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Fragility and thermodynamics in nonpolymeric glass-forming liquids Li-Min Wang, C. Austen Angell, and Ranko Richert
 

Summary: Fragility and thermodynamics in nonpolymeric glass-forming liquids
Li-Min Wang, C. Austen Angell, and Ranko Richert
Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287-1604
Received 10 April 2006; accepted 6 July 2006; published online 18 August 2006
For nonpolymeric supercooled liquids, the empirical correlation m=56Tg Cp Tg / Hm provides a
reliable means of correlating dynamic and thermodynamic variables. The dynamics are
characterized by the fragility or steepness index m and the glass transition temperature Tg, while
thermodynamics enter in terms of the heat capacity step Cp at Tg and the melting enthalpy Hm.
The combination of the above correlation with the 2/3 rule for the Tg/Tm ratio yields an expression,
m=40 Cp Tg / Sm, which was rationalized as the correlation of the thermodynamic and kinetic
fragilities. Defining a thermodynamic fragility via Cp Tg / Sm also reveals that the slopes in
Kauzmann's original S T / Sm versus T/Tm plot reflect the fragility concept Chem. Rev. 43, 219
1948 , so long as Tm/Tg=1.5. For the many liquids whose excess heat capacity is a hyperbolic
function of temperature, we deduce that the fragility cannot exceed m=170, unless the Tg/Tm
=2/3 rule breaks down. 2006 American Institute of Physics. DOI: 10.1063/1.2244551
I. INTRODUCTION
There has been considerable progress in recent years in
understanding both the glass transition phenomenon and the
structural relaxation dynamics of supercooled liquids. The
concept of fragility categorizes a wide range of liquids in

  

Source: Angell, C. Austen - Department of Chemistry and Biochemistry, Arizona State University

 

Collections: Materials Science; Chemistry