A Direct Observation by XRD of Reorientation in a Supramolecular Liquid Crystal Polymer Induced by Magnetic Field

Abstract

ABSTRACT Sulfonated polyaramide poly(p-phenylene-sulfo-terephthalamide), or “Sulfo Invert PPTA”, self-assembles in water to form rod-shaped supramolecular aggregates that exhibit nematic liquid crystalline behaviour at remarkably low polymer concentration. The phase diagram is found to be rather athermal, which is an indication that the nematic phase stability is dominated by entropic excluded volume interactions. We describe the transient reorientation of this supramolecular nematic liquid crystal when an aligned sample is subjected to a magnetic field perpendicular to the original orientation of the director. It is directly visible from time-resolved X-ray diffraction that the director alignment changes to the direction of the external field via two different pathways. These pathways consist of regions of the director field turning either clockwise or counter-clockwise leading to the doubling of the diffraction peak during the transient reorientation process. Analysing this process in more detail may provide means to determine the viscous and elastic coefficients of our supramolecular nematic liquid crystal polymer.