Search results for "neutron"
showing 10 items of 2330 documents
Surface and Intercalation Chemistry of Polycarboxylate Copolymers in Cementitious Systems.
2009
International audience; The Ca–Al-layered double hydroxide, the so-called AFm phase, is a product of cement hydration. It is shown that the interaction of this phase with anionic polycarboxylate ether (PCE)-based dispersant polymers is not a simple adsorption but a more complex intercalation phenomenon leading to the transient sequestration of the PCE within the AFm crystallites. As a result, part of the PCE is immobilized, forming a layered organo-mineral composite, and does not play its role of a dispersing agent. This article presents, along general considerations on the links between cement chemistry and rheology, a detailed investigation of the formation, structure, and stability of a …
Segmental dynamics in polymer electrolytes
2002
Polymer dynamics in poly(ethylene oxide) (PEO)–salt mixtures is investigated by means of quasi-elastic neutron scattering (QENS). In a previous study, we reported QENS data from the NEAT spectrometer (BENSC) that evidenced, for the first time, a dynamic heterogeneity in PEO–salt mixtures induced by salt addition. This finding is supported by molecular dynamics (MD) simulations carried out by Borodin et al. In agreement with MD simulations, our QENS data revealed two distinct processes: a fast motion corresponding to the bulk polymer and a slower relaxation, which we attribute to formation of PEO–cation complexes. In this paper we present new QENS data from the high-resolution spectrometer I…
Polymer Dynamics in a Polymer-Solid Interphase: Molecular Dynamics Simulations of 1,4-Polybutadiene At a Graphite Surface
2014
A chemically realistic model of 1,4-polybutadiene confined by graphite walls in a thin film geometry was studied by molecular dynamics simulations. The chemically realistic approach allows for a quantitative determination of a variety of experimentally accessible relaxation functions (e.g., dielectric, NMR, or neutron scattering responses). The simulations yield these experimental observables. Additionally, the simulations can be resolved as a function of distance to the solid interface on a much finer scale than experimentally possible, providing a detailed mechanistic picture of the segmental and large scale motions of polymers in the interfacial region between bulk polymer melts and soli…
QENS investigation of filled rubbers
2002
The polymer segmental dynamics is investigated in a series of silica-filled rubbers. The presence of inert fillers in polymers greatly affects the mechanical and physical performance of the final materials. For example, silica has been proposed as a reinforcing agent of elastomers in tire production. Results from quasielastic neutron scattering and Dynamic Mechanical Thermal Analysis (DMTA) measurements are presented on styrene–ran-butadiene rubber filled with silica. A clear indication is obtained of the existence of a bimodal dynamics, which can be rationalized in terms of the relaxation of bulk rubber and the much slower relaxation of the rubber adsorbed on the filler surface.
Effect of physical aging on the low-frequency vibrational density of states of a glassy polymer
2003
The effects of the physical aging on the vibrational density of states (VDOS) of a polymeric glass is studied. The VDOS of a poly(methyl methacrylate) glass at low-energy (<15 meV), was determined from inelastic neutron scattering at low-temperature for two different physical thermodynamical states. One sample was annealed during a long time at temperature lower than Tg, and another was quenched from a temperature higher than Tg. It was found that the VDOS around the boson peak, relatively to the one at higher energy, decreases with the annealing at lower temperature than Tg, i.e., with the physical aging.
Neutron reflectometry studies on the interfacial width between polystyrene and various poly(alkylmethacrylates)
1999
From neutron reflectometry we have obtained the interfacial width (typically 2-8 nm) between incompatible polymers above the glass transition temperatures. The investigated polymer bilayers consist of a deuterated polystyrene top layer and various poly(alkylmethacrylates) as a bottom layer. We obtained interesting effects of the length of the alkyl group on the interfacial width. Using mean-field theory we calculate Flory-Huggins-Stavermann interaction parameters X from the interfacial width a I data. These results are compared with investigations of the interfacial width between deuterated poly(methylmethacrylate) and respective polyalkyl-methacrylates.
Determination of the conformation of polymers in the amorphous solid state and in concentrated solution by neutron diffraction
1975
Abstract From the coherent neutron scattering on dilute solid solutions of the ordinary polymer within the deuterated polymer, conformation parameters of polymer chains in amorphous solid states can be determined. In this way vitreous poly(methyl methacrylate) (PMMA) has been investigated. The chains form unperturbed coils and the radius of gyration is very near to the corresponding value in dilute solutions of the same polymer in the low molecular θ-solvent butyl chloride. The same principle of measurement has been applied to concentrated solutions of PMMA in D-acetone. The solutions contained 50% polymer, the main part of which (98% and more) was deuterated so that the system was opticall…
Preparation and determination of the structure of high-performance polymer blends by small-angle neutron scattering
1995
Amorphous blends from a deuterated polyaryletherketone and a polyetherimide have been prepared and investigated by neutron scattering. The used components differ remarkably in their structure antheir solution properties. The blends on the other hand are combinatorial mixtures : the scattering quantity Φ 1 Φ 2 /S(q) is independent of the composition of the blends if the polymer chains have the same length
Relaxation processes and glass transition of confined polymer melts: A molecular dynamics simulation of 1,4-polybutadiene between graphite walls.
2017
Molecular dynamics simulations of a chemically realistic model for 1,4-polybutadiene in a thin film geometry confined by two graphite walls are presented. Previous work on melts in the bulk has shown that the model faithfully reproduces static and dynamic properties of the real material over a wide temperature range. The present work studies how these properties change due to nano-confinement. The focus is on orientational correlations observable in nuclear magnetic resonance experiments and on the local intermediate incoherent neutron scattering function, Fs(qz, z, t), for distances z from the graphite walls in the range of a few nanometers. Temperatures from about 2Tg down to about 1.15Tg…
The structure of high-performance polymer blends by small-angle neutron scattering
1997
Abstract Amorphous blends from a deuterated polyaryletherketone and a polyetherimide have been prepared and investigated by small-angle neutron scattering (SANS). The blends are combinatorial mixtures: the scattering quantity Φ1Φ2/S(q) is independant of the composition of the blends.