What is the distinction between glass transition temperature and melting temperature?

Glass transition temperature (Tg) is the temperature at which an amorphous solid, such as a glass or a polymer, transitions from a hard, brittle state to a more flexible, rubbery state. This transition is not a phase change like in the case of melting, and it occurs over a range of temperatures. At the glass transition temperature, the material's mechanical and thermal properties change, but the material remains a disordered, amorphous solid. #

Melting temperature (Tm) is the temperature at which a solid material transitions from the solid phase to the liquid phase. This phase change involves a change in the molecular arrangement of the material. In crystalline materials, the molecules or atoms are arranged in an orderly, repeating pattern. As the temperature increases and reaches the melting point, the material's structure breaks down, and the material becomes a liquid with a random arrangement of molecules or atoms. Melting occurs at a specific temperature for a given material under constant pressure. #

1. Glass transition occurs in amorphous solids, while melting occurs in crystalline materials. 2. Glass transition temperature (Tg) is a range of temperatures, whereas melting temperature (Tm) occurs at a specific temperature under constant pressure. 3. During glass transition, the material's mechanical and thermal properties change, but the material remains a disordered, amorphous solid. In contrast, melting involves a phase change from solid to liquid, with a change in molecular or atomic arrangement. 4. Glass transition does not involve the breaking of chemical bonds, but melting involves breaking bonds in the crystalline structure. 5. The glass transition temperature is generally lower than the melting temperature of a material.