Microactuators from a main-chain liquid crystalline elastomer via thiol-ene "click" chemistry

Recently it has been described that liquid crystalline elastomer (LCE) particles of the side-chain type can be prepared in microfluidic devices. Here we present the preparation of micrometer-sized LCE particles of the main-chain type by thiol-ene chemistry. The LCE particles are UV-crosslinked via thiol-ene click chemistry of the nematic monomer, carrying terminal thiol and ene groups, and non-mesogenic tetrathiol and tetraene crosslinkers. The preparation of the LCE particles with a microfluidic device by a continuous "on the fly" technique allows their fast processing with an irradiation time of less than 2 seconds. The resulting particles undergo a temperature-driven volume change up to 25% upon the nematic-isotropic phase transition and the extent of the shape change can be controlled by adjusting the microfluidic parameters. The reversibility of the shape change and the chemical durability of the thiol-ene network towards reducing agents demonstrate the usability of the LCE particles as soft microactuators.