Electric-field-induced patterns and their temperature dependence in a bent-core liquid crystal

Abstract

Two kinds of electroconvection patterns in an ether-bridged bent-core nematic liquid crystal material (BCN), which appear in different frequency ranges, are examined and compared. One is a longitudinal pattern with the stripes parallel to the orientation of the BCN and with a periodicity of approximately the cell thickness, occurring in the high-frequency range of several hundreds Hz; the other one is oblique stripes, which results in a zigzag pattern, and appears in the low-frequency range of several tens Hz. In addition, within an intermediate-frequency range, transformations from oblique to longitudinal and then to normal stripes occur at increased ac voltages. In particular, we investigated the temperature behavior of longitudinal and oblique stripes: When the temperature T increases and approaches the clearing temperature Tc, the contrast of the domains is enhanced and the frequency range of existence becomes wider, while the onset voltages increase only moderately instead of diverging, thus suggesting an isotropic mechanism of pattern formation.

Photoswitchable Bent-Core Nematic Liquid Crystals with Methylated Azobenzene Wing Exhibiting Optic-Field-Enhanced Fréedericksz Transition Effect

“…With the known dielectric constants of 5CB, together with the planar and homeotropic cells, the dependences of dielectric constants of compound 2/12 on f and I 365 were deduced. In contrast, for the conventional BCNs, only negative dielectric anisotropy (Δε < 0) was present, together with the absence of homeotropic alignment; it was difficult to observe and examine the FT effect induced by a perpendicular electric field. − …”

Unusual polarity-dependent patterns in a bent-core nematic liquid crystal under low-frequency ac field

“…The behavior of 9P-CF20 -0 D B P differs also from that of the shorter members (8P-CF20 -0 D B P [19] and 7P-CF?0-0DBP [48]) of the same homologous series. Though this might be surprising at first sight, it is not unprecedented.…”

“…The bentcore nematics (BCNs) studied so far mostly exhibit various nonstandard EC patterns [7][8][9][10][11][12][13][14][15][16][17][18][19][20], whose characteristics may substantially differ from those in calamitic LCs. Moreover, there are some unprecedented scenarios, like prewavy patterns at ultrahigh ( / > 50 kHz) frequencies with negative slope of Uc(f), which have been found so far only in BCN compounds [7,[11][12][13], These banana-specific features still wait for explanation.…”

Dislocations and metastable chevrons in the electroconvective inplane normal roll state of a bent core nematic liquid crystal

“…18 The various electroconvective chevron states discovered thus far are all exhibited by straight-core or calamitic nematogens. The reported electroconvection phase diagrams of bent core nematics [19][20][21][22][23][24][25] do not show any chevron instability, although chevrons have been reported beyond the dielectric inversion frequency for a bent-rod nematic liquid crystal. 26 This study concerns the transient chevron instability induced in bent core nematics by a sudden, large jump in the control parameter S ¼ (U 2 /U c 2 ) À 1, U and U c being the applied and threshold voltages, respectively.…”