Publisher’s Note: “Polymer-specific effects of bulk relaxation and stringlike correlated motion in the dynamics of a supercooled polymer melt” [J. Chem. Phys. 119, 5290 (2003)]

Abstract

FIG. 8. Temperature dependence of the ratio of ͗s seg (t str max)͘ and ͗s(t str max)͘. t str max is the peak time of ͗s seg ͘ and ͗s͘ at different temperatures. T MCT ϭ0.45.

Local polymer dynamics under strong connectivity constraints: The dendrimer case

“…10,12,20,21 At this transition region connectivity effects become increasingly important. 9,16 Instead of the free diffusion realized in simple unassociated liquids, a subdiffusive behavior is observed in monomer motion due to bonding, before final diffusion sets in. 4,6,9,16 Close examination of the motional mechanisms at this time and length scales in different kinds of glass-forming systems 9,20,22,23 revealed the key role of mobility-correlated subregions in the realization of cooperative motion.…”

“…9,16 Instead of the free diffusion realized in simple unassociated liquids, a subdiffusive behavior is observed in monomer motion due to bonding, before final diffusion sets in. 4,6,9,16 Close examination of the motional mechanisms at this time and length scales in different kinds of glass-forming systems 9,20,22,23 revealed the key role of mobility-correlated subregions in the realization of cooperative motion. In the case of polymers chain connectivity may provide alternative routes, not present in simple liquids, for short range spatially correlated dynamics.…”

“…[3][4][5][6] At such subnanometer scale and in the dynamic range of the ␤-relaxation where the glass-forming units are moving within a "cage" formed by their immediate neighbors, [7][8][9][10] polymer specific effects are seemingly not directly involved. Notwithstanding, even at these very short spatial dimensions indirect effects such as the modification of local packing characteristics due to the applied intramolecular potentials in polymeric models, 4 or even correlation of motion within the cage 11,12 should properly be taken into account.…”

“…The time t * at which NGP exhibits a maximum demarcates a characteristic lifetime of the transient cage 7,9,19,20 and has been correlated with the time scale at which local dynamic heterogeneities approach a maximum. 10,12,20,21 At this transition region connectivity effects become increasingly important.…”

“…[27][28][29][30][31] These attributes may essentially "filter out" certain dynamic features met either in liquids or linear polymers allowing a better assessment of the relative importance of each factor. For instance, in both of these glass-forming systems, regions of low or high mobility may fluctuate through the sample in a finite time scale, promoting specific mechanisms for cooperative particle rearrangements ͑e.g., stringlike particle/monomer clusters 9,22 ͒ that are expected to be suppressed in dendrimers. Identification and monitoring of regions possessing distinct mobilities rely on a proper selection of subensembles of "fast" and "slow" moving units, for the definition of which various approaches have been followed so far.…”