No abstract

Liquid crystals (LCs) are key functional materials that are broadly adopted in various fields due to their stimuli‐responsiveness. Recently, LCs with hierarchical architectures have brought new effects to optics and attracted intensive attention. In smectic A phase, the parallel molecular layers are periodically wrapped to form toric focal conic domains (TFCDs) under antagonistic boundary conditions (i.e., hybrid alignment conditions). TFCD shows great potential in nanofabrication and integral imaging. However, the arbitrary tailoring of TFCD is still challenging, and the robustness of hierarchical configuration hinders the tunability. Here, a radial alignment lattice is adopted to guide the local orientation of LCs and thus facilitates predefining the lattice symmetry and domain size of TFCDs. By introducing polymer stabilization and optimizing the composition, the sample simultaneously maintains the director distribution inside smectic layers and possesses the stimuli‐responsiveness of nematic phase at room temperature. By this means, microlens arrays are demonstrated with reversible electrical tunability. The strategy can be extended to other smectic configurations and may upgrade existing dynamic optics.

We introduce a diffuse-interface Landau-de Gennes free energy for free-boundary nematic liquid crystals (NLC) in three dimensions submerged in isotropic liquid, where a phase field is introduced to model the deformable interface. The energy we propose consists of the original Landau-de Gennes free energy, three penalty terms and a volume constraint. We prove the existence and regularity of minimizers to the diffuse-interface energy functional. We also prove a uniform maximum principle of the minimizer under appropriate assumptions, together with a uniqueness result for small domains. Then, we establish a sharp-interface limit where minimizers of the diffuse-interface energy converge to a minimizer of a sharp-interface energy under the framework of Γ-convergence. Finally, we conduct numerical experiments with the diffuse-interface model, the findings of which are compared with existing works.

Chirality and hierarchy are two representative features of complex configurations inspiring exotic functions. Chiral additives are adopted to break the mirror symmetry of molecular orientation inside smectic layers, and overcome the restriction on in‐layer helical arrangement by virtue of the surface electroclinic effect. The chirality strength of liquid crystals is regulated via the photo‐isomerization of chiral molecular switch, the doping concentration control, and the mixing of different chiral additives. The dynamic evolution of chiral smectic superstructures leads to the reversible rotation of oily streaks (OSs), and even structural transformation between OSs and focal conic domains is demonstrated. This releases new freedom of chiral hierarchical configurations and may inspire fantastic applications in active optics, sensing, and micro‐manufacturing.