Ferroelectric-like switching in the nematic phase of four-ring bent-core liquid crystals

Abstract

The recent discovery of a ferroelectric response to a switching electric field in nematic phases exhibited by bent-core polar molecules, particularly 1,2,4-oxdiazole derivatives, could lead to new avenues for the development of electro-optic devices. For the first time, we report ferroelectric-like switching under the influence of a triangular wave electric field in the nematic phase exhibited by unsymmetrical achiral four-ring bent-core compounds. These bent-core molecules, exhibiting a large nematic phase range (>70 C), consist of two unequal lengths in two wings and possess a polar moiety at one end and an alkyloxy chain at the other end. An anomalous variation in spontaneous polarization as a function of temperature in the nematic phase is distinctly observed, which is similar to the results reported only in the low temperature region of the nematic phase. Electro-optical, current-response and dielectric studies of aligned samples corroborate earlier reports of the proposed polar structure of the cybotactic clusters and the ferroelectric-like polar switching of these nematic phases.

Impact of terminal polar substitution on elastic, electro-optic and dielectric properties of four-ring bent-core nematic liquid crystals

“…4(a)) as observed earlier for its lower homologues (n ¼ 6, 7). 31,32 The high frequency (2 MHz) peak P2 corresponds to a molecular mode occurring due to rotation of the molecules along their long axes whereas other peak P1 appears at extremely low frequency (50 Hz) range where the polarization peak appears in E-O studies. P1 is collective mode and appears as a result of cooperative movement of the molecules in cybotactic clusters.…”

One-dimensional theoretical analysis of coupling and confinement effects on the cybotactic clusters of bent-core nematic liquid crystals

“…The N phase of calamitic LCs possesses long-range orientational order, but lacks in any definite positional correlation or ordering. In contrast, the N phase of bent-core LCs possesses small domains with an additional short-range smecticlike local positional ordering besides the usual long-range orientational order, referred to as cybotactic clusters [2,[4][5][6][7][8]. It is believed that the bent-shaped LC molecules, owing to their kinked molecular shape, lock themselves together to form these clusters [9].…”

Insights into Biaxial Ordering of Bent-Core Nematics: X-Ray Diffraction Evidence

“…the interaction with a field or a surface). Although this assumption was supported by several experimental findings [15,[21][22][23][24][26][27][28][29] and molecular simulations [15,30,31], there was in the past no direct experimental evidence of cluster biaxiality. In particular, XRD has long been considered unfit to probe biaxial order due to the inherently small molecular biaxiality of bent-core mesogens coupled with the typical broadness of X-ray scattering from nematics [2,4].…”

“…After a decade of experimental investigations, it is now widely recognized that the four-spot pattern is instead the signature of a cybotactic N phase, i.e., a N phase consisting of nano-sized molecular aggregates (the cybotactic clusters) characterized by tilted layered (i.e., smectic-C-like) positional order [10,[15][16][17][18][19][20][21]. In addition, cybotactic clusters are usually assumed to be inherently biaxial (and possibly polar [15,[22][23][24]), with cluster transverse axes randomly oriented with respect to neighboring clusters [25]. Hence, the cybotactic N phase is macroscopically uniaxial with a single common director, unless steps are taken to coherently align the biaxial clusters over large spatial scales with an external agent (e.g.…”