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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Dry period length of dairy cows : milk composition and quality
Vries, Ruben de - \ 2017
University. Promotor(en): Toon van Hooijdonk; K. Holtenius, co-promotor(en): Kasper Hettinga; H.L.M. Lindmark-Månsson. - Wageningen : Wageningen University - ISBN 9789463430463 - 141
dairy cows - dry period - milk composition - milk quality - milk - casein - micelles - melkkoeien - gustperiode - melksamenstelling - melkkwaliteit - melk - caseïne - micellen

A dry period of dairy cows is historically seen as a period during which the cow can restore its body condition and regenerate its mammary epithelium in order to be high yielding in the successive lactation. Recent work has indicated that high yielding cows generally experience a severe negative energy balance in early lactation. Dry period reduction is a strategy to improve the energy balance of dairy cows in early lactation. This thesis aimed at evaluating the influence of dry period length on milk composition and milk quality. Milk composition parameters indicate the processing quality of milk for the dairy plant, and may also reflect the physiological condition and energy status of the cow.

In this work, omission of the dry period was related to a reduced β-casein fraction in early lactation milk. Applying a short (4 weeks) instead of a conventional (8 weeks) dry period resulted in increased plasmin activity in milk, but did not affect the β-casein fraction. Increased plasmin activity in relation to a shortened dry period was particularly found in milk of cows of third or higher parity, that generally had relatively high somatic cell count. At low somatic cell counts, dry period reduction or omission only tended to result in an increased plasmin activity due a higher casein concentration in milk. From increased concentrations of a number of low abundant proteins in colostrum of cows with a short dry period it was hypothesized that a short dry period was related to increased proliferation of mammary epithelial cells during the first days in lactation.

Although the casein composition of milk was related to both plasmin activity in milk and the metabolic status of cows, which are both influenced by dry period length, quantitative differences in casein composition of cows with different dry period length were small. It was concluded that shortening or omitting the dry period of cows with good mammary health obtains milk with a higher protein content with little differences in protein composition.

Probing Nanoscale Coassembly with Dual Mechanochromic Sensors
Cingil, Hande E. ; Boz, Emre B. ; Wang, Junyou ; Cohen Stuart, Martien ; Sprakel, Joris - \ 2016
Advanced Functional Materials 26 (2016)9. - ISSN 1616-301X - p. 1420 - 1427.
complex coacervation - conjugated polymers - micelles - self-assembly

Attractive electrostatic forces between polymers can be exploited to create well-defined and responsive nanoscale structures. In the process of charge-driven coassembly, the polymers involved undergo subtle conformational changes. However, ascertaining these conformational transitions, and relating this to the nanostructures that are formed, has remained elusive to date. Here it is shown how the force-optical response of tailored mechanochromic polymers can be used to detect structural transitions that occur at the nanoscale during assembly. It is shown that at low-charge stoichiometry, electrostatic binding causes individual macromolecules to stretch and stiffen. Remarkably, at stoichiometries close to full charge compensation a gradual transition from single molecular complexes to multimolecular micelles is observed. Moreover, the same macromolecular sensors reveal how the assembly pathways are fully reversible as the binding strength is weakened. These results highlight how mechanochromic polymer sensors can be used to detect the molecular transitions occur during supramolecular structure formation with high precision.

Intracellular & extracellular lipolysis : regulation by the PPAR targets ANGPTL4 & HILPDA
Dijk, Wieneke - \ 2016
University. Promotor(en): Sander Kersten. - Wageningen : Wageningen University - ISBN 9789462579460 - 248
foams - foaming - milk products - processing - aggregates - casein - micelles - physical properties - schuim - schuimen - melkproducten - verwerking - bodemdeeltjes - caseïne - micellen - fysische eigenschappen

The body efficiently stores energy in the form of triglyceride (fat) molecules. However, triglycerides cannot directly enter or exit our cells, but first need to be degraded to so-called fatty acids before moving in or out a cell. This degradation process, called lipolysis, is crucial for human physiology and is tightly regulated to prevent the accumulation of fats either within organs or within the bloodstream - hallmarks of diseases such as obesity and cardiovascular disease.

To allow for uptake by underlying organs, triglycerides in the circulation are efficiently broken down by an enzyme called lipoprotein lipase (LPL) that sits in the bloodstream of multiple organs (extracellular lipolysis). In this thesis, we characterized a protein named angiopoietin-like 4 (ANGPTL4) that potently inhibits LPL and, thereby, inhibits the breakdown of triglycerides in the bloodstream. Our data show that by adjusting the tissue expression levels of ANGPTL4, different organs collaborate to ensure that triglycerides are distributed to organs in need of energy. Moreover, we uncovered that, in the fat tissue, ANGPTL4 starts to inhibit LPL before LPL arrives in the bloodstream. By preventing the arrival of LPL in the bloodstream, ANGPTL4 is capable of rapidly adjusting the rates of triglyceride degradation and the concomitant uptake of fatty acids from the circulation to the energy requirements of the underlying organ.

To exit our cells, stored triglycerides, such as present in our fat tissue, need to be broken down to fatty acids. Subsequently, the released fatty acids can fuel other organs in need of energy. To further clarify the mechanisms underlying this process of intracellular lipolysis, we investigated the role of a promising new protein called HILPDA. Our data show, however, that loss of HILPDA did not impact the release of fatty acids from the fat tissue, while a high abundance of HILPDA only had a mild attenuating effect on the release of fatty acids. This suggests that HILPDA is not a major physiological regulator of intracellular lipolysis in fat cells.

In conclusion, in this thesis, we have clarified the regulation of intracellular and extracellular lipolysis by studying the respective roles of the proteins ANGPTL4 and HILPDA. Such efforts are clinically relevant, as regulators of lipolysis are potential therapeutic targets to lower cardiovascular disease risk.

The role of casein micelles and their aggregates in foam stabilization
Chen, Min - \ 2016
University. Promotor(en): Erik van der Linden; Toon van Hooijdonk, co-promotor(en): Marcel Meinders; Guido Sala. - Wageningen : Wageningen University - ISBN 9789462579842 - 124
foams - foaming - milk - casein - micelles - physical properties - stabilization - schuim - schuimen - melk - caseïne - micellen - fysische eigenschappen - stabilisatie

Many foam products derived from milk or specific dairy ingredients suffer from drainage, coalescence and/or disproportionation. Previous studies indicated that foam properties of milk are strongly influenced by the composition of the milk as well as by the processing conditions during foam production. The aim of this research was to get a better understanding of these two factors. Interestingly, the presence of aggregates of casein micelles was found to result in very stable foams. The interfacial properties (adsorption speed, adsorption energy, dynamical interfacial tension, interfacial dilatational moduli), thin film stability (rupture time) and foam properties (foamability, drainage, coalescence) of casein micelle dispersions were determined. Based on these data, the very stable foams were concluded to result from properties of the thin films in the foam, which were affected drastically by the presence of the large aggregates of casein micelles.

Self-assembled structures of PMAA-PMMA block copolymers: Synthesis, characterization, and self-consistent field computations
Li, F. ; Schellekens, J. ; Bont, J.A.M. de; Peters, R. ; Overbeek, A. ; Leermakers, F.A.M. ; Tuinier, R. - \ 2015
Macromolecules 48 (2015)4. - ISSN 0024-9297 - p. 1194 - 1203.
controlled radical polymerization - laser-light scattering - emulsion polymerization - association behavior - aqueous-medium - micelles - surfactants - vesicles - thermodynamics - morphologies
Block copolymers composed of methacrylic acid (MAA) and methyl methacrylate (MMA) blocks are interesting candidates for replacing surfactants in emulsion polymerization methods. Here the synthesis and experimental characterization of well-defined PMAA–PMMA block copolymers made via RAFT polymerization are reported. It is shown that these block copolymers self-organize in water into micellar spherical or cylindrical structures or into highly size disperse structures (probably vesicles) in aqueous salt solutions upon increasing the pH. The physical properties of the polymer dispersions depend on the self-organization morphology which is determined by the diblock copolymer PMAA and PMMA block lengths. The relation between diblock copolymer block lengths and the self-organized structures is rationalized using self-consistent field theory (SCFT). Theoretically predicted self-assembled structures of MAAx–MMAy block copolymers are compared with the results obtained from experiments. Size and morphology of the self-assembled structures are in good agreement with SCFT.
Interactions between nodes in a physical gel network of telechelic polymers; self-consistent field calculations beyond the cell model
Bergsma, J.P. ; Leermakers, F.A.M. ; Gucht, J. van der - \ 2015
Physical Chemistry Chemical Physics 17 (2015)14. - ISSN 1463-9076 - p. 9001 - 9014.
aqueous-solutions - statistical thermodynamics - chain molecules - adsorption - micelles - formulation - copolymers - scattering - neutron - layer
Triblock copolymers, with associative end-groups and a soluble middle block, form flower-like micelles in dilute solutions and a physical gel at higher concentrations. In a gel the middle blocks form bridges between domains/nodes that contain the ends. We combine the self-consistent field theory with a simple molecular model to evaluate the pair potential between the nodes. In this model the end-groups are forced to remain in nodes and the soluble middle blocks are in solution. When the distance between the centres of the nodes is approximately the corona diameter, loops can transform into bridges, and the pair potential is attractive. Due to steric hindrance, the interaction is repulsive at smaller distances. Till now a cell-model has been used wherein a central node interacts through reflecting boundary conditions with its images in a spherical geometry. This artificial approach to estimate pair potentials is here complemented by more realistic three-gradient SCF models. We consider the pair interactions for (i) two isolated nodes, (ii) nodes positioned on a line (iii) a central node surrounded by its neighbours in simple cubic ordering, and (iv) a central node in a face centred cubic configuration of its neighbours. Qualitatively, the cell model is in line with the more refined models, but quantitative differences are significant. We also notice qualitative differences for the pair potentials in the specified geometries, which we interpret as a breakdown of the pairwise additivity of the pair potential. This implies that for course grained Monte Carlo or molecular dynamics simulations the best choice for the pair potentials depends on the expected node density.
Organogel formation via supramolecular assembly of oleic acid and sodium oleate
Nikiforidis, C.V. ; Gilbert, E.P. ; Scholten, E. - \ 2015
RSC Advances : An international journal to further the chemical sciences 5 (2015)59. - ISSN 2046-2069 - p. 47466 - 47475.
system - solvent - liquid - amphiphiles - particles - micelles - lecithin - bilayers - laurate - water
To create materials with novel functionalities, the formation of gels within hydrophobic media has become popular. This is often accomplished through the assembly of low molecular weight organogelators into a variety of complex phases through intermolecular interactions. In the case of edible materials, the assembly of saturated fatty acids to form fat crystal networks is often used for structuring. Here, the first example of structuring with unsaturated fatty acids is reported, namely mixtures of oleic acid and sodium oleate, to structure edible lipid phases. Small-angle scattering demonstrates that the resultant structures, which vary with oleic acid and sodium oleate molar ratio, comprise either inverse micellar or lamellar phases, combined with the formation of crystalline space-filling networks. Network formation was found for filler concentrations above 10 wt%. Rheological measurements show that gel strength depends on the ratio of oleic acid to sodium oleate, and is greater when only oleic acid is used. The addition of up to 1.5 wt% of water enhanced the strength of the organogels, probably through supplementary hydrogen bonding but, for concentrations greater than 2.0 wt%, the assembly was inhibited leading to collapse of the gel.
Towards colloidal size control by precipitation
Lebouille, J.G.J.L. - \ 2014
University. Promotor(en): Martien Cohen Stuart; Frans Leermakers; R. Tuinier. - Wageningen : Wageningen University - ISBN 9789461738677 - 151
micellen - colloïden - nanotechnologie - deeltjesgrootte - deeltjesgrootteverdeling - micelles - colloids - nanotechnology - particle size - particle size distribution

Many active ingredients like drugs, preservatives and vitamins are hydrophobic. In most applications for food and pharma, however, they need to be functional in aqueous environments. In order to facilitate their usage in aqueous environments one needs a way to enable the dispersion of hydrophobic compounds into submicron particles in water in a controlled manner. We investigated the stabilization by surfactants and encapsulation into micelles of hydrophobic compounds using the nanoprecipitation method. The research described in this thesis is about building more understanding of the nanoprecipitation method in relation to the relevant physical chemical parameters. The theoretical results led to predictions that were compared to experimental data. For water-soluble surfactants as stabilizers in the nanoprecipitation process a new theory was developed to relate the process parameters to the final particle size. For non-water-soluble surfactants self-consistent field theory was used in order to unravel the structure-function relationship between used copolymer chemistry and the form and morphology of the obtained particles, spherical micelles and their size.

We analyzed new and existing experiments on the nanoprecipitation method using water-soluble surfactants as stabilizers in a systematic manner. These were interpreted in terms of a new theory that links the process and material properties to the final particle size. The nanoprecipitation procedure consists of quenching a polymer solution from a good to a poor solvent containing surfactant solution. Three characteristic time scales can be identified which affect the final particle size. First, the mixing time (τmix) was identified; the time needed to mix the polymer solution (polymer in good solvent) into the surfactant solution (poor solvent). Second, the coalescence time (τcls) was identified; the time needed for the collapsed polymer chains to coalesce into bigger droplets and subsequently to harden out into particles with long term storage stability. Last, the protection time (τpro) was identified; the time that the surfactant molecules need to completely cover the coalescing droplets and by this stop the coalescence of the collapsed polymer chains/droplets. The two latter characteristic times are intrinsic properties of the used solvents, surfactants and polymers and cannot be changed without addition of extra/new molecules. However, the mixing time is the only parameter which can be changed without modifying the material properties of the system. The mixing time can be easily varied by the method of mixing the good and the poor solvent. Using a pipette to mix the two solutions will result in a 'slow' mixing time regime and utilizing for instance an impingent jet mixer can result in a 'fast' mixing regime. For both mixing regimes a clear analytical expression could be derived enabling more efficient experimentation in order to obtain a specific final particle size. For the 'slow' mixing regime the relation between final particle size ()was found only to be dependent of the used polymer concentration (cmp) as ~cmpThe practical interpretation of this analytical expression is rather simple; an eight times higher polymer concentration will result in a two times bigger final particle size. For the 'fast' mixing regime the analytical expression can be interpreted also in an easy way; the faster the mixing the smaller the final particle size. Below a certain value for the mixing time the final particle size attains a plateau value; even faster mixing will not further decrease the final particle size. When using water-soluble surfactants the release of the cargo, which in practice often takes place after significant dilution, is expected to be fast. In order to increase the release of the encapsulated compound(s) in time we incorporated the surfactant functionality into a non-water soluble triblock copolymer. This results, even upon huge dilution, in an extended release profile in time.

We employed self-consistent field theory for non-water-soluble surfactants in order to relate the (block copolymer) surfactant chemistry to the size and composition of the resulting spherical equilibrium micelles. The surfactants, triblock copolymers synthesized via ring-opening polymerization, were employed in the nanoprecipitation process in order to make spherical micelles. The theoretical predictions were compared to the experimental results and it was concluded that self-consistent field theory is an accurate theoretical tool to predict the size of spherical micelles given a certain chemistry and composition of the copolymers and the conditions required to form these micelles.

We experimentally studied whether hydrophobic compounds (polymers, different active ingredients or a mixture of the two) were added in order to verify whether these spherical micelles could be loaded by these compounds. We investigated the encapsulation behavior of these micelles for hydrophobic compounds both theoretically and experimentally and considered the influence of the size for the micelles. From both the theoretical predictions and the experimentally obtained data it followed that these micelles can be used for encapsulation of hydrophobic compounds. Moreover, the theoretical predictions matched with the experimentally obtained data. It was concluded that self-consistent field predictions can be used to predict the size and stability of spherical micelles with encapsulated hydrophobic compounds.

Tuning size and loading is mandatory for passive targeting applications because the particle size mainly determines the biologic faith. In order to enable active targeting, utilizing a targeting moiety and (specific) receptor interaction is needed while maintaining the stealthy nature of the spherical particles. We performed a theoretical self-consistent field study on spherical block copolymer micelles to investigate whether it is feasible to hide the targeting moiety within the micellar corona while maintaining receptor interaction. We determined the maximum interaction distance wherefrom targeting moiety receptor connection can be established and the required energy barrier at different distances. The outcome of these calculations was used to design a (theoretical) optimized system for active targeting.

We used self-consistent field theory to calculate the size, loading and targeting capability of triblock copolymer based micelles enabling both passive and active targeting and verified our calculation results experimentally. Although the active targeting predictions were not verified experimentally we established a design for passive and active targeting micellar applications for, for instance, drug delivery applications while maintaining the stealthy nature of these micelles.

Structure and dynamics of polyelectrolyte complex coacervates studied by scattering of neutrons, X-rays, and light
Spruijt, E. ; Leermakers, F.A.M. ; Fokkink, R.G. ; Schweins, R. ; Well, A.A. van; Cohen Stuart, M.A. ; Gucht, J. van der - \ 2013
Macromolecules 46 (2013)11. - ISSN 0024-9297 - p. 4596 - 4605.
gelatin/polyelectrolyte complexes - angle scattering - reversible gels - micelles - polymer - protein - macromolecules - chloride) - interface - hydrogels
We investigate the microscopic structure and density fluctuations of complex coacervates of flexible polyelectrolytes using scattering of neutrons, X-rays, and light. Poly(acrylic acid) and poly(N,N-dimethylaminoethyl methacrylate) offer a well-defined model system that allows for selective labeling and systematic variation of the strength of the attractive electrostatic interactions. Two neutron scattering experiments have been carried out: (i) we use deuterated polymeric tracers in a complex coacervate with an overall neutron scattering length density that is matched to that of the solvent, to probe the conformation of single polymer chains in the complex coacervates, and (ii) we measure complex coacervates in which all polymer chains of one type are deuterated, to probe their overall structure. The single chain static structure factors reveal that both polycations and polyanions have an ideal Gaussian chain conformation in the complex coacervates. At the same time, the overall structure is similar to that of a semidilute polymer solution, with polycations and polyanions strongly overlapping to form a network with a mesh size that is much smaller than the radius of gyration of the polymers. The mesh size decreases with decreasing salt concentration, following a scaling that is in good agreement with predictions from the corresponding salt–polymer phase diagram. These findings are confirmed by complementary X-ray scattering experiments. Finally, in all scattering experiments with light, X-rays, and neutrons, and for all polymer chain lengths and salt concentrations, we find a remarkable low-q excess scattering, following a power law with a slope close to -2. This points to the presence of equilibrium, large-scale density fluctuations in the complex coacervates. Dynamic light scattering experiments reveal two complementary diffusive modes in the complex coacervates, corresponding to fluctuations of the polymer mesh and diffusion of domains of varying density, respectively
PFG-NMR self-diffusion in casein dispersions: effect of probe size and protein aggregate size
Salami, S. ; Rondeau, C. ; Duynhoven, J.P.M. van; Mariette, F. - \ 2013
Food Hydrocolloids 31 (2013)2. - ISSN 0268-005X - p. 248 - 255.
dynamic light-scattering - sodium caseinate - mechanical-properties - electron-microscopy - gel microstructure - wave spectroscopy - micelles - suspensions - coagulation - milk
The self-diffusion coefficients of different molecular weight PEGs (Polyethylene glycol) and casein particles were measured, using a pulsed-gradient nuclear magnetic resonance technique (PFG-NMR), in native phosphocaseinate (NPC) and sodium caseinate (SC) dispersions where caseins are not structured into micelles. The dependence of the PEG self-diffusion coefficient on the PEG size, casein concentration, the size and the mobility of casein obstacle particles are reported. Wide differences in the PEG diffusion coefficients were found according to the casein particle structure. The greatest reduction in diffusion coefficients was found in sodium caseinate suspensions. Moreover, sodium caseinate aggregates were found to diffuse more slowly than casein micelles for casein concentrations >9 g/100 g H2O. Experimental PEG and casein diffusion findings were analyzed using two appropriate diffusion models: the Rouse model and the Speedy model, respectively. According to the Speedy model, caseins behave as hard spheres below the close packing limit (10 g/100 g H2O for SC (Farrer & Lips, 1999) and 15 g/100 g H2O for NPC (Bouchoux et al., 2009)) and as soft particles above this limit. Our results provided a consistent picture of the effects of diffusant mass, the dynamics of the host material and of the importance of the casein structure in determining the diffusion behavior of probes in these systems.
Physical gels based on charge-driven bridging of nanoparticles by triblock copolymers
Lemmers, M. ; Spruijt, E. ; Akerboom, S. ; Voets, I.K. ; Aelst, A.C. van; Cohen Stuart, M.A. ; Gucht, J. van der - \ 2012
Langmuir 28 (2012)33. - ISSN 0743-7463 - p. 12311 - 12318.
dynamic light-scattering - shear-induced gelation - nanocomposite hydrogels - formulation process - colloidal silica - aqueous-solution - reversible gels - micelles - macromolecules - adsorption
We have prepared an aqueous physical gel consisting of negatively charged silica nanoparticles bridged by ABA triblock copolymers, in which the A blocks are positively charged and the B block is neutral and water-soluble. Irreversible aggregation of the silica nanoparticles was prevented by precoating them with a neutral hydrophilic polymer. Both the elastic plateau modulus and the relaxation time increase slowly as the gel ages, indicating an increase both in the number of active bridges and in the strength with which the end blocks are adsorbed. The rate of this aging process can be increased significantly by applying a small shear stress to the sample. Our results indicate that charge-driven bridging of nanoparticles by triblock copolymers is a promising strategy for thickening of aqueous particle containing materials, such as water-based coatings.
Salt-modulated structure formation in a dense calcium caseinate system
Grabowska, K.J. ; Goot, A.J. van der; Boom, R.M. - \ 2012
Food Hydrocolloids 29 (2012)1. - ISSN 0268-005X - p. 42 - 47.
shear-flow - microbial transglutaminase - rheological behavior - micelles - temperature - dispersions - scattering
A 30 wt% calcium caseinate dispersion can be transformed in an anisotropic and fibrous structure by applying well-defined flow and enzymatic gelation. The formation of an anisotropic structure is thought to be due to the micellar structure of the caseinate and the mild adhesion between the micelles caused by the divalent calcium ions. Both micellar structure and interaction can be influenced by the presence of salt in the solution. This paper therefore describes the effect of salt addition on the structure formation. It turned out that the presence of sodium chloride (NaCl) facilitated the structure formation and led to clear development of fibres. Addition of a low concentration of the sequestrant sodium triphosphate (pentabasic; STP) had a similar effect on fibrousness, but reduced the fibre strength. A higher concentration of STP led to homogeneous gel formation and inhibited the formation of a fibrous structure. Rheological measurements were used to explain the results. Dispersions containing NaCl and low concentrations of STP showed non-linear behaviour just as the dispersion to which no salt was added. This rheological behaviour suggested a rearrangement of the internal structure in the protein mixture. The higher STP concentrations resulted in a slightly shear-thinning behaviour of the material, suggesting that the material became less susceptible to structure changes due to shear flow.
On the stability and imaging applications of metal-containing coacervate micelles
Wang Junyou, Junyou - \ 2012
University. Promotor(en): Martien Cohen Stuart, co-promotor(en): Jasper van der Gucht; Henk van As. - S.l. : s.n. - ISBN 9789461733993 - 113
micellen - elektrolyten - stabiliteit - micelles - electrolytes - stability
Influence of calcium chelators on concentrated micellar casein solutions : from micellar structure to viscosity and heat stability
Kort, E.J.P. de - \ 2012
University. Promotor(en): Toon van Hooijdonk; Erik van der Linden, co-promotor(en): M. Minor. - S.l. : s.n. - ISBN 9789461732378 - 152
melkproducten - calcium - chelaatvormers - caseïne - micellen - viscositeit - hittebestendigheid - milk products - chelating agents - casein - micelles - viscosity - heat stability

In practice it is challenging to prepare a concentrated medical product with high heat stability
and low viscosity. Calcium chelators are often added to dairy products to improve heat stability,
but this may increase viscosity through interactions with the casein proteins. The aim of this
thesis was to obtain a better understanding of the influence of different calcium chelators on the
physico-chemical properties of casein micelles and the resulting effect on viscosity and heat
stability of concentrated micellar casein isolate (MCI) solutions. The calcium chelators disodium
uridine monophosphate (Na2UMP), disodium hydrogen phosphate (Na2HPO4), trisodium citrate
(TSC), sodium phytate (SP), and sodium hexametaphosphate (SHMP) were studied.
Initially, the calcium-binding capacity of the phosphates was investigated and found to be
directly related to the amount of charges. The resulting effects on physical changes of casein
micelles were subsequently explored before and during heating. The viscosity of the MCI
solutions increased upon addition of the calcium chelators, which was attributed to swelling of
the caseins at decreasing calcium-ion activity. The calcium chelators induced different changes
in turbidity of the MCI solutions, which could be related to the degree of dissociation of the
casein micelles. Simulations of the ion equilibria indicated that the extent of casein micelle
dissociation followed the calcium-binding capacity of the calcium chelators. Micelle
dissociation occurred in the order of SHMP > SP > TSC > Na2HPO4 > Na2UMP. The results on
heat stability indicated that the calcium-ion activity and state of the micellar structure before and
during heating determined the heat stability of the MCI solutions. Na2UMP was the most
effective heat stabilizer, as it bound sufficient free calcium ions to reduce protein aggregation
without affecting the micellar structure. SHMP was the least effective heat stabilizer because of
heat-induced changes occurring during heating. For polyphosphates, SHMP and SP, it was
found that they decreased the isoint of casein by forming direct bindings with the caseins, for
which calcium ions were not required.
In conclusion, this thesis has provided new insights in the relationships between calcium
chelators and their influence on the casein micelle structure and on the physico-chemical
properties of concentrated MCI solutions. Also, the practical relevance for the dairy industry
was described, demonstrating how different calcium chelators can manipulate the viscosity and
heat stability of dairy products.

Fluorescence enhancement by microphase separation-induced chain extension of Eu3+ coordination polymers: phenomenon and analysis
Yang, L. ; Ding, Y. ; Yang, Y. ; Yan, Y. ; Huang, J. ; Keizer, A. de; Cohen Stuart, M.A. - \ 2011
Soft Matter 7 (2011)6. - ISSN 1744-683X - p. 2720 - 2724.
complexes - ions - naphthoate - copolymer - micelles - eu(iii) - ligand - core
In this paper, we report on the fluorescence enhancement of Eu coordination complexes in dilute solutions through electrostatic complex micelle formation with an oppositely charged block polyelectrolyte. The coordination complexes alone are oligomeric structures which have many ends where partially coordinated europium is exposed to water. In the presence of oppositely charged polyelectrolytes, the local concentration of the coordination complexes is greatly enhanced, so that they transform into polymeric structures and form electrostatically induced micelles with the block polyelectrolytes. This effectively decreases the number of europium–water coordination bonds, which leads to the enhancement of fluorescence emission. This is the first report that utilizes the concentration responsiveness of the smart coordination polymers to promote the function of the colloids made from them
Reduction of protein adsorption on surfaces coated with Complex Coacercate Core Micelles
Brzozowska, A.M. - \ 2010
University. Promotor(en): Martien Cohen Stuart; Willem Norde, co-promotor(en): Arie de Keizer. - [S.l. : S.n. - ISBN 9789085856832 - 246
micellen - afdeklagen - eiwitten - adsorptie - oppervlaktechemie - micelles - coatings - proteins - adsorption - surface chemistry
The structure and formation of Ionomer Complexes (ICs) consisting of linear polyelectrolytes
(C3Ms) has been extensively studied in the past years. Recently, these structures were also
considered for several applications. This thesis deals with the possible application of ICs as a
surface coating suppressing protein adsorption independent of the properties of the native
surface. To reach this goal it was crucial to understand the principles governing the adsorption
and the stability of the IC layers on solid surfaces, as well as their interactions with proteins.
Therefore, this research was limited to well defined model substrates: silica (model hydrophilic
surface), polystyrene (model hydrophobic surface), and polysulfone (a surface mimicking
polymeric membrane material), and model proteins: β-lactoglobulin, bovine serum albumin,
fibrinogen, and lysozyme. The ultimate goal, however, was to apply the coating on surfaces of
membranes used in water purification to suppress biofilm growth. We have observed that
reduction of protein adsorption by coating formed by regular C3Ms is not satisfactory due to
relatively low density of the polymer brushes formed on the coated surface. We increased the
grafting density, and hence significantly improved the reduction of protein adsorption, by
introducing grafted block and grafted copolymers into the micelles. In our work we discuss an
influence of various factors, i.e. physical-chemical properties of the native surfaces, lengths of the
charged blocks, distribution of the grafts along the backbone of the copolymer, salt concentration
etc., on the performance of the formed coatings. In the final part we focus on the mechanical
stability of the coatings formed with ICs, and discuss their applicability as a membrane surface
coating.
Multi-responsive reversible gels based on charge-driven assembly
Lemmers, M. ; Sprakel, J.H.B. ; Voets, I.K. ; Gucht, J. van der; Cohen Stuart, M.A. - \ 2010
Angewandte Chemie-International Edition 49 (2010)4. - ISSN 1433-7851 - p. 708 - 711.
transfer radical polymerization - indirect fourier transformation - small-angle scattering - rheological properties - block-copolymers - methyl-methacrylate - chain-length - polyelectrolyte - micelles - polymers
Linked in? Coassembly of an ABA triblock copolymer with charged end blocks and an oppositely charged polyelectrolyte yields gels that respond to changes in concentration, temperature, ionic strength, pH value, and charge composition. Above the critical gel concentration, the triblock copolymers bridge micelles, forming a sample-spanning transient network of interconnected micelles
Interfacial tension between a complex coacervate phase and its coexisting aqueous phase
Spruijt, E. ; Sprakel, J.H.B. ; Cohen Stuart, M.A. ; Gucht, J. van der - \ 2010
Soft Matter 6 (2010). - ISSN 1744-683X - p. 172 - 178.
atomic-force microscope - microencapsulation - thermodynamics - micelles - polymer - system
Complex coacervation is the associative phase separation in a solution of positively and negatively charged macroions. Despite the widespread use of coacervation in e.g. micellar assemblies (complex coacervate core micelles), drug carriers and thin films, there is virtually no experimental data on the interfacial tension between such coacervate phases (polyelectrolyte complexes) and their coexisting aqueous phases or on the influence of salt thereon. In this paper we use colloidal probe AFM measurements of capillary adhesion forces to obtain the interfacial tension between a complex coacervate phase of two polyelectrolytes with high charge density and its coexisting aqueous phase. We find that the interfacial tension is of order 100 µN/m, decreases with increasing salt concentration and vanishes at the critical point. Interestingly, we find that the critical scaling exponent for the interfacial tension found in segregative demixing also applies here
Hierarchical Adsorption of Network-Forming Associative Polymers
Sprakel, J.H.B. - \ 2009
Langmuir 25 (2009)12. - ISSN 0743-7463 - p. 6923 - 6928.
poly(ethylene oxide) - micelles - behavior - kinetics
In this paper, we discuss the hierarchical adsorption of micelles formed from network-forming, telechelic, associative polymers at an air-water interface. We propose an interfacial mechanism that involves three distinct steps: (i) adsorption of the micellar coronas at the interface, (ii) unfolding of the micelles to anchor the hydrophobic tails at the interface, and (iii) formation of a secondary adsorption layer by bridging between the primary layer and micelles in the bulk. While the first, transport-limited process is relatively fast, the latter processes are surprisingly slow; it may take up to 10(6) s for the adsorption to complete.
Block copolymer micellisation in a common solvent modeled by self-consistent field calculations
Leermakers, F.A.M. - \ 2009
Macromolecular Symposia 278 (2009)1. - ISSN 1022-1360 - p. 57 - 66.
statistical thermodynamics - bilayer-membranes - micelles - adsorption - stability - molecules
Recently it was shown that it is possible that block copolymers form micellar solutions in non-selective solvents. Such micellisation is the result of a pure form of self-assembly. A molecular realisation is given by asymmetric Poly-(methacrylic acid)-block-Poly(ethylene oxide) copolymers (PMAA-b-PEO) in water at a pH <5. As both the (short) methacrylic acid block and the (long) ethylene oxide are water soluble in the conditions used, it was concluded that the driving force is interchain hydrogen bonding between the PMAA and the PEO units. The mismatch in length of the blocks forces one block to accumulate at the micellar periphery and this eventually stops the phase separation process. We have performed self-consistent field calculations to examine this scenario. With very reasonable parameters we are able to mimic the properties of these micelles, elaborate the pH dependence and confirm the trend found for the electrophoretic mobility. A nontrivial result of the calculations is that the ratio EO/MAA in the core is close to two
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