Dongyu Zhao

Polymer stabilized liquid crystal films reflecting both right-and left-circularly polarized light

A single-layer polymer stabilized liquid crystal (PSLC) film reflecting both right- and left-circularly polarized light has been developed by a wash-out/refill method. The PSLC film was achieved by prefabricating the polymer network with a left-handed helical structure and then refilling a cholesteric liquid crystal with a right-handed helical structure into the network. The reflection intensity of the PSLC film is close to 100% when the pitch lengths of the two opposite helical structures are the same. It was demonstrated that the memory effect of the polymer network is an important mechanism for the resulting film properties.

Synthesis of Nickel Bowl-like Nanoparticles and Their Doping for Inducing Planar Alignment of a Nematic Liquid Crystal

Nickel bowl-like nanoparticles have first been synthesized by a magnetic self-assembly process stabilized by polyvinyl pyrrolidone (PVP) without any sphere-like materials as templates. A trace of doped bowls can induce liquid crystal (LC) molecules into a perfect planar alignment, attributable to their bowl-like shape and magnetic self-assembly into a 1D structure. It would provide a novel method of establishing LCs alignment by doping special nanostructured materials.

Alignment of Liquid Crystals Doped with Nickel Nanoparticles Containing Different Morphologies

Uniform homeotropic and homogeneous alignment of liquid crystals (LCs) is facilely achieved by dispersing Ni nanoparticles (Ni NPs) into the LCs. The alignment mode depends on the morphology of the Ni NPs. The mechanism of NP-induced LC alignment is elucidated clearly, indicating that the perfect orientation arises from the adsorption of Ni NPs on the substrate.

Homeotropic Alignment of Nematic Liquid Crystals by a Photocross-Linkable Organic Monomer Containing Dual Photofunctional Groups

In this paper, we report a novel organic monomer containing dual photocross-linkable groups and success in realizing photoinduced homeotropic alignment of nematic liquid crystals (LCs) with it. It was first revealed that direct irradiation of the photoalignment thin film with nonpolarized ultraviolet (UV) light at 365.0 nm brought out homeotropic orientation of the photopolymer as a result of the photocross-linking of the dual photoreactive groups. When the thin film was obliquely irradiated with nonpolarized UV light, the pretilt angles of nematic LC were generated. Interestingly, we find that the hydrophobicity of the photopolymer increases with increasing irradiation time. In discussing the mechanism of the homeotropic alignment, it was found that the incorporation of the dual photofunctional group of the photoalignment molecules as well as the extreme hydrophobicity of the photopolymer play the essential roles. This monomer cross-linked film is expected as a promising homeotropic alignment film with rubbing-free processing for the fabrication of advanced vertical alignment LC displays.

New micro‐structure designs of a wide band reflective polarizer with a pitch gradient

New microstructure designs for fabricating a wide band reflective polarizer (WBRP) from cholesteric liquid crystals are reported. The pitch difference in the WBRP is formed by orienting a single layer consisting of different glassy siloxane cyclic side chain oligomer powders on a heater. The molecular arrangement obtained is frozen by quenching. The experimental results show that various micro‐areas exhibiting different reflection wavelengths and pitch gradients are formed in the WBRP. A WBRP exhibiting the reflection properties of the original cholesteric liquid crystals is fabricated by a novel experimental process and the experimental results are in accordance with the microstructure designs of the WBRP.

Liquid crystalline and thermo-optical properties of cyclic siloxane tetramers containing cholestryl-4-allyloxy-benzoate and biphenyl-4-yl 4-allyloxybenzoate

A series of cyclic siloxane tetramers covering the whole composition range were synthesised using cyclotetrasiloxane, cholestryl-4-allyloxy-benzoate and biphenyl-4-yl 4-allyloxybenzoate, and the effects of the cholesteryl-based mesogenic units on liquid crystalline and thermo-optical properties were studied. The presence of a cholesteric mesogen was observed to widen the mesogenic temperature range and tended to induce smectic A phases in the tetramers containing a higher mole fraction of cholestryl-4-allyloxy-benzoate (X chol). The selective reflection of cholesteric tetramers shifted to shorter wavelengths with increasing X chol and temperature. Blue phases can be easily observed for those tetramers containing more than 50.0 mol% cholesteric mesogen. The shorter pitch sample showed the wider blue phases range. The blue phases range width increased from 2.8°C to 18.5°C as X chol increased from 0.5 to 1.0.

Facet-dependent Cu2O nanocrystals in manipulating alignment of liquid crystals and photomechanical behaviors

Manipulating the alignment of liquid crystals (LCs) is a hot and fundamental issue for their applications in block copolymers, photonics, actuators, biosensors, and liquid-crystal displays. Here, the surface characteristic of Cu2O nanocrystals was well controlled to manipulate the orientation of the LCs. The mechanism of the orientation of the LCs induced by Cu2O nanocrystals was elucidated based on the interaction between the LCs and Cu2O nanocrystals. To comprehensively prove our assumption, different types of LCs (nematic, cholesteric, and smectic) as well as the same type of LCs with different polarities were selected in our system. Moreover, the photomechanical behaviors of the LC polymer composites demonstrated that the alignment of LCs can be effectively manipulated using Cu2O nanocrystals.

Super wide-band reflective polarisers from polymer stabilised liquid crystal films

A polymer stabilised liquid crystal film with the order and the molecular alignment of a smectic-A phase at a microscopic level, but with the planar molecular alignment of a chiral nematic phase at a macroscopic level, was prepared. This kind of order and alignment of the molecules of the liquid crystal resulted in the film reflecting circularly polarised incident light with the bandwidth of the spectrum over the wavelength range of 300–2500 nm.

Liquid Crystal Elastomer Actuators from Anisotropic Porous Polymer Template

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.

Controllable alignment of liquid crystals based on the surface relief gratings from a photocross-linkable organic monomer

The orientational control of liquid crystal (LC) molecules is essential for high-quality liquid crystal displays, and the photo-induced surface relief grating (SRG) is a facile and effective non-contact process. Here, SRGs with different period and depth were prepared with a photocross-linkable organic monomer 4-propyldiphenylacetylenecarboxylic acid cinnamyl ester (PDACE), and the LC alignment induced by SRG was studied. It is found that both the surface topography and the chemical nature of the surface are responsible for the LC alignment, which is strongly dependent on the groove geometry of the gratings. Furthermore, the patterned LC cell was fabricated with the patterned SRG surface. These results demonstrate that the planar, perpendicular and patterned orientations of LC can be easily photo-controllably obtained with PDACE, which have important applications in optical devices.