On the nature of enhanced segmental mobility at entangled amorphous polymers interfaces

The long-range segmental mobility at symmetric polymer–polymer interfaces and in the polymer bulk has been compared by employing the adhesion approach and differential scanning calorimetry, respectively, by the example of the nascent and vacuum-dried powders of an entangled random-coiled ultra-high-molecular-weight polystyrene (UHMWPS) with a molecular weight of 10⁶ g/mol. It has been shown that the depression in the surface glass transition temperature of UHMWPS with respect to its bulk glass transition temperature cannot be explained by plasticisation of a near-surface nanometre-thick layer via the surface segregation of the solvent and/or monomer residues. Driving forces of the enhanced long-range segmental mobility in ultrathin polymer layers have been discussed.