Rheofluorescence studies of poly(p-phenylenevinylene) derivatives in simple shear flow

Abstract

Common manufacturing approaches for polymer displays expose light emitting polymer solutions (LEPs) to high shear rates during film deposition. Little is yet known about the effects of shear on LEP conformation and alignment; the ability to manipulate these polymers in flow may prove critical for enhanced device performance. A novel spectroscopic approach that employs an optically accessible Couette cell has been developed to investigate the effects of a uniform shear field on LEP luminescence. Orientation and deformation in polymer solutions are observed as shear-dependent changes in fluorescence emission. We report the influence of simple shear flow on steady state fluorescence emission from MEH-PPV and two other poly(p-phenylenevinylene) derivatives, in dilute solution and a polystyrene matrix. Rheochromism, a shear-induced red shift of 4–6 nm in spectra recorded at shear rates of 100–1000 s −1, indicates a small extension of conjugated polymer coils. Changes in fluorescence emission intensity as a function of shear rate and observation geometry are attributed to alignment of prolate polymer coils in the flow field.