Neutron spin-echo investigations on the dynamics of polymers

Abstract

Neutron spin-echo spectroscopy allows the observation of long-range internal relaxation mechanisms of macromolecules simultaneously in space and time. Thereby, it facilitates a microscopic study of molecular models applied for the explanation of macroscopic viscoelastic properties of polymer materials. After a short outline of the method, this paper discusses experimental results on chain relaxation in dilute solution of linear as well as of branched polymer chains choosing the star polymer as a prototype. Thereafter, chain motion in dense polymer systems under varying topological constraints is addressed. Results on concentrated solutions, melts and chains trapped in networks with different mesh sizes are presented and compared with theoretical models. Finally aspects of the dynamics of polymer networks are discussed and spin-echo results on the motion of labelled cross links are presented.

Neutron Spin Echo Investigations on the Segmental Dynamics of Polymers in Melts, Networks and Solutions

“…Neutron Spin Echo Investigations on the Segmental Dynamics 13 13 In Eq. (19) we used the fact that the mean square displacement of the center-ofmass provides the diffusion constant according to D 0 "(1/6t)1(x (t)!x (0))2.…”

“…In the equation of motion (13), the friction force with the solvent is now added to the entropic force. The flow field v(r ) is the result of all forces exercised on the solvent by all other segments…”

“…Here, quasi-elastic scattering methods play a crucial role since they allow the measurement of the corresponding correlation functions. In particular, the high-resolution neutron spin echo (NSE) spectroscopy [12][13][14][15] is very suitable for such investigations since this method covers an appropriate range in time (0.005)t/ns)40) and space (r/nm :15). Furthermore, the possibility of labelling by hydrogen-deuterium exchange allows the observation of single-chain behavior even in the melt.…”

Polymer Dynamics in Block Copolymer Electrolytes Detected by Neutron Spin Echo

“…LiTFSI was added to the copolymer blends such that the final molar salt ratios, , were 0, 0.025, 0.075, and 0.10. The block copolymer system was designed such that the NSE data are dominated by relaxation of the PEO segments as they interact with salt ions; in particular, the incoherent background from the PEO chains is minimized at the scattering vectors, Q , chosen for NSE …”

“…The block copolymer system was designed such that the NSE data are dominated by relaxation of the PEO segments as they interact with salt ions; in particular, the incoherent background from the PEO chains is minimized at the scattering vectors, Q, chosen for NSE. 39 Small-angle neutron scattering (SANS) experiments were performed at 90 °C on the NGB-30m beamline at the NIST Center for Neutron Research (NCNR, Gaithersburg, MD). Sample preparation for the SANS experiments is described elsewhere.…”