X-ray and Dielectric Spectroscopy Studies Of Chiral Ferroelectric Liquid Crystals With Keto Group Maja Stojanovic , Dusanka Z. Obadovic , Alexej Bubnov , Vera Hamplova and ?y Miroslav Kaspar 1 Department of Physics, Faculty of Sciences, University of Novi Sad, TrgD. Obradovica 4, 21000 Novi Sad, Serbia 2 Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 182 21 Prague, Czech Republic Abstract. Series of ferroelectric liquid crystals with the keto group attached to the molecule core and one lactate group as the chiral centre have been studied by X-ray and dielectric spectroscopy. The thickness of smectic layers and the average distance between the long axes of neighboring molecules increases with increase of both chains. Keywords: X-ray, dielectric spectroscopy, complex permittivity, layer spacing, chiral liquid crystal. PACS: 61.10.Eq; 61.30.-v; 77.84.Nh INTRODUCTION Recently, series of ferroelectric liquid crystals with the keto group attached to the molecule core and one lactate group as the chiral centre possessing the broad paraelectric SmA and ferroelectric SmC* phases have been synthesized and studied [1-4]. General formula of the compounds is: o , , , v o , , n o Rl ° \U/\vy/ co \vJv coc * HCOR 2 ^ ^ ^ ^ CH 3 where Ri = C n H 2n +i, R2 = C m H 2m +i. The aim of this work is to study the influence of the length of the chiral (m) and non-chiral {ri) alkyl chains on the properties of the studied compounds by X-ray analysis and dielectric spectroscopy. RESULTS AND SUMMARY The change of the non-chiral chain length has only a small influence on mesomorphic properties, while the increasing of the chiral chain length results in broadening of the SmA and shift of the SmC* phase to the lower temperatures. Spontaneous polarization (reaches values up to 190 nC cm" 2 ) and spontaneous tilt angle increase with (m) decrease, but remain nearly the same while (ri) changing. On temperature dependence of the layer spacing, the phase transition from the orthogonal SmA to the tilted SmC* phase was observed as gradual decrease of the layer thickness, which is connected with increase of molecule's tilt. Average distance between the long axes of neighbouring molecules increases with increase of both (ri) and (m) chain lengths. The analysis of the frequency dispersion of the complex permittivity provides relaxation frequency and dielectric strength of the Goldstone mode in the SmC* and of the soft mode in the SmA phases. Relaxation frequency of the soft mode linearly decreases and dielectric strength steeply increases when approaching the transition temperature to the SmC* phase. Due to viscosity increase there is a slight decrease of relaxation frequency of the Goldstone mode on cooling. The detailed X-ray and dielectric studies are in progress now and will be presented elsewhere. The studied compounds can be useful as chiral dopants in mixtures for optical applications. ACKNOWLEDGMENTS This work was supported by Grants: COST D35 WG13-05; CSF 202/05/0431; 141020 from the Min. of Sci. and Env. Prot. of the Republic of Serbia. REFERENCES 1. V. Hamplova, A. Bubnov, M. Kaspar, V. Novotna, M. Glogarova, Liq. Cryst. 30, 493-498, (2003). 2. V. Hamplova, A. Bubnov, M. Kaspar, V. Novotna, D. Pociecha, M. Glogarova, Liq. Cryst. 30, 627-632, (2003). 3. A. Bubnov, M. Glogarova, Y. Semenova, Y. Panarin, M. Kaspar, V. Hamplova, Proc. SPIE 5565, 13-18, (2004). 4. A. Bubnov, V. Hamplova, V. Novotna, M. Kaspar, and M. Glogarova, Proc. SPIE - in print, (2006). CP899, Sixth International Conference of the Balkan Physical Union, edited by S. A. Cetin and I. Hikmet © 2007 American Institute of Physics 978-0-7354-0404-5/07/$23.00 659 Downloaded 11 May 2007 to 129.69.100.160. Redistribution subject to AIP license or copyright, see http://proceedings.aip.org/proceedings/cpcr.jsp