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.
We present polymeric MEMS materials which reversibly respond to either thermal or UV stimuli by moving between nearly flat (r ~ infinity) and tightly curled states (r ~ 5mm) with variations in the radiation environment or temperature. The molecular orientation gradient of a liquid crystal network controls the primary bending axes, while controlled order parameter variations are responsible for the degree of deformation. In the case of thermal activation, these order changes are dominated by thermal motion, while UV-switchable defects bring about reduced network order in the case of UV actuation. We report fabrication and operation of the actuators and supplementary data regarding alignment configurations for controllable deformations, the phase behaviour of the liquid crystal constituents, thermal expansions, and absorption of the UV dyes are included. We find that splayed molecular configurations are preferred over twisted modes due to their single deformation axis, and that the optimum concentration of active molecules for UV-driven actuation is on the order of 7-8wt.%.
The formation of mirrors reflecting a single colour or reflecting the whole visible spectrum by application of a liquid crystalline layer followed by UV polymerisation (photo-polymerisation) is described. Also, the formation of patterned films obtained by a sequence of UV exposure steps is discussed. Such films play an important role in the improvement of the performance of liquid crystal displays.
Photopolymerization of liquid-crystalline (LC) monomers produces polymer films with a spatial control over the molecular organization. A powerful tool for creating even more complex molecular architectures than by LC order alone is photo-induced diffusion during polymerization of these monomers. Photo-induced diffusion during polymerization of chiral-nematic monomers yields a cholesteric network in which the helical pitch gradually changes over the cross-section of the film. The polarization selective reflection band can thus be made much wider than those of single pitch materials and may expand the whole visible spectrum. Performing photo- induced diffusion on a length-scale of half the cholesteric pitch by using a liquid-crystalline photoinitiator yields a cholesteric network with a deformed helix. Helix deformation gives higher order reflections and a built-in optical retardation. When the deformed helix is combined with a pitch gradient over the film thickness, the built-in retardation can be used for wide-band cholesteric polarizers that directly generate linearly polarized light without an additional quarter-wave foil.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.