UV isomerisation in nematic elastomers as a route to photo-mechanical transducer.

The macroscopic shape of liquid-crystalline elastomers strongly depends on the order parameter of the mesogenic groups. This order can be manipulated if photo-isomerisable groups, e.g. containing N=N bonds, are introduced into the material. We have explored the large photo-mechanical response of such an azobenzene-containing nematic elastomer at different temperatures, using force and optical birefringence measurements, and focusing on fundamental aspects of population dynamics and the related speed and repeatability of the response. The characteristic time of "on" and "off" regimes strongly depends on temperature, but is generally found to be very long. We were able to verify that the macroscopic relaxation of the elastomer is determined by the nematic order dynamics and not, for instance, by the polymer network relaxation.