INIFTA   05425
INSTITUTO DE INVESTIGACIONES FISICO-QUIMICAS TEORICAS Y APLICADAS
Unidad Ejecutora - UE
artículos
Título:
Numerical determination of the exponents controlling the relationship between time, length, and temperature in glass-forming liquids
Autor/es:
CAMMAROTA, C; CAVAGNA, A.; GRADENIGO, G.; GRIGERA, T. S.; VERROCCHIO, P.
Revista:
JOURNAL OF CHEMICAL PHYSICS
Editorial:
AMER INST PHYSICS
Referencias:
Año: 2009 vol. 131 p. 194901 - 194901
ISSN:
0021-9606
Resumen:
There is a certain consensus that the very fast growth of the relaxation time occurring in glass-forming liquids on lowering the temperature must be due to the thermally activated rearrangement of correlated regions of growing size. Even though measuring the size of these regions has defied scientists for a while, there is indeed recent evidence of a growing correlation length    in glass formers. If we use Arrhenius law and make the mild assumption that the free-energy barrier to rearrangement scales as some power of the size of the correlated regions, we obtain a relationship between time and length, T log au ~ xi^psi. According to both the Adam­-Gibbsand the random first order theory the correlation length grows as      xi ~ (T - Tk)^(-1/(d- heta)) , even though the two theories disagree on the value of heta. Therefore, the super-Arrhenius growth of the relaxation time with the temperature is regulated by the two exponents psi and heta and through the relationship T log au ~  (T - Tk)^(psi/(d- heta)). Despite a few theoretical speculations, up to now there has been no experimental determination of these two exponents. Here we measure them numerically in a model glass former, finding psi= 1 and heta= 2. Surprisingly, even though the values we found disagree with most previous theoretical suggestions, they give back the well-known VFT law for the relaxation time, T log au ~ (T - Tk)^-1.