Europhys. Lett.
Volume 73, Number 4, February 2006
Page(s) 553 - 559
Section Condensed matter: structural, mechanical and thermal properties
Published online 18 January 2006
Europhys. Lett., 73 (4), pp. 553-559 (2006)
DOI: 10.1209/epl/i2005-10442-2

Orientational order and dynamics of a nematic liquid crystal in porous media

C. Fehr1, 2, C. Goze-Bac2, E. Anglaret2, C. Benoit2 and A. Hasmy3

1  Hahn-Meitner Institut - 100 Glienicker Strasse, 14109 Berlin, Germany
2  Laboratoire des colloïdes, verres et nanomatériaux, UMR 5587 CNRS-Université Montpellier II - Place E. Bataillon, 34095 Montpellier, France
3  Laboratorio de Física Estadística de Sistemas Desordenados, Centro de Física, IVIC Apartado 21827, Caracas 1020A, Venezuela

received 23 June 2005; accepted in final form 2 January 2006
published online 18 January 2006

We report on orientational order and dynamics of a nematic liquid crystal confined in porous silica. 13C NMR lineshape is used as a fingerprint for this study. A procedure based on exchange of non-coupled sites is implemented in order to obtain the corresponding local order parameter S and the characteristic time for molecular reorientation $\tau$. Our results evidence that in the nematic phase, S decreases when confinement increases. By means of Langevin dynamics simulations of confined liquid crystals, we show that this behavior is due to topological defects, originated by the absorbed-layers phenomenon as a consequence of the strong anchoring of these molecules on silica surfaces.

61.30.Hn - Surface phenomena: alignment, anchoring, anchoring transitions, surface-induced layering, surface-induced ordering, wetting, prewetting transitions, and wetting transitions.
61.30.Jf - Defects in liquid crystals.
64.70.Md - Transitions in liquid crystals.

© EDP Sciences 2006