Molecular packing, temperature-induced

It appeared that the fractional free-volume in filled systems increased in proportion to the polymer fraction in the surface layer, determined independently, and ranging from 0.025 to 0.043. This fact was explained by the diminishing molecular packing density on the surface. There was at the same time a decrease in the temperature Tq-The findings indicate that the criterion of constancy of the free-volume fraction at T% cannot be applied to filled systems because of the influence of the filler on the polymer structure. Thus, even for one and the same polymer, the difference in its physical structure induced by physical actions capable of changing the structure causes polymer behavior to deviate from that predicted within the framework of the iso-firee-volume concept. 

It has recently been shown that introduction of a small, hydrophobic molecule like isoprene may lead to a more ordered and better packed lipid membrane as revealed by MD simulations. The stabilized membrane is then protected against temperature-induced disordering of the tails. Similar thermoprotective effects are induced by cholesterol which also increases the molecular packing of the tails and, in contrast to isoprene, affects the dynamics of the lipids in the bilayer. ... 

The mechanism of improving hardness and wear resistance is supposed to be the dense packing of molecules induced by chain scission at the Tg. The original PC has an amorphous structure, where the free volume may exist among the entanglanent molecules. The small amount of chain scission at Tg temperature induces the molecular rearrangement to result in an increase of density, that is, dense packing of molecules. 

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