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Effect of doping by enantiomers with the different absolute configuration and phase sequence on mesomorphic, helical and electro-optical properties of highly tilted chiral anticlinic mixture
摘要： The main objective of the present work is to contribute to better understanding of the effect of the absolute configuration and phase sequences of dopants on the self-assembling and physicochemical properties as well as on the electro-optical parameters of a specific liquid crystalline mixture with a broad temperature range of the antiferroelectric phase. In order to establish this effect, the mesomorphic behaviour, helical pitch length and its handedness, spontaneous polarization and tilt angle, as well as electro-optical performance for all design mixture, are determined. The results show a broad temperature range of the antiferroelectric phase and very low melting points in all mixtures. Mixtures doped with (R) enantiomers exhibit longer helical pitch lengths, lower values of spontaneous polarization and rotational viscosity, comparable values of a tilt angle but also longer switch off times in comparison to similar mixtures doped with (S) enantiomers. The doping by the enantiomers exhibiting isotropic-ferroelectric-antiferroelectric phase sequence reveals the most significant impact on properties of the base mixture. The knowledge gained will very advantageous while designing new multicomponent liquid crystalline mixtures exhibiting the chiral tilted smectic mesophases for application in surface stabilized modes with passive and active matrix drive for utilization in photonics and optoelectronics.
关键词： rotational viscosity,multicomponent mixtures,antiferroelectric liquid crystals,spontaneous polarization,helical pitch,tilt angle,(S) and (R) enantiomers
更新于2025-09-23 15:21:01
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short-range order on the activation energies of translational and rotational viscosities of nematic liquid crystals with highly polar molecules
摘要： We report experimental studies on the temperature-dependent translational and rotational viscosities of a few nematic liquid crystals made of highly polar molecules. Cyanobiphenyl (nCB) with longitudinal and cyanobicyclohexane molecules (CCN-mn) with transverse dipole moments were chosen and the measurements were made in the nematic phase. The translational viscosity (shear viscosity) is measured by using a rheometer and the rotational viscosity is measured from the dynamics of the Freedericksz transition by measuring the optical phase-retardation decay of the sample. The associated activation energies are obtained from the ?tting of the appropriate equation in the nematic phase. Only 8CB and CCN-47 exhibits N to Sm-A phase transition and their activation energies of translational and rotational viscosities are larger compared to the shortest homologs in the respective series. Both activation energies of 8CB are signi?cantly larger than that of CCN-47. The temperature-dependent steady states of the director distribution under shear are comprehensibly re?ected in the rheodielectric measurements of 8CB than that of CCN-47. The results are explained based on the differences in the Sm-A short-range orders and the critical slowing down of the order parameter ?uctuations. We present a simple physical model of molecular association that gives rise to different Sm-A short-range orders in both classes of compounds.
关键词： nematic liquid crystals,rotational viscosity,activation energies,Sm-A short-range order,translational viscosity
更新于2025-09-04 15:30:14