Lasisinirtymä

Lasisinirtymä, also known as the glass transition, is a phenomenon observed in amorphous solids, most notably polymers, where a transition occurs between a hard, glassy state and a more flexible, rubbery state. This transition is not a true phase transition like melting or boiling, which involves a change in heat capacity and a latent heat. Instead, it is a kinetic phenomenon that depends on the cooling rate.

At temperatures below the glass transition temperature (Tg), the molecular segments of the amorphous material have very limited mobility. The material is rigid and brittle, behaving like a solid. As the temperature increases and reaches Tg, sufficient thermal energy is available for larger segments of the polymer chains to begin to move. This increased molecular motion allows the material to deform more easily, transitioning into a softer, more pliable state.

The glass transition temperature is a characteristic property of a given amorphous material and is influenced by factors such as molecular weight, branching, cross-linking, and the presence of plasticizers. It is an important parameter in material science and engineering, as it dictates the service temperature range for many polymeric materials. For instance, a polymer used in a cold environment needs to have a Tg below the expected operating temperature to remain flexible, while a material intended for high-temperature applications will have a significantly higher Tg.