ISSN:
0025-116X
Schlagwort(e):
Chemistry
;
Polymer and Materials Science
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
,
Physik
Notizen:
The dynamics of polymer melts is well reflected in the complex shear compliance J*(ω,T,M) measured in wide ranges of frequency and temperature and for various molecular weights. In the frame of the meander model all typical features of J*(ω,T,M) are quantitatively described: (1) JeNo is due to intra-meander shear, and decreases by incorporating pairs of chain ends within the superstructure folds, i.e. with decreasing M. (2) This shear motion is guaranteed by a certain amount of edge-dislocations (with Burgers vector b equal to the chain distance d- for some polymers equal to d/2). The glass relaxation and its activation diagram are understood by asking for the probability for just this amount of dislocation segments to be present. The dielectric relaxation strengths and those of the thermal properties support the chosen segment lengths. (3) The step height to the steady state compliance, Jeo - JeNo (proportional to JeNo above MC, but strongly dependent on M-distribution), is due to inter-meaner shear (formation of shear bands). (4) These bands relax by disentanglement via chain reptation across half the length of a molecule within the flow relaxation time τF. (5) The Viscosity follows from η = τF/Δeo, and is proportional to M3.3 above and M1.3 below Mc. (6) The critical molecular weight Mc is predicated by the model in fair agreement with experimental data.(7) Neglecting flow, the stress-strain curves of uncrosslinked high molecular weight polymer metals can be derived by taking into account intra-and inter-meander shear deformation.
Zusätzliches Material:
18 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/macp.1979.020031979114
