lasisiirtymälämpötilaa

Lasisiirtymälämpötila, often abbreviated as Tg, refers to the temperature at which an amorphous solid, such as glass or certain polymers, transitions from a hard, brittle, glassy state to a softer, more pliable, rubbery state. This transition is not a sharp melting point like that of crystalline solids, but rather a gradual change in physical properties over a temperature range. Below Tg, the material behaves like a solid with a high viscosity, while above Tg, it exhibits a significantly lower viscosity, becoming more deformable.

The glass transition is a second-order thermodynamic transition, meaning that certain thermodynamic properties like heat capacity change abruptly at Tg, but enthalpy and entropy do not. This phenomenon is crucial in the processing and application of many materials. For instance, polymers are often heated above their Tg to allow for molding or extrusion. Conversely, materials are cooled below their Tg to ensure structural integrity and prevent deformation under stress. The specific Tg value varies greatly depending on the chemical composition and molecular structure of the amorphous material. Factors such as chain flexibility, intermolecular forces, and the presence of plasticizers can influence the glass transition temperature. Understanding Tg is therefore essential for predicting material behavior and designing products for specific environmental conditions and performance requirements.