Unveiling the potential of polymer cholesteric liquid crystal interpenetrating networks as a label-free alcohol biochemical sensor.

In this study, an optical sensor is developed, incorporating hydrogen-bonded photonic array dots containing poly(acrylic acid) (PAA) within a polymer cholesteric liquid crystal interpenetrating polymer network (PCLCIPN) framework, thereby effectively controlling porosity. This methodology involves the fabrication of a porous photonic film, subsequent infusion with a hydrogel (PAA), and precise UV-curing to generate patterned array dots. The sensor exhibits exceptional discriminatory capability between methanol and ethanol, accurately discerning their varying concentrations within alcohol solutions. The optical sensing performance of the film is rigorously evaluated through continuous monitoring of wavelength shifts in the transmission spectrum across various alcohol concentrations. Notably, the observed wavelength shifts demonstrate a linear correlation with the concentration of alcohol, thereby enabling precise quantitative analysis of the alcohol solutions. The sensor exhibits a sensitivity of 0.44 nm/% for ethanol concentrations ranging from 5% to 60%, increasing to 2.1 nm/% for concentrations between 60% and 80%. Similarly, for methanol, sensitivities of 0.68 nm/% (5-60%) and 2.2 nm/% (60-80%) are recorded. Remarkably, this sensitivity trend extends seamlessly to 1 : 1 ethanol/methanol ratios, with values of 0.49 nm/% (5-60%) and 2.25 nm/% (60-80%). Furthermore, these sensors demonstrate colorimetric response to different alcohols, rendering them accessible and cost-effective biosensors for visual detection, thus obviating the necessity for complex analytical instruments.

In-fiber Mach-Zehnder interferometer based on hollow optic fiber for metal ion detection.

A new, to the best of our knowledge, in-fiber Mach-Zehnder interferometric sensor is proposed and experimentally demonstrated for detecting Cu2+ ions in an aqueous environment. The sensor is fabricated simply and cost-effectively by arc-fusing a short section of hollow optical fiber between two standard single-mode fibers and is functionalized by depositing chitosan and poly(acrylic acid) bilayers using electrostatic self-assembly. The proposed sensor shows a linear response with sensitivity of 42 nm/mM in the Cu2+ ion concentration from 0 to 40 µM. Moreover, the fiber sensor exhibits good reusability and repeatability and is a promising candidate for contamination detection in drinking water and industrial waste water.

Alcohol Selective Optical Sensor Based on Porous Cholesteric Liquid Crystal Polymer Networks.

A responsive hydrogen-bonded cholesteric liquid crystal polymer (CLCP) film with controlled porosity was fabricated as an optical sensor to distinguish between methanol and ethanol in alcohol solutions. To facilitate responding the alcohols, porosity was generated by removing the nonreactive liquid crystal agent, and the hydrogen bridges of CLCP were broken. The sensitivities of CLCPs to ethanol and methanol were obtained by monitoring the wavelength shifts of the transmission spectrum at different alcohol concentrations and ratios of methanol/ethanol. Changes in the central wavelength of the CLCP network transmission spectrum allowed the methanol-ethanol ratio to be discriminated. A linear relationship between wavelength shift of CLCP networks and alcohol concentration was obtained experimentally, and the sensor characteristics were explored. The sensitivities of the CLCPs were 1.35 and 0.18 nm/% to ethanol and methanol, respectively. The sensing sensitivity of cholesteric networks to alcohol molecules increased as the methanol-ethanol ratio declined. Therefore, CLCP could act as a stimuli-responsive material to distinguish the concentrations of acetone and ethanol in mixed solutions. Furthermore, the impact of UV intensity for curing a CLC mixture on the sensing sensitivity to the different alcohol concentrations was also studied. The higher UV intensity could enhance the sensitivity to alcohol molecules and distinguishing ability between methanol and ethanol.

Temperature effects of Mach-Zehnder interferometer using a liquid crystal-filled fiber.

We demonstrated a simple and cost-effective method to fabricate all fiber Mach-Zehnder interferometer (MZI) based on cascading a short section of liquid crystal (LC)-filled hollow-optic fiber (HOF) between two single mode fibers by using automatically splicing technique. The transmission spectra of the proposed MZI with different LC-infiltrated length were measured and the temperature-induced wavelength shifts of the interference fringes were recorded. Both blue shift and red shift were observed, depending the temperature range. Based on our experimental results, interference fringe was observed with a maximum interferometric contrast over 35dB. The temperature-induced resonant wavelength blue-shifts 70.4 nm for the MZI with an LC length of 9.79 mm and the wavelength temperature sensitivity of -1.55 nm/°C is easily achieved as the temperature increases from 25°C to 77°C.

Improvement of performance of liquid crystal microlens with polymer surface modification.

An electrically controllable liquid crystal (LC) microlens with polymer crater, which is simply prepared by droplet evaporation, has been previously proposed as a focusing device possessing excellent characteristics in optical performance, especially for the capability of tunable focal lengths. As the alignment layer on the crater surface cannot be effectively rubbed, non-uniformly symmetrical electric fields in the LC lenses usually induce disclination lines during operation. In this paper, a polymer surface stabilization technique is applied to successfully prevent disclination lines and greatly improve the performance of the LC microlens with the polymer crater.

Tunable liquid crystal microlenses with crater polymer prepared by droplet evaporation.

A simple and low-cost technique is proposed to construct a tunable liquid crystal (LC) microlens with a crater polymer structure, which is prepared using micro-drop technology and 2-step UV polymerization. The dimensions and the geometric profile of the restructured polymer surface significantly depend on the volume of the micro droplet, and the UV irradiation dose. In this work, the focal length of the LC microlens is controlled electrically from infinity to 7.8 cm. Such a microlens has prospective applications in optical communications, image processing, and switchable 2D/3D displays.

Electrically switchable liquid crystal Fresnel lens using UV-modified alignment film.

A simple method to make a switchable liquid crystal (LC) Fresnel lens with high diffraction efficiency and a low driving voltage was proposed based on the photo-induced surface modification of the vertical alignment layer. UV illumination alters the pretilt angle of alignment layers, a Fresnel zone-distribution hybrid alignment in the homeotropic LC cell can be straightforwardly achieved through UV exposure, yielding a concentric structure of the Fresnel phase LC lens. A remarkable diffraction efficiency of ~31.4%, close to the measured diffraction efficiency of the used Fresnel-zone-plate mask of 32%, was detected using a linearly polarized incident beam.

Cholesteric liquid crystal devices with nanoparticle aggregation.

A broadband cholesteric liquid crystal (CLC) device with a multi-domain structure is demonstrated by using an aggregation of polyhedral oligomeric silsesquioxane (POSS) nanoparticles in the CLC layer. The aggregation pattern of the self-assembled POSS nanoparticles depends on the concentration of POSS doped in the mixture of POSS/CLC and the cooling rate of the mixture from a temperature higher than the clear point. POSS-induced changes in the bulk and surface properties of the cholesteric cells, such as a promotion of homeotropic alignment, help to form a cholesteric structure with a broadband reflection of light; the latter can be used for improvement of bistable CLC devices. A higher POSS concentration and a higher cooling rate both improve the appearance of the black-white CLC device.

Nanoparticle-doped polyimide for controlling the pretilt angle of liquid crystals devices.

The pretilt angles of liquid crystal molecules can be controlled by using conventional polyimide (PI) alignment material doped with different concentrations of Polyhedral Oligomeric Silsequioxanes (POSS) nanoparticles, which have been observed to spontaneously induce vertical alignment. The addition of POSS in the homogenous PI changes the surface energy of the alignment layer and generates a variable pretilt angle. Experimental results demonstrate that the pretilt angle thetap is a function of the POSS concentration, and can be tuned continuously over the range of 0 degrees

Tunable pretilt angles based on nanoparticles-doped planar liquid-crystal cells.

The nanoparticles-induced vertical alignment technique was applied to generate variable liquid-crystal pretilt angles based on doping different concentrations of polyhedral oligomeric silsesquioxane (POSS) nanoparticles in the planar-aligned liquid crystal cells. Competition between the homogeneously aligned polyimide layer and POSS-induced spontaneous vertical alignment domain generated the variable pretilt angle. Experimental results demonstrated that the pretilt angle theta(p) is a function of the doped POSS concentration and can be controlled continuously over the range of 0 degrees