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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End-to-End Vector Dynamics of Nonentangled Polymers in Lamellar Block Copolymer Melts: The Role of Junction Point Motion

Macromolecules (2013)

Reidar Lund Fabienne Barroso‐Bujans Mohammed Zakaria Slimani Angel J. Moreno Lutz Willner

By using dielectric spectroscopy, we investigate the chain dynamics of nonentangled polyisoprene (PI) under soft confinement in lamellar domains of block copolymer melts with polydimethylsiloxane (PDMS). The data show a dramatic difference in the end-to-end vector dynamics of the PI blocks as compared not only with that of the corresponding homopolymer PI chains but also with respect to previous results for the same blocks under soft confinement in cylindrical domains. Two contributions to the dielectric normal mode relaxation are detected. The data are analyzed by means of a model including contributions from internal chain modes (accounting for the fastest component) and a slow component attributed to the junction point dynamics. The contribution of the internal chain modes is modeled according to the analysis of the Rouse modes obtained from simulations of a generic bead–spring model for strongly segregated symmetric diblock copolymers. In this way it is shown that the internal chain modes of the blocks have time scales close to those expected from the homopolymer chain independently of the structural details. In contrast, the contribution attributed to the junction point dynamics depends critically on minor structural differences. We interpret these findings as a result of the presence of fast moving defects and/or grain boundaries in the lamellar structures formed by these relatively short, nonentangled diblock copolymers.

Chain (unit)

Polydimethylsiloxane

Dynamics

Component (thermodynamics)

10.1021/ma401162b

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Citations (11)

Micellization of symmetric PEP-PEO block copolymers in water: molecular weight dependence

Applied Physics A (2002)

Håkon Kaya Lutz Willner Jürgen Allgaier Jörg Stellbrink Dieter Richter

Dispersity

Static light scattering

10.1007/s003390101113

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Citations (23)

Effect of Core Crystallization on Molecular Exchange in Amphiphilic Block Copolymer Micelles

Lutz Willner Vitaliy Pipich Reidar Lund Nico König Dieter Richter

Source

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Citations (0)

Perspectives of Deuteron Field-Cycling NMR Relaxometry for Probing Molecular Dynamics in Soft Matter

The Journal of Physical Chemistry B (2016)

M. Flämig M. Becher M. Hofmann T. Körber B. Kresse

Due to the single-particle character of the quadrupolar interaction in molecular systems, (2)H NMR poses a unique method for probing reorientational dynamics. Spin-lattice relaxation gives access to the spectral density, and its frequency dependency can be monitored by field-cycling (FC) techniques. However, most FC NMR studies employ (1)H; the use of (2)H is still rare. We report on the application of (2)H FC NMR for investigating the dynamics in molecular liquids and polymers. Commercial as well as home-built relaxometers are employed accessing a frequency range from 30 Hz to 6 MHz. Due to low gyromagnetic ratio, high coupling constants, and finite FC switching times, current (2)H FC NMR does not reach the dispersion region in liquids (toluene and glycerol), yet good agreement with the results from conventional high-field (HF) relaxation studies is demonstrated. The pronounced difference at low frequencies between (2)H and (1)H FC NMR data shows the relevance of intermolecular relaxation in the case of (1)H NMR. In the case of the polymers polybutadiene and poly(ethylene-alt-propylene), very similar relaxation dispersion is observed and attributed to Rouse and entanglement dynamics. Combination with HF (2)H relaxation data via applying frequency-temperature superposition allows the reconstruction of the full spectral density reflecting both polymer as well as glassy dynamics. Transformation into the time domain yields the reorientational correlation function C2(t) extending over nine decades in time with a long-time power law, C2(t) ∝ t(-0.45±0.05), which does not conform to the prediction of the tube-reptation model, for which ∝ t(-0.25) is expected. Entanglement sets in below C2(t = τe) ≅ S(2) = 0.001, where τe is the entanglement time and S the corresponding order parameter. Finally, we discuss the future prospects of the (2)H FC NMR technique.

10.1021/acs.jpcb.6b05109

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Citations (24)

Quasielastic Neutron Scattering and Molecular Dynamics Simulation Study on the Structure Factor of Poly(ethylene-alt-propylene)

Macromolecules (2009)

Roberto Pérez-Aparicio Arantxa Arbe F. Álvarez Juan Colmenero Lutz Willner

By combining neutron scattering and fully atomistic molecular dynamics simulations, we have investigated the static [S(Q)] and dynamic [S(Q,t)] structure factor of poly(ethylene-alt-propylene) in a wide momentum-transfer Q range (0.2 < Q < 3 Å−1) spanning over inter- and intramolecular length scales and including also the region of intermediate length scales. The experiments consist of diffraction with polarization analysis and neutron spin-echo measurements on a fully deuterated sample. These results have been used to thoroughly validate the simulations, which have been subsequently exploited to unravel the different contributions to S(Q) and S(Q,t) and provide insights into real space. We have first disentangled the short-range order in this polymer. At the first peak of S(Q) which is clearly dominated by the interchain contribution of the main-chain/main-chain correlations, the dynamics above the glass transition reveal the genuine α-relaxation. The direct observation of the α-relaxation in this way has allowed establishing the viscosity scaling, the stretching, and the deGennes narrowing. An in-phase modulation with S(Q) is observed for the amplitude and shape parameter of the slow decay of S(Q,t) around the first peak. The corresponding time scale also displays a maximum that shifts with temperature in a much stronger way than that of S(Q). Coherency effects in the slow decay are lost above ≈1.5 Å−1, where intramolecular correlations dominate. Interestingly, the apparent activation energy of the characteristic time mirrors the structure factor in the whole Q range investigated.

Structure factor

Dynamic structure factor

Quasielastic neutron scattering

Momentum transfer

Neutron spin echo

10.1021/ma9016407

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Citations (25)

A dynamic light scattering study of random 1,2‐1,4 polybutadiene copolymers near the glass transition

Acta Polymerica (1996)

L. Reinhardt G. Fylas E. W. Fischer Lutz Willner

The relaxational characteristics of the density and segmental orientation fluctuations in six homogeneous random copolymers of 1,2 and 1,4 polybutadiene (PB) with 1,2 composition varying between 7 and 95% were studied by photon correlation spectroscopy in the polarized and depolarized mode near and above the glass transition temperature T g . Unlike the situation in homogeneous diblock copolymers and blends of 1,2 and 1,4 PB, a single α‐relaxation function with moderately broad and temperature‐independent distribution of relaxation times can adequately represent the experimental time correlation functions. This dynamic homogeneity probably reflects local miscibility and randomness of the chain microstructure. The variation of the microstructure affects not only the value of T g but also the distribution of relaxation times (cooperativity) and the fragility (dlogτ/d( T g / T )) in the composition region rich in 1,2 units.

10.1002/j.1521-4044.1996.tb00005.x

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Citations (6)

ChemInform Abstract: Synthesis and Characterization of Oligosiloxanes (III), (IV) with Hydroxyalkyl Substituents.

ChemInform (1989)

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

10.1002/chin.198941225

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A New View of the Anionic Diene Polymerization Mechanism

Macromolecular Symposia (2004)

Aizhen Niu Jörg Stellbrink Jürgen Allgaier Lutz Willner Dieter Richter

Abstract We investigated the anionic polymerization of butadiene in d‐heptane solvent using tert ‐butyl lithium as initiator. Two complementary techniques were used to follow the polymerization processes: 1 H NMR and small angle neutron scattering (SANS). The time resolved 1 H NMR measurements allowed us to evaluate quantitatively the kinetics of the processes involved. The initiation event commences slowly and then progressively accelerates. This indicates an autocatalytic mechanism. The microstructure of the first monomer units attached is to a high extent 1,2. The disappearance of initiator ‐‐‐ at about 10% monomer conversion ‐‐‐ signals the onset of the normal ∼6% vinyl content of the chain. Small angle neutron scattering was used to study the aggregation behavior of the carbon lithium head groups. It is well known that the polar head groups aggregate and form micellar structures. For dienes in non‐polar solvents the textbook mechanism assumes the formation of only tetramers during the propagation reaction. By combining 1 H NMR and SANS results we were able to determine quantitatively the aggregation number during all stages of the polymerization. Our measurements show the existence of large‐scale structures during the initiation period. The initial degree of aggregation of more than 100 living polymer chains diminished as the polymerization progressed. In addition, even larger, giant structures with N agg >>1000 and R g ≈ 1000Å were found.

Degree of polymerization

Precipitation polymerization

Kinetic chain length

Chain-growth polymerization

10.1002/masy.200451101

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Citations (22)

Cooperative Dynamics in Homopolymer Melts: A Comparison of Theoretical Predictions with Neutron Spin Echo Experiments

The Journal of Physical Chemistry B (2008)

Michaela Zamponi A. Wischnewski M. Monkenbusch Lutz Willner Dieter Richter

We present a comparison between theoretical predictions of the generalized Langevin equation for cooperative dynamics (CDGLE) and neutron spin echo data of dynamic structure factors for polyethylene melts. Experiments cover an extended range of length and time scales, providing a compelling test for the theoretical approach. Samples investigated include chains with increasing molecular weights undergoing dynamics across the unentangled to entangled transition. Measured center-of-mass (com) mean-square displacements display a crossover from subdiffusive to diffusive dynamics. The generalized Langevin equation for cooperative dynamics relates this anomalous diffusion to the presence of the interpolymer potential, which correlates the dynamics of a group of slowly diffusing molecules in a dynamically heterogeneous liquid. Theoretical predictions of the subdiffusive behavior, of its crossover to free diffusion, and of the number of macromolecules undergoing cooperative motion are in quantitative agreement with experiments.

Neutron spin echo

Dynamics

Langevin equation

Langevin dynamics

10.1021/jp807035z

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Citations (67)

Characterization of star polymers in solution by small angle neutron scattering

Makromolekulare Chemie Macromolecular Symposia (1992)

Lutz Willner O. Jucknischke Dieter Richter Lewis J. Fetters J. S. Huang

Abstract In this paper we present the small angle neutron scattering characterization of two polyisoprene and one poly(ethylenepropylene) star polymers in solution. In the limit of low scattering vector, Q , and low concentration, φ, the molecular characteristics were determined. The molecular weights obtained are in good agreement with light scattering data. Deviations in second virial coefficients are due to a difference in solvent quality. Radii of gyration of the stars are well determined by the use of Kratky plots as is shown by the good agreement with average values of Zimm and Guinier analysis. Additionally, some thermodynamic properties were investigated in dilute and semidilute solutions. We have found that the concentration dependence of the osmotic compressibility is influenced by an expected step at the overlap concentration in both concentration regions.

Radius of gyration

Gyration

Characterization

Biological small-angle scattering

10.1002/masy.19920610110

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Citations (1)