Dynamics of the α relaxation of a glass-forming polymeric system: Dielectric, mechanical, nuclear-magnetic-resonance, and neutron-scattering studies

Abstract

The dynamics of the a relaxation in a glass-forming polymeric system, poly(vinyl methyl ether) (PVME) has been studied by means of dielectric and mechanical spectroscopies and nuclear magnetic resonance, as well as by means of quasielastic neutron scattering. By using these techniques we have covered a wide time scale ranging from mesoscopic to macroscopic times (10 ' -10' sec). The dielectric and mechanical data have been interpreted in terms of a Havriliak-Negami relaxation function, NHN.Nuclear-magnetic-resonance data were interpreted by means of a spectral density function J(e) based on C&HN. Neutron-scattering data were described in terms of a scattering law S(Q, co) which was also built starting from @HN. The results obtained from different experimental techniques indicate that the dynamics of the a relaxation in PVME can be well described by means of (i) a common temperatureindependent spectral shape and (ii) a common temperature behavior of the relaxation times. We deduce for the spectral shape very similar parameters by fitting the Havriliak-Negami relaxation function to the different experimental data. These shape parameters are found to be not very sensitive to changes of temperature. The resulting characteristic relaxation times follow a Vogel-Fulcher-like temperature behavior in the temperature range T~-5 K& T& T +150 K. Therefore, this implies a self-consistent description of the dynamics of the a relaxation obtained by very different probes in PVME.

Comparison of glass formation kinetics and segmental relaxation in polymers

“…Such a trend is not unusual, having previously been seen in PVE [58], polyisoprene [59], and PVAc [60]. On the other hand, a b that is nearly independent of temperature is found for many amorphous polymers, including poly(propyleneglycol) [61,62], poly(vinylmethylether) [63,64], and poly(styreneco-vinylphenol) [16].…”

Correlated ion hopping in single-crystal yttria-stabilized zirconia

“…The HN function was first introduced by Havriliak and Negami 8 to describe the relaxation of glass-forming polymeric systems and it has been frequently used with this purpose afterwards. 9 It takes the form…”

Electron spin–lattice relaxation of nitroxyl radicals in temperature ranges that span glassy solutions to low-viscosity liquids

“…8), the slopes of the curves were much steeper than for the experimental rates (Figure 9). NMR relaxation studies in viscous solution indicate that 1/T 1 may not follow the BPP spectral density [44,45], which is attributed to a distribution of tumbling correlation times that can be modeled with a Cole-Davidson spectral density function (Eq. (9)) [18,19,22,45].…”