Liquid-crystalline behaviour and electrorheological effect of phthalocyanine-based ionic liquid crystals

Abstract

ABSTRACT Series of phthalocyanine-based ionic liquid crystals (PILCs) electrorheological (ER) materials were synthesised using brominated polyesters and a phthalocyanine (Pc)-containing monomer, and the chemical structure, liquid-crystalline behaviour, dielectric property and ER performance were characterised. All PILCs showed nematic phase, but some PILCs with more phthalocyanine moieties showed discotic hexagonal columnar mesophase. The dielectric permittivity increase with the increasing temperatures, but decrease with the increase of frequency for these PILCs. The PILCs-based electrorheological fluids (ERFs) contained an integrated character of liquid crystal, poly(ionic liquid) and Pc-base ER suspensions. The ERFs were made by PILC particles and silicone oil, and the ER effect was investigated at controlled test conditions including concentration, electric field strength, temperature and shear rate. When the ERFs were applied an external electric field strength, the shear stress increased instantly, and they showed non-Newtonian behaviour. At the same conditions, the ER effect improved as the measured temperature raised. Furthermore, the ER effect increased with the increase of ionic Pc moieties in the polymer systems. These results were originated from the synergetic effect among the mesogenic orientation and rearrangement of ionic Pc droplets induced by the electric field, forming an alignment-aggregated fibrillation chain.