Description of the Primary Relaxation in Supercooled Liquids through the Timescale Steepness Function
نویسندگان
چکیده
The primary relaxation in glass forming supercooled liquids (SCLs) above the glass transformation temperature Tg is discussed in terms of the first-order (steepness) and the second-order (curvature) temperature derivatives of the observed primary relaxation timescale. We report new insights into the problem of the domain of the Vogel-Fulcher-Tamman (VFT) equation, raised by Stickel et al. (J. Chem. Phys. 102, 6251 (1995), ibid. 104, 2043 (1996)) and discussed by Richert and Angell (ibid. 108, 9016 (1998)). A new ergodic-cluster Gaussian statistical approach to the problem is given based on Onsager’s thermodynamic principle. The primary relaxation is described by the VFT equation below the crossover temperature Tc (known from mode coupling theory (MCT)), and above Tc by an extended (VFTE) equation obtained after accounting for cluster-size fluctuations. The timescale is parametrized by a finite number of observable
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