplets obtained by hot melt extrusion (HME) and injection moulding (IM). Zein is good candidate as a sustained release agent, because it is insoluble in two studies. In the first study zein matrices were loaded with the drug paracetamol. Physical mixtures of zein, water and crystalline paracetamol are extruded and injection moulded into caplets. Characterisation of these caplets is performed using differential scanning calorimetry, IR- spectroscopy, scanning electron microscopy and powder X-ray diffraction. The hydration and drug release kinetics from the caplet slices is measured. We find that the drug release kinetics is broadly independent of the dissolution medium and drug loading. The release kinetics is diffusion limited and could be well described by a 2D diffusion model. The results demonstrate that the drug release rate from zein caplet slices can be tuned by its dimensions.

In the second study, a wider range of drugs differing in hydrophobicity is studied. Next to paracetamol, we have used two other model drugs: the hydrophobic indomethacin and the more hydrophilic ranitidine. The zein matrix is capable to stabilize the different dugs in a non-crystalline state, which is promising especially for increasing the bioavailability of poorly water-soluble drugs. Overall crystallinity of the drugs in the caplets increases with its degree of hydrophobicity. For the poorly soluble indomethacin, dissolution rates at low pH were higher from caplet slices, compared to the dissolution rates of indomethacin crystals by themselves. In addition, we found that the electrostatic interactions between zein and drugs can also be used to influence the release kinetics.

Various aspects were found to be of importance both for drying and hydration of concentrated protein systems. The homogeneity during both processes deserves attention as its manipulation can strongly influence final properties if the system. Also the plasticising effect of water on dense proteins is often found essential, when understanding the dynamics of both drying and hydration processes. Finally protein hydrophobicity and its manipulation can provide a window of opportunities in many applications which are involve by drying or hydration.

Ecology of tree roots in substrates of The Hague
Arhipova, L. ; Spijker, J.H. ; Kopinga, J. - \ 2007
Wageningen : Alterra (Alterra-rapport 1590) - 111
wortels - straatbomen - stedelijke gebieden - groeimedia - rizosfeer - substraten - bodemdegradatie - kationenuitwisselingcapaciteit - waterafstotende gronden - hydrofobiciteit - nederland - zuid-holland - roots - street trees - urban areas - growing media - rhizosphere - substrates - soil degradation - cation exchange capacity - water repellent soils - hydrophobicity - netherlands
The ecology of uniformly and non-uniformly distributed roots in layered and/or heterogeneous substrates, especially sand-peat-clay mixes, have been studied from literature and through a case study. There is a strong interaction between soil layering and/or heterogeneity and local root growth and local branching rate. In principle, the minimum area of root surface that a plant needs is very low. Real situations have much higher root surface areas for several reasons, one being the absence of synchronisation and synlocation of supply and demand of nutrients and water
Bioflocculation of mesophilic and thermophilic activated sludge
Vogelaar, J.C.T. ; Keizer, A. de; Spijker, S. ; Lettinga, G. - \ 2005
Water Research 39 (2005)1. - ISSN 0043-1354 - p. 37 - 46.
geactiveerd slib - afvalwaterbehandeling - biologische behandeling - temperatuur - uitvlokking - adsorptie - hydrofobiciteit - activated sludge - waste water treatment - biological treatment - temperature - flocculation - adsorption - hydrophobicity - paper-mill - water - effluent - temperatures - whitewater - reactors - flocs
Thermophilic activated sludge treatment is often hampered by a turbid effluent. Reasons for this phenomenon are so far unknown. Here, the hypothesis of the temperature dependency of the hydrophobic interaction as a possible cause for diminished thermophilic activated sludge bioflocculation was tested. Adsorption of wastewater colloidal particles was monitored on different flat surfaces as a function of temperature. Adsorption on a hydrophobic surface varied with temperature between 20 and 60 °C and no upward or downward trend could be observed. This makes the hydrophobic interaction hypothesis unlikely in explaining the differences in mesophilic and thermophilic activated sludge bioflocculation. Both mesophilic and thermophilic biomass did not flocculate with wastewater colloidal particles under anaerobic conditions. Only in the presence of oxygen, with biologically active bacteria, the differences in bioflocculation behavior became evident. Bioflocculation was shown only to occur with the combination of wastewater and viable mesophilic biomass at 30 °C, in the presence of oxygen. Bioflocculation did not occur in case the biomass was inactivated or when oxygen was absent. Thermophilic activated sludge hardly showed any bioflocculation, also under mesophilic conditions. Despite the differences in bioflocculation behavior, sludge hydrophobicity and sludge zetapotentials were almost similar. Theoretical calculations using the DLVO (Derjaguin, Landau, Verweij and Overbeek) theory showed that flocculation is unlikely in all cases due to long-range electrostatic forces. These calculations, combined with the fact that bioflocculation actually did occur at 30 °C and the unlikelyness of the hydrophobic interaction, point in the direction of bacterial exo-polymers governing bridging flocculation. Polymer interactions are not included in the DLVO theory and may vary as a function of temperature.
Modelling maximum adsorption capacities of soot and soot-like materials for PAHs and PCBs
Noort, P.C.M. van; Jonker, M.T.O. ; Koelmans, A.A. - \ 2004
Environmental Science and Technology 38 (2004)12. - ISSN 0013-936X - p. 3305 - 3309.
aromatische koolwaterstoffen - polycyclische koolwaterstoffen - adsorptie - sorbaten - hydrofobiciteit - organische verbindingen - monitoring - waterkwaliteit - waterbodems - aromatic hydrocarbons - polycyclic hydrocarbons - adsorption - sorbates - hydrophobicity - organic compounds - water quality - water bottoms - polycyclic aromatic-hydrocarbons - hydrophobic organic-chemicals - partition-coefficients - aqueous solubilities - black carbon - sorption - water - sediment - extraction - biphenyls
Recent studies have shown that not partitioning but adsorption is the main mechanism for sorption of hydrophobic organic compounds to soot and soot-like materials. For compounds that adsorb by van der Waals forces only, variation in soot-water distribution coefficients will result from differences in these forces for adsorption, as well as the maximum number of accessible sites. This maximum number of accessible sites may a priori be expected to vary due to differences in both sorbent characteristics and sorbate dimensions. In this modeling study, variation in maximum adsorption capacities is explained from sorbent and sorbate properties. Maximum adsorption capacities were calculated using (a) literature values for soot-water distribution coefficients for polycyclic aromatic hydrocarbons and polycholorobiphenyls on 10 different soot and soot-like materials and (b) Langmuir affinities for adsorption at a carbonaceous surface estimated using a recently reported method
Recent studies have shown that not partitioning but adsorption is the main mechanism for sorption of hydrophobic organic compounds to soot and soot-like materials. For compounds that adsorb by van der Waals forces only, variation in soot-water distribution coefficients will result from differences in these forces for adsorption, as well as the maximum number of accessible sites. This maximum number of accessible sites may a priori be expected to vary due to differences in both sorbent characteristics and sorbate dimensions. In this modeling study, variation in maximum adsorption capacities is explained from sorbent and sorbate properties. Maximum adsorption capacities were calculated using (a) literature values for soot-water distribution coefficients for polycyclic aromatic hydrocarbons and polychlorobiphenyls on 10 different soot and soot-like materials and (b) Langmuir affinities for adsorption at a carbonaceous surface estimated using a recently reported method. The variation in maximum adsorption capacities could be explained by the variation in sorbent specific surface area, sorbent organic carbon content, and the sorbent-sorbate contact area. Furthermore, increasing sorbate thickness was related to a decrease in maximum adsorption capacities, which points to adsorption in micropores. Maximum adsorption capacities decreased by 1-2 orders of magnitude as the contact area increased by 50%. This points to adsorption sites being hardly larger than sorbates.
Modeling gravity driven unstable flow in a water repellent soil
Nguyen, H.V. ; Nieber, J.L. ; Ritsema, C.J. ; Dekker, L.W. ; Steenhuis, T.S. - \ 1999
Journal of Hydrology 215 (1999)1-4. - ISSN 0022-1694 - p. 202 - 214.
waterafstotende gronden - hydrofobiciteit - simulatiemodellen - stabiliteit - bodemwater - infiltratie - water repellent soils - hydrophobicity - simulation models - stability - soil water - infiltration
Relation between mass-transfer and biodegradation of hydrophobic pollutants in soil
Mulder, H. - \ 1999
Agricultural University. Promotor(en): W.H. Rulkens; A.M. Breure. - S.l. : Mulder - ISBN 9789058080875 - 208
bodemverontreiniging - biodegradatie - massaoverdracht - bodem - volksgezondheidsbevordering - polycyclische koolwaterstoffen - hydrofobiciteit - soil pollution - biodegradation - mass transfer - soil - sanitation - polycyclic hydrocarbons - hydrophobicity
<p>The Dutch soil is contaminated at numerous locations with toxic organic compounds, such as polycyclic aromatic hydrocarbons (PAHs). To reduce the risks at these sites bioremediation can be applied as an alternative for the more destructive and energy intensive physicochemical soil sanitation techniques. During bioremediation microorganisms convert pollutants to less harmful compounds. Implementation of bioremediation is, however, limited because the strongly hydrophobic PAHs possess low water-solubilities and interact with soil organic matter. This results in a low mobility of PAHs in the soil as well as a low rate at which they become available for microbiological transformation. This thesis describes a study on the mutual influence of mass transfer and biodegradation processes which has been performed to gain a better insight in the mechanisms causing the persistence of PAHs in soil.</p><p>To achieve this goal, well-defined experimental systems have been applied to obtain reproducible results. In these systems, PAHs were used in defined solid states, either solid phase PAHs immobilized in stainless steel cups with a specified surface area, or PAHs adsorbed on chromatographic porous spheres (Amberlite resins) of hydrophobic material.</p><p>The influence of mixing on the dissolution rate and biodegradation rate of solid phase naphthalene has been investigated with the PAH immobilized in stainless steel cups in stirred fermentors (Chapter 2). Results of combined dissolution and degradation experiments have shown the necessity of quantification of the hydrodynamic flow conditions when studying the conversion of poorly water-soluble compounds. When the potential biodegradation rate of the bacterial population present exceeds the maximum dissolution rate, mass-transfer becomes limiting for naphthalene conversion. The maximum dissolution rate is strongly related to the extent of mixing and an increase of the latter results in an increase of the PAH biodegradation rate under such circumstances.</p><p>During the above-mentioned experiments biofilm formation by the applied bacterial strain ( <em>Pseudomonas</em> 8909N) has been observed at the naphthalene-water interface. On the basis of relatively long-term experiments, in which biofilms have been grown in chemostats, it was shown that the presence of a biofilm on the solid-liquid interface resulted in a 90% reduction of the biological availability of the solid naphthalene (Chapter 3).</p><p>The low solubilities of PAHs in water result in relatively low dissolution rates. The apparent solubility of hydrophobic compounds can be increased by the addition of surface active chemicals (surfactants) resulting in higher mass-transfer rates. This implies that the bioavailability can be increased by the use of surfactants. It was shown in Chapter 4 that the model system used in the foregoing chapters is very suitable for the investigation and modeling of the influence of surfactant addition on the dissolution and biodegradation of (initially) solid naphthalene. Results indicate that besides the increase in the apparent solubility due to the partition of naphthalene in micelles (aggregates of surfactant molecules), also the diffusion coefficient of micelles is a determining factor for the efficiency of surfactant addition. The flux of PAH to the bulk liquid phase is positively correlated with an the partitioning of the PAH in the micelles and the micellar diffusion coefficients.</p><p>When PAHs are present as diffuse soil contaminants, they will exist in a sorbed physical state. To gain insight in the influence of sorption processes and mass transfer in porous soil aggregates on the biodegradation of PAHs, chromatographic material (Amberlite XAD4 and XAD7) is used as a model soil system (Chapter 5). A mathematical model was developed that simultaneously accounted for nonlinear sorption, for internal and external mass transfer, and for nonlinear bacterial transformation kinetics. This model was checked for its applicability on the basis of experiments with naphthalene as a model pollutant. By variation of the mixing conditions in the reactors it was shown that characterization of the external diffusion limitations is necessary in the system used. The fate of naphthalene in the porous particles could be predicted adequately by the mechanistic model. The crucial model parameters that determine the mass transfer of PAHs in soil aggregates are: the particle size, the sorption coefficient, and the effective diffusion coefficient. Nonlinear sorption results in relatively low desorption rates compared to linear sorption and, therefore, a longer clean-up period is necessary.</p><p>To check whether the model developed in Chapter 5 could be used to describe the fate of PAHs in real soil aggregates, experiments were performed with Koopveen soil (Chapter 6). Aggregates with three different size fractions but with equal organic matter content (± 30%) were produced from this peat soil and proved to be stable during dynamic desorption and biodegradation experiments. These aggregates were artificially contaminated with either naphthalene or phenanthrene. The experimental results indicated that solid PAHs were probably present in the two lower size fractions due to the contamination method. However, mass transfer and biodegradation processes could be adequately modeled in the case of the largest naphthalene contaminated fraction. Results with similar soil material, that were fitted in earlier research with an empirical compartment model, could equally well be described with the current mechanistic model. The predictive capabilities of the current model are, however, superior because model parameters are related to measurable quantities.</p><p>Finally, three different physical states of PAH pollutants in soil have been postulated and mass transfer models have been developed to predict the release of PAHs to an aqueous phase (Chapter 7). The effect of the different physical states of PAHs in soil on the period necessary for a certain degree of bioremediation are calculated by coupling of the mass transfer models to a biodegradation module. It was calculated that, under mass transfer limited growth conditions, micro-organisms can effectively lower the dissolved PAH concentration and maximize the driving force for mass transfer. Therefore, simple mass transfer models can be applied to calculate bioremediation periods under these conditions.</p><p>The main conclusions that are formulated on the basis of the findings in this thesis and some recommendations for future research are presented in Chapter 8. The most important conclusion is that the use of model soil systems is a very powerful tool to investigate the interactions between mass transfer and biological transformation of hydrophobic compounds. These interactions could be studied in both model systems and models could be developed that make it now possible to estimate the behavior of PAHs in soil. These models can be useful to estimate ecotoxicological risks on the basis of released quantities instead of total concentrations and to estimate the feasibility of soil bioremediation or the development of new sanitition treatments.</p>
Long-term bioconcentration kinetics of hydrophobic chemicals in Selenastrum capricornutum and Microcystis aeruginosa
Koelmans, A.A. ; Woude, H. van der; Hattink, J. ; Niesten, D.J.M. - \ 1999
Environmental Toxicology and Chemistry 18 (1999). - ISSN 0730-7268 - p. 1164 - 1172.
benzeen - chloride - polychloorbifenylen - hydrofobiciteit - waterverontreiniging - microcystis aeruginosa - algen - cyanobacteriën - ecotoxicologie - bioaccumulatie - aquatische ecosystemen - benzene - polychlorinated biphenyls - hydrophobicity - water pollution - algae - cyanobacteria - ecotoxicology - bioaccumulation - aquatic ecosystems
Hydrophobically modified polyelectrolytes : synthesis, properties and interactions with surfactants
Nieuwkerk, A.C. - \ 1998
Agricultural University. Promotor(en): E.J.R. Sudhölter; Ton Marcelis. - S.l. : Nieuwkerk - ISBN 9789054858126 - 156
wasmiddelen - oppervlaktespanningsverlagende stoffen - hydrofobiciteit - elektrolyten - detergents - surfactants - hydrophobicity - electrolytes
Hydrophobically modified polyelectrolytes can form micelle-like aggregates, so-called microdomains, in aqueous solution. The hydrophobic side chains constitute the apolar inner part of these microdomains and the hydrophilic groups on the polyelectrolyte backbone are at the surface of the microdomains. The microdomain formation is mainly determined by the polyelectrolyte charge density, which can be varied by changing the pH of the solution, and the length of the hydrophobic side chains. The flexibility of the backbone and the structure of the side chains are also important.<p>From literature it is known that the interaction between hydrophobically modified polyelectrolytes, also called polysoaps, and surfactants strongly depends on the charge density on the polyelectrolyte and the length of the hydrophobic side chains. These factors also determine the microdomain formation. The interaction between <em></em> surfactants and polyelectrolytes in aqueous solution is thus highly dependent on the presence of microdomains. The research described in this thesis was aimed at determining the effects of charge density and hydrophobicity of polyelectrolytes on the interaction with surfactants.<CENTER><img src="/wda/abstracts/i2394_1.gif" height="220" width="400"/></CENTER>Copolymers from maleic anhydride and alkyl vinyl ethers ( <strong>I-n</strong> ) have been synthesised by radical polyrnerisation. These polymers were hydrolysed to polyelectrolytes <strong>II-n</strong> By reaction of <strong>I-n</strong> with 2- aminoethanesulfonic acid polyelectrolytes <strong>III-n</strong> were obtained. The alkyl vinyl ethers are substituted with rigid aromatic units, (cyanobiphenylyl)oxy units, which can induce the formation of liquid crystalline phases. Polymers <strong>I-n</strong> and <strong>II-n</strong> indeed form these phases. The isotropisation temperature of II-n is higher than for <strong>I-n</strong> due to the more flexible backbone of <strong>II-n</strong> . The enthalpy gain associated with the formation of the liquid crystalline phase increases with increasing spacer length and is larger for <strong>II-n</strong> than for <strong>I-n</strong> at comparable spacer length (Chapter 2).<p>The (cyanobiphenylyl)oxy units can also be used as chromophores. By the use of spectroscopic techniques one can study the microdomain formation of the polyelectrolytes and the interaction with surfactants. The UV spectra of the polyelectrolytes depend on the pH of the solution, thus on the charge density of the polyelectrolyte, and on the hydrophobicity of the side chain. When the chromophores aggregate a blue shift of the absorption maximum of the (cyanobiphenylyl)oxy chromophores as compared to the monomeric absorption maximum is observed. So-called π <strong>-π</strong> stacking interactions between parallel oriented aggregated chromophores are responsible for the blue shift. The extent of the blue shift is indicative for the conformation of the polyelectrolyte. UV measurements show that microdomains are formed by the polyelectrolytes <strong>II-n</strong> and <strong>III-n</strong> at 2 &lt; pH &lt; 13, and that more compact microdomains. are formed at lower pH.<p>Dynamic light scattering experiments confirm the formation of large aggregates in which the polyelectrolyte chains are highly entangled. Generally, the aggregates swell upon increasing the charge density, due to increased electrostatic repulsion on the polyelectrolyte backbone, and upon decreasing the side chain length (Chapter 3).<p>Oppositely charged surfactant molecules bind strongly to polyelectrolytes <strong>II-n</strong> and <strong>III-n</strong> in aqueous solution. Measurements using a dodecyltrimethylammonium (DTA +) selective electrode shows that DTA+ binds strongly and noncooperatively to both labelled and nonlabelled polyelectrolytes. The surfactant molecules bind individually to the microdomains formed by a polyelectrolyte, indicating the formation of mixed micellar aggregates.<p>Surface tension measurements also show the very strong binding between the polyelectrolytes and DTAB which results in a synergistic lowering of the surface tension. The hydrophilicity of the polyelectrolytes is lowered in the presence of DTAB which results in a decrease in water solubility and an increase in the amount of polyelectrolyte-DTA+ complex at the airsolution interface (Chapter 4).<p>By UV spectroscopy it is shown that within the microdomains the (cyanobiphenylyl)oxy chromophores are aggregated which results in a blue shift of the absorption maximum. Upon addition of surfactant molecules the blue shift decreases because the surfactant molecules penetrate between the hydrophobic side chains of the polyelectrolyte. The decrease in blue shift depends on the charge of the surfactant headgroup and on its hydrophobicity. The negatively charged sodium dodecyl sulfate (SDS) shows no influence on the wavelength of the absorption maximum and does not penetrate the microdomains. A non-ionic surfactant like polyoxyethylene(4)lauryl ether (Brij 30) interacts with the polyelectrolytes by purely hydrophobic interactions which results in a small decrease of the blue shift of the (cyanobiphenylyl)oxy chromophores. In addition to the results from the DTA+ selective electrode and the surface tension measurements, the UV measurements also show the very strong interaction between polyelectrolytes and oppositely charged surfactants. Addition of a cationically charged surfactant causes the largest decrease in blue shift, thus the largest destacking of the (cvanobiphenylyl)oxy chromophores. The hydrophobicity of the surfactant is also of importance as is clear from the larger decrease in blue shift observed for the addition of hexadecyltrimethyl ammonium bromide as compared to dodecyltrimethylammonium bromide. Upon increasing the surfactant concentration the blue shifts decrease gradually indicating noncooperative binding between the surfactants and hydrophobically modified polyelectrolytes. This agrees with the results obtained from measurements with the DTA+ selective electrode (Chapter 4).<CENTER><img src="/wda/abstracts/i2394_2.gif" height="132" width="400"/></CENTER>The addition of surfactant molecules which are labelled with a chromophore to a polyelectrolyte solution yields extra information on the interactions. Therefore new surfactants carrying azobenzene chromophores, <strong>X-Cn-Br,</strong> were synthesised. The azobenzene units are substituted at the 4'-position with a cyano, methoxy or fluoro groulp Initially, the interaction between these surfactants and nonlabelled polyelectrolytes was studied. The addition of <strong>X-Cn-Br</strong> to poly(maleic acid-co-n-butyl vinyl ether) results immediately in a maximum blue shift of the absorption maximum of the azobenzene groups. This indicates that the surfactants bind cooperatively to poly(maleic acid- <em>co-n</em> -butyl vinyl ether) allowing direct stacking between the azobenzene units. At the pH values used, poly(maleic acid- <em>co-n</em> -butyl vinyl ether) is in its extended conformation. When surfactant is added, the surfactant molecules form micelle-like aggregates surrounded by polyelectrolyte, and the counterions are disposed into solution. Upon increasing the side chain length of the polyelectrolyte the cooperatively decreases as is clear from the fact that the maximum blue shift is not immediately attained. The cooperativity also decreases upon decreasing the charge density on the polyelectrolyte. Both changes induce the formation of microdomains by the polyelectrolyte. When surfactants bind to these microdomains, mixed micelles are formed in which the surfactants sometimes cluster.<p>By labelling both polyelectrolyte and surfactant, the effects of interaction between polyelectrolytes and surfactants on the surfactant aggregation and on the disruption of the polyelectrolyte microdomains can be monitored. The measurements show that both the polyelectrolyte charge density and the length of the side chains influence the amount of interaction. These factors not only influence the electrostatic and hydrophobic attraction of surfactants to the polyelectrolytes, but they also determine the compactness of the microdomains. The spacer length of the surfactants and their terminal group seem to influence mainly the interaction between surfactant molecules (Chapter 4 and 5).<p>By use of the Langmuir technique the behaviour of polyelectrolytes <strong>I-n</strong> and <strong>II-n</strong> at the airwater interface is studied. Immediately after spreading both polymers form homogeneous layers on the subphase. The lift-off area per repeating unit indicates that the cyano groups of the chromophores of <strong>I-11</strong> and <strong>I-12</strong> are immersed into the subphase. For <strong>I-6, I-8</strong> and <strong>I - 10</strong> the side chains are oriented randomly into the air. Polyelectrolytes <strong>II-n</strong> have a more flexible backbone than <strong>I-n</strong> which allows the (cyanobiphenylyl)oxy chromophores of <strong>II-11</strong> and <strong>II-12</strong> to assume a flat orientation on the subphase. This flat orientation is hindered for the shorter chained polyelectrolytes, but the cyano groups of <strong>I-6, I-8</strong> and <strong>I-10</strong> are thought to interact with the subphase. Polymers <strong>II-n</strong> all show a plateau in their π-A isotherms. In this plateau a triple layer is formed by folding a polymeric double layer onto a monolayer. At a molecular area of one third of the onset of the plateau the pressure starts to rise again, after which the triple layer collapses. The triple layer formation is confirmed by the semi -reversibility of compression-expansion experiments and Brewster angle microscopy.<p>The addition of both positively and negatively charged surfactants results in an increase in the lift-off area of <strong>II-n</strong> . This results from electrostatic interactions between the polyelectrolyte backbone and the surfactant headgroups, and hydrophobic interactions between the surfactant tails and polyelectrolyte side chains.<p>Monolayers of polyelectrolytes <strong>II-n</strong> can be transferred from pure water and from a I mM DTAB solution onto hydrophilic quartz or glass in a Z-type fashion. However, both UV spectroscopy and Second Harmonic Generation measurements show there is no overall order within the transferred layers (Chapter 6).<p>Besides the addition of the azobenzene substituted surfactants to solutions containing polyelectrolytes, their thermotropic and lyotropic phase behaviour in the absence and presence of SDS is also studied. The terminal substituent on the azobenzene chromophores and the counterion, bromide or dodecyl sulfate, influence the physical properties. Smectic A phases are found for <strong>CN- Cn-Br, F-C12-Br, CN-Cn-DS, MeO-C10--DS</strong> and <strong>F-Cn-DS.</strong> The formation of myelin structures of <strong>CN-Cn-Br</strong> and <strong>MeO-Cn-Br</strong> in water is seen by optical microscopy. These myelins transform into giant vesicles which are, however, not very stable and crystallise at room temperature. Vesicles formed in the presence of SDS, from so-called ion pair amphiphiles, are more stable due to the electrostatic and hydrophobic interactions. UV spectra of the ion pair amphiphiles display a blue shift of the azobenzene chromophores as compared to the monomeric chromophores, which indicates that the chromophores are parallelly aggregated within these mixed vesicles (Chapter 7).
Modeling gravity driven fingered flow in a field soil having a hydrophobic layer
Nguyen, H.V. ; Nieber, J.L. ; Ritsema, C.J. ; Dekker, L.W. ; Misra, D. - \ 1995
In: Vadose zone hydrology : cutting across disciplines : Kearny Foundation of Soil Science international conference proceedings / Silva, D., - p. 103 - 104.
hydrofobiciteit - modellen - bodem - hydrophobicity - models - soil
Gravity-driven fingered flow in porous media is recognized to be an important process with respect to solute transport in the unsaturated zone. Recent continuous and nondestructive measurements of water content distribution in a water-repellent sandy field soil in the Netherlands reveals a very complicated wetting pattern with fingered flow being quite prevalent. Recent success in modelling gravity-driven unstable flow enables the complicated patterns observed at field sites to be simulated. In this study an attempt is made to simulate the patterns observed at the water-repellent field site using a numerical solution intended for modelling gravity-driven unstable flow.
Waterwingebied Goedereede (Ouddorp) : onderzoek van uitgemijnde duinzandgronden naar de relatie tussen de bodemkundig - bodemfysische eigenschappen en de mate van hydrofobie
Dekkers, J.M.J. ; Dekker, L.W. ; Holst, A.F. van - \ 1986
Wageningen : STIBOKA (Rapport / Stichting voor Bodemkartering no. 1897) - 61
grondwaterwinning - horizontale bronnen - bodemwater - grondwaterspiegel - hydrofobiciteit - zuid-holland - zuidhollandse eilanden - groundwater extraction - horizontal wells - soil water - water table - hydrophobicity
Check title to add to marked list

Show 20 50 100 records per page

Please log in to use this service. Login as Wageningen University & Research user or guest user in upper right hand corner of this page.