New insights into the fragility dilemma in liquids

Abstract

A compilation of data for small molecule organic, polymeric, and inorganic glass-forming liquids shows that the original expectation, that there be a positive correlation between the thermodynamic measure of fragility Cpl/Cpg (or Cpl/Cpc) and the dynamic fragility index m, is not generally true. The results are consistent with three classes of behavior: (1) a decrease in m with increasing Cpl/Cpg for the polymeric glass formers; (2) a nearly constant value of m independent of Cpl/Cpc for small molecule organics and hydrogen bonding small molecules; (3) an increasing value of m with increasing Cpl/Cpc for inorganic glass formers as originally considered by Angell.