Microscopic nature of the Johari-Goldstein secondary relaxation · revision history

Revision 2

Accepted · core change · record

Changes against revision 1:

Title
Microscopic nature of the Johari-Goldstein secondary relaxation
Plain
Below the glass point most molecules are frozen, yet glasses of even rigid molecules still show a faster, smaller relaxation, the Johari-Goldstein $\beta$ process. Which molecular motions produce it, and whether it is the precursor of the main relaxation, is disputed.
Precise · changed · core
Revision 1: In molecular glass formers, including glasses of rigid molecules, dielectric and mechanical spectra show a secondary $\beta$ relaxation that persists below $T_g$ with Arrhenius $\tau_\beta(T)$ and an empirical activation energy of roughly $24\ k_B T_g$ per molecule (approximate). Determine whether it is carried by localized islands of mobility or by small-angle motion of all molecules, and whether it is the precursor of the alpha relaxation as assumed in coupling-type models. An answer identifies the motions in a model glass equilibrated near or below T_g and reproduces the measured $\beta$ peak and its link to $\tau_\alpha$.
Revision 2: In molecular glass formers, including glasses of rigid molecules, dielectric and mechanical spectra show a secondary $\beta$ relaxation that persists below $T_g$ with Arrhenius $\tau_\beta(T)$ and an empirical activation energy of roughly $24\ k_B T_g$ per molecule (approximate). Determine whether it is carried by localized islands of mobility or by small-angle motion of all molecules, and whether it is the precursor of the $\alpha$ relaxation as assumed in coupling-type models. An answer identifies the motions in a model glass equilibrated near or below $T_{g}$ and reproduces the measured $\beta$ peak and its link to $\tau_\alpha$.
Settled by
Simulation of a swap-equilibrated model glass that resolves which particles and motions produce the $\beta$ peak and reproduces its activation energy and its relation to $\tau_{\alpha}$, consistent with NMR and dielectric data.
Kind
phenomenon
Answer type
mechanism
References
(empty)
Literature status
contested
Status note
(empty)
Posed since
1970

Decisions