Birefringence of Dilute PS Solutions in Abrupt Contraction Flow

摘要: Transient elongational flow was created by forcing dilute PS solutions across a narrow contraction. Rheo-optical measurements revealed localized birefringence zone above critical strain-rate in the immediate orifice entrance. Birefringence studied with polarization-modulation technique for (50–500 ppm) as function of fluid rate (1000-38000 s-1), polymer molecular weight (M = 1.93–24 • 106) and solvent quality (decalin 1-methyl-naphthalene). is complicated presence local orientation distribution along different streamlines. To account this effect, numerical has been devised to compute (An) from experimental retardation (δ). Orientation correction turned out be unimportant except at dosest distances Results show steep decrease axial distance. profiles determined direction perpendicular maximum, not center, but vicinity walls. This effect explained means simulation which indicated extreme strain rates near re-entrant corners. Molecular extension ratio calculated Kuhn-Grun theory suggests that polymers may uncoil up one third chain contour length approach capillary Notable departure affine deformation model is, however, observed multiple saturation levels changing conditions.