Berlin 2008 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 5: New Materials

CPP 5.2: Vortrag

Montag, 25. Februar 2008, 10:15–10:30, C 230

Novel electro-optic multistage switching in a polar smectic material — •Stephan Stern, Alexey Eremin, Alexandru Nemes, and Ralf Stannarius — Otto-von-Guericke-Universität Magdeburg

We report a very unusual and totally unprecedented electro-optic behaviour in a polar smectic phase of a bent-core mesogen, which cannot be attributed to either conventional antiferro-, ferri- or ferroelectric structures. Although x-ray investigations have shown a tilted smectic phase without in-plane order, the switching properties are very distinctive from those of typical ferro- or antiferroelectric liquid crystals. In order to determine the spontaneous polarization in dependence of the electric field we applied a triangular wave across the liquid crystal cell and found five peaks per half period. This behaviour can be attributed to five switching processes and corresponds to a hysteresis curve containing four loops (four stages of discontinuous switching) at high voltages and one continuous switching at lower voltages. The results were confirmed by measurements of optical transmission, birefringence and Second-Harmonic-Generation activity in the distinct states of the switching process. Based on this experimental results, possible structural arrangements of the mesogens in these distinct states of this mesophase are discussed.