Dynamics of glass-forming liquids. II. Detailed comparison of dielectric relaxation, dc-conductivity, and viscosity data

Abstract

We have studied the temperature dependence of dielectric relaxation times in terms of the peak frequency f max (T) of dielectric loss ⑀Љ͑͒ and the dc-conductivity dc (T) of several glass-forming liquids, covering 12 decades in the peak frequency f max and 9 decades in dc . Although dc-conductivity samples the mobility of ionic tracers, its variation with temperature is similar to that of f max (T). The f max (T) and dc (T) are analyzed using the temperature-derivative method and compared to the viscosity data Ϫ1 (T). While most liquids reveal a common Vogel-FulcherTammann ͑VFT͒ behavior for f max , dc and Ϫ1 in an extended temperature range TуT m , some liquids deviate from this behavior by displaying a crossover at TϭT A to an Arrhenius regime. In these cases the quantity f max (T) decouples from the common curves for dc (T) and Ϫ1 (T) and attains activation energies in excess ͑ϳ40% for alcohols͒ of those related to translational processes. For many samples a departure from the VFT behavior occurs at lower temperatures T B ϽT m which tends to retard the glass transition. The onset of this qualitative change in the temperature dependence at T B turns out to be a characteristic temperature also in other experiments.

Relationship between the Nonexponentiality of Relaxation and Relaxation Time in the Problem of Glass Transition

“…[7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] At each temperature, and τ were determined from the location and width of the dielectric loss peak, respectively. Prompted by our recent work on the glass transition, [24][25][26] we have plotted log(τ) as a function of 1/ .…”

“…This is consistent with experimental results. 8 The same reasoning applies to the crossover of . V 1 increases on lowering the temperature because V 1 ∝ ln(d el ) in eq 1.…”

Relaxational dynamics in the glassy, supercooled liquid, and orientationally disordered crystal phases of a polymorphic molecular material

“…The interesting point is that this temperature, which also marks the limit of stability of the supercooled liquid, signals a strong departure from Arrhenius behavior of a number of momentum and charge transport properties. 34 The model cannot follow the strong temperature dependence of (T) but still predicts the presence of additional relaxations which show an Arrhenius behavior of their frequencies, and show characteristic residence times HB within 100-350 ps. The failure of Eq.…”

“…In a nutshell, it simply illustrates the breakdown of the Browniandynamics regime, a departure which is also witnessed by several transport properties. 34 …”

Real space origin of temperature crossovers in supercooled liquids

“…(11,17,18). Again, the difference between e s and e IS comes from the clusters of defects which are relaxed during the descent to the inherent structure.…”