Hysteresis‐Free Blue Phase Liquid‐Crystal‐Stabilized by ZnS Nanoparticles

Abstract

Liquid-crystalline blue phases (BPs) have sparked an enormous interest due to their exotic optical properties, exhibiting no birefringence but selective refl ection of circularly polarized light, and potential for advanced applications in a wide variety of fi elds including self-assembling tunable photonic crystals and fast-response display. [ 1 ] BPs are made up of double-twist cylinders arranged in a highly fl uid self-assembled cubic lattice with periods of ∼ 100 nm, which is stabilized by a network of topological -1/2 disclination lines. The competition between the chiral forces and the packing topology leads to at least three different lattice structures, labeled as blue phase III (BPIII), blue phase II (BPII), and blue phase I (BPI) upon decreasing the temperature from the isotropic (I) to the chiral nematic phase. [ 2 ] The packing structures are macroscopically amorphous, simple cubic, and body-centered cubic, respectively. [ 3 ] As is known, the main obstacles to the potential applications of the BPs are the narrow temperature range as well as the instability of cubic structure against an electric fi eld. [ 4 ] Recent developments that introduce BPs with an extended temperature range [ 5 ] make them more attractive for applications. However, the stability of cubic structures against an electric fi eld, such as heavy hysteresis or irreversible switching, is still a big challenge on the road toward practical applications.Theoretical investigations of the BP switching dynamics in presence of an electric fi eld have shown that cubic structure (especially, BPI) is unstable and diffi cult to be reversibly switched in the strong fi eld region. [ 6 ] It has been experimentally demonstrated that serious hysteresis was observed in the pure BPs, which may be due to the fi eld induced phase transition from BP to a chiral nematic phase. [ 7 ] Interestingly, polymer-stabilized BPs (PSBP) could be reversibly switched with microsecond response time, [ 5 ] but the driving voltage of these system is relatively high due to the doping of ∼ 10.0 wt% monomers, and the long-term stability of polymer network is a remaining technical challenge. [ 1 , 8 ] Moreover, BPIII could also undergo a reversible switching with an AC fi eld of less than 10.0 V μ m − 1 but the response speed is relatively slow (about several millisecond) due to the fact that BPIII with wide temperature range is usually observed in the systems with high chirality or viscosity. [ 9 ] Therefore, there is an urgent need to explore a novel strategy to solve the instability of cubic BPs against an electric fi eld and develop the BP composites without hysteresis, with fast response speed, and with low driving voltage.Liquid-crystal nanoscience has attracted special attention in recent years due to the potential applications in developing new composite materials with exciting optical as well as electro-optical properties. [ 10 ] Doping nematic liquid crystals (LC) with nanoparticles (NPs) has lead to many promising LC electro-optical characteristics including low ...

Self-activating liquid crystal devices for smart laser protection

“…It has been experimentally and theoretically confirmed that the BP II and BP I exhibit simple cubic and body-centered cubic nanostructures (Figure 8(a)), respectively. Due to the unique 3D structures of BPLCs, they exhibit many revolutionary features such as optically isotropic and alignment-layer-free, while possess superior electrooptic properties and non-linear optical responses comparable to nematics [134][135][136][137][138][139][140][141][142][143][144][145][146][147][148]. Furthermore, because of the tightly wound spatial arrangement of the crystalline axis, the scattering loss due to thermal fluctuations of the director axis is considerably smaller than nematics, allowing longer interaction length and higher process efficiency.…”

Low voltage and hysteresis-free blue phase liquid crystal dispersed by ferroelectric nanoparticles

“…However, further addition of the NPs amplified the hysteresis loop, which may result from the fact that the cubic structures of BPI would be disordered when doping the excessive amount of the NPs. 4 The V on increases with increasing the concentration of the ZnS NPs ranging from 0.1 wt% to 1.5 wt%, in contrast, the V on would decrease after doping more than 0.5 wt% BaTiO 3 NPs. Importantly, all the samples dispersed by ferroelectric BaTiO 3 NPs show a much lower driving voltage and faster response speed (see ESI †) than that of BPLC doped with ZnS NPs.…”

“…4 Ferroelectric NPs possess not only a large dipole moment, but also a spontaneous electric polarization which can be reversibly switched by an electric field. The strong local polarization fields from the NPs would polarize a large number of neighboring LC molecules, as shown in Fig.…”

Electro-optics of polymer-stabilised blue phase liquid crystal in in-plane switching mode

“…Other techniques for BP stabilisation involve T-shaped molecules, [20] binaphthyl derivatives, [21,22] bent-shaped molecules, [23] hydrogen-bonded selfassembled complexes [24] and nanoparticles. [25][26][27][28][29][30][31] Coles and co-workers reported a dimeric LC having large flexo-electric coefficient and extended the BP range to 44 K. [32] PS-BPLC seems to be most promising but high onstate voltage (V on ), hysteresis, residual transmittance and long-term stability are a few remaining challenges yet to be resolved. The practical applications of BPs are limited due to hysteresis effect and many groups are actively engaged to meet this challenge.…”