Here we report the chemical induction of the twist-bend nematic phase in a nematic mixture of ether-linked liquid crystal dimers by the addition of a dimer with methylene links; all dimers have an odd number of groups in the spacer connecting the two mesogenic groups. The twist-bend phase has been identified from its optical texture and x-ray scattering pattern as well as NMR spectroscopy, which demonstrates the phase chirality. Theory predicts that the key macroscopic property required for the stability of this chiral phase formed from achiral molecules is for the bend elastic constant to tend to be negative; in addition the twist elastic constant should be smaller than half the splay elastic constant. To test these important aspects of the prediction we have measured the bend and splay elastic constants in the nematic phase preceding the twist-bend nematic using the classic Frederiks methodology and all three elastic constants employing the dynamic light scattering approach. Our results show that, unlike the splay, the bend elastic constant is small and decreases significantly as the transition to the induced twist-bend nematic phase is approached, but then exhibits unexpected behavior prior to the phase transition.

Electro-optical switching of the liquid crystalline Blue Phase exhibits extremely fast response times. However, the unstabilized Blue Phase is characterized by a rather narrow temperature range on the order of a few K. For display applications the operating temperature range needs to be increased. One very promising way is to broaden the stable temperature range by polymer-stabilization of the Blue Phase. Successful stabilization is achieved by proper material selection/matching of reactive mesogens (RMs) and the chiral host. One prerequisite for application in display manufacturing is excellent UV and heat stability as well as good processability. Improvements in relevant performance parameters will be presented and discussed. Fig. 1 Principal constituents of a Blue Phase (BP) mixture include the nematic host mixture, chiral dopant and monomers. 4.4 / M. Wittek SID 2012 DIGEST • 25 ISSN 0097-966X/12/4301-0025-$1.00

The performance of a polymer-stabilized blue phase system based on a nematic host with large dielectric anisotropy and a chiral dopant with high helical twisting power is investigated and the influence of the reactive monomer composition on the electro-optic characteristics is studied. Field-induced birefringence with a Kerr coefficient greater than 1 nm V−2 can be achieved in a large temperature range from well below 20 °C to above 55 °C. The disturbing influences of electro-optic hysteresis and memory effects can be reduced by diligent choice of the composition and appropriate electric addressing.

Blue phases—special chiral liquid crystalline mesophases—are promising candidates for electro‐optic devices with improved performance and simplified fabrication. A necessary precondition for possible applications is a significantly enhanced temperature range of their existence, which can be achieved by a cross‐linked polymer network formed by in situ polymerization. Unlike many other mesophases, blue phases are optically isotropic if no voltage is applied. Regarding the transmission of a blue phase cell placed between crossed polarizers, the optical isotropy enables—at least in principle—a perfect dark state, independent of the viewing angle, without the necessity of any alignment layer. The application of an in‐plane electric field induces a strong birefringence (Kerr effect). The effective Kerr constants are much larger than those of isotropic liquids, and the switching times between the dark and the induced bright state are in the submillisecond range. Some basic properties of blue phases, state‐of‐the‐art performance, and remaining challenges of the development of polymer‐stabilized blue phases are reviewed in this article. Copyright © 2014 John Wiley & Sons, Ltd.

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