At the wall in a hybrid nematic cell with strong anchoring, the nematic director is parallel to one wall and perpendicular to the other. Within the Landau-de Gennes theory, we have investigated the dynamics of s = ±1/2 wedge disclinations in such a cell, using the two-dimensional finite-difference iterative method. Our results show that with the cell gap decreasing, the core of the defect explodes, and the biaxiality propagates inside the cell. At a critical value of d_c* ≈ 9ξ (where ξ is the characteristic length for order-parameter changes), the exchange solution is stable, while the defect core solution becomes metastable. Comparing to the case with no initial disclination, the value at which the exchange solution becomes stable increases relatively. At a critical separation of d_c ≈ 6ξ, the system undergoes a structural transition, and the defect core merges into a biaxial layer with large biaxiality. For weak anchoring boundary conditions, a similar structural transition takes place at a relative lower critical value. Because of the weakened frustration, the asymmetric boundary conditions repel the defect to the weak anchoring boundary and have a relatively lower critical value of d_a, where the shape of the defect deforms. Further, the response time between two very close cell gaps is about tens of microseconds, and the response becomes slower as the defect explodes.

Polymer-stabilised blue-phase liquid crystal (PS-BPLC) is a soft artificial three-dimensional photonic crystal (PC) functional material for optics and optoelectronics because of its superior optical properties. In this work, we demonstrated that PS-BPLC film could sense and selectively detect the xylene, heptane, cyclohexane, dichloromethane and ethyl alcohol vapours rapidly and accurately. When the PS-BPLC film was alternately exposed to volatile vapours and air, the Bragg reflection wavelength of the PS-BPLC could reversibly and significantly shift because of the adsorption and desorption of the volatile vapours. Different organic vapours could be well discriminated by the linearity and the critical concentration at which the Bragg reflection disappeared. This organic vapour sensor also had a good sensitivity, high repeatability, humidity independence and long-term stability, which promote a widespread use in environmental monitoring, point-of-care biomedical analysis and optical security coatings. Graphical abstract

The dynamics of a disclination loop (s = ±1/2) in nematic liquid crystals constrained between two coaxial cylinders were investigated based on two-dimensional Landau–de Gennes tensorial formalism by using a finite-difference iterative method. The effect of thickness (d = R₂ − R₁, where R₁ and R₂ represent the internal and external radii of the cylindrical cavity, respectively) on the director distribution of the defect was simulated using different R₁ values. The results show that the order reconstruction occurs at a critical value of d_c, which decreases with increasing inner ratio R₁. The loop also shrinks, and the defect center deviates from the middle of the system, which is a non-planar structure. The deviation decreases with decreasing d or increasing R₁, implying that the system tends to be a planar cell. Two models were then established to analyze the combined effect of non-planar geometry and electric field. The common action of these parameters facilitates order reconstruction, whereas their opposite action complicates the process.

On the basis of Landau–de Gennes theory and the finite-difference iterative method, spontaneous chiral structures in cylinders with degenerate planar boundary conditions are investigated. A double-twist director configuration can be achieved by the saddle–splay contribution, corresponding to the L₂₄ term in Landau–de Gennes theory. The twist angle increases as the radius R of the cylinder is reduced because the curvature of the cylindrical surface becomes larger. Moreover, we find fine structures of the domain walls and point defects between opposite-handed domains. An energy comparison shows that domain walls are the stable state for K₂₄/K> 0.6 (K₁₁ = K₃₃ = K, K₁₁, K₃₃ and K₂₄ are the splay, bend, saddle–splay elastic constants in Frank theory), whereas point defects are the stable state for K₂₄/K< 0.6.

Based on Landau-de Gennes theory and differential iteration method, in a cylindrical shell with degenerate planar anchoring at both interfaces, the double-twist director configuration caused by large saddle-splay elasticity is investigated. The combined effects of saddle-splay elasticity and the curvature on the spontaneous chiral structure are analysed. Between opposite-handed domains, we find two domain wall structures and a new 1/2 defect ring structure. The stabilities of these structures are analysed by an energy comparison. GRAPHICAL ABSTRACT