Growth of a smectic A from a bent nematic phase and the smectic light valve

Abstract

We show that for certain liquid crystals, characterized by very small nematic/smectic−A latent heats, the transition from a nematic phase, held firmly in a bent state, to a smectic−A phase takes place via an intermediate state which is stable in a given temperature range and which we have called ’’striped texture’’. This state consists of a corrugated layer of bent nematic which is sandwiched between two smectic−A layers whose planes are oriented in two different directions. As the temperature of the sample is further decreased, the ’’striped texture’’ becomes unstable. The corrugated layer undergoes axial buckling leading to the final smectic−A ’’honeycomb texture’’. This texture is the scattering phase of Kahn’s smectic light valve. We explain the occurrences of these phenomena on the basis of elastic and surface energy considerations.

Towards tunable defect arrangements in smectic liquid crystal shells utilizing the nematic–smectic transition in hybrid-aligned geometries

“…The resulting frustration phenomenon leads to a characteristic striped pattern sometimes referred to as 'oily streaks' or 'striations', which has been found in several previous studies of flat samples with antagonistic boundary conditions. We however note that the striped pattern can be classified into two types depending on if the striations are along 24 or perpendicular 25,26 to the projected c director field (further details will be discussed in a separate paper). As seen in Fig.…”

“…along c(r, φ , θ ), corresponding to the observations of stripes along c(x, y) in the flat hybrid samples studied by Cladis and Torza. 24 They found that the director bend is initially compressed to an increasingly thin layer within the sample bulk that remains in a nematic state due to a depression of the phase transition temperature induced by the bend distortion. In order to minimise the distortion this internal nematic layer buckles in alternating directions (Fig.…”

“…The smectic layers eventually eliminate the suppressed nematic membrane by curving such that they can connect to each other throughout the shell while still satisfying the opposing boundary conditions. The process first leads to a "virgule" texture 24 which then transforms into a focal conic texture once the curved layers have formed complete hemispherical domains. The details are illustrated schematically for the very simplified case of only a few smectic layers in Fig.…”

Doubly periodic instability pattern in a smectic-Aliquid crystal

“…This important result for a closed form of the generating curve is derived, based on the competition between anchoring and magnetic energy, mediated by elasticity (1) under the global geometric constraint of equidistant layers (4), rather than assumed a priori as in refs. [6,7,18]. To obtain a spacefilling two dimensional structure we perform a parallel transport of the generating curve ζ 0 (ξ) along its normal ν = ν x e x + ν z e z (see Fig.…”

“…In contrast, patterns in smectic LC phases are more difficult to describe due to the additional one-dimensional positional order. Many, sometimes rather complex, smectic patterns have been observed, such as undulations of the smectic layers in an applied magnetic field (HelfrichHurault instability) [1,3] or other periodic structures, like stripes [6,7], squares [8], or hexagons [9]. Usually, those structures are explained by the formation of focal conic domains or curvature walls, characterized by one typical length scale [3,[10][11][12].…”