Dynamics of poly(oxyethylene) melts: Comparison of 13C nuclear magnetic resonance spin-lattice relaxation and dielectric relaxation as determined from simulations and experiments
Abstract
Molecular dynamics simulations of poly(oxyethylene) (POE) melts have been performed using a previously derived quantum-chemistry-based force field. Local chain dynamics for POE melts in the form of 13C nuclear magnetic resonance (NMR) spin-lattice relaxation times (T1) and NOE values and dielectric relaxation behavior have been determined from molecular dynamics simulations and compared with experimental measurements. 13C NMR T1 and NOE values for the methyl, α, and interior carbons from molecular dynamics simulations are in good agreement with experimental values over a wide range of temperatures. Similar agreement is seen for the dielectric relaxation strength and maximum dielectric loss frequency as a function of temperature. Non-Arrhenius behavior is seen for the correlation times of the PCH2 orientational autocorrelation function (OACF), the molecular dipole moment OACF, and the torsional autocorrelation function (ACF). Very close correspondence between the torsional ACF and the molecular dipole moment OACF indicates that dielectric relaxation in POE melts is due almost exclusively to local conformational motions. © 1997 American Institute of Physics.