² H-NMR-Stimulated Echo Study of Ultraslow Reorientational Motion in Viscous Glycerol near Its Glass Transition Temperature

Abstract

2H-NMR stimulated echo experiments have been performed in order to study the molecular basis of the a-process in viscous glycerol near its glass transition temperature. Decay functions following modified Jeener-Broekaert pulse sequences were compared with predictions from different models for molecular reorientation. Rotational diffusion, rotational random jumps, rotational fixed-angle jumps and combinations of diffusive and jump motions have been tested. AIl data are fitted with a log-Gaussian distribution of correlation times. Thereby, smallbut finite-angle reorientation processes turn out to dominate in the s . .. loo s regime. Pure large-angle rotational jumps can be ruled out with high significance. The mean rotational correlation time, (7,), agrees with results from other relaxation experiments which monitor the a-process of the glass transition.

Sensitivity of Saturation Transfer Electron Spin Resonance Extended to Extremely Slow Mobility in Glassy Materials

“…[3], T g was found to be 185 K, which is identical to the literature value where h H and h C are the heights of the high field and central lines in the ESR spectra, respectively. DB 0 is the linewidth (20,21). This validates the use of the universal values for the constants C 1 and C 2 in Eq.…”

“…It has been observed the L Љ / L ratio is almost insensitive to T 1 effects, and that in glycerol that in general dynamical processes follow the changes in T 1 are the main cause for sensitivity for motion WLF Eq. [3] (21,28,29). This is also true for the rotational for t R ú 10 03 s. This means that by using the relative correlation times obtained from NMR hole-burning experi-integrated intensity I rel of ST-ESR spectra, the range of ments in glycerol (20).…”

On the nature of the high-frequency relaxation in a molecular glass former: A joint study of glycerol by field cycling NMR, dielectric spectroscopy, and light scattering

“…66 In the case of glycerol, being a nonrigid molecule, again 2 H NMR investigations showed that in the glass transition range the molecules behave as if they were rigid. 67 The 2D NMR experiments analyzed in the time domain and mentioned in the Introduction established the most detailed picture of the reorientation process close to T g . 6,21,36 They showed that the reorientational process close to T g involves predominantly small angle jumps of 2°-3°although also large angle jumps occur.…”

Reorientational dynamics of glycerol derived from temperature‐dependent multi‐nuclear magnetic resonance relaxation data

“…Furthermore, geometrical parameters, known from other sources are included, because the fitted parameters depend on their prefixed values. The distance parameters were obtained from a semi-empirical quantum-mechanical (AM1) calculation, the quadrupole coupling constants are experimental literature values 8,9 and the field-gradient parameter Á Q was set equal to zero. The relaxation rates of the deuterons were fitted together with the 13 C nuclei of the CH 2 group.…”

“…Even, if this were not a problem, however, the separate relaxation rates for the CH and CH 2 groups could not be obtained and again, therefore, a comparison would not be possible. For the deuteron studies, differently substituted glycerols were used: [ 10 The other two articles on deuteron relaxation 9,11 are concerned with the glass transition, and thus cover a different temperature range.…”