Gerd Heppke

Ferroelectric liquid crystals with high spontaneous polarisation

Preparation de nouveaux composes ferroelectriques par esterification dalkyloxy-4 hydroxy-4 biphenyles avec des acides α-chlorocarboxyliques optiquement actifs obtenus a partir des acides α-amino correspondants. Ces substances presentent des phases smectiques chirales C* dans une gamme de temperatures appropriee et ont des valeurs elevees de polarisation spontanee, jusqua 300 nC/cm 2

Esters of (S)-1,2-propanediol and (R,R)-2,3-butanediol — Chiral Compounds Inducing Cholesteric Phases with a Helix Inversion ·

Mesogenic chiral esters of optically active (S)-1,2-propanediol and (R,R)-2,3-butanediol were synthesized. The compounds, added to a nematic phase induce cholesteric phases exhibiting a helix inversion with temperature variation. This effect is independent of the molecular structure of the nematic solvent. The inversion temperature varies only slightly with concentration but can be influenced by the mesogenic substituent.

Chirale Dotierstoffe mit außergewöhnlich hohem Verdrillungsvermögen

Mesogenic chiral esters of 1-phenyl-1,2-ethandiol, 1-cyclohexyl-1,2-ethanediol, 1,2-diphenyl- 1,2-ethanediol, 1,1´-bi-2-naphthol, 1-phenylethanol, 1-phenyl-2,2,2-trifluorethanol and 1-(9- anthryl)-2,2,2-trifluorethanol were synthesized. The temperature dependence of the molecular twisting power was determined in the nematic wide range mixture RO-TN 404. All compounds show good solubility and unusual high values of the molecular twisting power.

Smectic A1 — Smectic Ad Transition in Binary Mixtures of Compounds with Strongly Polar Terminal Groups

On the basis of high pressure studies we present here the evidence for the existence of a smectic A1 - smectic Ad transition at high pressure in a binary liquid crystal mixture consisting of terminally polar compounds. A feature of this observation is that both the constituent compounds are three phenyl ring systems wherein the bridging dipoles are disposed additive with respect to the polar end group.

Xray studies on bilayer Smectic A (A2 and bilayer Smectic C (C2) phases

AbstractXray studies on the smectic A and smectic C phases of 4-n-heptacylphenyl-4′-(4″-cyanobenzoyloxy) benzoate show that both these phases are bilayer phases (A2 and C2) characterised by strong second order Bragg reflections and a large d/l ratio (∼1. 8). Direct determination of the tilt angle from Xray photographs shows that the decrease in the layer spacing on going over from the A2 to the C2 phase is entirely due to the tilt of the molecular pairs and not due to any change in the interdigitation of the molecules.