A new series of dimeric chiral antiferroelectric materials using a trisiloxane as the central connecting linker and having fluorinated tails has been synthesized together with their corresponding monomers. Spacer lengths of 3–6 and 11 methylene groups were used. As a comparison to see the effect of the siloxane length on the phase behaviour, one dimer with a tetrasiloxane core was also synthesized. Monomers with 3–6 carbons in the spacer showed just orthogonal smectic phases and only the long 11 carbon spacer 7F4PPB11 showed tilted phases in a very similar way to what was found in the unfluorinated monomers previously studied. All trisiloxanes showed a high temperature antiferroelectric phase and those with a spacer length of 4 or more carbons also showed one or two columnar antiferroelectric phases when decreasing the temperature. The spontaneous polarisation Ps was high, especially in the columnar phases where it ranged from 800–1200 nC cm–2 and upward. The apparent tilt angles were exceptionally high, above 45 degrees for all materials studied. In accordance with the trend described previously, the tetrasiloxane containing dimer showed a ferroelectric phase at high temperature. But in this case the columnar phase was found to be antiferroelectric. Hence, the general idea that trisiloxane cores promote antiferroelectricity and tetrasiloxanes promote the ferroelectric phase is still correct also for these materials in the SmC* phase, but not for the columnar phase. It can also be noted that the phase separation between siloxane, fluorinated tail and mesogenic parts of the molecules was so high that the material became columnar on lowering the temperature.

Two new chiral liquid crystalline monomers with bilactate or trilactate chiral units were synthesized and studied. The monomers show the paraelectric SmA and ferroelectric SmC* phases. The antiferroelectric SmCA* phase was detected only for the monomer possessing the bilactate unit. The temperature dependences of the spontaneous polarization and spontaneous tilt angle were measured. Real and imaginary parts of the complex permittivity were studied as a function of frequency and temperature. The synthesized monomers contain a double bond at the end of the achiral terminal chain, and were used to prepare liquid crystalline polysiloxanes.

The scope of the present study is the response of a series of antiferroelectric dimeric or bimesogenic siloxanes to an applied electric field with focus on their pretransitional behaviour and the field-induced antiferro-ferroelectric (AF-F) transition. Most of these compounds possess a molecular tilt close to 45 degrees and spontaneous polarization in the field-induced ferroelectric (F) phase in the range of 250 - 300 nC cm(-2). In the dimers with a spacer length exceeding five carbons, a transformation from first to second order of the field-induced AF-F transition is found with temperature. Several different indications for this transformation are identified and their characteristics are discussed in the framework of the existing theoretical models. A large field-induced in-plane deviation of the sample optic axis was observed in the pretransitional region of several of the siloxane dimers and is likely due to the flexibility of the linking chains. The potential of the antiferroelectric bimesogenic siloxanes for displaying high contrast images and grey scale capability is shortly discussed. The large molecular tilt close to 45 degrees in combination with the field-induced AF-F transition of second order seems to be the most attractive features of these materials.

In this paper, we report the study of a new series of symmetric chiral liquid crystalline siloxane dimers, their related monomers, and two of those monomers with heptamethyltrisiloxane attached. All the dimers coupled with a trisiloxane show the SmCA phase, which in several cases has a large tilt angle greater than 40° over a wide temperature range, as well as high spontaneous polarisation in the field‐induced ferroelectric state. Spacer lengths of 3–6 and 11 carbons between the siloxane central unit and the mesogenic cores were used. Monomers with 3–6 carbons in the spacer showed only orthogonal phases while the monomer with an 11‐carbon spacer, as well as the monomers with siloxane attached, have a high tilt angle ferroelectric phase. The materials were characterized by means of DSC, NMR, X‐ray diffraction, electro‐optical methods (tilt angle and texture characterization) and polarization measurements.

The syntheses of chiral liquid crystalline side chain polysiloxanes with lateral nitro substituents in the mesogenic core are described. The influence of the substituents and substituent positions on phase behaviour and electro-optical properties are investigated and compared. The lateral nitro groups strongly affect the phase behaviour of the side chain precursors as well as the liquid crystalline polymers. Properties in smectic A and C* phases are discussed with respect to substituent position. One side chain precursor exhibits very large spontaneous polarization of ∼700 nC cm–2 .

The synthesis of a series of side-chain liquid crystalline siloxane copolymers is reported, and comparative studies of physical properties of members with different side-chain length have been attempted. Measurements of ferroelectricity and relaxation times aimed at studying structure-property relationships for the longer side-chain members. It was found that the stability of the chiral smectic C phase decreases with decreasing length of the terminal alkyl ester.

Measurements of the soft-mode and electroclinic behavior in the smectic A*-phase of a compound with very high spontaneous polarization (about 5 mC/m2 (0.5 µC/cm2) in the smectic C*-phase) are presented. It is found that for large induced tilt angles, one observes a strip texture giving rise to a strong characteristic light scattering. Once created this periodic stripe pattern remains even when the field is turned off. Furthermore, the electric field-induced modulation of the pattern allows scattering intensity modulation, resulting in anomalous electroclinic behavior.

AbstractElectro‐optic and polarization reversal measurements were performed on a side‐chain polymer exhibiting a chiral smectic phase. Based on the observed electro‐optic and current responses, we discuss the possibility of an antiferroelectric structure in the polymer. In order to establish a model for the observed behavior, a detailed comparison with the properties of the low molar mass antiferroelectric substance MHPOBC was made. The birefringence modulation in the chiral smectic polymer, originating from the field‐induced antiferroelectric‐to‐ferroelectric transition, is analyzed for the case of a randomly oriented sample. The result shows that the coincidence of birefringence modulation and polarization current peaks is strong evidence for the existence of antiferroelectric order in the smectic layers. Such coincidence was observed both for MHPOBC and the chiral side‐chain polyacrylate.