High-resolution dielectric study reveals pore-size-dependent orientational order of a discotic liquid crystal confined in tubular nanopores.
We report a high-resolution dielectric study on a pyrene-based discotic liquid crystal (DLC) in the bulk state and confined in parallel tubular nanopores of monolithic silica and alumina membranes. The positive dielectric anisotropy of the DLC molecule at low frequencies (in the quasistatic case) allows us to explore the thermotropic collective orientational order. A face-on arrangement of the molecular discs on the pore walls and a corresponding radial arrangement of the molecules is found. In contrast to the bulk, the isotropic-to-columnar transition of the confined DLC is continuous, shifts with decreasing pore diameter to lower temperatures, and exhibits a pronounced hysteresis between cooling and heating. These findings corroborate conclusions from previous neutron and x-ray-scattering experiments as well as optical birefringence measurements. Our study also indicates that the relative simple dielectric technique presented here is a quite efficient method in order to study the thermotropic orientational order of DLC-based nanocomposites.
Faculty of Electrical Engineering, Czestochowa University of Technology, 42-200 Czestochowa, Poland.
Sylwia
S
Całus
Faculty of Electrical Engineering, Czestochowa University of Technology, 42-200 Czestochowa, Poland.
Andriy V
AV
Kityk
Faculty of Electrical Engineering, Czestochowa University of Technology, 42-200 Czestochowa, Poland.
Lech
L
Borowik
Institut de Physique de Rennes, UMR 6251, Université de Rennes 1, 35042 Rennes, France.
Ronan
R
Lefort
Institut de Physique de Rennes, UMR 6251, Université de Rennes 1, 35042 Rennes, France.
Denis
D
Morineau
BAM Federal Institute for Materials Research and Testing, D-12203 Berlin, Germany.
Christina
C
Krause
BAM Federal Institute for Materials Research and Testing, D-12203 Berlin, Germany.
Andreas
A
Schönhals
Institute of Materials Physics and Technology, Hamburg University of Technology (TUHH), D-21073 Hamburg-Harburg, Germany.
Mark
M
Busch
Institute of Materials Physics and Technology, Hamburg University of Technology (TUHH), D-21073 Hamburg-Harburg, Germany.
Patrick
P
Huber