A5039633464- Advanced Polymer Synthesis and Characterization
- Material Dynamics and Properties
- Surfactants and Colloidal Systems
- Polymer crystallization and properties
- Polymer Nanocomposites and Properties
- Rheology and Fluid Dynamics Studies
- NMR spectroscopy and applications
- Block Copolymer Self-Assembly
- Electrostatics and Colloid Interactions
- Advanced NMR Techniques and Applications
- Polymer composites and self-healing
- biodegradable polymer synthesis and properties
- Lipid Membrane Structure and Behavior
- Nanopore and Nanochannel Transport Studies
- Phase Equilibria and Thermodynamics
- Liquid Crystal Research Advancements
- Hydrogels: synthesis, properties, applications
- Polymer Surface Interaction Studies
- Force Microscopy Techniques and Applications
- Theoretical and Computational Physics
- Organometallic Complex Synthesis and Catalysis
- Advanced Battery Materials and Technologies
- Synthesis and properties of polymers
- Dendrimers and Hyperbranched Polymers
- Nuclear Physics and Applications
Forschungszentrum Jülich
2016-2025
Stadtwerke Jülich (Germany)
2015-2023
Institut Laue-Langevin
2007-2021
Institute for Complex Systems
2015-2019
Material Physics Center
2016
University of the Basque Country
2016
Heinz Maier-Leibnitz Zentrum
2016
National Institute of Standards and Technology
2008
NIST Center for Neutron Research
2008
University of Maryland, College Park
2008
Combining statistical-mechanical theories and neutron-scattering techniques, we show that the effective pair potential between star polymers is exponentially decaying for large distances crosses over, at a density-dependent corona diameter, to an ultrasoft logarithmic repulsion small distances. We also make theoretical prediction in concentrated polymer solutions, this interaction induces anomalous fluid structure factor which exhibits unusually pronounced second peak.
We present experiments and theory on the melt dynamics of monodisperse entangled polymers H-shaped architecture. Frequency-dependent rheological data a series polyisoprene H-polymers are in good agreement with tube model that combines path-length fluctuation (like star polymer melts) at high frequency, reptation self-entangled "cross-bars" low frequencies linear melts). account explicitly for mild polydispersity. Nonlinear step-strain transient shear extension confirm presence relaxation...
We have measured the linear rheology of critically purified ring polyisoprenes, polystyrenes, and polyethyleneoxides different molar masses. The ratio zero-shear viscosities polymer melts η0,linear to their counterparts η0,ring at isofrictional conditions is discussed as a function number entanglements Z. In unentangled regime η0,linear/η0,ring virtually constant, consistent with earlier data, atomistic simulations, theoretical expectation = 2. entanglement regime, Z-dependence viscosity...
Neutron spin echo has revealed the single chain dynamic structure factor of entangled polymer chains confined in cylindrical nanopores with dimensions either much larger or smaller than lateral pore sizes. In both situations, a slowing down dynamics respect to bulk behavior is only observed at intermediate times. The results long times provide direct microscopic measurement entanglement distance under confinement. They constitute first experimental evidence dilution total density melt strong...
Ring polymers have fascinated theorists, simulators, and experimentalists as they are the simplest polymer without ends, giving rise to important topology related properties. We present state of art recent synthetic efforts investigations into structure dynamics dense nonconcatenated ring systems. Analyzing existing knowledge, we identify challenges for future research: In realm synthesis creation well-defined high molecular weight rings based on different monomers highly desirable. field...
We demonstrate that block copolymers of the poly(ethylenepropylene)-co-poly(ethylene oxide) (PEP−PEO) type dramatically enhance solubilization capacity medium-chain surfactants in microemulsions, for example, ternary system water−n-decane−C10E4. The effect exhibits itself an enormous increase swelling middle phase with associated structural length scale microemulsion, while at same time (already ultralow) interfacial tension between water- and oil-rich phases decreases even further....
We present high resolution neutron spectroscopic investigations of polyethylene glycol matrices interacting attractively with neat SiO2 nanoparticles. observe a very rich dynamical picture that significantly contradicts earlier conclusions on such systems. Investigating short chain matrix we realized fraction chains is attached at the nanoparticle surface suppressing completely its translational diffusion. Nevertheless these undergo an unchanged segmental dynamics seemingly forming...
The dynamics of ${\mathrm{Li}}^{+}$ transport in polyethylene oxide (PEO) and lithium bis(trifluoromethanesulfonyl)imde mixtures are investigated by combining neutron spin-echo (NSE) dielectric spectroscopy with molecular (MD) simulations. results summarized a relaxation time map covering wide ranges temperature time. dependence the dc conductivity $\ensuremath{\alpha}$ is found to be identical, indicating strong coupling between both. times obtained from NSE measurements at $0.05\text{...
The absence of entanglements, the more compact structure and faster diffusion in melts cyclic poly(ethylene oxide) (PEO) chains have consequences on their crystallization behavior at lamellar spherulitic length scales. Rings with molecular weight below entanglement (M < Me), attain equilibrium configuration composed from twice-folded a periodicity that is half corresponding linear chains. M > Me undergo distinct step-like conformational changes to crystalline configuration. melt this crystal...
The synthesis of amphiphilic AB block copolymers, having 1,4-polydiene or corresponding hydrogenated aliphatic polyolefin blocks and poly(ethylene oxide) (PEO) blocks, is described. materials are obtained in a two-step process. In the first step isoprene polymerized anionically hydrocarbon solvent with sec-butyllithium tert-butyllithium as initiator. end-capping living polymer ethylene oxide (EO) yields polyisoprene, which functionalized hydroxyl end group (PI-OH). This product can be to...
The effect of amphiphilic diblock copolymers several molecular weights on the structure and phase behavior ternary systems (water, oil, nonionic surfactant) is investigated. Small amounts block copolymer polyethyleneoxide–polyethylpropylene lead to a dramatic decrease amount total surfactant needed solubilize given equal volumes water oil in bicontinuous microemulsion. Neutron scattering experiments employing high-precision two-dimensional contrast variation technique demonstrate that...
A time-resolved SANS method was developed for the determination of unimer exchange kinetics polymeric micelles under equilibrium conditions. Measurements were performed on system PEP-PEO/DMF exploiting large difference in scattering length density protonated and deuterated species. In contrast to theoretical predictions observed consists two well-separated processes. From temperature-dependent measurements corresponding activation energies EA could be determined. comparison basis a scaling...
The dynamic viscoelastic properties of anionically polymerized model 1,4-polyisoprene (PI) with 6−8% 3,4 microstructure and in the range molecular weights between 1.5 × 103 3.2 106 g/mol were reanalyzed using linear rheology. Viscosities obtained zero shear-rate limit, η0, up to sufficiently high weight PI samples indicated a clear transition pure reptation regime. All characteristic weights, dividing [η0,M]-interval three different regimes could be accuracy new “triangle” is proposed....
The chain dynamics and viscoelastic properties of poly(ethylene oxide) (PEO) were studied covering a wide range molecular weights temperatures. Two experimental techniques used: rheology, in order to study the large scale properties, neutron spin−echo (NSE) spectroscopy, investigate at level. We aimed explore characteristic dynamical parameters pure homopolymer system describe its dependence on polymer weight temperature. will show that, after accounting for weigth glass transition...
We present a static and quasi-elastic neutron scattering study on both the structure dynamics of ring polymer in linear melt, respectively. In first case, proved to be significantly more compact compared chain with same molecular weight. mixture, molecules swell as was confirmed by small angle (SANS) accordance theory simulation work. The dynamical behavior systems, which for time has been explored spin echo spectroscopy (NSE), shows surprisingly fast center mass diffusion polymer. These...
The combination of a set complementary techniques allows us to construct an unprecedented and comprehensive picture the internal structure, temperature dependent swelling behavior, dependence these properties on cross-linker concentration microgel particles based N-vinylcaprolactam (VCL). microgels were synthesized by precipitation polymerization using different amounts cross-linking agent. Characterization was performed small-angle neutron scattering (SANS) two instruments cover uniquely...
We present a neutron scattering analysis of the structure and dynamics PEO polymer rings with molecular weight 2.5 times higher than entanglement mass. The melt was found to be more compact Gaussian model would suggest. With increasing time center mass (c.o.m.) diffusion undergoes transition from sub-diffusive diffusive behavior. agrees well decorrelation predicted by mode coupling approach. As novel feature pronounced non-Gaussian behavior c.o.m. that shows surprising analogies cage effect...
Using neutron spin echo spectroscopy, we show that the segmental dynamics of polymer rings immersed in linear chains is completely controlled by host. This transforms into ideal probes for studying entanglement embedding matrix. As a consequence unique ring topology, long chain matrices spacing directly revealed, unaffected local reptation host molecules beyond this distance. In shorter entangled matrices, where time frame experiment secondary effects such as contour length fluctuations or...
We present a comprehensive experimental and theoretical study covering micro-, meso- macroscopic length time scales, which enables us to establish generalized view in terms of structure–property relationship equilibrium dynamics soft colloids.
The bulk modulus, K , quantifies the elastic response of an object to isotropic compression. For soft compressible colloids, knowing is essential accurately predict suspension crowding. Most colloids have complex architectures characterized by different softness, which additionally depends on Here, we determine values for various morphological parts individual nanogels and probe changes with Our method uses a partially deuterated polymer, exerts required stress, small-angle neutron...
The co-assembly of polyelectrolytes (PE) with proteins offers a promising approach for designing complex structures customizable morphologies, charge distribution, and stability targeted cargo delivery. However, the complexity protein structure limits our ability to predict properties formed nanoparticles, goal is identify key triggers morphological transition in protein/PE complexes evaluate their encapsulate multivalent ionic drugs. A positively charged PE can assemble at pH above...
Cationic surfactants have a wide range of applications, often associated with their affinity for solid surfaces and anti-microbial properties. Manipulating adsorption self-assembly properties is key to most this commonly achieved through surfactant mixtures or manipulating headgroup alkyl chain structure. Achieving adjustments structure less common in cationic than anionic surfactants. Ethoxylation provides the ability adjust hydrophilic / hydrophobic balance, as extensively demonstrated
The ubiquitous use of plastics demands thoughtfulness about their fate in the environment. Biodegradability is, therefore, a prerequisite for future many applications, including agriculture. Here, we bring forward stable isotope (resonance) Raman microspectroscopy at single-cell level to broaden mechanistic understanding microbial degradation (micro)plastics natural systems. We selected perdeuterated d-polylactic acid (dPLA) as model plastic, synthesized from d-lactic acid-d4, via...
Motional heterogeneity for the grafted chains in OCNC depends on confinement strength.