Fragility in liquids and polymers: New, simple quantifications and interpretations

In order to provide a firmer base for efforts to interpret the different fr agilities of liquids (i.e., the different deviations from simple Arrhenius temperature dependence of relaxation processes), a new and simple one-scan method of quantifying fragility is described and verified. It is based on d etecting, by simple differential thermal analysis (DTA), the temperature of maximum energy dissipation during temperature scanning under single-freque ncy excitation (electrical or mechanical) of the liquid. The frequency is c hosen so that the DTA signal indicates directly not only T-g but also the t emperature T-1/2 (where the relaxation time reaches 10(-6) s) of the new an d unambiguous fragility metric F-1/2,(1) which is defined by F-1/2 = 2(T-g/ T-1/2) - 1. The measurement is verified against dielectric data for liquids of widely varying fragility. The usefulness of such rapid scan methods in confirming or denying a vibrational density of states origin of fragility i n liquids is considered.