Meyer-Neldel Compensation as a feature of the Johari-Goldstein Beta relaxation


  Shimon E Lerner [1]  ,  Paul Ben Ishai [2]  ,  Yuri Feldman [2]  
[1] JCT Lev Academic Center
[2] Hebrew University of Jerusalem

   Despite its appearance in a large number of glass formers the full scope of the Johari-Goldstein beta-relaxation is not yet completely understood.  It is clear that it originates on the molecular level, often serving as a precursor to the a-relaxation. Relations between the Activation Energy and the Glass Transition Temperature (Tg) have been extensively studied and analyzed. We wish to introduce a new ubiquitous relation, one involving the Activation Energy on the one hand and the minimal relaxation time on the other.

   Collected data from a wide array (>80) of glass formers show a common feature in the behavior of the prefactor of these relaxations. They all obey the Meyer-Neldel compensation law linking the relaxation behavior to the entropy of a multi-exitation process. The glass formers involved include; Hydrogen bonded networks (simple as well as poly alcohols), van der Walls liquids, hydrated proteins,  polymer blends,  small organic molecules, epoxy systems, saccarides and some others as well. This connection between the Activation Energy and the relaxation precursor has been noted in isolated instances before, but never characterized as a universal feature. 

  It shall be demonstrated that this relation shows much promise towards improving our understanding of glass formers. The universal behavior must be intrinsically connected to the microscopic origins of the process and should help shed light on its nature. It may also help provide a definitive way of distinguishing between different types of beta relaxation, as well as a clear indication when an excess wing actually emanates from such a process. A preliminary explanation for this universal feature is provided and its implications are discussed.