G. Scherowsky

Ferroelectric liquid crystals and dopants containing the chiral thiirane unit. A comparison with analogous oxiranes

Abstract The synthesis and mesomorphic properties of a new type of ferroelectric liquid crystals and dopants (for induced ferroelectric phases) containing cis or trans disub-stituted thiiranes as the chiral unit are described. A comparison of the thiiranes with the corresponding oxiranes is given. In the thiirane series the tendency to exhibit mesophases is less pronounced. S*C phases occur for three aromatic cores in the mesogenic part of the molecule. The temperature ranges of the liquid crystal phases are broader and the transition temperatures are higher in the trans compared with cis configured thiiranes and oxiranes. Cis configured thiiranes exhibit a higher spontaneous polarization than the corresponding trans compounds.

Order parameters from U.V. spectra with incompletely polarized absorption bands

Abstract A new method is developed for the determination of Saupes order parameters S* and D* from I.R. or U.V. spectra and the temperature dependence of their degree of anisotropy R. This method can be applied to molecules with one uniformly polarized band and another band of mixed polarization if all bands concerned are polarized in the same plane. For that a relation D* = f(S*) between the order parameters as a function of temperature is necessary, which can be obtained from the lines of constant entropy in the order triangle. These isentropics are calculated from the orientational distribution function of the ordered system. The resulting function D* = f(S*) is equal to that of the mean field theory given by Luckhurst et al., but can be derived here in a very easy way. The method is applied to diaminoanthraquinones with a point symmetry C2v.

A coloured ferroelectric side chain polymer

Abstract Coloured ferroelectric liquid-crystalline side chain copolymers containing 5 per cent and 15 per cent of an azo dye were synthesized and characterized by DSC, GPC and optical microscopy. Order parameters, S, of the azo compound exceeding 0·8 were measured in the frozen smectic phase for the 5 per cent copolymer. The copolymers exhibit fast electrooptic switching in the range of a few hundred microseconds to milliseconds in the Sc* phase. Both linear (i.e. electroclinic-like) and ferroelectric switching have been observed. Tilt angles of ∼19° and spontaneous polarization of ∼300nC cm−2 have been recorded in the Sc* phase.

E.S.R. investigation of helix inversion in induced cholesteric phases

Abstract The phenomenon of a reversible helix inversion in induced cholesteric mesophases caused by variation of the temperature has been investigated by E.S.R. spectroscopy using the nitroxide radical tempone as spin probe. Chiral esters of optically active (R)-(+)-2,2′-dihydroxy-1,1′-binaphthyl were added as dopants to the nematic mixture RO-TN 404. The inversion temperatures and the handedness of the helices were determined. In addition to the distortion parameter which is a measure of the helix pitch, order parameters and rotational correlation times of the spin probe were obtained from line-shape analyses.

Liquid-crystalline side chain polymers containing a chiral spacer unit exhibiting chiral smectic phases

Abstract The synthesis and mesomorphic properties of two liquid-crystalline side chain polymers with a chiral centre in the α or β position of the α-hydroxy acid representing the spacer unit are described. The chiral α branching leads to a dramatic decrease in the transition temperatures and a strong narrowing of the smectic mesophase (compared with the unbranched model compound I). The chiral β branching results in a chiral smectic phase, a pronounced contraction of the Sc phase, and the loss of the higher ordered Sf phase. The S*c phase was confirmed by X-ray investigations of oriented samples. Depending on the polymerization conditions samples were obtained which were oriented in melt drawn fibres either with their smectic layers or their mesogenic units in the direction of stress.

New dopants for induced ferroelectric SC* phases containing 1,3-dioxolan-2-one as a chiral heterocycle

Abstract The synthesis, phase behaviour and spontaneous polarization of a new class of chiral dopants for induced ferroelectric phases of general structure 6 and 9, possessing a 1,3-dioxolan-2-one ring, are described. One of the new compounds exhibits a SA phase. When the chiral ring system is positioned terminally to the mesogen (6) the cis disubstituted compounds show higher induced spontaneous polarization than those with an analogous trans configuration.

Novel liquid crystals and dopants (for induced ferroelectricity) possessing a chiral 2-oxetanone unit. A comparison with corresponding dioxolanones

Abstract The mesomorphic properties, induced spontaneous polarizations, and response times of a new type of liquid crystal and ferroelectric liquid crystal mixtures containing di- or trisubstituted 2-oxetanones as a chiral unit are described. By heating above 140°C oxetanones, bearing a three core mesogenic part, suffer cycloelimination of carbon dioxide yielding liquid-crystalline olefines with nematic, smectic C and higher ordered smectic phases, which are best suited as host materials for induced Sc∗ phases using the corresponding oxetanones as dopants. Compared with 1,3-dioxolan-4-ones recently synthesized and investigated, the oxetanones show minor mesomorphism.

Broadband dielectric spectroscopy on ferroelectric liquid-crystalline side group polymers

Abstract Broadband dielectric spectroscopy (10−1 to 107Hz, 100 to 450 K) has been applied, for the first time, to investigate the molecular dynamics of recently synthesized fast switching ferroelectric side group polymers. The softmode could be studied in detail in the Sc∗ phase and in the S1∗ phase. At the transition a pronounced increase of the relaxational strength was found whereas its relaxational frequency remains constant The softmode is the molecular basis for the electroclinic effect which has high application potential for ferroelectric liquid crystal polymers.

Two unusual mesophases in chiral side chain polymers

Abstract We have reported in a previous paper the synthesis, characterization, structural and electro-optic properties of a new family of chiral mesomorphic side chain polyacrylates. The most salient finding was that many of these polymers presented two S*C phases of similar structure, but differing in their switching properties. In addition, two unusual mesophases called U1 and U2 were also discovered in this family. We describe here in more detail the symmetries and molecular organizations for these U1 and U2 phases. We also discuss their relation, on the one hand, to the newly discovered antiferroelectric chiral S*CA and S*o phases, and, on the other hand, to the 2-dimensional fluid smectic A and smectic °C phases displayed by strongly polar low molar mass mesogens. The occurrence of chevron-like ordering in the U1 and U2 phases may give a clue to an understanding of this peculiar S*C polymorphism.

Ferroelectric liquid crystalline side group polymers derived from mesogenic vinyl ether monomers

Abstract Two classes of ferroelectric polymers, polysiloxanes and polyvinyl ethers, have been synthesized, starting from the same mesogenic vinyl ether as precursor. The polysiloxane materials obtained by polymer analogous reaction of vinyl ethers with H-siloxanes exhibit larger ranges of ferroelectric S*C phases than the corresponding polyvinyl ethers. The effect of changing the nature of the link of the terminal chiral end group on the phase behaviour and ferroelectric properties of the new side chain polymers is reported.