Rheology of Small Spherical Polystyrene Microgels: A Direct Proof for a New Transport Mechanism in Bulk Polymers besides Reptation

Mode-coupling theory of the slow dynamics of polymeric liquids: Fractal macromolecular architectures

“…However, these simplifications are not appropriate for other topologies such as stars, some types of branched polymers, and rigid rods. For example, the nearly exponential dependence of star melt vis-cosity and diffusion constant on arm molecular weight predicted by phenomenological arm retraction ideas within the tube model, 2,3,49 and found in many ͑but not all͒ experiments, 16,50-52 is not predicted. A very large enhancement of the rotational relaxation time and shear viscosity of isotropic rigid rod solutions [53][54][55] is also not captured.…”

“…Melts of cyclic polymers, 10,11 star polymers, 12,13 H-shaped polymers, 14 comb-like polymers, 15 and of differently crosslinked micro-networks or micro-gels [16][17][18] have been prepared and studied for entanglement effects. In contrast to a naive interpretation of the reptation picture, it is found that macromolecules irrespective of their molecular architecture show a slow relaxation process above a certain crossover degree of polymerization.…”

“…Let us mention one striking observation, namely, the plateau value in the shear modulus which is rather close for polystyrene molecules of different topologies ͑including spherical microgels͒, whereas for linear polymers of different chemical units larger variations are observed. 1,[10][11][12][13][14][15][16] Of course, one has to caution that the impression that a slow dynamical entanglement process is a common feature of strongly interacting macromolecules may be premature as experiments may often be in a broad crossover region, where different transport processes compete and simplified theoretical models do not yet apply. At present this question appears to preclude the possibility of experimentally verifying the original tube model for linear chains and N→ϱ, although it is well known that systematic deviations are observed.…”

“…[24][25][26] However, the wealth of experimental studies suggests a more universal underlying mechanism for entanglement formation and relaxation in macromolecular liquids than implicitly assumed in most phenomenological models. 16 Recently, one of us has put forward a new microscopic approach to the entanglement problem in melts, [27][28][29][30][31][32] which was extended to solutions, 33,34 blends 35,36 and copolymers. [37][38][39] It generalizes established techniques and approximations from theories for the equilibrium structure and dynamics of simple liquids, and addresses the question how the microscopic equations of motion containing the molecular potentials explicitly lead to entanglement effects.…”

Mechanical Behavior of Polystyrene Microgels

“…Their unique morphologysdensely packed, unentangled polyhedronss markedly affects the microgels' mechanical properties. 1,2 Our efforts to characterize the rheology of PS microgels will be reported elsewhere; 4 we restrict our attention herein to the mechanical behavior at higher frequencies.…”