Neutron Spin Echo Spectroscopy Viscoelasticity RheologyViscoelasticandtransportpropertiesofpolymersintheliquid(solution,melt)or liquid-like (rubber) state determine their processing and application to a large extent and are of basic physical interest [1—3]. An understanding of these dynamic properties at a molecular level, therefore, is of great importance. However,thisunderstandingiscomplicatedbythefactsthatdi?erentmotional processes may occur on di?erent length scales and that the dynamics are governed by universal chain properties as well as by the special chemical structure of the monomer units [4,5]. The earliest and simplest approach in this direction starts from Langevin equations with solutions comprising a spectrum of relaxation modes [1—4]. Special features are the incorporation of entropic forces (Rouse model, [6]) which relax uctuations of reduced entropy, and of hydrodynamic interactions (Zimm model, [7]) which couple segmental motions via long-range back ow elds in polymer solutions, and the inclusion of topological constraints or entanglements (reptation or tube model, [8—10]) which are mutually imposed within a dense ensemble of chains. Another approach, neglecting the details of the chemical structure and concentratingontheuniversalelementsofchainrelaxation,isbasedondynamic scalingconsiderations[4,11].Inparticularinpolymersolutions,thisapproach o?ers an elegant tool to specify the general trends of polymer dynamics, although it su?ers from the lack of a molecular interpretation. A real test of these theoretical approaches requires microscopic methods, which simultaneously give direct access to the space and time evolution of the segmental di?usion. Here, quasi-elastic scattering methods play a crucial role sincetheyallowthemeasurementofthecorrespondingcorrelationfunctions.In particular,thehigh-resolutionneutronspinecho(NSE)spectroscopy[12—15]is very suitable for such investigations since this method covers an appropriate range in time (0.005)t/ns)40) and space (r/nm [15). Furthermore, the possibilityoflabellingbyhydrogen-deuteriumexchangeallowstheobservation of single-chain behavior even in the melt. |
Contents
3 | |
Polymer Motion in Dense Environments | 11 |
Polymer Networks | 59 |
Conclusion and Outlook | 125 |
Deformation and Viscoelastic Behavior of Polymer Gels | 130 |
Rheology of Polymers Near LiquidSolid Transitions | 165 |
235 | |
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American Chemical Society anode anode side average contrast behavior calculated chain characteristic frequencies Chem Phys cluster concentration copolymer Copyright critical exponent critical gel crosslinking crossover deformation density dependence deuterated diblock dilute solutions dynamic structure factor elastic modulus electric field entanglement distance equation Ewen experimental function g/mol Gaussian gel point gelation homopolymers hydrodynamic hydrodynamic interactions increasing length scales linear liquid-solid transition longest relaxation Macromolecules material microscopic molecular mass molecular weight molecules monomer motion neutron scattering NSE spectra observed Oseen tensor osmotic pressure parameter particles PDMS phase Polym Sci polymer gels power law predicted properties protonated PVA-PAA gel Q-values regime relaxation exponent relaxation modes Reprinted with permission reptation rheological Richter Rouse model Rouse relaxation sample segmental diffusion self-similar semi-dilute solutions shear solid lines solvent solvent conditions spectrum star static temperature theoretical theory viscoelastic viscosity Winter HH Zimm model Zimm relaxation