Dresden 2009 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 39: POSTERS Colloids and Liquids

CPP 39.28: Poster

Thursday, March 26, 2009, 17:00–19:30, P3

Investigations of the Molecular Structure of Bent-Core Liquid Crystals by NMR — •Günter Hempel — Martin-Luther-Universität, Institut für Physik, D-06099 Halle, Germany

Liquid crystals consisting of molecules with bent cores exhibit an interesting phase behaviour. For example, ferroelectricity is observed even if the molecules are achiral. The phase structure depends strongly on the geometry of the molecules, particularly on the angle by which the mesogenic core is bent. Because of absence of long-range periodicity, a non-scattering method was needed for estimating the structure directly in the nematic phase.

In our NMR experiments, the dipolar coupling among nuclear spins was explored. For monitoring the 1H-13C interaction we applied the cross-polarization procedure. It relies on the exchange of polarization between 1H and 13C spin systems which can take place as oscillation. Its frequency is proportional to the dipolar coupling. Furthermore the interaction among the 1H spins was investigated by means of the decay of the proton magnetic resonance signal (WISE experiment). In both cases a two-dimensional Fourier transformation was performed which gives two frequency axes: One related to chemical-shift scale, the other related to the interaction frequency scale. The interaction between two magnetic moments depend on the angle between the connection line and the magnetic field. At this way it was possible to calculate intramolecular angles from the coupling constants.