Possible structures for the lamellar–isotropic (Lam‐I) and lamellar–nematic (Lam‐N) liquid crystalline phases

Abstract

The three refractive indices of a liquid crystal that exhibits lamellar analogues of the threedimensional isotropic, nematic, and smectic A phases are reported as functions of temperature for the Lam-I and Lam-N phases. The data suggest a number of striking behaviour types. The orientational distribution of the mesogenic moieties becomes more highly peaked in two dimensions on cooling from the Lam-I to the Lam-N phase; the twodimensional order associated with mesogenic director n in the Lam-N phase is weak; and conformational changes in the side chain result in an increase in the refractive index perpendicular to the lamellae with decreasing temperature in the Lam-N phase.

Lamellar Liquid Crystals of In‐Plane Lying Rod‐Like Mesogens with Designer Side‐Chains: The Case of Sliding versus Locked Layers

“…However, planar alignment can only rarely be obtained, and then only over small areas. The usually observed mode of alignment is homeotropic, that is, with the layers parallel to the surfaces, as also confirmed by XRD investigations. In homeotropic regions the Lam Iso –Lam N transition is characterized by development of a schlieren textures and, in the Lam Sm phase, by the formation of focal conic‐like domains due to the emerging in‐plane periodicity (Figure a,c,e) .…”

The Giant‐Hexagon Cylinder Network—A Liquid‐Crystalline Organization Formed by a T‐Shaped Quaternary Amphiphile

“…In the two lamellar phases adjacent to the polygonal cylinder phases (Lam Sm and Lam N ) the biphenyl cores remain parallel to the layer planes before the layers become disordered in the Lam Iso phase (Figure 4 b)8d,e and finally disappear in the isotropic liquid. As the mean direction of the aromatic cores does not fundamentally change during the transition from the Col rec / c 2 mm phase to the Lam Sm phase at 89 °C (Δ H =0.4 kJ mol −1 ), there is also no significant change in the texture at this phase transition (Figure 4 c); only an increase in the birefringence is seen 16.…”

Complex tiling patterns in liquid crystals

“…Unlike the usual smectic phases (figure 5a) formed by rod-like molecules without lateral chains, in these lamellar phases, the rod-like cores are oriented parallel to the layer plane (denoted as Lam phases) [7,33,34,37,38,53,54]. In the two lamellar phases occurring adjacent to the polygonal cylinder phases (Lam Sm and Lam N ), the biphenyl cores remain parallel to the layer planes and retain in-plane positional and orientational order (Lam Sm , figure 5k) or only orientational order (Lam N , figure 5l ), before the in-plane molecular order is completely lost in the Lam Iso phase occurring at higher temperature or for longer side chain lengths (figure 5m) [53][54][55]. These Lam phases are of significant interest for condensed matter physics in general, as they offer the possibility to investigate phase transitions in quasi-two-dimensional systems [55].…”