Technical Glossary Glass Transition Point / Melting Point

[Glass Transition Point / Melting Point]

The melting point describes the temperature at which a material changes from a solid to a liquid. For most materials, the melting point is the same as the freezing point, at which liquids change into solids.
However, there is another phenomenon seen in inorganic glass, plastic, rubber, and other polymers, called the glass transition point.
For these substances, the temperature below the melting point at which regular crystalline structures do not form, liquid motion stops, is called the glass transition point (Tg).
The glass transition point of polymers is defined as the temperature at which free volume increases and Brownian motion commences. At temperatures below their glass transition points, plastics and glass become brittle. Their physical properties, including elasticity and dielectric permittivity, drastically differ above and below this point.