Question

Please describe in terms of molecular motion and inter-chain attractive forces, the motion of polymer chains of a viscous polymer film as it is cooled at a constant rate as the sample moves through three temperature regimes:

a. Above Tg

b. Near or at Tg

c. Below Tg

Answer 1

In terms of molecular motion and inter-chain attractive forces, the motion of polymer chains of a viscous polymer film as it is cooled at a constant rate as the sample moves through three temperature regimes:

a) At temperatures above glass transition temperature (T_g) (how much the temperature exceeds the T_g ) - a non-crystalline polymer material behaves like a viscous fluid or like a rubbery , depending on the molecular weight . Above T_g molecular motion or transition and inter-chain attractive forces will takes place as free volume increases thus , the motion of polymer chains of a viscous polymer film will occur.

b) Near or at T_g - At this point polymer experience transition from glassy state to rubbery state, Loss of modulus (or stiffness) occur and also significant loss of volume take place. Near or At glass transition temperature transition molecular motion and inter-chain attractive forces will remain constant as free volume does not change.

c) Below T_g (how much it is cooled down), a bulk polymer which is described as a glass and it is less or more brittle depending on the structural complexity (and the remaining flexibility might be provided by side-chains) and also reduce in free volume does not allow molecular motion or transition to takes place.