Vogel-Fulcher-Tammann temperature

Unfortunately, reliable experimental estimates of the configurational entropy are unavailable to enable explicit application of the AG model for polymer fluids. Instead, the temperature dependence of t in polymer melts is often analyzed in terms of the empirical Vogel-Fulcher-Tammann-Hesse (VFTH) equation [103],... [Pg.153]

Most viscosity-temperature relationships for glasses take the form of an Arrhenius expression, as was the case for binary metal alloys. The Vogel-Fulcher-Tammann (VFT) equation is one such relationship. [Pg.293]

A Vogel-Fulcher-Tammann-Hesse equation can be used to characterize the temperature dependence of the relaxation times for these six different degrees of cure, 0.70, 0.75, 0.80, 0.825, 0.90, and 0.95 ... [Pg.143]

The relaxation kinetics of the Arrhenius and Eyring types were found for an extremely wide class of systems in different aggregative states [7,52-54]. Nevertheless, in many cases, these laws cannot explain the experimentally observed temperature dependences of relaxation rates. Thus, to describe the relaxation kinetics, especially for amorphous and glass-forming substances [55-59], many authors have used the Vogel-Fulcher-Tammann (VFT) law ... [Pg.13]

Inserting Eq. (4-16) into Eq. (4-10) gives the Vogel-Fulcher-Tammann-Hesse equation, where now the Vogel temperature To = U/A.2R can be computed from the energy U between trans and gauche states. The values of U obtained indirectly in this way, using... [Pg.204]

It appears, however, that the mode-coupling theory is not able to explain some of the most significant slow-relaxation processes of these more complex glass formers. In particular, it cannot explain the success of the Vogel-Fulcher-Tammann-Hesse (VFTH) equation for the temperature-dependence of the relaxation time near the glass transition. The mode-coupling theory predicts instead a power-law dependence of the longest relaxation... [Pg.216]

CONSISTENCY OF THE VOGEL - FULCHER - TAMMANN (VFT) EQUATIONS FOR THE TEMPERATURE-, PRESSURE-, VOLUME-AND DENSITY- RELATED EVOLUTIONS OF DYNAMIC PROPERTIES IN SUPERCOOLED AND SUPERPRESSED GLASS FORMING LIQUIDS/SYSTEMS... [Pg.93]

In order to determine the structural relaxation times for the octa-O-acetyl-lactose we analyzed dielectric loss spectra of this carbohydrate with use of the Havriliak- Negami function. The temperature dependence of logioTa was fitted to the Vogel- Fulcher- Tammann (VFT) function... [Pg.371]

E0 and the infinite temperature relaxation time To are independent of temperature, and (ii) in the isotropic phase near the I-N transition, the temperature dependence of ts2(T) shows marked deviation from Arrhenius behavior and can be well-described by the Vogel-Fulcher-Tammann (VFT) equation ts2(T) = TyFrQxp[B/(T — TVFF), where tvff, B, and tvft are constants, independent of temperature. Again these features bear remarkable similarity with... [Pg.295]

In the a-process, the viscosity and consequently the relaxation time increase drastically as the temperature decreases. Thus, molecular dynamics is characterized by a wide distribution of relaxation times. A strong temperature dependence presenting departure from linearity or non-Arrhenius thermal activation is present, owing to the abrupt increase in relaxation time with the temperature decrease, thus developing a curvature near T. This dependence can be well described by the Vogel-Fulcher-Tammann-Hesse (VFTH) equation [40, 41], given by Equation 2.1 ... [Pg.17]

The polymer dynamics involves several relaxation processes, some of which start within the vitreous region and cross into high-temperature melts. For example, the fast relaxations of the backbone chain or side groups start near the Vogel-Fulcher-Tammann-Hesse (VFTH) temperature and extend io T>Tc. The linearized VFTH expression is... [Pg.261]

If the free volume shows a linear expansion with the temperature, Vf = Ef(T- T ), where Ef=dVf IdT is its specific thermal expansivity and Tq < Tg is the temperature where the (linearly extrapolated) free volume disappears, one obtains from Eq. (11.7) the well-known Vogel-Fulcher-Tammann-Hesse (VFTH) equation [Vogel, 1921 Fulcher, 1925 Tammann and Hesse, 1926] ... [Pg.447]

In the high-temperature range, both relaxation modes exhibit Vogel-Fulcher-Tammann-Hesse (VFTH) behavior ... [Pg.533]

Vogel-Fulcher-Tammann-Hesse equation or temperature vinyl alcohol... [Pg.714]

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