An interplay between molecular pairing, smectic layer spacing, dielectric anisotropy and re-entrant phenomena in ω-alkenyloxy cyanobiphenyls

<p>In this article, we report on the liquid-crystalline properties of the 4-ω-alkenyloxy-4′-cyanobiphenyl series of compounds up to a total aliphatic chain length of eleven. When compared to the analogous fully saturated compounds, we find that the smectic layer spacing is significantly larger for the alkene-terminated materials; conversely the dielectric anisotropy in the nematic phase was found to be significantly smaller. The ability to manipulate bulk properties of nematic and smectic mesophases may have future relevance for display applications.</p

Etheric bimesogens and the twist-bend nematic phase

<p>Despite the relationship between molecular structure and the occurrence of the twist-bend nematic phase being partially understood, very little is known about how these relationships are manifested for ether-linked bimesogens. In this article, we report several novel ether-linked bimesogens that exhibit the N_TB phase and explore how the thermal properties of these materials are largely governed by the angle between the two aromatic, carbocyclic or rigid cyclic units.</p

Relationship between Molecular Association and Re-entrant Phenomena in Polar Calamitic Liquid Crystals

The relationship between molecular association and re-entrant phase behavior in polar calamitic liquid crystals has been explored in two families of materials: the 4′-alkoxy-4-cyano­biphenyls (6OCB and 8OCB) and the 4′-alkoxy-4-nitro­biphenyls. Although re-entrant nematic phase behavior has previously been observed in the phase diagram of 6OCB/8OCB, this is not observed in mixtures of the analogous nitro materials. As there is no stabilization of the smectic A phase in mixture studies, it was conjectured that the degree of association for the nitro systems is greater than that for the cyano analogues. This hypothesis was tested by using measured dielectric anisotropies and computed molecular properties to obtain a value of the Kirkwood factor, <i>g</i>, which describes the degree of association of dipoles in a liquid. These computed values of <i>g</i> confirm that the degree of association for nitro materials is greater than that for cyano and offer a useful method for quantifying molecular association in systems exhibiting a re-entrant polymorphism

Geometric aspects influencing N-N_TB transition - implication of intramolecular torsion

<p>Herein we report a comprehensive study on novel carbonyl- and ethenyl-linked symmetric dimers that combine synthesis, mesomorphic properties and molecular modelling. The study has been focused on the impact of geometry imposed by the linkage group on the incidence of the twist-bend nematic (N_TB) phase. Comparison of the mesomorphic properties of these two series complemented with computational studies of conformational space around the linkage group points molecular curvature and intramolecular torsion plays important role in the appearance of the N_TB phase and can be regarded as the basic structural requirements for design of new twist-bend nematogen materials.</p