(90a) A Continous Flow Synthesis for Microscopically Structured Actuators Based on Liquid Crystalline Elastomers

Monodomains of liquid crystalline elastomers perform a reversible shape change at a phase transition, which makes them possible materials for actuator applications. These so called ?intelligent materials? change their properties on certain external stimuli, like temperature or UV iradiation. Mainly macroscopically structured actuators, like films or fibers, have been made from liquid crystalline materials so far, showing shape changes of up to 300%.

Using microfluidics, we realized a continous flow synthesis for spherically shaped particles in the upper micrometer size region from liquid crystalline elastomers. In this approach, a mixture of a liquid crystalline monomer with crosslinker and photoinitiator is melted and injected into a co-flowing stream of a non-miscible carrier fluid. The resulting dropletts are then cooled into the liquid crystalline phase and are polymerized by UV-irradiation in the flow. By variation of the flow rates and the viscosity of the carrier fluid, the particle size was controlled between 200 and 500 micrometers with a size variation coefficient of below 1%.

Due to the flow velocity profile in the tubing, the mesogens are preferentially oriented parallel to the flow direction, which gives the particles characteristics of a liquid crystalline monodomain. Upon heating them into the isotropic phase under a microsope a fully reversible shape change into a rod shaped conformation can be observed. Thereby they exhibit a length change of more then 70%. The same change in conformation can be achieved by swelling the particles with a suitable solvent, which also induces a phase transition.