VISUALIZATION OF THE FLOW OF A THERMOTROPIC LIQUID-CRYSTALLINE POLYMER IN A TUBE WITH A CONICAL CONTRACTION

Flow visualization experiments have been used to characterize the flui d dynamics of a thermotropic liquid crystalline polymer, Vectra A, in the barrel and conical entry of a capillary rheometer. The displacemen t profiles indicate shear-thinning in the straight section, with a pow er law index much lower than that measured rheometrically. The contrac tion flow is complex and three-dimensional. There are asymmetrical vor tices and signs of macroscopic structural changes. For flow in a corne r, the profiles display patterns that cannot be predicted by the shear -thinning effects alone. These characteristics are in striking contras t to the results on lyotropic solutions in thin slit geometries (see J .N. Baleo and P. Navard, J. Rheol., 38 (1994) 1641-1655, and B.D. Bedf ord and W.R. Burghardt, J. Rheol., 38 (1994) 1657-1679). (C) 1997 Else vier Science B.V.