A structural model for the amorphous state of polymers: Folded-chain fringed micellar grain model

A more realistic, two-phase structural model is proposed for the amorphous solid state of polymers. The model is based on structural evidence reported to date, in particular the evidence from our own electron diffraction and microscopy studies of crystallizable and non-crystallizable amorphous polymers, including near-molten rubbers. This model is different from either Kargin's chain-packet or Hose-mann's paracrystalline model. The two major elements of the model are the grain, which consists of an ordered domain and a distinct grain boundary, and the intergrain region, which consists of molecules that are in a more truly random conformation. In the ordered domain (∼20∼40 Å) the molecular chain segments are aligned parallel to one another with a nearly constant spacing. A natural consequence of the present model is the concentration of excess free volume in the intergrain region. The amount of excess free volume has been estimated for typical polymers in their glassy amorphous state and found to be large for polymers that possess good ductility, but small for brittle polymers. Phenomena, such as the contributions of changes in entropy and energy to the rubbery elastic force, the increasingly extended rubbery plateau with increasing molecular weight, the non-Newtonian behavior of viscous flow and lamella crystallization and formation, are also discussed and appear to be consistent with the proposed two-phase granular model.