Rheo-optics of a conjugated polymer system in shear

Abstract

The polymeric chromophore, poly(4-butoxycarbonylmethylurethane), p-4BCMU, has a diacetylene backbone that displays a broad range of optical properties directly attributed to its conformation. The UV-Vis spectral properties of the polymer solution are dependent upon the backbone conjugation length, which describes the length over which the π-electrons are delocalised. The persistence length of the polymer chain describes the curvature of the polymer chain and is dependent upon the solvent quality and thermal properties of the system. Changes in persistence length, which are accompanied by a change in polymer conformation, lead to changes in the conjugation length and, therefore, the measured absorption spectra. However, under an applied shear force, the persistence length of the polymer chain is assumed, through kinetic theories, to remain constant even though the polymer chain may change conformation. A novel rheo-optic experimental system was developed, where a wavelength region of light about the absorption maximum of the polymer backbone is scanned for each shear rate. From the experimental results it was confirmed that while the polymer chain segments aligned in the shear direction, there was no change in the polymer chain persistence length with shear, which is consistent with kinetic theory.