Influence of an Imposed Network on One- and Three-Dimensional Photonic Liquid Crystal Structures through the Polymer Template Technique.

Abstract

We describe the first investigations on the influence of an imposed network on the photonic band gap (PBG) structure of the liquid crystal (LC) phase through the polymer template technique. The technique consists of using a cholesteric (Ch) phase as a base for photopolymerizing a difunctional monomer, which is then removed after polymerization, leaving only the polymer scaffold template. The templated structure obtained is utilized to adjust the PBG structure of the filled LC material, exhibiting both a one-dimensional PBG (Ch phase) and a three-dimensional PBG structure (TGBC* phase with smectic C* blocks). Selective reflection measurements indicate that the imprint polymer network of the template impacts the pitch of the Ch and TGBC* phases. The absorption peaks are visible because of two distinct twisted arrangements, one originating from the template and the other from the refilled chiral substance. In the templated cell, the central wavelength (λ_min) of PBG of the refilled sample red-shifts, as well as the width of the PBG gets enhanced compared to that for the sample in the regular (nontemplated) cell. For example, in the TGBC* phase, the λ_min value red-shifts by 369 nm, and the width of the PBG enlarges by 50%. Additionally, the lattice spacing arising due to the periodicity of the SmC* helix in 2-dimension in the TGBC* phase gets enhanced. These findings demonstrate the polymer template method's effectiveness in tuning the mesophase's PBG in all three dimensions.