The new insight into dynamic crossover in glass forming liquids from the apparent enthalpy analysis

Julio Cesar Martinez-Garcia, Jorge Martinez-Garcia, Sylwester J. Rzoska, Jürg Hulliger
2012 Journal of Chemical Physics  
One of the most intriguing phenomena in glass forming systems is the dynamic crossover (T B ), occurring well above the glass temperature (T g ). So far, it was estimated mainly from the linearized derivative analysis of the primary relaxation time τ (T) or viscosity η(T) experimental data, originally proposed by Stickel et al. ]. However, this formal procedure is based on the general validity of the Vogel-Fulcher- Tammann equation, which has been strongly questioned recently [T. Hecksher et
more » ... [T. Hecksher et al. Nature Phys. 4, 737 (2008); P. Lunkenheimer et al. Phys. Rev. E 81, 051504 (2010); J. C. Martinez-Garcia et al. J. Chem. Phys. 134, 024512 (2011) ]. We present a qualitatively new way to identify the dynamic crossover based on the apparent enthalpy space (H a = d ln τ /d(1/T )) analysis via a new plot ln H a vs. 1/T supported by the Savitzky-Golay filtering procedure for getting an insight into the noise-distorted high order derivatives. It is shown that depending on the ratio between the "virtual" fragility in the high temperature dynamic domain (m high ) and the "real" fragility at T g (the low temperature dynamic domain, m = m low ) glass formers can be splitted into two groups related to f < 1 and f > 1, (f = m high /m low ). The link of this phenomenon to the ratio between the apparent enthalpy and activation energy as well as the behavior of the configurational entropy is indicated.
doi:10.1063/1.4739750 pmid:22897287 fatcat:vd54pjji4na2tldgzvb6clsv7e