Fast-switching displays with memory properties are provided, which can display digits, symbols, and images, and which contain as chemically and thermally stable ferroelectric liquid crystalline substances, according to the invention, liquid crystalline derivatives which contain a chiral alkyl halide residue corresponding to the general formula ##STR1## are used in mixtures of one another as well as in conjunction with other liquid crystalline or non-crystalline liquid substances.

Ferroelectric liquid crystals

A thermodynamic model of the ferroelectric SmC* phase, based on an extended Landau expansion of the free-energy density, is presented We discuss how the signs of the parameters entering the model are depending on whether the pitch of the helix is right-handed or left-handed and whether the compound is of the (+) or (-) type in regard to the sign of the polarization With the introduced Landau expansion as a basis, we derive the equations governing the behaviour of the tilt, polarization, pitch, dielectric susceptibility and heat capacity of the system We show that by rewriting the equations into dimensionless form, we can transform the original set of eleven parameters in the Landau expansion into a new set, consisting of six dimensionless parameters and five scaling factors The six dimensionless parameters are the only ones which enter the calculations of the quantities mentioned above, ie we need six dimensionless parameters to describe the temperature dependence of the five basic quantiti

Thermodynamic Model of Ferroelectric Chiral Smectic C* Liquid Crystals

In this article, we present the formulation and characterization of a ferroelectric liquid crystal (FLC) mixture W301 composed of pyrimidine compounds. We observed that upon doping magnesium oxide nanoparticles (MgO NPs) into the host FLC, the MgO NPs/FLC composite showed significantly faster response and improved optical tilt angle. The decreased response time in the MgO NPs/FLC composite has been attributed to the decrease in rotational viscosity and increase in surface anchoring energy. The decrease in rotational viscosity of the composite is due to the torque experienced by both MgO NPs and FLC in the presence of an electric field and perturbations of order parameters of FLC. Due to the enhanced surface interaction of MgO NPs having surface defects with mesogens, strong surface anchoring is experienced on the FLC molecules that not only increased the speed of the response but also improved the optical tilt angle of the MgO NPs/FLC composites, which ultimately resulted in improved contrast. A systematic approach has been followed to elucidate the idea of designing faster display devices with improved contrast based on MgO NPs/FLC composites.

/pdf/preparation-and-characterization-of-mgo-nanoparticles-3i65plp7lh.pdf

Preparation and characterization of MgO nanoparticles/ferroelectric liquid crystal composites for faster display devices with improved contrast

New relaxation processes are observed in ferroelectric liquid crystals with considerable high spontaneous polarization. These processes are attributed to the formation of ferroelectric domains in FLC cells. The domains have different characteristic periodicities and relaxation times in the bulk of FLC cell and near the surfaces of the electrodes. Characteristic relaxation processes are found in the dielectric response at frequencies VDB and VDS corresponding to both cases. The behaviour of dielectric strengths δϵv;DB and δϵDS versus d.c. field, spontaneous polarization and pitch of the helix is investigated.

Domain mode—A novel relaxation process in ferroelectric liquid crystals

Employing thermodynamical, optical and comprehensive dielectric studies, we have investigated a freshly synthesized chlorinated MHPOBC analogue antiferroelectric liquid crystal; it exhibits different chiral SmC sub-phases, viz. SmCα*, SmC* and SmCγ*, at considerably lower temperature in comparison with MHPOBC, and a wide range room temperature antiferroelectric SmCA* phase. Dielectric spectroscopy investigations under planar molecular anchoring were carried out in the frequency range 1 Hz to 10 MHz. The data measured for low and high frequency regions were corrected by the method of fitting operation of the theoretical equations. Seven different modes of dielectric relaxation in the different phases were identified. Soft mode relaxation was identified in the SmA* and SmCα* phases. The Goldstone mode, characteristic of the ferroelectric phase, was observed in the SmC* and SmCγ* phases. Two characteristic peaks are seen in the spectrum of the SmCA* phase: one, at high frequency, corresponds to fluctuation w...

Study of different modes of dielectric relaxation in a newly synthesized material exhibiting ferro-, ferri- and antiferro-electric phases

The complex dielectric constant has been measured in a room-temperature ferroelectric liquid-crystal mixture. We have resolved the experimental data into the Goldstone mode and the soft mode and for each mode determined the dielectric strength and the corresponding relaxation frequency. The results are compared with the dielectric strength calculated using the extended Landau type of free-energy density proposed by Z\ifmmode \check{}\else \v{}\fi{}eks\ifmmode \check{}\else \v{}\fi{} [Mol. Cryst. Liq. Cryst. 114, 259 (1984)], and it is shown that this calculation is able to describe the experimental data well. We have shown that by reasonable assumptions we can derive a simple relation between the Goldstone-mode contribution to the dielectric susceptibility (${\ensuremath{\chi}}_{2}$) and the polarization (${P}_{0}$), tilt (${\mathrm{theta}}_{0}$), and pitch (p) of the system: ${\mathrm{\ensuremath{\chi}}}_{2}$=(${\mathrm{P}}_{0}$p${\mathit{theta}}_{0}$${)}^{2}$/${8\mathrm{K}}_{3}$${\mathrm{\ensuremath{\pi}}}^{2}$), where ${K}_{3}$ is a bend nematic curvature elastic constant. We also predict, on theoretical grounds, a small peak of the dielectric strength to exist at ${T}_{c}$.

T Carlsson

Papers

Goldstone mode and soft mode at the smectic-A-smectic-C phase transition studied by dielectric relaxation.