Steering cholesteric liquid crystal elastomer properties by positional variation of chiral molecular building blocks

Crosslinked Liquid Crystal Elastomers (CrLCEs) are at the forefront of the development of optoelectronics and photonics. Over the years, a materials toolset has been developed ranging from bulk synthesised nematic monomers to dedicated smectic and chiral monomers with advanced applications such as polarisation optics, iridescent coatings, and photo-responsive mechanics. CrLCEs are often prepared through a two-step approach. First, conventional reactive liquid crystal monomers are chain-extended into (short) oligomer chains which are then crosslinked to form the elastomer network. The advantage of this approach is that it gives access to a wide range of processing methods, including conventional techniques suited for liquid crystal monomers, but also emerging processing techniques such as 3D- or roll-to-roll printing. Adding chiral molecules to a nematic oligomer forms the chiral nematic or cholesteric liquid crystal phase, well-known for its characteristic helicoidal ordering of the calamitic molecules. Currently we are interested in the effect of the position of the chiral component in relation to the elastomer network: either as part of the oligomer main chain or as a pendant group to it. In this contribution we found that the dopant position may influence the way in which the cholesteric material aligns. The main chain dopant follows behaviour previously reported in similar systems, while the side chain dopant adds more process-related complexity to the optical properties. With this work we aim to add a new design consideration to the already versatile platform of CrLCEs.