Lutz Willner

Forschungszentrum Jülich

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Dieter Richter

Forschungszentrum Jülich

110

Reidar Lund

University of Oslo

Jörg Stellbrink

Forschungszentrum Jülich

M. Monkenbusch

Forschungszentrum Jülich

Juan Colmenero

Donostia International Physics Center

D. Schwahn

Forschungszentrum Jülich

B. Farago

Institut Laue-Langevin

Vitaliy Pipich

Heinz Maier-Leibnitz Zentrum

Jürgen Allgaier

Forschungszentrum Jülich

Lewis J. Fetters

Cornell University

Cooperative Institutions

Forschungszentrum Jülich

101

Centre National de la Recherche Scientifique

Institut Laue-Langevin

Stadtwerke Jülich (Germany)

Heinz Maier-Leibnitz Zentrum

University of Bayreuth

University of the Basque Country

Oak Ridge National Laboratory

Material Physics Center

ExxonMobil (United States)

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Molecular observation of contour length fluctuations in polymer melts

Physica B Condensed Matter (2004)

A. Wischnewski Michaela Zamponi M. Monkenbusch Lutz Willner Wim Pyckhout‐Hintzen

Reptation

Chain (unit)

Length scale

10.1016/j.physb.2004.04.024

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Citations (1)

Direct observation of the transition from free to constrained single segment motion in entangled polymer melts

Physica B Condensed Matter (2004)

M. Monkenbusch A. Wischnewski Lutz Willner Dieter Richter

Reptation

Neutron spin echo

Mean squared displacement

10.1016/j.physb.2004.04.030

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Citations (3)

Chain Motion in an Unentangled Polyethylene Melt: A Critical Test of the Rouse Model by Molecular Dynamics Simulations and Neutron Spin Echo Spectroscopy

Physical Review Letters (1998)

Wolfgang Paul Grant D. Smith Do Y. Yoon B. Farago Silke Rathgeber

We have investigated the dynamic structure factor for single-chain relaxation in a polyethylene melt by means of molecular dynamics simulations and neutron spin echo spectroscopy. After accounting for a 20% difference in the chain self-diffusion coefficient between simulation and experiment we find a perfect quantitative agreement of the intermediate dynamic structure factor over the whole range of momentum transfer studied. Based on this quantitative agreement one can test the experimental results for deviations from standard Rouse behavior reported so far for only computer simulations of polymer melt dynamics.

Neutron spin echo

Dynamic structure factor

Dynamics

Structure factor

Self-diffusion

10.1103/physrevlett.80.2346

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Citations (166)

Kinetic Pathway of the Cylinder-to-Sphere Transition in Block Copolymer Micelles Observed in Situ by Time-Resolved Neutron and Synchrotron Scattering

ACS Macro Letters (2013)

Reidar Lund Lutz Willner Dieter Richter Peter Lindner Theyencheri Narayanan

Here we present an in situ study of the nonequilibrium cylinder-to-sphere morphological transition kinetics on the millisecond range in a model block copolymer micelle system revealing the underlying mechanism and pathways of the process. By employing the stopped-flow mixing technique, the system was rapidly brought (≈100 μs) deep into the instability region, and the kinetics was followed on the time scale of milliseconds using both time-resolved small-angle neutron and X-ray scattering (TR-SANS and TR-SAXS, respectively). Due to the difference in contrast and resolution, SAXS and SANS provide unique complementary information. Our analysis shows that the morphological transition is characterized by a single rate constant indicating a two-state model where the transition proceeds through direct decomposition (fragmentation) of the cylinders without any transient intermediate structures. The cylindrical segments formed in the disintegration process subsequently grow into spherical micelles possibly through the molecular exchange mechanism until near equilibrium micelles are formed. The observation of a two-step kinetic mechanism, fluctuation-induced fragmentation and ″ripening″ processes, provides unique insight into the nonequilibrium behavior of block copolymer micelles in dilute solutions.

Small-angle X-ray scattering

Millisecond

10.1021/mz400521p

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Citations (49)

Complex phase behavior near the Lifshitz line in a ternary polymer blend

Applied Physics A (2002)

Vitaliy Pipich D. Schwahn Lutz Willner

Polystyrene

Line (geometry)

10.1007/s003390101099

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Citations (4)

Study of the Dynamic Structure Factor in theβRelaxation Regime of Polybutadiene

Physical Review Letters (1996)

Arantxa Arbe U. Buchenau Lutz Willner Dieter Richter B. Faragó

Using neutron spin echo and dielectric spectroscopy we have studied the molecular motions of 1-4 polybutadiene in the $\ensuremath{\alpha}\ensuremath{-}\ensuremath{\beta}$ relaxation regime. At the first peak of the static structure factor the relaxation times follow the temperature dependence of the viscosity, while near the second peak the Arrhenius law of the $\ensuremath{\beta}$ relaxation is observed. Considering localized motions on a length scale of 1.5 \AA{} with the barrier distribution from dielectric spectroscopy the dynamic structure factor in the $\ensuremath{\beta}$ relaxation regime can be described quantitatively.

Dynamic structure factor

Structure factor

10.1103/physrevlett.76.1872

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Citations (90)

Free volume in PEP-silica nanocomposites with varying molecular weight

Polymer (2013)

Christian Ohrt Tönjes Koschine Klaus Rätzke Franz Faupel Lutz Willner

10.1016/j.polymer.2013.11.021

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Citations (10)

Kinetics of Block Copolymer Micelles Studied by Small-Angle Scattering Methods

Advances in polymer science (2013)

Reidar Lund Lutz Willner Dieter Richter

Small-angle X-ray scattering

10.1007/12_2012_204

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Citations (76)

Self-Assembly of Mixtures of Telechelic and Monofunctional Amphiphilic Polymers in Water: From Clusters to Flowerlike Micelles

Macromolecules (2017)

Thomas Zinn Lutz Willner Kenneth D. Knudsen Reidar Lund

We study the self-assembly of mixtures of n-alkyl mono- and difunctionalized poly(ethylene oxide) (PEO) chains in the dilute concentration regime. The monofunctional PEOs were prepared by living anionic polymerization with varying n-alkyl length (n = 14, 16, 22, 28) and constant PEO molecular weight of 5 kg/mol. The difunctional materials were obtained through end-to-end coupling of two of the monofunctionalized PEOs via their terminal hydroxyl groups. The chosen synthetic pathway yields well-defined model compounds with narrow molecular weight distribution and complete end-group functionalization. By using both small-angle neutron scattering (SANS) and dynamic light scattering (DLS) combined with theoretical data modeling, we have systematically investigated both the global and inner structure of the self-assembled micellar structures. For short n-alkyl chain-ends, we find a formation of clustered micelles with a finite size whereas, intriguingly, at longer n-alkyls, we observe a crossover to flowerlike micelles. This was confirmed both by DLS, which is very sensitive to formation of larger clusters, as well as with SANS, which also showed a clear transition from attractive to repulsive intermicellar interactions upon increasing n-alkyl length. We attribute this to the balance between the hydrophobic enthalpic terms that favor anchoring of both chain-ends to the core and the entropic cost associated with the bending of the polymer chains. For short n-alkyls, exposure of the chain-ends in the corona structure leads to net dominance of the attractive interactions while for longer hydrophobic chains it leads to a stabilization of loops and consequently flowerlike micellar morphology. Using contrast-variation SANS, the contribution of mono- and difunctional chains could be separated, confirming the flowerlike micellar structure.

10.1021/acs.macromol.7b01501

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Citations (29)

Synthesis of disoloxanes containing hydroxyalkyl groups

Journal of Organometallic Chemistry (1987)

F. N. Braun Lutz Willner Michael Heß R. Kosfeld

Trimethylsilyl

10.1016/0022-328x(87)85123-9

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Citations (18)