Labyrinthine instability in freely-suspended smectic films
Final Report Abstract
In the frame of the DFG-Project we investigated formation of periodic structures and labyrinthine patterns in freely-suspended smectic films of novel liquid crystalline materials formed by bentcore mesogens. The investigation of the structure of the director field and its interaction with the external electric field in the modulated state helped us understand the underlying mechanisms of the pattern formation. Two different scenario of the pattern formation have been found. The first scenario is responsible for formation of alternating bent deformations in films of SmCPF phase independently of the local chirality of the structure. We attribute this instability to the sign inversion of the bend-elastic constant. The second scenario is the formation of the patterns with a spontaneous splay of polarization and labyrinthine patterns of the layer dislocations in the films. In these patterns the defect lines separate the stripes of the polarization splay. We believe, this behavior is caused by the intrinsic structure of the polarization-modulated layer-undulated phase (PM-SmCP), which has been characterized by X-ray diffraction technique. Couplings between the tilt and the polarization in the bent-core materials can destabilize the homogeneous state of the director field and give rise to pattern formation as well as unusual types of behavior in bulk. In this project we have found and investigated an achiral analogue of the electroclinic effect in SmA and SmC phases of bent-core molecules and multistage switching in polar SmCP phase. All planed in the project experimental investigation have been accomplished including X-Ray and Second Harmonic Generation (SHG) studies.
Publications
- Labyrinthine instability in polar free-standing liquid crystalline films. e-Liq. Cryst, 2005
A. Eremin, R. Stannarius
- c-director relaxation around a vortex of strength +1 in free-standing smectic-C films. Eur. Phys. J. E, 21(1):57–67, Sep 2006
A. Eremin, C. Bohley, and R. Stannarius
- Microscopic structures of the B7 phase: AFM and electron microscopy studies. Liq. Cryst., 33(7):789– 794, 2006
A. Eremin, L. Naji, A. Nemes, R. Stannarius, M. Schulz, and K. Fodor-Csorba
- Colloidal inclusions in smectic films with spontaneous bend. Eur. Phys. J. E, 23:25 – 30, 2007
C. Bohley and R. Stannarius
- Ambidextrous bend patterns in freestanding polar smectic- SPF films. Phys. Rev. E, 78(6 Pt 1):061705, 2008
A. Eremin, A. Nemes, R. Stannarius, and W. Weissflog
- Electrically induced tilt in achiral bent-core liquid crystals. Phys. Rev. Lett., 101(24):247802, 2008
A. Eremin, S. Stern, and R. Stannarius
- Multistage polar switching in bent-core mesogens. Eur. Phys. J. E, 25:395, 2008
S. Findeisen-Tandel, M. W. Schröder, G. Pelzl, U. Baumeister, W. Weissflog, S. Stern, A. Nemes, R. Stannarius, and A. Eremin
- Spontaneous bend patterns in homochiral ferroelectric SmCP films: evidence for a negative effective bend constant. Soft Matter, 70:1139, 2008
A. Eremin, A. Nemes, R. Stannarius, G. Pelzl, and W. Weissflog
- At the boundary to banana-shaped liquid crystals: polar properties of phases formed by new asymmetric achiral four-ring bent-core mesogens. Soft Matter, 5:1840, 2009
W. Weissflog et al.
- PhD Thesis Magdeburg (2009)
A. Nemes
