Electroconvection in dimeric nematic liquid crystals with short-range smectic C order: dynamical characteristics

Competing Instability Modes in an Electrically Driven Bent-Core Nematic Liquid Crystal

“…The large initial tilt required for a low threshold as obtained here is ordinarily not conceivable in a sample bound between buffed polyimide coatings. However, as recently emphasized, the presence of supramolecular smectic C clusters in the N phase may involve a large tilt favoring inlayer fluctuations; this could promote the PI instability. A further facilitating factor is this: As shown by Derzhanski and Petrov for the dc case the PI threshold reduces substantially when the gradient flexoterm is included in the torque balance equation.…”

Variable pitch hydrodynamic electro-optic gratings utilising bent liquid crystal dimers

“…Studies have been carried out in driving bent-core LCs into a state of EHDI 58,61,[81][82][83] and there are a few similar reports on odd-spaced dimeric LCs. [84][85][86] Both bent-core and dimeric LCs tend to exhibit significantly different EHDI behaviour (termed non-standard electroconvection) to those observed in conventional (calamitic) NLCs. [87][88][89] These differences are attributed to the sizeable effect of flexoelectricity in the EHDI of these novel materials, 41,[83][84][85] where the standard Carr-Helfrich model assumes such effects are negligible.…”

“…[84][85][86] Both bent-core and dimeric LCs tend to exhibit significantly different EHDI behaviour (termed non-standard electroconvection) to those observed in conventional (calamitic) NLCs. [87][88][89] These differences are attributed to the sizeable effect of flexoelectricity in the EHDI of these novel materials, 41,[83][84][85] where the standard Carr-Helfrich model assumes such effects are negligible. 34,39,40 The EHDI of bent-core and dimeric LCs show different frequency dependencies of V C and optical textures, compared to calamitics, making a direct evaluation between standard and non-standard EHDI difficult.…”

“…However, it is unlikely that they are responsible for the observed change in the conduction regime, where such effects should be magnitudes smaller than the ionic effects. [83][84][85]109,110 Flexoelectric rolls are observed in both bent-core and odddimer liquid crystals. [111][112][113] However, it is unlikely the rolls investigated here are flexoelectric in origin since they depend strongly on sample conductivity, 81 have the normal parallel to the director, 82 and have a different frequency and voltage dependence of the onset behaviour.…”