Open AccessOrigin of nonlinearities in the Bagley plots of thermotropic copolyesters
Author(s) -
Paula Moldenaers,
Jan Vermant,
Jan Mewis,
Ingrid Heynderickx
Publication year - 1996
Publication title -
journal of rheology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.098
H-Index - 107
eISSN - 1520-8516
pISSN - 0148-6055
DOI - 10.1122/1.550799
Subject(s) - thermotropic crystal , nonlinear system , rheometer , piston (optics) , materials science , viscosity , hydrostatic equilibrium , slit , orientation (vector space) , mechanics , hydrostatic pressure , rheology , polymer , physics , optics , composite material , geometry , mathematics , liquid crystalline , quantum mechanics , wavefront
Synopsis The origin of the nonlinearity observed in Bagley plots of thermotropic copolyesters has been investigated experimentally. With the aid of a two-piston slit rheometer the dependence of the viscosity on the hydrostatic pressure has been determined directly. This dependence only accounts for part of the nonlinearity of the Bagley plots. Using slit dies with either a convergent or a divergent entrance, concave as well as convex pressure profiles are obtained. This can only be explained by a change in the molecular orientation induced by the flow in the entrance zone. The presence of wall effects has been evaluated by measuring the pressure profiles in slits of different heights; it does not explain the nonlinearity of the Bagley plots. The origin of the nonlinearity of Bagley plots must be due to both pressure and molecular reorientation effects. The nature and importance of these reorientation effects are shown to depend on the entrance geometry. © 1996 Society of Rheology. I. INTRODUCTION
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