Glasövergångst

Glasövergångst is a Swedish term that translates to "glass transition" in English. It refers to a phenomenon observed in amorphous materials, particularly polymers and glasses, where a material changes from a hard, brittle, glassy state to a softer, more flexible, rubbery state. This transformation is not a sharp melting point but rather a gradual change in physical properties over a specific temperature range.

The glass transition temperature, often denoted as Tg, is the temperature at which this transition occurs. Below Tg, the polymer chains are largely frozen in place, leading to a rigid structure. Above Tg, the polymer chains gain enough thermal energy to move more freely, allowing the material to deform under stress. This molecular motion is the underlying cause of the observed change in mechanical properties.

Factors influencing the glass transition temperature include the molecular weight of the polymer, the presence of plasticizers which lower Tg by increasing chain mobility, and the cross-linking density, which generally increases Tg by restricting chain movement. The glass transition is a crucial property for material scientists and engineers as it dictates the temperature range within which a material can be effectively used for its intended application. For example, materials used in cold environments need a Tg well below the operating temperature, while those intended for high-temperature applications must have a Tg significantly above it.