Directed self-assembly of liquid crystalline blue-phases into ideal single-crystals

Abstract

Chiral nematic liquid crystals are known to form blue phases—liquid states of matter that exhibit ordered cubic arrangements of topological defects. Blue-phase specimens, however, are generally polycrystalline, consisting of randomly oriented domains that limit their performance in applications. A strategy that relies on nano-patterned substrates is presented here for preparation of stable, macroscopic single-crystal blue-phase materials. Different template designs are conceived to exert control over different planes of the blue-phase lattice orientation with respect to the underlying substrate. Experiments are then used to demonstrate that it is indeed possible to create stable single-crystal blue-phase domains with the desired orientation over large regions. These results provide a potential avenue to fully exploit the electro-optical properties of blue phases, which have been hindered by the existence of grain boundaries.

Mesoscale martensitic transformation in single crystals of topological defects

“…The symmetry of the Kossel diagram shown in Fig. 3C is consistent with the formation of a hexagonal blue-phase (BPH) layer in the proximity of the patterned surface (33) (Fig. S5).…”

“…When the BPs are formed by cooling from the isotropic phase, the chemical pattern mediates the nucleation of the BP. The binary striped pattern of alternative planar and homeotropic anchoring with 150-nm period produces single-crystal BPII (100) specimens (33). The uniform homeotropic anchoring, imposed by the top surface, prefers to induce a BPII (111) .…”

“…The specifically designed chemical patterns are used to impose planar or homeotropic (perpendicular) molecular alignments at the surface with nanoscale precision. The chemical pattern's characteristics were inferred from theoretical calculations, using state-of-the-art simulations that enable description of large samples of chiral LCs (33). In this work, we capitalize on such pattern designs and our ability to pattern surface-grafted LC polymer brushes to produce macroscopic single-crystal BPI and BPII samples with cubic lattices where the (1 1 0) and the (1 0 0) planes are parallel to the substrate, respectively.…”

“…Motivated by the challenges outlined above, and building on demonstrations from our group where chemically patterned surfaces were used to direct the self-assembly of sphere-forming block copolymer into ordered structures by controlling the boundary conditions and film thickness (32), we recently proposed a different strategy to direct the formation of stable monodomain, single-crystal BP specimens over macroscopic (millimeter) length scales (33). A central feature of that strategy is the ability to control the lattice orientations of the BPs during the course of a phase transition, be it from isotropic to BP (I to BP), or from cholesteric to BP (Chol to BP).…”

Photoresponsive Structural Color in Liquid Crystalline Materials

“…Traditional alignment layers have little effect on the arrangements and size of the platelets. Recent reports have shown, however, that there are ways to control the orientation of the crystal lattice in the blue phases and the size of the crystallites …”