Glasövergången

Glasövergången, a Swedish term often translated as "glass transition," refers to a phenomenon observed in amorphous materials, particularly polymers and glasses. It is not a sharp melting point but rather a temperature range where the material undergoes a significant change in its physical properties. Below the glass transition temperature (Tg), the material behaves like a rigid, brittle solid. Above Tg, it becomes softer, more flexible, and exhibits rubbery elasticity.

This transition is a kinetic process, meaning it depends on the rate at which the material is cooled or heated. At temperatures below Tg, the molecular chains within the amorphous material have very limited mobility. They are essentially frozen in place. As the temperature increases and approaches Tg, the thermal energy becomes sufficient to allow segments of these molecular chains to begin moving and sliding past each other. This increased molecular mobility leads to the observed softening and increased deformability.

The glass transition is crucial in understanding the behavior and applications of polymers. For instance, a plastic bottle might be rigid and retain its shape at room temperature (below its Tg) but can be easily deformed if heated above its Tg. Conversely, materials designed to be flexible at room temperature will have a Tg below this ambient temperature. Factors like molecular weight, chain structure, and the presence of plasticizers can influence the Tg of a polymer.