Manifestation Of Glass Transition Research Articles

Manifestation of glass transition in electronic charge transport in Si and Ge Backbone polymers

Electronic transport of photoinjected holes in high molecular weight linear polymers with silicon and germanium backbone is electric field dependent and thermally activated. At fixed electric fields, during both rate and step heating, the mobility activation energies (ϵ) in all these polymers change abruptly and reversibly at critical temperatures (ifT c) without concurrent abrupt changes in mobilities. These critical temperatures coincide with the respective glass transition temperatures. In all cases, ϵ at T > T g is lower than ϵ at T < T g, typically by a factor of 2 to 3. In polymers with aliphatic side groups ϵ ( T > T g) is extremely low, practically approaching zero. The change of activation near T g is similar to that observed in amorphous charge-transporting polymers and other glasses, including selenium and its alloys. The universality of this phenomenon is emphasized.

On mechanisms of structural relaxation in a Pd48Ni32P20 glass

Abstract Structural relaxation processes are investigated calorimetrically for a pre-conditioned Pd48Ni32P20 glass over a wide temperature range from well below to just above the glass transition. The low temperature anneals further stabilize the glassy structure. Upon heating, the annealed sample shows an excess endothermic specific heat ΔCp above the annealing temperature and completely recovers the initial enthalpy before any manifestation of glass transition, Tg. Significantly the ΔCp peak evolves in a continuous manner with annealing time. A physically reasonable activation energy spectrum N 0 ∗ (Q) is obtained with the proper choice of coupling constants which are dependent on annealing temperature. Results suggest the existence of localized relaxation modes which do not contribute to macroscopic flow. A concept of distribution in glass transition temperatures H(Tg,m) is conceived to account for the reversible relaxation with temperature. A model glass transition based on percolation theory is proposed and is found to reproduce the calorimetric relaxation phenomena well.