Untersuchung des Cotton-Mouton-Effektes in der isotropen Phase flüssigkristalliner Substanzen

In the first part of the thesis a short description of the theory of liquid crystaline phases, of the Cotton-Mouton effect, critical laws and the Landau-de Gennes theory is given. In the second part a device is described, which allows the very exact determination of the magnetically induced birefringence (Cotton-Mouton (CM) constant) in the isotropic phase. Measurements of the CM constants of a larger number of liquid crystaline substances are presented. These values are used to discuss existing theories on pretransition effects in liquid crystals.

In this work the conclusion is drawn that at the moment no theory exists which describes the pretransition phenomena at the phase transition isotropic-liquid crystalline correctly.