Abstract
ABSTRACTEight novel liquid crystalline materials were prepared containing highly branched terminal chains, either 2,4,4-trimethylpentyl or 3,5,5-trimethylhexyl. All materials exhibit nematic mesophases, with additional smectic (Sm) C, hexatic B and SmI phases for certain homologues. Analysis by small- and wide-angle X-ray scattering reveals continual build-up of the correlation length within the nematic phases, where we also observe splitting of the small angle peak into four lobes, indicating pretransitional Sm fluctuations. Connoscopy confirms the nematic phase to be uniaxial and optically positive. We observe that in the solid state, the molecules exist as staggered antiparallel pairs as a consequence of the sterically demanding bulky terminal group, and this would also appear to manifest in the hexatic B phase, where the layer spacing was found to be greater than the molecular length. If true, this is an example of pair formation driven by sterics rather than dipole–dipole interactions and suggests that reentrant systems driven purely by steric frustration may be found.
Highlights
Ferroelectric liquid crystals have the potential to out-perform nematic liquid crystals in electrooptic devices [1]
We observe that in the solid state, the molecules exist as staggered antiparallel pairs as a consequence of the sterically demanding bulky terminal group, and this would appear to manifest in the hexatic B phase, where the layer spacing was found to be greater than the molecular length
Optimisation of one parameter can be to the detriment of others, for example, birefringence can be lowered by incorporating cyclohexyl rings in lieu of phenyl at the cost of reduced phase stability and tilt angle
Summary
Ferroelectric liquid crystals have the potential to out-perform nematic liquid crystals in electrooptic devices [1]. We observe that in the solid state, the molecules exist as staggered antiparallel pairs as a consequence of the sterically demanding bulky terminal group, and this would appear to manifest in the hexatic B phase, where the layer spacing was found to be greater than the molecular length.
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