Recyclable liquid crystal polymeric sensor beads based on the assistance of radially aligned liquid crystals

Abstract

In this study, we first demonstrate the synthesis of recyclable polymer beads for Cu2+ sensing based on radially aligned liquid crystal (LC) assistance. To detect metal ions in water, sensing probe monomers and polymers derived from rhodamine B were synthesized. Recyclable polymeric LC beads were prepared from LC monomers RM257 and RM105, a nonreactive mesogen of 5CB and a rhodamine B-derived monomer. Due to the assistance of radially aligned LCs, highly sterically hindered spirocyclic terminal groups of rhodamine B-derived monomers were aligned and fixed at the outer surface of liquid crystal beads. The color of the polymeric LC beads changed from light pink to deep pink after the beads were dropped into an aqueous Cu2+ solution. The results were ascribed to the spiro ring-opening mechanism. The addition of a nonreactive mesogen resulted in the porous structure of the polymeric LC beads. The high sensitivity of the Cu2+ solution using polymeric LC beads was confirmed. The fabricated polymeric LC beads were recycled by putting the polymeric LC beads into aqueous ammonia. The removal of Cu2+ from polymeric LC beads was due to the formation of [Cu(NH3)4]2+. This recyclable LC bead sensor is an easy method for the detection of metal ions in aqueous solutions. The fabricated polymeric liquid crystal beads surfaces consist of aligned rhodamine B-derived active sites possess capacity of sensing copper ions in tested solutions. The color of the beads changed to deep pink while copper ions exist in the solutions, whereas it can be easily recycled by adding aqueous ammonia, indicating the beads applied as a powerful monitoring tool.