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.

We present magneto-optic measurements on two materials that form the recently discovered twist-bend nematic (N_{tb}) phase. This intriguing state of matter represents a fluid phase that is orientationally anisotropic in three directions and also exhibits translational order with periodicity several times larger than the molecular size. N_{tb} materials may also spontaneously form a visible, macroscopic stripe texture. We show that the optical stripe texture can be persistently inhibited by a magnetic field, and a 25T external magnetic field depresses the N-N_{tb} phase transition temperature by almost 1{∘}C. We propose a quantitative mechanism to account for this shift and suggest a Helfrich-Hurault-type mechanism for the optical stripe formation.

We present the first shear alignment studies and rheological measurements in the twist-bend nematic (N tb ) liquid crystal phase of odd numbered flexible dimer molecules. It is found that the N tb phase is strongly shear-thinning. At shear stresses below 1Pa the apparent viscosity of N tb is 1000 times larger than in the nematic phase. At stress above 10 Pa the N tb viscosity drops by two orders of magnitude and the material exhibits Newtonian fluid behavior. This is consistent with the heliconic axis becoming normal to the shear plane via shear-induced alignment. From measurements of the dynamic modulus we estimate the compression modulus of the pseudo-layers to be B~2kPa; this value is discussed within the context of a simple theoretical model based upon a coarse-grained elastic free energy.

An innovative approach to producing reflective systems is presented by using Reactive Mesogen based Cholesteric Particles (ChRMPs). The versatility of the novel ChRMPs opens the door to produce single-or multi-wavelength reflective systems by mixing particles with Bragg reflection located at different wavelength values. Particulate based films can be prepared in absence of any alignment layer on any kind of substrate with very wide viewing angle behaviour, which is in clear contrast to conventional reflective films based on cholesteric liquid crystals with planar alignment. The straightforward film preparation, flexibility of the synthesis and the excellent viewing-angle property make ChRMPs a very interesting new approach to produce reflective films for applications including, but not limited to, flat panel display such as in brightness enhancement or colour filters. Cholesteric RMPPlanar film REFLECTIO N ʎon-axis ˃ ʎoff-axis ʎon-axis = ʎoff-axis Novel approach to producing cholesteric mono-or multi-wavelength reflective systems which drive the reflection by mixing isolated Bragg-reflectors is presented.

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