Clusters of B7 Fibers Reveal Origin of Blue Phase Stability in a Binary Mixture of Chiral Rod-like and Achiral Bent-Core Molecules.

Abstract

Liquid crystal (LC) blue phases (BPs) have gained relevance because of their potential applicability as tunable photonic band gap materials. However, their narrow temperature range often restricts technical usage. Doping with an LC made of achiral bent-core (BC) molecules is one of the strategies employed to increase BP stability. It is now shown that mixing a BCLC exhibiting the polarization-modulated lamellar B7 phase, with a calamitic chiral LC made of rod-like (R) molecules, enhances the BP range considerably. The special feature in this system is the spontaneous expulsion of clusters of B7 fibers in the chiral nematic (N*) phase occurring below the BPs. This gives a clear indication that islands rich in BC molecules lie interspersed between the R molecules. Based on several experimental studies, it is shown that the BP stability may be attributed to an interplay of conformational and intrinsic chirality of the BC and R molecules across the interface of these islands. This study provides new insights from a molecular point of view and provides a novel technique for designing stable-induced BPs. The additional novelty is the occurrence of a phase transition within the fibers. Further, the electro-responsive fibers may also have a potential to form new materials.