Evaluation of the Dyre shoving model using dynamic data near the glass temperature.

The temperature dependence of the dynamics of glass-forming systems remains an important fundamental problem in glass physics. Here we use literature data [S. A. Hutcheson and G. B. McKenna, J. Chem. Phys. 129, 074502 (2008)] reanalyzed with the Baumgärtel-Schausberger-Winter (BSW) [M. Baumgärtel, A. Schausberger, and H. H. Winter, Rheol. Acta 29, 400 (1990); M. Baumgärtel and H. H. Winter, ibid. 28, 511 (1989); M. Baumgärtel and H. H. Winter, J. Non-Newtonian Fluid Mech. 44, 15 (1992)] model of complex fluid dynamics to evaluate the Dyre shoving model [J. C. Dyre, N. B. Olsen, and T. Christensen, Phys. Rev. B 53, 2171 (1996); J. C. Dyre, Rev. Mod. Phys. 78, 953 (2006)] that relates the temperature dependence of viscosity to the infinite-frequency shear modulus and its temperature dependence. In Dyre's model, the free-energy barrier for a "flow event" is attributed to the work done in shoving aside the surrounding molecules; the free-energy barrier is proportional to the glassy modulus, which increases as the temperature decreases. In the present work, the glassy modulus was obtained by the extrapolation to zero time or infinite frequency of the Kohlrausch-Williams-Watts (KWW) [G. Williams and D. C. Watts, Trans. Faraday Soc. 66, 80 (1970); F. Kolrausch, Pogg. Ann. Phys. 12, 393 (1847)] and BSW [M. Baumgärtel, A. Schausberger, and H. H. Winter, Rheol. Acta 29, 400 (1990); M. Baumgärtel and H. H. Winter, ibid. 28, 511 (1989); M. Baumgärtel and H. H. Winter, J. Non-Newtonian Fluid Mech. 44, 15 (1992)] functions to experimental data for m-toluidine and sucrose benzoate. It was found that the glassy modulus obtained from the KWW function for m-toluidine and sucrose benzoate [S. A. Hutcheson and G. B. McKenna, J. Chem. Phys. 129, 074502 (2008)] provides a consistent picture of the temperature-dependent dynamics within the framework of the shoving model. A similar analysis using a BSW description of the dynamics provides consistency for the sucrose benzoate but not for the m-toluidine.