Paul H. J. Kouwer

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Organization: Radboud University Nijmegen , Belgium
Department: Institute for Molecules and Materials
Title: (PhD)

TOPICS

Co-reporter:Hongbo Yuan, Jialiang Xu, Eliane P. van Dam, Giulia Giubertoni, Yves L. A. Rezus, Roel Hammink, Huib J. Bakker, Yong Zhan, Alan E. Rowan, Chengfen Xing, and Paul H. J. Kouwer
Macromolecules November 28, 2017 Volume 50(Issue 22) pp:9058-9058
Publication Date(Web):November 15, 2017
DOI:10.1021/acs.macromol.7b01832
Enhancing the thermal stability of proteins is an important task for protein engineering. There are several ways to increase the thermal stability of proteins in biology, such as greater hydrophobic interactions, increased helical content, decreased occurrence of thermolabile residues, or stable hydrogen bonds. Here, we describe a well-defined polymer based on β-helical polyisocyanotripeptides (TriPIC) that uses biological approaches, including hydrogen bonding and hydrophobic interactions for its exceptional thermal stability in aqueous solutions. The multiple hydrogen bonding arrays along the polymer backbone shield the hydrophobic core from water. Variable temperature CD and FTIR studies indicate that, on heating, a better packed polymer conformation further stiffens the backbone. Driven by hydrophobic interactions, TriPIC solutions give fully reversible hydrogels that can withstand high temperatures (80 °C) for extended times. Cryo-scanning electron microscopy (cryo-SEM), small-angle X-ray scattering (SAXS), and thorough rheological analysis show that the hydrogel has a bundled architecture, which gives rise to strain stiffening effects on deformation of the gel, analogous to many biological hydrogels.
Co-reporter:Pim van der Asdonk;Peter J. Collings
Advanced Functional Materials 2017 Volume 27(Issue 28) pp:
Publication Date(Web):2017/07/01
DOI:10.1002/adfm.201701209
Lyotropic chromonic liquid crystals have great potential in both biosensing and optical devices due to their biocompatible nature and strong optical characteristics. These applications, however, demand a homogeneous and stable alignment on anisotropic surfaces, a challenge that, so far, has not been solved adequately. In this work, it is shown how to drastically increase the quality of in-plane alignment and stability of these liquid crystals on conventional rubbed polyimide substrates by the addition of a small amount of a nonionic surfactant. Samples with surfactant show excellent alignment that is stable for months, while control samples without surfactant show much poorer alignment that further deteriorates in days. Also, well-aligned dry films of chromonics can be prepared following this approach. It is demonstrated how to obtain high-quality alignment by controlling the concentration and the nature of the surfactant, in particular its molecular structure and hydrophilic/lipophilic balance (HLB value) and other critical parameters are discussed. It is believed that this approach may very well be essential for advancing the applicability of these water-based, biocompatible, and often highly dichroic materials for a wide range of uses.
Co-reporter:Pim van der Asdonk
Chemical Society Reviews 2017 vol. 46(Issue 19) pp:5935-5949
Publication Date(Web):2017/10/02
DOI:10.1039/C7CS00029D
Chemistry quickly moves from a molecular science to a systems science. This requires spatial and temporal control over the organisation of molecules and molecular assemblies. Whilst Nature almost by default (transiently) organises her components at multiple different length scales, scientists struggle to realise even relatively straightforward patterns. In the past decades, supramolecular chemistry has taught us the rules to precisely engineer molecular assembly at the nanometre scale. At higher length scales, however, we are bound to top-down nanotechnology techniques to realise order. For soft, biological matter, many of these top-down techniques come with serious limitations since the molecules generally show low susceptibilities to the applied stimuli. A new method is based on liquid crystal templating. In this hierarchical approach, a liquid crystalline host serves as the scaffold to order polymers or assemblies. Being a liquid crystal, the host material can be ordered at many different length scales and on top of that, is highly susceptible to many external stimuli, which can even be used to manipulate the liquid crystal organisation in time. As a result, we anticipate large control over the organisation of the materials inside the liquid crystalline host. Recently, liquid crystal templating was also realised in water. This suddenly makes this tool highly applicable to start organising more delicate biological materials or even small organisms. We review the scope and limitations of liquid crystal templating and look out to where the technique may lead us.
Co-reporter:Pim van der Asdonk;Hans C. Hendrikse;Marcos Fernez-Castano Romera;Dion Voerman;Britta E. I. Ramakers;Dennis W. P. M. Löwik;Rint P. Sijbesma
Advanced Functional Materials 2016 Volume 26( Issue 16) pp:2609-2616
Publication Date(Web):
DOI:10.1002/adfm.201504945

Controlling the organization of functional supramolecular materials at both short and long length scales as well as creating hierarchical patterns is essential for many biological and electrooptical applications. It remains however an extremely challenging objective to date, particularly in water-based systems. In this work, it is demonstrated that water-processable self-assembling materials can be organized from micrometers to centimeters in any direction using liquid crystal templating in combination with photoaddressable command layers. The structural assemblies that are prepared are readily transformed into optically active π-conjugated polymers after photopolymerization. After this step, the template may be removed to leave the functional material well-organized on the substrate. The advantage of this approach is that it lacks specific molecular interactions and uses simple techniques such as spin coating and photoillumination and it may therefore be applied to a wide range of (aqueous) materials.

Co-reporter:Pim van der Asdonk, Stijn Kragt, and Paul H. J. Kouwer
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 25) pp:16303-16309
Publication Date(Web):June 6, 2016
DOI:10.1021/acsami.6b03910
Directing the spatial organization of functional supramolecular and polymeric materials at larger length scales is essential for many biological and molecular optoelectronic applications. Although the application of electrical fields is one of the most powerful approaches to induce spatial control, it is rarely applied experimentally in aqueous solutions, since the low susceptibility of soft and biological materials requires the use of high fields, which leads to parasitic heating and electrochemical degradation. In this work, we demonstrate that we can apply electric fields when we use a mineral liquid crystal as a responsive template. Besides aligning and positioning functional soft matter, we show that the concentration of the liquid crystal template controls the morphology of the assembly. As our setup is very easy to operate and our approach lacks specific molecular interactions, we believe it will be applicable for a wide range of (aqueous) materials.
Co-reporter:Pim van der Asdonk, Masoumeh Keshavarz, Peter C. M. Christianen and Paul H. J. Kouwer  
Soft Matter 2016 vol. 12(Issue 31) pp:6518-6525
Publication Date(Web):13 Jun 2016
DOI:10.1039/C6SM00652C
An alignment technique based on the combination of magnetic fields and a liquid crystal (LC) template uses the advantages of both approaches: the magnetic fields offer non-contact methods that apply to all sample sizes and shapes, whilst the LC templates offer high susceptibilities. The combination introduces a route to control the spatial organization of materials with low intrinsic susceptibilities. We demonstrate that we can unidirectionally align one such material, peptide amphiphiles in water, on a centimeter scale at a tenfold lower magnetic field by using a lyotropic chromonic liquid crystal as a template. We can transform the aligned supramolecular assemblies into optically active π-conjugated polymers after photopolymerization. Lastly, by reducing the magnetic field strength needed for addressing these assemblies, we are able to create more complex structures by initiating self-assembly of our supramolecular materials under competing alignment forces between the magnetically induced alignment of the assemblies (with a positive diamagnetic anisotropy) and the elastic force dominated alignment of the template (with a negative diamagnetic anisotropy), which is directed orthogonally. Although the approach is still in its infancy and many critical parameters need optimization, we believe that it is a very promising technique to create tailor-made complex structures of (aqueous) functional soft matter.
Co-reporter:T. Zinkevich;B. Venderbosch;M. Jaspers;P. H. J. Kouwer;A. E. Rowan;E. R. H. van Eck;A. P. M. Kentgens
Magnetic Resonance in Chemistry 2016 Volume 54( Issue 4) pp:328-333
Publication Date(Web):
DOI:10.1002/mrc.4379

Abstract

In aqueous media, ethylene glycol substituted polyisocyanopeptides (PICPs) change their state (undergo a sol-to-gel transition) as a response to temperature. This makes them promising materials for various biomedical applications, for instance, for controlled drug release and non-damaging wound dressing. To utilize PICP in biomedical applications, understanding of the origin of the gelation process is needed, but this is experimentally difficult because of the notoriously low gelator concentration in combination with the slow polymer dynamics in the sample. This paper describes a detailed characterization of the dried state of PICPs by solid-state NMR measurements. Both the 13C and the 1H NMR resonances were assigned using a combination of 1D cross-polarization magic angle spinning, 2D 13C–1H heteronuclear correlation spectra and 1H–1H single quantum–double quantum experiments. In addition, the chemical groups involved in dipolar interaction with each other were used to discuss the dynamics and spatial conformation of the polymer. In contrast to other PICP polymers, two resonances for the backbone carbon are observed, which are present in equal amounts. The possible origin of these resonances is discussed in the last section of this work. The data obtained during the current studies will be further used in elucidating mechanisms of the bundling and gelation. A comprehensive picture will make it possible to tailor polymer properties to meet specific needs in different applications. Copyright © 2015 John Wiley & Sons, Ltd.

Co-reporter:Maarten Jaspers, A. C. H. Pape, Ilja K. Voets, Alan E. Rowan, Giuseppe Portale, and Paul H. J. Kouwer
Biomacromolecules 2016 Volume 17(Issue 8) pp:
Publication Date(Web):July 13, 2016
DOI:10.1021/acs.biomac.6b00703
Bundling of single polymer chains is a crucial process in the formation of biopolymer network gels that make up the extracellular matrix and the cytoskeleton. This bundled architecture leads to gels with distinctive properties, including a large-pore-size gel formation at very low concentrations and mechanical responsiveness through nonlinear mechanics, properties that are rarely observed in synthetic hydrogels. Using small-angle X-ray scattering (SAXS), we study the bundle formation and hydrogelation process of polyisocyanide gels, a synthetic material that uniquely mimics the structure and mechanics of biogels. We show how the structure of the material changes at the (thermally induced) gelation point and how factors such as concentration and polymer length determine the architecture, and with that, the mechanical properties. The correlation of the gel mechanics and the structural parameters obtained from SAXS experiments is essential in the design of future (synthetic) mimics of biopolymer networks.
Co-reporter:Maarten Jaspers;Alan E. Rowan
Advanced Functional Materials 2015 Volume 25( Issue 41) pp:6503-6510
Publication Date(Web):
DOI:10.1002/adfm.201502241

The mechanical properties of hydrogels are commonly modified by changing the concentration of the molecular components. This approach, however, does not only change hydrogel mechanics, but also the microstructure, which in turn alters the macroscopic properties of the gel. Here, the Hofmeister effect is used to change the thermoresponsiveness of polyisocyanide hydrogels. In contrast to previous Hofmeister studies, the effect is used to change the phase transition temperatures and to tailor the mechanics of the thermoresponsive (semiflexible) polymer gels. It is demonstrated that the gel stiffness can be manipulated over more than two orders of magnitude by the addition of salts. Surprisingly, the microstructure of the gels does not change upon salt addition, demonstrating that the Hofmeister effect provides an excellent route to change the mechanical properties without distorting other influential parameters of the gel.

Co-reporter:Alexandra Alvarez Fernandez, Masoumeh Keshavarz, Peter C. M. Christianen, and Paul H. J. Kouwer
Macromolecules 2015 Volume 48(Issue 4) pp:1002-1008
Publication Date(Web):February 9, 2015
DOI:10.1021/ma501867f
Polymer-stabilized liquid crystals (PSLCs) are materials composed of a polymer mesh in a continuous phase of liquid crystal. The polymer mesh provides an anchor point for alignment of the liquid crystalline bulk. The macroscopic extent of order in such systems depends on the order parameter of the liquid crystal (given by the temperature) and the domain order parameter, induced by external stimuli, such as (rubbed) substrates or magnetic or electric fields. We studied thick PSLCs where substrate interactions cannot be employed and used magnetic fields instead. We show how the polymerization conditions, i.e., the temperature and the magnetic field, influence the overall order parameter in 4-octyl-4′-cyanobiphenyl (8CB)-based PSLCs. Optimal macroscopic alignment was obtained in samples polymerized at room temperature and at magnetic fields in excess of 5 T. The effect of mesh network can be quantified by introducing a phenomenological constant, which is correlated to the order parameter at the polymerization conditions, into a straightforward model that describes the overall order parameter in terms of a thermally dependent local order parameter and a magnetic field dependent domain order parameter.
Co-reporter:Alexandra Alvarez Fernandez, Marcel J. A. van Dongen, Daniel Blanco-Ania and Paul H. J. Kouwer  
RSC Advances 2014 vol. 4(Issue 57) pp:30267-30273
Publication Date(Web):30 Jun 2014
DOI:10.1039/C4RA04884A
Ionic liquids, organic room-temperature molten salts have percolated into many fields of science. A major problem for many applications, however, is caused by the commonly fluorinated anion, that on contact with water decomposes to release HF. Ionic liquids with hydrophilic anions do not have these problems. In addition, because of their tuneable hydrophilicity, they interface better with biotechnology, providing a route to truly ‘tuneable water.’ Currently available synthetic routes, however, contain strong disadvantages which may have caused the underexposure of this class of ionic liquids. In this manuscript, we provide a novel facile route to ionic liquid crystals with different hydrophilic anions, yielding pure materials as a result of our very mild reaction conditions. Our generic approach may be used to prepare conventional ionic liquids, but also provides access to functionalised ionic liquids.
Co-reporter:Alexandra Alvarez Fernandez, Laurens T. de Haan and Paul H. J. Kouwer  
Journal of Materials Chemistry A 2013 vol. 1(Issue 2) pp:354-357
Publication Date(Web):05 Oct 2012
DOI:10.1039/C2TA00133K
Ionic liquid crystals (ILCs) with displaying birefringence have great potential in various (bio)sensor schemes. So far, their high transition temperatures prevent their application. We demonstrate in a novel series of ILCs, based on archetypical mesogens, how to reduce clearing temperatures and we explain our results qualitatively.
Co-reporter:Sebastian Albert-Seifried;ChrisE. Finlayson Dr.;Frederic Laquai Dr.;RichardH. Friend ;TimothyM. Swager ;PaulH.J. Kouwer Dr.;Michal Jurí&x10d;ek;HeatherJ. Kitto Dr.;Sanne Valster;RoelJ.M. Nolte ;AlanE. Rowan
Chemistry - A European Journal 2010 Volume 16( Issue 33) pp:10021-10029
Publication Date(Web):
DOI:10.1002/chem.201000677

Abstract

We describe the synthesis of a series of phthalocyanine (Pc)–perylenediimide (PDI)8 “octad” molecules, in which eight PDI moieties are attached to a Pc core through alkyl-chain linkers. There is clear spectroscopic evidence that these octads can exist as non-aggregated “monomers” or form aggregates along the Pc cores, depending on the type of Pc and the solvent medium. In the low dielectric constant solvents, into which the octads are soluble, photoexcitation of the PDI units leads to rapid energy transfer to the Pc centre, rather than a charge separation between moieties. In octad monomers, the Pc singlet excited-state decays within tens of ps, whereas the excitons are stabilised in the aggregated form of the molecules, typically with lifetimes in the order of 1–10 ns. By contrast, in an octad design in which π–π interactions are suppressed by the steric hindrance of a corona of incompatible glycol tails around the molecule, a more straightforward photophysical interaction of Förster energy transfer between the PDI moieties and Pc core may be inferred. We consider these molecules as prototypical multichromophoric aggregates, giving delocalised states with considerable flexibility of design.

Co-reporter:Paul H. J. Kouwer and Georg H. Mehl  
Journal of Materials Chemistry A 2009 vol. 19(Issue 11) pp:1564-1575
Publication Date(Web):09 Feb 2009
DOI:10.1039/B819877B
Shape-amphiphilic liquid crystals offer a route towards complex assemblies at the difficult 10 nanometer length scale. We present the preparation and mesomorphic characterisation of three novel shape amphiphiles based on azobenzenes. Their mesophases range from a simple nematic to complex lamellar phases of alternating layers of discotic and calamitic mesogens. In all smectic phases, the discotic and calamitic moieties are nanophase separated. As the different sub-layers start to tilt and/or display in-layer order independently, the mesophase assignment becomes more complex. Using temperature dependent X-ray diffraction we studied their characteristics.
Co-reporter:Paul H. J. Kouwer and Georg H. Mehl
Journal of Materials Chemistry A 2009 - vol. 19(Issue 11) pp:NaN1575-1575
Publication Date(Web):2009/02/09
DOI:10.1039/B819877B
Shape-amphiphilic liquid crystals offer a route towards complex assemblies at the difficult 10 nanometer length scale. We present the preparation and mesomorphic characterisation of three novel shape amphiphiles based on azobenzenes. Their mesophases range from a simple nematic to complex lamellar phases of alternating layers of discotic and calamitic mesogens. In all smectic phases, the discotic and calamitic moieties are nanophase separated. As the different sub-layers start to tilt and/or display in-layer order independently, the mesophase assignment becomes more complex. Using temperature dependent X-ray diffraction we studied their characteristics.
Co-reporter:Alexandra Alvarez Fernandez, Laurens T. de Haan and Paul H. J. Kouwer
Journal of Materials Chemistry A 2013 - vol. 1(Issue 2) pp:NaN357-357
Publication Date(Web):2012/10/05
DOI:10.1039/C2TA00133K
Ionic liquid crystals (ILCs) with displaying birefringence have great potential in various (bio)sensor schemes. So far, their high transition temperatures prevent their application. We demonstrate in a novel series of ILCs, based on archetypical mesogens, how to reduce clearing temperatures and we explain our results qualitatively.
Co-reporter:Pim van der Asdonk, Hans C. Hendrikse, Atang C. Sauli, Stijn P. M. Kraaijkamp and Paul H. J. Kouwer
Journal of Materials Chemistry A 2016 - vol. 4(Issue 35) pp:NaN8269-8269
Publication Date(Web):2016/08/12
DOI:10.1039/C6TC02790C
Controlling the spatial and temporal organization of functional polymers is essential for the development of switchable soft-matter based electro-optical devices. By using a combination of a liquid crystal template, a photopatternable substrate (for spatial control) and electric fields (for dynamically switching) we show that we are able to dynamically control the spatial organization of polymers across multiple length scales (conveyed through the patterned liquid crystal template). The polymer that we organize is an azobenzene-functionalized polyisocyanide, whose stiff polymeric helix and laterally attached pendant azobenzene units induce tangential anchoring to the liquid crystal host. Due to the donor–acceptor functionalized azobenzene units, the polymeric material is strongly absorbing in the visible range for characterization purposes. We find that polymers align locally to the liquid crystal director field and reversibly change its orientation by the application of an electric field. Since this hybrid technique can be easily applied to other functional polymeric materials and relies on simple techniques, such as spincoating, photoalignment and electric fields, we believe it has great potential for the development of a wide range of switchable electro-optical devices.
1H-1,2,3-Triazole, 5-iodo-4-phenyl-1-(phenylmethyl)-
1H-1,2,3-Triazole-4-methanamine, 1-(1,1-dimethylethyl)-N,N-bis[[1-(1,1-dimethylethyl)-1H-1,2,3-triazol-4-yl]methyl]-
Silane, [(4,5-dimethoxy-1,2-phenylene)di-2,1-ethynediyl]bis[trimethyl-
1H-IMIDAZOLE, 1-HEXYL-2-METHYL-
1,2-Benzenedicarbonitrile, 4,5-dibromo-
Cyclohexane, azido-
Dichlorotetrakis[2-(2-Pyridyl)Phenyl]Diiridium(Iii)
1,4-Bis[(trimethylsilyl)ethynyl]benzene
Benzene, 1,2-diethynyl-