Viscosity-temperature function for sorbitol from combined viscosity and differential scanning calorimetry studies

Physical Processes

“…In Eq. 3.21, z * is inversely proportional to the configurational entropy that increases with T so that both z * and the effective activation energy (i.e., z * Δμ) decrease with T. Note that even before the first applications [30,46] of isoconversional methods to the glass transition kinetics, the trend for the activation energy to decrease with increasing temperature was observed in other studies [47][48][49]. In them, the activation energy was determined from the shift in the value of T g with the heating rate in accord with the equation proposed by Moynihan et al: [42,43] (3.…”

“…However, the value of T g can be defined in the order of its increase as the onset temperature, the temperature of the midpoint step in the heat flow, and the endset temperature. For the glass transition of sorbitol, Angell et al [47] have found that Eq. 3.22 gives rise to a significantly larger E when T g is determined as the onset temperature than when T g is estimated as the temperature of the heat capacity peak.…”

Variation of the Effective Activation Energy Throughout the Glass Transition

“…The decrease in the effective activation energy on transition from the glassy to liquid state has been detected by several workers who used several different definitions of T g in Equation (3). For the glass transition of sorbitol, Angell et al [31] have found that Equation (3) gives rise to a significantly larger E when T g is determined as the onset temperature than when T g is estimated as the temperature of the heat capacity peak. A similar effect was reported by Lacey et al [32] for polystyrene oligomer and side-chain polysiloxane, and by Hancock et al [33] for some pharmaceutical glasses including poly(vinylpyrrolidone), indomethacin, and several sugars.…”

Comparative Relaxation Dynamics of Glucose and Maltitol

“…Low variability of the effective activation can be expected only for the strong glass-forming systems such as B 2 O 3 and As 2 Se 3 that were used in the original work by Moynihan et al (20) Their respective dynamic fragilities, m, are 32 (23) and 37 (24). On the other hand, for sorbitol (m = 93 (23)) Angell et al (25) obtained a significantly smaller E when T g is taken as the temperature of the heat capacity peak than when it is estimated as the onset temperature. A decrease in the E values determined, respectively, from the onset, midpoint, and offset temperature was also observed by Hancock et al (26) on heating and on cooling of several glassy sugars, including sucrose, raffinose, trehalose, and lactose.…”