Lyotropic liquid crystals of a soluble polydiacetylene. A comparative investigation by means of optical and electron microscopy

Abstract

The liquid crystalline properties of a concentrated solution of poly{5,7-dodecadiyne-1,12-diol bis[(4-butoxycarbonyl)methyl)urethane]} (P-4-BCMU) -a soluble polydiacetylene- in chloroform, beyond the critical concentration, have been investigated. Optical microscopy shows the anisotropic liquid crystal solution of P-4-BCMU in chloroform to be a polymer nematic. Disclinations with strengths of s= +½ and −½ are the most frequent type. Some disclinations with s= +1 were observed, but rarely disclinations with s= −1. Therefore, the liquid crystal texture usually displays a schlieren with two brushes in the vicinity of the singularities. The supramolecular structure observed by transmission electron microscopy shows a lamellar type morphology. As previously shown, the thickness of the lamellae is correlated to the molecular chain length. The chain length distribution leads to segregation with respect to molecular length and can be observed by thickness variations of both individual and subsequent lamellae. A kinetic study of disclination annihilation induced by isothermal relaxation in the liquid crystalline phase is presented. Possible mechanisms of the relation of the lamellar texture and the disclination annihilation are discussed. A stripe texture observed over large regions of the solid film is suggested to be a decoration effect due to internal stress as a result of solvent evaporation when the films are prepared by solution casting.