Dynamical and orientational structural crossovers in low-temperature glycerol.

Area of Science:

• Condensed matter physics
• Materials science
• Chemical physics

Background:

• Incoherent elastic neutron scattering reveals kinks in hydrogen atom mean-square displacements in glass-formers and proteins.
• This dynamical transition is often attributed to the freezing of molecular modes when relaxation times match the observation window.

Purpose of the Study:

• Investigate the origin of the dynamical transition in glass-forming glycerol using molecular dynamics simulations.
• Clarify the nature of the observed crossovers and their relationship to material properties.

Main Methods:

• Extensive molecular dynamics simulations of glycerol.
• Analysis of center-of-mass translations and molecular rotations.
• Calculation of the orientational Kirkwood factor and dielectric constant.

Main Results:

• The dynamical transition occurs at the same temperature for both translational and rotational dynamics, independent of the observation window.
• Glycerol exhibits a dynamic crossover from structural to secondary relaxation at the transition temperature.
• A discontinuous increase in the orientational Kirkwood factor and dielectric constant is observed at the transition.

Conclusions:

• The dynamical transition in glycerol is dynamic in character, not a true thermodynamic phase transition.
• Observed crossovers are dynamic, with the dielectric constant increase linked to the freezing of dipolar domains on simulation timescales.