Orientational order and dynamics of a nematic liquid crystal in porous mediaC. 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 . 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