<title>Dielectric properties of nematic liquid crystals in porous membranes</title>

Abstract

Broadband dielectric spectroscopy (10<SUP>2</SUP> Hz-10<SUP>9</SUP> Hz) is employed to study the molecular dynamics of the liquid crystal 4-n-pentyl-4'-cyanobiphenyl (5CB) in cylindrical channels of Anopore membranes having a diameter between 0.2 micrometers and 0.02 micrometers , and thickness about 60 micrometers . The surfaces of channels are modified using the coupling agent C<SUB>9</SUB>H<SUB>19</SUB>COOH. In the bulk 5CB two relaxation processes are observed: the hindered rotation of the molecules around their short molecular axis ((delta) -relaxation, and tambling of the molecules around short molecular axis. In untreated Anopore membranes the first process is only observed, which is nearly uninfluenced by the presence of the inner surfaces. In contrast, in treated Anopore membranes the second process connected with tambling of the molecules around their short molecular axis becomes detectable. This phenomenon is connected with a changing of the planar axial to planar radial alignment of the molecules. The relaxation rate in the isotropic phase is nearly uninfluenced by the presence of the inner surfaces, it is in the nematic phase by two orders of magnitude faster for the porous materials with modified surface as compared to the bulk. The dielectric strength of the (delta) -relaxation is considerably weakened for the 5CB/Anopore system.