Physics
Understanding Glass Transition Temperature in Polymer Materials
Quick fact
The glass transition is not a true phase transition like melting; it's a kinetic effect, meaning the measured Tg depends on how fast you cool or heat the material. That's why the same polymer might have different Tg values in different labs or applications.
Why this is interesting
You've noticed that a plastic spoon bends before it snaps, but a hard candy cracks when you try to bend it. What decides whether a material is stiff and brittle or soft and flexible? It's not melting—it's a hidden 'glass transition' that even plays a role in your chocolate bar's texture.