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Gaussian excitations model for glass-former dynamics and thermodynamics Dmitry V. Matyushova
 

Summary: Gaussian excitations model for glass-former dynamics and thermodynamics
Dmitry V. Matyushova
Department of Chemistry and Biochemistry and Department of Physics, Arizona State University,
P.O. Box 871604, Tempe, Arizona 85287-1604
C. Austen Angellb
Department of Chemistry and Biochemistry, Arizona State University, P.O. Box 871604,
Tempe, Arizona 85287-1604
Received 21 November 2006; accepted 11 January 2007; published online 6 March 2007
We describe a model for the thermodynamics and dynamics of glass-forming liquids in terms of
excitations from an ideal glass state to a Gaussian manifold of configurationally excited states. The
quantitative fit of this three parameter model to the experimental data on excess entropy and heat
capacity shows that "fragile" behavior, indicated by a sharply rising excess heat capacity as the glass
transition is approached from above, occurs in anticipation of a first-order transition--usually
hidden below the glass transition--to a "strong" liquid state of low excess entropy. The distinction
between fragile and strong behavior of glass formers is traced back to an order of magnitude
difference in the Gaussian width of their excitation energies. Simple relations connect the excess
heat capacity to the Gaussian width parameter, and the liquid-liquid transition temperature, and
strong, testable, predictions concerning the distinct properties of energy landscape for fragile liquids
are made. The dynamic model relates relaxation to a hierarchical sequence of excitation events each
involving the probability of accumulating sufficient kinetic energy on a separate excitable unit.

  

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

 

Collections: Materials Science; Chemistry