Glasübergang

Glasübergang refers to a reversible physical change in amorphous solids, such as polymers and glass, where they transition from a hard, brittle state to a softer, more pliable state. This transformation occurs over a specific temperature range known as the glass transition temperature (Tg). Below Tg, the material behaves like a rigid, glassy solid with a highly ordered molecular structure. Above Tg, the material enters a rubbery or leathery state, allowing for some molecular motion and increased deformability.

The glass transition is not a true phase transition like melting, which involves a distinct change in enthalpy. Instead, it is characterized by a change in the material's properties, such as viscosity, heat capacity, and thermal expansion coefficient. The exact Tg of a material depends on its chemical composition, molecular weight, and the presence of plasticizers or other additives. For example, pure silica glass has a very high Tg, while many polymers used in everyday objects have lower glass transition temperatures that allow them to be molded and shaped.

Understanding the glass transition is crucial in material science and engineering. It dictates the processing conditions for many materials, influencing how they can be molded, extruded, or formed into desired shapes. It also determines the service temperature range for products made from these materials, as exceeding Tg can lead to loss of structural integrity and deformation. Researchers continuously study the glass transition to develop materials with tailored properties for specific applications.