A deuterium nuclear magnetic resonance investigation of orientational order and director kinetics in aramid solutions

Abstract

We have studied the molecular orientational order and director kinetics of the nematic phase formed by dissolving poly-p-phenylene-terephthalamide (PPTA) in sulphuric acid using deuterium NMR spectroscopy. Measurements were made on standard polymer samples using deuterated sulphuric acid and with deuterated PPTA in normal H2SO4. The influence of temperature and polymer concentration on the quadrupolar splittings which reflect the orientational order of the solvent and the solute are reported. The biphasic gap, between the nematic and the isotropic phase, for an 8.84%(w/w) solution was found to be about 10 °C. The influence of polymer concentration on the orientational order of the polymer solute is consistent with the predictions of a modified Maier–Saupe theory. By measuring the time dependence of the spectra the kinetics of field-induced director reorientation has been studied. The reorientation process from a multidomain sample to a uniform director alignment can be adequately described using an approach in which the different domains are decoupled.