What is the glass transition temperature?

The glass transition temperature is specifically relevant to amorphous solids, which include materials like glass and certain polymers. At this temperature, the material transitions from a hard and relatively brittle "glassy" state into a more rubbery or viscous state. This change is not a phase transition like melting; rather, it signifies a change in the molecular motion within the material. Below the glass transition temperature, the molecular chains are more rigid and have limited mobility, while above this threshold, they gain more freedom to move, affecting the material's mechanical properties.

Understanding this concept is essential, especially when working with materials that exhibit amorphous behavior, as it influences their processing and application in various industrial and scientific contexts.