Hydrogen bond dynamics at the glass transition

Abstract

The glass transition in hydrogen-bonded glass formers differs from the glass transition in other glass formers. The Eshelby rearrangements of the highly viscous flow are superimposed by strongly asymmetric hydrogen bond rupture processes, responsible for the excess wing. Their influence on the shear relaxation spectrum is strong in glycerol and close to zero in PPE, reflecting the strength of the hydrogen bond contribution to the high frequency shear modulus. An appropriate modification of a recent theory of the highly viscous flow enables a quantitative common description of the relaxation spectra in shear, dielectrics, heat capacity and depolarized dynamic light scattering.

Sound absorption in glasses

“…From NMR measurements [117], it is known that an irreversible relaxation in the primary relaxation peak of glycerol is a motion of many molecules, of which only about 2 percent make large angle (30 to 50 degrees) jumps; the rest make small angle jumps of a few degrees. With this information in mind, it seems possible that the excess wing is due to reversible reorientational jumps of single hydrogen bonds [118] in strongly asymmetric double-well potentials, similar to the fast reversible hydrogen bond jumps in water [119], the large dipole moment change providing a signal strength able to compensate the weakening factor from the strong asymmetry.…”