Search results for "Neutron spin echo"
showing 6 items of 6 documents
Some Things We Can Learn from Chemically Realistic Polymer Melt Simulations
2005
We present in this contribution results from Molecular Dynamics (MD) simulations of a chemically realistic model of 1,4-polybutadiene (PB). The work we will discuss exemplifies the physical questions one can address with these types of simulations. We will specifically compare the results of the computer simulations with nuclear magnetic resonance (NMR) experiments, neutron scattering experiments and dielectric data. These comparisons will show how important it is to understand the torsional dynamics of polymers in the melt to be able to explain the experimental findings. We will then introduce a freely rotating chain (FRC) model where all torsion potentials have been switched off and show …
Chain Motion in an Unentangled Polyethylene Melt: A Critical Test of the Rouse Model by Molecular Dynamics Simulations and Neutron Spin Echo Spectros…
1998
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.
Dynamics at the Temperature Crossover in Dilute Polymer Solutions Investigated by Neutron Spin-Echo Spectroscopy
1980
Applying ultrahigh-resolution neutron spin-echo spectroscopy the existence of a $q$-dependent temperature crossover in the dynamics of dilute polymer solutions was proved. It is associated with the transition from $\ensuremath{\theta}$ to good solvent conditions. At small momentum transfers $q$ a nearly stepwise increase of the reduced quasielastic linewidth versus the reduced temperature was observed. With increasing $q$, both the sharpness of the transition and the step height decrease.
Atomistic Molecular Dynamics Simulations of the Static and Dynamic Properties of a Polyethylene Melt
1999
I will discuss in this work the atomistic modelling of polymer melts using Molecular Dynamics (MD) simulations. After a general introduction into the problems one faces in the computer simulation of polymers in general and the atomistic simulations in particular, I will present some recent work on the atomistic modelling of an — C 100 H 202 melt,i.e. short chain polyethylene (PE). The aim of this work is to establish a quantitatively validated atomistic model which then can be used in two directions. One direction is the generation of input for the calibration of parameters in coarse-grained models, which in turn can be used to simulate the polymer under investigation over a much broader te…
A Ramsey apparatus for the measurement of the incoherent neutron scattering length of the deuteron
2008
Abstract A Ramsey apparatus for cold, polarised neutrons is described, which enables us to measure neutron precession angles with an absolute accuracy of about 1 ∘ . This is necessary to perform a planned high-accuracy measurement of the incoherent neutron scattering length b i , d of the deuteron. The performance of the apparatus is demonstrated in systematic stability measurements as well as in two selected examples using samples containing polarised nuclear spins.
Dynamical Scaling in Polymer Solutions Investigated by the Neutron Spin-Echo Technique
1979
Chain dynamics in polymer solutions was investigated by means of the recently developed neutron spin echo spectroscopy. — By this technique, it was possible for the first time to verify unambiguously the scaling predictions of the Zimm model in the case of single chain behaviour and to observe the cross over to many chain behaviour. The segmental diffusion of single chains exhibits deviations from a simple exponential law, indicating the importance of memory effects. Mit Hilfe der erst kurzlich entwickelten Neutronen-Spin-Echo-Spektroskopie wurde die Kettendynamik von Polymermolekulen im gelosten Zustand untersucht. - Die Methode eroffnete die Moglichkeit, zum ersten Mal fur das Einzelkette…