No abstract

Quantum dots (QDs) are semiconductor nanoparticles (NPs) that have gained significant interest in the academia and industry because of their unique optoelectronic properties such as tunable emission wavelength, high color purity, wide color gamut, and high photoluminescence quantum yield. However, it remains a challenge to fabricate a QD colloid or solution into solid devices featuring the desired patterns and maintaining high efficiency. Recently, researchers have shown significant progress in the efficiency improvement and device fabrication of QD-based displays, contributed by the development of both materials and device engineering. In this review, the recent progress in the engineering of QDs will be discussed, with an emphasis on the encapsulation methods and patterning strategies by which QDs are packaged into solid-state devices with pixelated patterns as well as luminescence enhancement and modulation.

The reflection band of polymer stabilized cholesteric liquid crystals with negative dielectric anisotropy can be broadened by DC electric fields, which was ascribed to the pitch gradient caused by the motion of the structural chirality, that is, the polymer network. They systematically varied the mixture components, such as the photo‐initiator concentration, the monomer functionality, and the chiral dopant, to explore their influences on the reflection band broadening behavior. They learned how to control the polymer network morphology and ion density, which in turn determined the reflection bandwidth. By optimizing the mixture, they have greatly enhanced the broadening effect and achieved large bandwidth at low voltages. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 835–846

Controlling self-assembly behaviors of liquid crystals is a fundamental issue for designing them as intelligent actuators. Here, anisotropic porous polyvinylidene fluoride film is utilized as a template to induce homogeneous alignment of liquid crystals. The mechanism of liquid crystal alignment induced by anisotropic porous polyvinylidene fluoride film is illustrated based on the relationship between the alignment behavior of liquid crystals and surface microstructure of anisotropic polyvinylidene fluoride film. Liquid crystal elastomer actuators with fast responsiveness, large strain change, and reversible actuation behaviors are achieved by the photopolymerization of liquid crystal monomer in liquid crystal cells coated with anisotropic porous films.

When subjected to an AC electric field perpendicular to its layers, the cholesteric planar state may undergo a periodic layer undulation, known as the Helfrich deformation, which generates a color change of the reflected light. The Helfrich deformation of regular cholesteric liquid crystals is, however, unstable and easily taken over by the focal conic state, and thus the color tuning range is narrow. We demonstrated that the Helfrich deformation can be stabilized in a large electric field region by doping a bent dimer with an anomalously small bend elastic constant and dispersing a small amount of polymer network. By varying the dimer concentration, we were able to systematically change the bend elastic constant and thus verify the theoretical prediction of the undulation threshold electric field and periodicity. We also achieved reflectance tuning with electric field less than 2 V μm and color tuning covering the entire visible light region with electric field as low as 4 V μm.

Chiral nematic liquid crystals possess a self-assembled helical structure and exhibit unique selective reflection in visible and infrared light regions. Their optical properties can be electrically tuned. The tuning involves the unwinding and restoring of the helical structure. We carried out an experimental study on the mechanism of the restoration of the helical structure. We constructed chiral nematic liquid crystals with variable elastic constants by doping bent-dimers and studied their impact on the restoration. With matched twist and bend elastic constants, the helical structure can be restored dramatically fast from the field-induced homeotropic state. Furthermore, defects can be eliminated to produce a perfect planar state which exhibits high selective reflection.

Solid polymer electrolytes (SPEs) have emerged as one of the most promising candidates for building solid‐state lithium batteries due to their excellent flexibility, scalability, and interfacial compatibility with electrodes. However, the low ionic conductivity and poor cyclic stability of SPEs do not meet the requirements for practical applications of lithium batteries. Here, a novel polymer dispersed ionic liquid‐based solid polymer electrolyte (PDIL‐SPE) is fabricated using the in situ polymerization‐induced phase separation (PIPS) method. The as‐prepared PDIL‐SPE possesses both outstanding ionic conductivity (0.74 mS cm−1 at 25°C) and a wide electrochemical window (up to 4.86 V), and the formed unique three‐dimensional (3D) co‐continuous structure of polymer matrix and ionic liquid in PDIL‐SPE can promote the transport of lithium ions. Also, the 3D co‐continuous structure of PDIL‐SPE effectively accommodates the severe volume expansion for prolonged lithium plating and stripping processes over 1000 h at 0.5 mA cm−2 under 25°C. Moreover, the LiFePO4//Li coin cell can work stably over 150 cycles at a 1 C rate under room temperature with a capacity retention of 90.6% from 111.1 to 100.7 mAh g−1. The PDIL‐SPE composite is a promising material system for enabling the ultrastable operation of solid‐state lithium‐metal batteries.

Polymer dispersed liquid crystals (PDLCs) have shown great potential in applications, such as displays and smart windows. However, the driving voltage and contrast ratio are still far from requirement. In this work, acrylate monomers with different alkyl chains were applied to prepare PDLC films. Then the electro‐optical performance and microstructure were characterized and compared. Results show that the contrast ratio can be improved by nearly 50% through adjusting the alkyl chain length. Meanwhile, the slightly increased driving voltages can be compensated by introducing branched chains. Contrarily, isomeric structure with more branched chains but short chain length would not contribute much. The chain structure can affect the phase separation process and furtherly the interaction between polymer matrix and liquid crystal droplets. Finally, an optimized PDLC film with high contrast ratio over 100 was demonstrated, which showed two distinct states: highly transparent state with transmittance over 87% at a 0.52 V μm−1 electric field and strong scattering state with transmittance less than 1% in the absence of an electric field. It is anticipated that the research can provide more design choices from material perspective and pave the way for further industrial utilizations of PDLC films.