ISSN:
1435-1528
Schlagwort(e):
Shear flow
;
UCST
;
polymer blend
;
phase separation
;
stored energy
;
closed miscibility gap
Quelle:
Springer Online Journal Archives 1860-2000
Thema:
Chemie und Pharmazie
,
Physik
Notizen:
Abstract Calculations were performed on the basis of a generalized Gibbs energy of mixing G γ, which is the sum of the Gibbs energy of mixing of the stagnant system and E s, the energy stored in the system during stationary flow. With increasing shear rate γ, the demixing temperatures shift to lower values (shear-induced mixing; diminution of the heterogeneous area), then to higher values (shear-induced demixing), and finally to lower values again before the effects fade out. The details of the rather complex phase diagrams resulting for a given shear rate are primarily determined by a band in the T/χ plane (χ = mole fraction) within which (∂2 E s/∂χ2) T 〈0 (i.e., E S acts towards phase separation). There are two ranges of γ within which closed miscibility gaps can exist: The more common outer islands are partly or totally situated outside the equilibrium gap (and within the above mentioned band). As γ is raised they break away from the “mainland” at the upper end of the first region of shear-induced mixing and shift to T〉UCST where they submerge. Bound to a suitable choice of parameters, a second kind of closed miscibility gaps, the inner islands, which always remain within the equilibrium solubility gap (and outside the band of negative curvature of E S) is additionally observed. This time the islands break away from the “mainland” at the lower end of the first region of shear-induced mixing where they also submerge. The present findings are compared with the results of previous calculations for LCSTs.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1007/BF00366754
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