Günter Scherowsky

New switchable columnar liquid crystals

Abstract Penta- and hexa-substituted phenanthrenes and penta-substituted benzo[c]-phenanthrenes have been synthesized; these exhibit columnar phases and are electrically switchable when bearing chiral side chains. The liquid crystalline and electro-optical properties are described. A strong tri-state switching behaviour is observed with the phenanthrene derivatives. A helical phase structure, responsible for this switching behaviour, is proposed and the possible mechanism of the columnar phase switching process is discussed.

FLUORESCENT FERROELECTRIC LIQUID-CRYSTALLINE COPOLYACRYLATES

Abstract Fluorescent liquid crystalline side chain polymers were synthesized by copolymerization of a ferroelectric monomer and 5 per cent of various blue fluorescent naphthalic imide dye comonomers. Those copolymers were characterized by DSC, X-ray, GPC and optical microscopy. In favourable cases, fast switching fluorescent ferroelectric polymers resulted, exhibiting high tilt angles (up to ∼ 34°) and spontaneous polarization values (up to ∼ 115 nC cm−2) in the S*c phase. One fluorescent copolymer shows orthogonal smectic phases exclusively due to the structure of the incorporated fluorescent comonomer. In this case a strong electroclinic effect and high induced tilt angles (12° 10 V μm−1) have been observed in the Sa phase. Order parameters, S, of the dye moieties up to 0.64 were measured in the room temperature Sb phase for the copolymers

Ferroelectric liquid-crystalline side group polymers - spacer length variation and comparison with the monomers

Abstract The phase behaviour and the ferroelectric properties of liquid-crystalline side group polyacrylates containing an (R)-4″(1-methylheptyloxy)-4′-biphenylyloxycarbonyl-4-phenoxy moiety are compared with the properties of their monomers. A S*C phase polymorphism including monolayer and bilayer structures was found for the polymers. Some of the S*C subphases, consisting of smectic mono- or bi-layers, do not exhibit ferroelectric properties. These unusual properties do not exist for the corresponding monomeric acrylates. Therefore, one has to take into account that the polymer chain exerts a strong influence on the phase behaviour and the ferroelectric properties.

Structural studies of columnar phases of some chiral disc-like molecules

We have performed a structural study of the mesophases of some isomeric hexa-substituted phenanthrenes. Evidence for a new hexagonal columnar mesophase with three columns per unit cell was found in a chiral isomer. Moreover, a rectangular columnar phase with four columns per lattice, similar to the low temperature mesophase of a hexa-substituted rufigallol, was found in a different material. The relations between the structures and the electro-optical behaviour of the different mesophases are discussed.

On the seemingly antiferroelectric behaviour of certain ferroelectric liquid crystals

Abstract Double current peak, double hysteresis loop and even in some sense three electro-optic states, the main characteristics of the antiferroelectric liquid crystal phase, are found also in the ferroelectric smectic C* phase, observed so far on several liquid crystal materials possessing a C*—N* phase sequence. In the observed cases, the confining surfaces bring about a pronounced monostable surface anchoring of the liquid crystal molecules forcing the layers to be broken in two alternating directions, corresponding to the equivalent surface directions of positive and negative molecular tilt relative to the layer normal. The resulting striped texture is very reminiscent of certain domain patterns in solid ferroelectrics. The seemingly anomalous electric switching behaviour of this C* texture mimics an antiferroelectric and may thus easily lead to an incorrect designation of the phase if not supplemented by other identification methods. Hysteresis shape and switching current peaks are thus by themselve...

4,5,6,7,8,9-Hexamethoxyindeno[1,2,3-ij]isoquinoline

The crystal and molecular structure of the title compound (I), has been determined to confirm the molecular conformation. We established by x-ray investigations the planarity of the polyaromatic ring-system, which is necessary for the formation of discotic mesophases.

Linear electromechanical effect in a polymeric ferroelectric liquid crystal

Abstract A linear electromechanical effect was detected in a ferroelectric side chain polymeric liquid crystal. Experimental data on temperature and frequency dependence are presented.

Chiral Hexa-and Nona-Substituted 1,3,5-Triphenylbenzenes

Abstract , 1997 1,3,5-Triphenylbenzenes, Chiral and Non-Chiral Substituents Aiming to design new discotic liquid crystals, chiral and non-chiral esters and ethers of hexa-and nonasubstituted 1,3,5-triphenylbenzenes were synthesized. The new compounds are crystalline or high viscous liquids. They do not form mesophases or columnar donor-acceptor-complexes with TNF, DNF or DBox-H. The chiral esters 5c and 5d. used as dopants, induce cholesteric phases in nematic discotics.

The influence of a γ-oxygen in the spacer of liquid crystal side group polysiloxanes on their ferroelectric properties

Abstract Two types of side group polysiloxanes which differ in their spacer between backbone and mesogenic part were synthesized via polymer analogous reaction. The impact of an oxygen atom localized in the γ position to the siloxane main chain on the ferroelectric properties was investigated. In addition, the link between the terminal chiral moiety and the mesogenic part in each series was varied. The phase transition behaviour, spontaneous polarization and the electro-optical response time for the two series of polymers are compared. The mesophase structures were determined by X-ray measurements on magnetically oriented samples at different temperatures. The additional oxygen atom in the spacer near to the main chain leads to broader range smectic C∗ phases and shorter electro-optical response times, which suggests that the ether linkage promotes a better decoupling between main chain and mesogenic side group.

Novel ferroelectric liquid crystals and dopants for induced ferroelectric phases containing 3,4-epoxy-2-octanols as chiral unit

Abstract The synthesis of a new class of chiral smectic liquid crystals is described, along with transition temperatures, phase behaviour, spontaneous polarizations and related data. The general structure is shown in A. possessing a chiral unit derived from 3,4-epoxy-2-octanol. Two of these new compounds show seemingly antiferroelectric behaviour. The influence of the mesogenic core structure on mesophase behaviour and ferroelectric properties was investigated. The non-liquid crystalline representatives were examined as dopants for induced ferroelectric phases in an achiral matrix.