Eur. Phys. J. E (2008) 26: 261-273
https://doi.org/10.1140/epje/i2007-10323-0

Regular Article

Rich polymorphism of a rod-like liquid crystal (8CB) confined in two types of unidirectional nanopores

¹ Institut de Physique de Rennes, CNRS-UMR 6251, Université de Rennes 1, F-35042, Rennes, France
² Institut des Sciences de la Terre, rue de la Férollerie, F-45071, Orléans, France
³ Laboratoire de Physique des Interfaces, Université Libre de Bruxelles, B-1050, Bruxelles, Belgique
⁴ Laboratoire d'Optronique, FOTON, CNRS-UMR 6082, Université de Rennes 1, F-22302, Lannion, France
⁵ Laboratoire Léon Brillouin (CEA-CNRS), F-91191, Gif-sur-Yvette, France
⁶ Fakultät für Physik und Elektrotechnik, Universität des Saarlandes, D-66041, Saarbrücken, Germany

^* e-mail: denis.morineau@univ-rennes1.fr

Received: 31 August 2007
Accepted: 10 April 2008
Published online: 29 May 2008

Abstract

We present a neutron and X-rays scattering study of the phase transitions of 4-n-octyl-4' -cyanobiphenyl (8CB) confined in unidirectional nanopores of porous alumina and porous silicon (PSi) membranes with an average diameter of 30nm. Spatial confinement reveals a rich polymorphism, with at least four different low temperature phases in addition to the smectic A phase. The structural study as a function of thermal treatments and conditions of spatial confinement allows us to get insights into the formation of these phases and their relative stability. It gives the first description of the complete phase behavior of 8CB confined in PSi and provides a direct comparison with results obtained in bulk conditions and in similar geometric conditions of confinement but with reduced quenched disorder effects using alumina anopore membranes.