Norman Dr. Häberle

Cyclosiloxanes with mesogenic side groups

Abstract Cyclic liquid crystalline siloxanes (CLCS) are optical uniaxial positive (SA, N) and negative (N*) materials in accordance with calamitic structures. X-Ray measurements indicate, that the distances of SA layers correspond with the length of the monomer unit. In the case of mesogens with high polarity the distance is 1.7 fold the length of the monomer unit. A bundle model is proposed for CLC siloxanes.

Dielectric relaxation in four cyclic liquid-crystalline oligosiloxanes with different ring size and spacer length

Using dielectric spectroscopy in the frequency range 100 Hz to 13 MHz, the molecular dynamics of cyclic liquid-crystalline oligosiloxanes have been investigated. Up to two relaxation processes were found, depending on different molecular dipole components. The compounds were aligned and as well as temperature-dependent spectra, bias-field-dependent spectra were recorded to show clearly the behaviour of each component while aligned in the electric field. The influence of the ring size on the dielectric relaxation behaviour is described as well as the influence of the spacer length.