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.

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    Liquid crystals of self-assembled DNA bottlebrushes
    Storm, I.M. ; Kornreich, M. ; Hernandez-Garcia, A. ; Voets, I.K. ; Beck, R. ; Cohen Stuart, M.A. ; Leermakers, F.A.M. ; Vries, R.J. de - \ 2015
    The Journal of Physical Chemistry Part B: Condensed Matter, Materials, Surfaces, Interfaces & Biophysical 119 (2015). - ISSN 1520-6106 - p. 4084 - 4092.
    hyaluronan-aggrecan complexes - molecular bottle-brushes - neurofilament networks - boundary lubricants - articular-cartilage - lyotropic behavior - diblock copolymers - persistence length - mesomorphic state - click chemistry
    Early theories for bottlebrush polymers have suggested that the so-called main-chain stiffening effect caused by the presence of a dense corona of side chains along a central main chain should lead to an increased ratio of effective persistence length (lp,eff) over the effective thickness (Deff) and, hence, ultimately to lyotropic liquid crystalline behavior. More recent theories and simulations suggest that lp,eff ~ Deff, such that no liquid crystalline behavior is induced by bottlebrushes. In this paper we investigate experimentally how lyotropic liquid crystalline behavior of a semiflexible polymer is affected by a dense coating of side chains. We use semiflexible DNA as the main chain. A genetically engineered diblock protein polymer C4K12 is used to physically adsorb long side chains on the DNA. The C4K12 protein polymer consists of a positively charged binding block (12 lysines, K12) and a hydrophilic random coil block of 400 amino acids (C4). From light scattering we find that, at low ionic strength (10 mM Tris-HCl), the thickness of the self-assembled DNA bottlebrushes is on the order of 30 nm and the effective grafting density is 1 side chain per 2.7 nm of DNA main chain. We find these self-assembled DNA bottlebrushes form birefringent lyotropic liquid crystalline phases at DNA concentrations as low as 8 mg/mL, roughly 1 order of magnitude lower than for bare DNA. Using small-angle X-ray scattering (SAXS) we show that, at DNA concentrations of 12 mg/mL, there is a transition to a hexagonal phase. We also show that, while the effective persistence length increases due to the bottlebrush coating, the effective thickness of the bottlebrush increases even more, such that in our case the bottlebrush coating reduces the effective aspect ratio of the DNA. This is in agreement with theoretical estimates that show that, in most cases of practical interest, a bottlebrush coating will lead to a decrease of the effective aspect ratio, whereas, only for bottlebrushes with extremely long side chains at very high grafting densities, a bottlebrush coating may be expected to lead to an increase of the effective aspect ratio.
    The influence of charge ratio on transient networks of polyelectrolyte complex micelles
    Lemmers, M. ; Spruijt, E. ; Beun, L.H. ; Fokkink, R.G. ; Leermakers, F.A.M. ; Portale, G. ; Cohen Stuart, M.A. ; Gucht, J. van der - \ 2012
    Soft Matter 8 (2012)1. - ISSN 1744-683X - p. 104 - 117.
    coacervate core micelles - transfer radical polymerization - associative polymers - diblock copolymers - block-copolymers - rheological properties - methyl-methacrylate - aqueous-solutions - phase-behavior - water
    We study the influence of charge ratio on the transient network formation of bridged polyelectrolyte complex micelles. The polyelectrolyte complex micelles are based on mixing an ABA triblock copolymer in which the A-blocks are positively charged and the B-block is neutral and hydrophilic, and a negatively charged homopolymer. We investigate the microstructure of our samples with (dynamic) light scattering and small-angle X-ray scattering, and the mechanical properties by rheometry. At charge stoichiometric conditions, we obtain flowerlike polyelectrolyte complex micelles. These micelles become interconnected at high concentrations, leading to a sample-spanning transient network. For excess negative charge conditions, we obtain so-called ‘soluble complexes’ which are small aggregates carrying the excess negative charge on the polyelectrolyte complex parts. For excess positive charge conditions, micelles stay intact, because the triblock copolymers can localize the excess positive charge at the periphery of the micellar corona. This structural asymmetry is not reflected in the mechanical properties, which show a strong decrease in viscosity on either side of the charge stoichiometric point.
    Nanomanufacturing of continuous composite nanofibers with confiment-induced morphologies
    Kamperman, M.M.G. ; Korley, L.T.J. ; Yau, B. ; Johansen, K.M. ; Joo, Y.L. ; Wiesner, U. - \ 2010
    Polymer Chemistry 1 (2010)7. - ISSN 1759-9954 - p. 1001 - 1004.
    block-copolymer nanofibers - styrene triblock copolymer - high-temperature ceramics - lamellar morphology - electrospun fibers - diblock copolymers - diameter fibers - nanocomposites - mesostructures - microphase
    Continuous core-shell nanofibers with poly(isoprene-block-dimethylaminoethyl methacrylate) (PI-b-PDMAEMA) block copolymer/polymer derived ceramic (PDC) precursor nanocomposites as cores enveloped in rigid polyacrylonitrile (PAN) shells were nanomanufactured using coaxial electrospinning. The cylindrical confinement imposed by the rigid shell led to ordered morphologies in the core not observed in bulk block copolymer nanocomposites.
    Multicompartment Nanoparticles Formed by a Heparin-Mimicking Block Terpolymer in Aqueous Solutions
    Uchman, M. ; Stepanek, M. ; Prochazka, K. ; Mountrichas, G. ; Pispas, S. ; Voets, I.K. ; Walther, A. - \ 2009
    Macromolecules 42 (2009)15. - ISSN 0024-9297 - p. 5605 - 5613.
    atomic-force microscopy - abc triblock copolymer - onion-type micelles - fluorescence correlation spectroscopy - diblock copolymers - selective solvents - light-scattering - poly(2-vinylpyridine)-block-poly(ethylene oxide) - wormlike micelles - star terpolymers
    A new amphiphilic block. terpolymer poly((sulfamate-carboxylate)isoprene)-block-polystyrene-block-poly(ethyl ene oxide), PISC230-PS52-PEO151, with a narrow molecular weight distribution (PDI = 1.05), was synthesized via the post. polymerization reaction of the anionically prepared precursor block terpolymer polyisoprene-block-polystyrene-block--poly(ethylene oxide) with chlorosulfonyl isocyanate. The formation and Structure of self-assemblies of the polyelectrolyte block terpolymer in dilute aqueous Solutions were studied by static and dynamic light scattering, atomic force and cryogenic transmission electron microscopy, fluorometry, and H-1 NMR spectroscopy. In acidic solutions, the terpolymers self-assemble into kinetically trapped multicompartment micelles, with the core consisting of discrete PS and PISC domains and PEO in the shell. If the solution pH is adjusted to the alkaline region, the multicompartment micelles undergo an irreversible transition to regular micelles, with a PS core and a mixed shell formed by PEO and PISC blocks.
    Self-consistent-field calculations of proteinlike incorporations in polyelectrolyte complex micelles
    Lindhoud, S. ; Cohen Stuart, M.A. ; Norde, W. ; Leermakers, F.A.M. - \ 2009
    Physical Review. E, Statistical nonlinear, and soft matter physics 80 (2009)5. - ISSN 1539-3755 - 15 p.
    interacting chain molecules - entrapping enzyme molecules - coacervate core micelles - neurofilament brush - diblock copolymers - polymeric micelles - statistical-theory - block-copolymer - lysozyme - adsorption
    Self-consistent field theory is applied to model the structure and stability of polyelectrolyte complex micelles with incorporated protein (molten globule) molecules in the core. The electrostatic interactions that drive the micelle formation are mimicked by nearest-neighbor interactions using Flory-Huggins X parameters. The strong qualitative comparison with experimental data proves that the Flory-Huggins approach is reasonable. The free energy of insertion of a proteinlike molecule into the micelle is nonmonotonic: there is (i) a small repulsion when the protein is inside the corona; the height of the insertion barrier is determined by the local osmotic pressure and the elastic deformation of the core, (ii) a local minimum occurs when the protein molecule is at the core-corona interface; the depth (a few kBT's) is related to the interfacial tension at the core-corona interface and (iii) a steep repulsion (several kBT) when part of the protein molecule is dragged into the core. Hence, the protein molecules reside preferentially at the core-corona interface and the absorption as well as the release of the protein molecules has annealed rather than quenched characteristics. Upon an increase of the ionic strength it is possible to reach a critical micellization ionic (CMI) strength. With increasing ionic strength the aggregation numbers decrease strongly and only few proteins remain associated with the micelles near the CMI
    pH and ionic strength responsive polyelectrolyte block copolymer micelles prepared by ring opening metathesis polymerization
    Stubenrauch, K. ; Voets, I.K. ; Popovski, G.F. ; Trimmel, G. - \ 2009
    Journal of Polymer Science. Part A, Polymer Chemistry 47 (2009)4. - ISSN 0887-624X - p. 1178 - 1191.
    angle scattering data - radical polymerization - functionalized norbornenes - cofe2o4 nanoparticles - diblock copolymers - nanoreactor route - aqueous-solution - acid) micelles - size control - polymers
    Well-defined amphiphilic block copolymers were prepared by ring opening metathesis polymerization and their stimuli responsive behavior of formed micelles in aqueous solution was investigated. The hydrophobic core of the micelles consists of either a poly[5,6-bis(ethoxymethyl)bicyclo[2.2.1]hept-2-ene]-block with a glass transition Tg at room temperature or a poly[endo,exo[2.2.1]bicyclohept-5-ene-2,3-diylbis (phenylmethanone)] with a Tg of 143 °C. For the polyelectrolyte shell, the precursor block poly[endo,exo[2.2.1]bicyclohept-5-ene-2,3-dicarboxyclic tert-butylester] was transformed into the free acidic block by cleavage of the tert-butyl groups using trifluoroacetic acid. Micellar solutions were prepared by dialysis, dissolving the copolymers in dimethyl sulfoxide which was subsequently replaced by water. All polymers form micelles with radii between 10 and 20 nm at a pH-value below 5, where the carboxylic acid groups are in the protonated state. The block copolymer micelles show a strong increase of the hydrodynamic radius with increasing pH-value, due to the repulsion among the formed carboxylate anions resulting in a stretching of the polymer chains. In this state, the micelles exhibit responsive behavior to ionic strength where a contraction of the micelles is observed as the carboxylate charges are balanced by sodium ions, whereas no changes of the hydrodynamic radius on addition of salt are observed at low pH
    Small monodisperse unilamellar vesicles from binary copolymer mixtures
    Li, F. ; Prévost, S. ; Schweins, R. ; Marcelis, A.T.M. ; Leermakers, F.A.M. ; Cohen Stuart, M.A. ; Sudhölter, E.J.R. - \ 2009
    Soft Matter 5 (2009). - ISSN 1744-683X - p. 4169 - 4172.
    diblock copolymers - polymer vesicles - micelles - water - oxide
    Small unilamellar vesicles are formed spontaneously by simple mixing of lamellae-forming diblock copolymer PB10PE10 (PB is a butylene oxide block, and PE an ethylene oxide block) with micelle-forming diblock copolymer PB10PE18. Small angle neutron scattering (SANS) measurements show that the average vesicle radius may be as small as 30 nm with a polydispersity index of 0.15. From the SANS measurements it can also be deduced that the vesicles have a 3.4 nm thick hydrophobic membrane core and a 1.2 nm hydrophilic corona. Furthermore, it is seen that the vesicles coexist with spherical micelles. The influence of the mixing ratio as well as the concentration of the polymeric components is studied. Results of the micelle size, the vesicle size and the shell structure are confirmed by cryo-TEM measurements
    Complex coacervate core micro-emulsions
    Hofs, P.S. ; Keizer, A. de; Burgh, S. van der; Leermakers, F.A.M. ; Cohen Stuart, M.A. ; Millard, P.E. ; Muller, A.H.E. - \ 2008
    Soft Matter 4 (2008)7. - ISSN 1744-683X - p. 1473 - 1482.
    block-copolymer micelles - interacting chain molecules - diblock copolymers - statistical-theory - aqueous-media - polyelectrolyte - kinetics - mechanism - polymerization - solubilization
    Complex coacervate core micelles form in aqueous solutions from poly(acrylic acid)-block-poly(acrylamide) (PAAxPAAmy, x and y denote degree of polymerization) and poly(N,N-dimethyl aminoethyl methacrylate) (PDMAEMA150) around the stoichiometric charge ratio of the two components. The hydrodynamic radius, Rh, can be increased by adding oppositely charged homopolyelectrolytes, PAA140 and PDMAEMA150, at the stoichiometric charge ratio. Mixing the components in NaNO3 gives particles in highly aggregated metastable states, whose Rh remain unchanged (less than 5% deviation) for at least 1 month. The Rh increases more strongly with increasing addition of oppositely charged homopolyelectrolytes than is predicted by a geometrical packing model, which relates surface and volume of the particles. Preparation in a phosphate buffer ¿ known to weaken the electrostatic interactions between PAA and PDMAEMA ¿ yields swollen particles called complex coacervate core micro-emulsions (C3-Es) whose Rh increase is close to that predicted by the model. These are believed to be in the stable state (lowest free energy). A two-regime increase in Rh is observed, which is attributed to a transition from more star-like to crew-cut-like, as shown by self-consistent field calculations. Varying the length of the neutral and polyelectrolyte block in electrophoretic mobility measurements shows that for long neutral blocks (PAA26PAAm405 and PAA39PAAm381) the -potential is nearly zero. For shorter neutral blocks the -potential is around -10 mV. This shows that the C3-Es have excess charge, which can be almost completely screened by long enough neutral blocks.
    Synthesis of novel well-defined poly(vinyl acetate)-b-poly(acrylonitrile) and derivatized water-soluble poly(vinyl alcohol)-b-poly(acrylic acid) block copolymers by cobalt-mediated radical polymerization
    Debuigne, A. ; Warnant, J. ; Jerome, R. ; Voets, I.K. ; Keizer, A. de; Cohen Stuart, M.A. ; Detrembleur, C. - \ 2008
    Macromolecules 41 (2008)7. - ISSN 0024-9297 - p. 2353 - 2360.
    fragmentation chain transfer - organocobalt porphyrin complexes - vinyl-acetate - diblock copolymers - nanostructured carbon - multiple morphologies - degenerative transfer - aqueous-solutions - molecular-weight - transfer agent
    Poly(vinyl acetate)¿Co(acac)2 macroinitiators, prepared by cobalt-mediated radical polymerization of vinyl acetate (VAc), were used to synthesize well-defined poly(vinyl acetate)-b-poly(acrylonitrile) (PVAc-b-PAN) block copolymers. Different solvents and temperatures were tested for the polymerization of the acrylonitrile segment by cobalt-mediated radical polymerization (CMRP), and copolymers with low polydispersity were obtained provided that dimethylformamide was used as solvent at 0 °C. The mechanism of control was assumed to change from a degenerative chain transfer mechanism for the VAc polymerization to a reversible-termination process for the AN polymerization. The hydrolysis of the ester groups of the PVAc block and the nitrile groups of the PAN sequence of the copolymer by potassium hydroxide in an ethanol/water mixture provided the double hydrophilic and pH-responsive poly(vinyl alcohol)-b-poly(acrylic acid) block copolymer. Finally, the pH responsiveness of these copolymers was demonstrated by DLS pH titration with formation of aggregates at pH <3.
    Sweet brushes and dirty proteins
    Bosker, W.T.E. ; Patzsch, K. ; Cohen Stuart, M.A. ; Norde, W. - \ 2007
    Soft Matter 3 (2007)6. - ISSN 1744-683X - p. 754 - 762.
    aqueous polymer systems - serum-albumin - polystyrene surfaces - diblock copolymers - grafting density - modified dextran - adsorption - polysaccharide - temperature - behavior
    We studied the protein repellency of dextran brushes. Dextran was grafted to a polystyrene surface in a broad range of grafting densities using polystyrene - dextran block copolymers and the Langmuir - Blodgett deposition technique. Ellipsometry measurements confirmed a successful transfer of the dextran brush from the air - water interface to the polystyrene surface. Water contact-angle measurements validated the presence of the dextran layer at the surface. At grafting densities <0.20 nm(-2), a heterogeneous dextran coating is detected with tapping mode AFM, consisting of aggregates of polystyrene - dextran and relatively large interstitial areas without dextran chains. This is probably due to surface micellization of the block copolymer in the Langmuir - Blodgett procedure. At grafting densities >= 0.20 nm(-2), a homogeneous dextran brush is observed. Adsorption studies of BSA and trypsin, using optical reflectometry, showed that adsorbed amounts at the heterogeneous coating (<0.20 nm(-2)) is only slightly lower, if at all, than at the bare polystyrene surface. Beyond 0.20 nm(-2), a drastic decrease in adsorbed amount was observed, due to excluded volume interactions between the protein and the homogeneous dextran brush. Almost complete protein repellency could be reached at high grafting densities. Comparison with adsorption studies of PEO brushes indicated that dextran brushes do not outperform PEO brushes in suppressing protein adsorption.
    Complex coacervate core micelles with a lysozyme-modified corona
    Danial, M. ; Klok, H.A. ; Norde, W. ; Cohen Stuart, M.A. - \ 2007
    Langmuir 23 (2007)15. - ISSN 0743-7463 - p. 8003 - 8009.
    block-copolymers - diblock copolymers - ionic-strength - drug-delivery - polyelectrolyte - adsorption - behavior - brushes - cells - ph
    This paper describes the preparation, characterization, and enzymatic activity of complex coacervate core micelles (C3Ms) composed of poly(acrylic acid) (PAA) and poly(N-methyl-2-vinyl pyridinium iodide)-b-poly(ethylene oxide) (PQ2VP-PEO) to which the antibacterial enzyme lysozyme is end-attached. C3Ms were prepared by polyelectrolyte complex formation between PAA and mixtures containing different ratios of aldehyde and hydroxyl end-functionalized PQ2VP-PEO. This resulted in the formation of C3Ms containing 0-40% (w/w) of the aldehyde end-functionalized PQ2VP-PEO block copolymer (PQ2VP-PEO-CHO). Chemical conjugation of lysozyme was achieved via reductive amination of the aldehyde groups, which are exposed at the surface of the C3M, with the amine groups present in the side chains of the lysine residues of the protein. Dynamic and static light scattering indicated that the conjugation of lysozyme to C3Ms prepared using 10 and 20% (w/w) PQ2VP-PEO-CHO resulted in the formation of unimicellar particles. Multimicellar aggregates, in contrast, were obtained when lysozyme was conjugated to C3Ms prepared using 30 or 40% (w/w) PQ2VP-PEO-CHO. The enzymatic activity of the unimicellar lysozyme-C3M conjugates toward the hydrolysis of the bacterial substrate Micrococcus lysodeikticus was comparable to that of free lysozyme. For the multimicellar particles, in contrast, significantly reduced enzymatic rates of hydrolysis, altered circular dichroism, and red-shifted tryptophan fluorescence spectra were measured. These results are attributed to the occlusion of lysozyme in the interior of the multimicellar conjugates.
    Stabilization of Polymersome Vesicles by an Interpenetrating Polymer Network
    Li, F. ; Ketelaar, M.J. ; Marcelis, A.T.M. ; Leermakers, F.A.M. ; Cohen Stuart, M.A. ; Sudhölter, E.J.R. - \ 2007
    Macromolecules 40 (2007)2. - ISSN 0024-9297 - p. 329 - 333.
    dilute aqueous-solution - diblock copolymers - triblock copolymer - block-copolymers - force microscopy - drug-delivery - nile red - micelles - microspheres - membranes
    Vesicles from Pluronic L121 (PEO5-PPO68-PEO5) triblock copolymers were stabilized by an interpenetrating polymer network from pentaerythritol tetraacrylate by UV or thermal initiator induced radical polymerization. Fluorescence labeling, atomic force microscopy, and electron microscopy studies were used to study the morphology of the particles and showed that stable vesicles are formed. The block copolymers are noncovalently trapped in the interpenetrating polyacrylate network. The stabilized vesicles retain their size for more than 1 month at room temperature. Upon cooling, the vesicles reversibly lose block copolymer
    Self-assembly of poly(ferrocenyldimethylsilane-b-methyl methacrylate) block copolymers in a selective solvent
    Korczagin, I. ; Hempenius, M.A. ; Fokkink, R.G. ; Cohen Stuart, M.A. ; Al-Hussein, M. - \ 2006
    Macromolecules 39 (2006)6. - ISSN 0024-9297 - p. 2306 - 2315.
    dynamic light-scattering - to-rod transition - diblock copolymers - thin-films - rotational diffusion - correlation spectroscopy - multiple morphologies - aqueous-solution - dilute-solution - co-polymer
    The self-assembly of poly(ferrocenyldimethylsilane-b-methyl methacrylate) block copolymers, with PFDMS contents of 9-61 wt % (block ratios 1:23-1:1.5), is described. PFDMS-b-PMMA block copolymers form remarkable cylindrical micelles with very narrow diameter distributions at block ratios in the range of 1:10-1:6 (18-26 wt % PFDMS) in the block-selective solvent acetone, which is a good solvent for PMMA and a nonsolvent for PFDMS. The micelles, with a PFDMS core and a PMMA corona, were studied in solution by means of dynamic light scattering, 1H NMR spectroscopy, and cryo-transmission electron microscopy. Micelles were also deposited on silicon substrates by dip-coating and characterized with atomic force microscopy and scanning electron microscopy. The micelles were over 3 m long and had an overall diameter of around 22 nm. Dynamic light scattering experiments confirmed the formation of rodlike micellar aggregates in acetone. The cylindrical micelles exhibited a rod-to-sphere transition around 60 C. When cooled below this transition temperature, the micelles reassembled back to their original aggregation state. Depolarized DLS experiments showed no rotational contribution to the measured decays of the autocorrelation functions. We ascribe this to the extreme length of the micelles, which arrests rotational movement. 1H NMR spectra recorded in acetone-d6 showed PFDMS signals, indicating that these blocks in the micellar cores have some mobility. This suggests that the cores are not in a crystalline state and that crystallization is not a driving force in the formation of these PFDMS-b-PMMA cylindrical micelles, but rather the contrast in solvophilicity between the blocks, which in the bulk are in the strong segregation limit
    Assembly of polyelectrolyte-containing block copolymers in aqueous media
    Cohen Stuart, M.A. ; Hofs, P.S. ; Voets, I.K. ; Keizer, A. de - \ 2005
    Current Opinion in Colloid and Interface Science 10 (2005)1-2. - ISSN 1359-0294 - p. 30 - 36.
    oppositely charged polyelectrolytes - coacervation core micelles - interpolyelectrolyte complexes - diblock copolymers - colloidal stability - amphiphilic block - light-scattering - abc terpolymer - behavior - micellization
    In this review we present an overview of the developments of (self-)assembly of linear block copolymers containing one or more polyelectrolyte blocks in aqueous solution. Different micellar structures and phase behaviour are described. The role of inter- and intramolecular complex coacervation is emphasised. Recent developments in applications of assembly of polyelectrolyte-containing copolymers are presented.
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