High resolution spatial modulation of order parameter in a liquid crystal

Localized UV-driven isomerization of an azobenzene additive in a nematic liquid crystal has been previously used to spatially modulate the local order parameter. However, azobenzene diffusion limits the sharpness with which the order parameter can be modulated. Here, we present two strategies to achieve microscale spatial modification by leveraging faster cis-to-trans isomerization. Firstly, simultaneous irradiation of the sample with blue light is shown to promote cis-trans conversion outside the illuminated region, leading to sharper modulation. Secondly, a push-pull azobenzene which shows rapid thermal cis-to-trans isomerization is used instead of a conventional azobenzene additive, yielding an even sharper profile. We show that the order parameter variation is consistent with two-dimensional diffusion of azobenzene coupled with isomerization kinetics.