Lasisiirtymällä

Lasisiirtymällä, often translated as "glass transition," is a phenomenon observed in amorphous materials, most notably in polymers and glasses, where a gradual transition occurs from a hard, brittle, glassy state to a softer, more flexible, rubbery or viscous state. This transition is not a sharp melting point like that seen in crystalline solids but rather a temperature range where the material's mechanical and thermal properties change significantly.

The molecular explanation for the glass transition lies in the restricted motion of polymer chains or molecular segments. Below the glass transition temperature, often denoted as Tg, molecular motion is largely confined to vibrations. As the temperature increases and approaches Tg, sufficient thermal energy is available for larger segments of the polymer chains to undergo cooperative rotational and translational movements. This increased mobility leads to a decrease in stiffness and an increase in ductility.

The Tg is a crucial parameter in determining the suitability of a material for a particular application. For instance, materials designed to be rigid at room temperature must have a Tg significantly above ambient temperatures. Conversely, elastomers or rubbers are characterized by a Tg below room temperature, allowing them to remain flexible. The Tg can be influenced by factors such as molecular weight, the presence of plasticizers, crosslinking, and the chemical structure of the material. Techniques like differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) are commonly used to measure the Tg of amorphous materials.