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Two series of fluorene-core compounds were successfully synthesised, one series of compounds have different rigid conjugated structures, and the other series of compounds have different substituted dialkyl chains at the 9-position of fluorene core. The thermotropic mesomorphic behaviours and fluorescence characteristics of the synthesised compounds were investigated. It was found that these derivatives exhibited well fluorescence performance and wide mesophases range up to 196°C. The short dialkyl chains substituted at the fluorenyl 9-position can improve the solubility of the compounds while maintaining the mesogenic properties. It was also found that the fluorene-derived compounds as dopants of chiral nematic liquid crystal can effectively stabilise the double-twisted structure due to the biaxiality of fluorene core, so as to induce the emergence of blue phase or broaden its temperature range. [ABSTRACT FROM AUTHOR]

We investigated the effects of fluorescent material doping on the morphology, electro-optical, and fluorescence properties of PDLC films. The acrylate-based PDLC films prepared by polymerisation induced phase separation via UV curing method were doped with fluorescent material. The impact of fluorescent material on the microstructure was studied using scanning electron microscopy. The effect of fluorescent material on the electro-optical properties of PDLC films was studied by liquid crystal composite parameter tester. The electro-optical study revealed that the addition of fluorescent material results in the reduction of rise time, threshold voltage. The development of fluorescent material doped PDLC films with faster rise time, lower threshold voltage and lower saturation voltage will significantly enhance the potential technological applications of PDLC-based devices for smart windows, sensors and flexible devices. [ABSTRACT FROM AUTHOR]

Chiral nematic liquid crystal (N*-LCs) films with wide pitch gradients covering the near infrared (NIR) region are facilely obtained by a simple controlling diffusion method. The polymer network can not only fix the orientation of N*-LCs, but also serves as a diffusion channel for substances, and has excellent compatibility. First, in the design of the pre-polymerisation (Incomplete polymerisation) layer, mainly by controlling the content of polymerisable monomer and UV-absorbing dyes in N*-LCs, a polymer network with density gradient distribution and suitable for material diffusion is formed, and the substrate of the oil repellent layer on the side of the low-density polymer network is easier to be peeled off. Then, nematic liquid crystals are injected between the pre-polymerisation layer and another oriented glass substrate. Due to the large concentration difference of chiral compounds and UV-327 between the two liquid crystals, the gradient distribution of spacing is formed by diffusion. Because of the gradient distribution of the UV-327, the gradient distribution of the pitch is further increased after polymerisation again. Finally, the effect of the UV-327 on the polymer network of the pre-polymerised layer is observed using SEM. Thus, a new method for reflective broadband in the near-infrared region is proposed. [ABSTRACT FROM AUTHOR]

In this study, polymer network is prepared by broadband reflective cholesteric liquid crystal (CLC) film with washing out method. By the method of photoinduced molecular diffusion, the CLC film is prepared by adding different concentrations of ultraviolet (UV) absorption dyes into the LC system and irradiated with a series of UV light intensities for different times. The selective reflection property and broadband reflection memory effect of the polymer network are proved, and the response mechanism is given. By refilling the polymer network with different LCs, reflective bands with different central wavelengths and bandwidths can be obtained. It is confirmed that different fillers can recurrence the initial reflection bandwidth of CLCs in different degrees. These results may provide a new idea for total reflection CLC films. [ABSTRACT FROM AUTHOR]

The electro-optical characteristics of nanoparticles-doped polymer dispersed liquid crystals (PDLCs) have been investigated for display applications. The PDLC samples were obtained by polymerisation induced phase separation of the nematic liquid crystal LC-nanoparticles-prepolymer mixtures under UV illumination with a constant intensity. The effect of Al2O3 nanoparticles doping on the PDLC system was studied. It was seen that the electro-optical characteristics of PDLC were dependent on the amount of Al2O3 nanoparticles used. The effect of morphology on the electro-optical properties was examined, and the experimental results indicated that the driving voltage was affected considerably by the amount of Al2O3 nanoparticles. The results showed that the nanoparticles concentration can be optimised to obtain promising electronic materials with a minimum threshold for display applications. [ABSTRACT FROM AUTHOR]

In this paper, rare earth oxide CeO2 nanoparticle-doped polymer dispersed liquid crystal (PDLC) films were prepared by the polymerisation induced phase separation (PIPS) process. The effects of the crosslinking agent TMPTA content, liquid crystal (LC) content and the CeO2 content on the polymer structures and electro-optical properties of the as-made PDLC films were investigated systematically. It has been found that by changing the TMPTA content, LC content and doping a small amount of CeO2 nanoparticles, the electro-optical properties of PDLC films can be optimised. After adding a low concentration of CeO2 nanoparticles, the electro-optical properties of the PDLC film have been well optimised: after adding 0.8% CeO2, Vth decreased from 26.6 V to 16.8 V, and CR increased from 89.5 to 137.6. Consequently, this work offers a meaningful approach to optimise the electro-optical properties of PDLC films, which indeed can form a wonderful footstone for the wide application of PDLC. [ABSTRACT FROM AUTHOR]

In this study, a polymer-stabilised cholesteric liquid crystal film with broadband reflection was prepared by using a nanofibre film loaded with chiral dopants as the carrier. The nanofibre film prepared by the electrospinning technology ensures that chiral dopants can be uniformly distributed on the film and can be controlled release during the heating process. In order to obtain the maximum non-uniform distribution of the pitch, a series of investigations were conducted on the concentration of the polymerised monomer, polymerisation temperature, and intensity of the ultraviolet light. By screening different experimental conditions, the optimal conditions for broadening the reflection band were obtained, and the reflection bandwidth was broadened from 270 to 425 nm. The prepared cholesteric liquid crystal films with broadband reflection characteristics have potential application value in many fields, such as light-brightening films, smart windows, infrared shielding devices, laser protective coatings, etc. [ABSTRACT FROM AUTHOR]

In this paper, a series of D–π–A type benzo[e]indolium salts with highly efficient nonlinear optical performance has been synthesized. Out of the three new benzo[e]indolium salts, (E)-2-(2-hydroxy-3-methoxystyryl)-1,1,3-trimethyl-1H-benzo[e]indol-3-ium iodide (HMTB-1) and (E)-2-(2-hydroxy-4-methoxystyryl)-1,1,3-trimethyl-1H-benzo[e]indol-3-ium iodide (HMTB-2) possess SHG properties, and their maximum powder second harmonic generation (SHG) efficiency is around 0.6 times that of DAST (4-N,N-dimethylamino-4′-N′-methyl-stilbazolium tosylate) at a non-resonant wavelength of λ = 1570 nm. Single crystals of the two noncentrosymmetric salts were successfully grown by using a slow cooling method, and we were able to obtain very large bulk single crystals, about 17 mm × 9 mm × 3 mm, of HMTB-2. X-ray crystallographic analysis indicated that both of the new salts belong to the monoclinic space group Cc (point group m, Z = 4). HMTB-1 forms a noncentrosymmetric phase with methanol through hydrogen bonding. [ABSTRACT FROM AUTHOR]

In the study, a novel method of broadening the bandwidth by fabricating the silica aerogel film composited with the chiral nematic liquid crystal (N*-LC) is proposed. Diffusion of chiral compound filled in the silica aerogel resulted in the non-uniform pitch distribution, which can be anchored by UV-radical polymerisation. The results strongly suggested that the reflection bandwidth could be broadened preferably by adjusting the silica aerogel condensation time, the content of UV polymerisable free radical monomer and the polymerisation temperature. The reflection bandwidth was broadened from 270 nm to 878 nm, and the centre wavelength was blue-shifted by 642 nm. A general correlation among the silica aerogel condensation time, the polymerisation condition, and the reflective region will be outlined. [ABSTRACT FROM AUTHOR]

Polymer dispersed liquid crystal (PDLC) films are fabricated by well-known polymerization-induced phase separation method. In this paper, the dispersion of multi-walled carbon nanotubes (MWCNT) in liquid crystals has been enhanced by chemical modification and we have investigated their effects on the morphology, electro-optical properties and conductivity of the PDLC films. Results indicated that the threshold voltage and the saturation voltage of PDLC films decreased with the increase of the doping concentration of MWCNT or chemically modified MWCNT, because carbon nanotubes can enhance the electric field by reducing the resistivity of the medium and increasing the capacitance of the cells. It can be viewed obviously that the contrast ratio of the PDLC films doped with the chemically modified MWCNT is higher than that of the MWCNT. [ABSTRACT FROM AUTHOR]