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Graphene-Augmented Polymer Stabilization: Drastically Reduced and Temperature-Independent Threshold and Improved Contrast Liquid Crystal Device
摘要： Polymers reinforced with nano?llers, especially graphene in recent times, have continued to attract attention to realize novel materials that are cheap and also have better properties. At a di?erent level, encapsulating liquid crystals (LCs) in polymer networks not only adds mechanical strength, but could also result in device-based refractive index mismatch. Here, we describe a novel strategy combining the best of both these concepts to create graphene-incorporated polymer-stabilized LC (PSLC) devices. The presence of graphene associated with the virtual surface of the polymer network besides introducing distinct morphological changes to the polymer architecture as seen by electron microscopy brings out several advantages for the PSLC characteristics, which include 7-fold lowered critical voltage, its temperature invariance, and enhanced contrast ratio between ?eld-o? scattering/?eld-on transparent states. The results bring to fore the importance of working at very-dilute-concentration limits of the ?ller nanoparticles in augmenting the desired properties. These observations open up a new vista for polymer?graphene composites in the area of device engineering, including substrate-free smart windows.
关键词： temperature invariance,graphene,electro-optic properties,threshold voltage,polymer-stabilized liquid crystals
更新于2025-09-23 15:23:52
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Comparative Raman study of two laterally fluorinated LC compounds having different terminal chains
摘要： In this article, we present the Raman study of two laterally fluorinated liquid crystal compounds, namely, C3PP(23F)P-NCS and C3PP(23F)PC3. The two compounds have different terminal groups, one with NCS which is more polar than the other which has an alkyl group. The Raman bands were deconvoluted with Lorentzian profiles to get the values of spectral parameters. The main feature of the work is the temperature-dependent behaviour of the spectra profiles of the C–H bending mode, C–F stretching modes and aromatic C–C stretching mode in the vicinity of the phase transitions. The effect on the charge distribution over different bonds of the molecule and the vibrational energy of the bonds due to the presence of the more polar group on the terminal chain is well observed. The contrasting behaviours of the spectral profiles at the Cr–N and N–I transitions were also observed which we have ascribed to some pre-transitional effect associated with the breaking of the orientational order near the N–I transition. Density functional theory using B3LYP exchange correlation with the 6-31G (d,p) basis set was also used to generate a theoretical spectra which were found to be matching with the experimental spectra.
关键词： laterally fluorinated liquid crystals,isothiocyanato (NCS) compound,phase transition,Raman study
更新于2025-09-23 15:23:52
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Patterning Smectic Liquid Crystals for OFETs at Low Temperature
摘要： The preparation of regular microstructures with liquid crystalline materials for organic field effect transistors (OFETs) is an attractive but challenging issue. However, it is usually limited by the difficulty of forming large-area single crystals aligned in a desirable direction. Herein, several terthiophene (TTP) smectic liquid crystals such as 8-TTP-8 and 12-TTP-11OH are patterned into highly crystalline microstripes by a sandwich system through a dewetting method. Morphology and orientation of the microstripes strongly depend on preparation temperature. Microstripes prepared below crystalline temperature are uniform, well-ordered, and show high field effect transistor (FET) mobility. Meanwhile, π–π stacking direction of the TTP backbone is perpendicular to the microstripe and the molecules stack in layer structure, standing up on the SiO2/Si substrate, which would provide an effective pathway for p-type charge transport. However, higher preparation temperatures at liquid crystalline or isotropic liquid range induce many defects in the crystal formation process and cause incline of the unit cell, thus leading to a sharp decrease in FET mobility. A possible mechanism of molecular stacking at different temperature range is proposed. This strategy promised to provide a new opportunity for the high cost-efficiency fabrication of OFETs.
关键词： OFETs,smectic liquid crystals,terthiophene,alignment,patterning
更新于2025-09-23 15:23:52
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A UV-Responsive Multifunctional Photoelectric Device Based on Discotic Columnar Nanostructures and Molecular Motors
摘要： Orientation control of ordered materials would not only produce new physical phenomenon but also facilitate the development of fancy devices. Discotic liquid crystals (DLCs) form 1D charge transport pathway by self-organizing into columnar nanostructures via π–π stacking. However, controlling the electrical properties in such nanostructures with some direct and instant way is a formidable task for their high viscosity and insensitivity to external stimuli. Herein, the arbitrary control over electrical conductivity of such columnar nanostructures is achieved with UV light by incorporating DLCs with molecular motors. Highly ordered DLC microstripe arrays are generated on desired substrate through a capillary bridge dewetting strategy. The conductivity of the microstripes could be continuously modulated by 365 nm light due to the influence of molecular motion under UV irradiation on the electron orbital overlap of columnar nanostructures. This is so because the disorder degree of the DLC molecules is associated with the intensity of UV light and the doping concentration of molecular motors. Moreover, the device shows memory effect and reversible conductivity change. The DLC microstripe arrays are very promising for the applications in UV detectors, memory devices, optical switches, and so on.
关键词： discotic liquid crystals,tunable conductivity,molecular motors,overcrowded alkenes,optical switches
更新于2025-09-23 15:22:29
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Topologically non-equivalent textures generated by the nematic electrohydrodynamics
摘要： Some classes of nematic liquid crystals can be driven through turbulent regimes when forced by an external electric field. In contrast to isotropic fluids, a turbulent nematic exhibits a transition to a stochastic regime that is characterised by a network of topological defects. We study the deformations arising after the electric field has been switched-off. In contrast to the turbulent regime, the relaxation of this topological-defect regime involves the annihilation of an interlacement of defect lines. We show that these defect lines separate regions of the nematic having topologically non-equivalent textures.
关键词： Nematic liquid crystals,electrohydrodynamics,twist deformation,topological defects
更新于2025-09-23 15:22:29
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Liquid crystal nose, chiral case: towards increased selectivity and low detection limits
摘要： In this paper, we describe a simple prototype of an olfaction system based on chiral liquid crystals (LCs) and suitable for sensing volatile organic compounds (VOCs). The detection of small concentrations of VOCs is based on measuring weak colour fluctuations on the surface of the LC droplet. Detection of larger concentrations is based on measuring colour changes (or shift of the selective reflection band) and isotropisation transition of the whole droplet. Thus, a broad range of VOC concentrations can be detected by this LC nose.
关键词： gas detection,LC nose,volatile organic compound,olfaction,electronic nose,VOC,liquid crystals,cholesteric
更新于2025-09-23 15:22:29
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Low-Threshold-Voltage and Electrically Switchable Polarization-Selective Scattering Mode Liquid Crystal Light Shutters
摘要： Low-threshold-voltage (Vth) and electrically switchable, polarization-selective scattering mode light shutters (PSMLSs) using polymer-dispersed liquid crystals (PDLCs) are demonstrated in this work. The optimized weight ratio of the nematic liquid crystals (LCs) to the adopted monomer (NBA107, Norland Optics) in the low-Vth PDLCs based on NBA107 is 7:3, [7:3]-PDLCsNBA107. The properties of the low-Vth PDLCsNBA107, such as light-scattering performance, initial transmission, Vth, and droplet size were investigated. Experiment results show that the surface anchoring (threshold-voltage) of NBA107 is weaker (lower) than or equal to that of the common NOA65. The cost is that the response time of the proposed PDLCsNBA107 is relatively long. A method to reduce the decay time, which can be applied to all other PDLC devices, will be elucidated. In addition to the low Vth of the proposed PDLCsNBA107, the operation voltage (~6 Vrms) to approach the maximum transmission is relatively low in a 7 μm-thick PDLCsNBA107 cell. Moreover, the polarization-selective light-scattering performances of the proposed PSMLSs based on the [7:3]-PDLCsNBA107, mainly driven by in-plane and vertical fields, are also demonstrated.
关键词： scattering,liquid crystals,polarization,polymers
更新于2025-09-23 15:22:29
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Liquid Crystals - Self-Organized Soft Functional Materials for Advanced Applications || Bent-Core Liquid Crystals: Structures and Mesomorphic Properties
摘要： Bent-core (BC) molecules became an attractive liquid crystal class due to their potential use in smart displays and photonic devices. In contrast to calamitic mesogens, bent-shaped mesogens are self-organized superstructures with remarkable properties, given the presence of polar order in mesophases, although the molecules themselves are not chiral. A particular interest represents the biaxial nematic liquid crystal materials that are used in display technology and allow a faster switching response, compared to calamitic liquid crystals, with considerably reduced costs. This chapter briefly reviews the bent-core liquid crystals with three different core units in the structure: (1) 2,5-disubstituted oxadiazole, (2) 1,3-disubstituted benzene, and (3) 2,7-disubstituted naphthalene. To the central bent units (BUs) containing reactive functional groups of phenolic or aminic type, various mesogenic groups are symmetrically or asymmetrically connected, via esterification or condensation reactions. The obtained compounds showed biaxial nematic and/or smectic mesophases with high transition temperatures in the case of oxadiazole derivatives or cholesteric and banana-type mesophases with lower transition temperatures in the case of benzene and naphthalene derivatives.
关键词： naphthalene,nematic,azomesogens,resorcinol,cholesteric,bent-core molecules,oxadiazole,biaxial,smectic,liquid crystals
更新于2025-09-23 15:22:29
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Light Control with Liquid Crystalline Elastomers
摘要： The facile synthesis of well-aligned, main-chain liquid crystalline elastomers that retain the cholesteric phase (CLCEs) is reported. The selective reflection inherent to this phase is thermally tuned more than 200 nm in these solid films, across the visible spectrum. The optical response is directly correlated to thermomechanical expansion of the CLCE film thickness. The bandwidth of the selective reflection of the CLCEs is increased to more than 200 nm by the incorporation of photosensitive chiral dopants that introduce heterogeneity in the pitch distribution. The mirror-like reflection of this CLCE film is also thermochromic, shifting from the visible to infrared. Reminiscent of cephalopods, when combined with the mechanical deformation of voxelated nematic liquid crystal elastomer, the thermochromic response of the CLCE produces solid-state elements with concurrent variation of specular and diffuse reflectance. These results demonstrate distinctive potential opportunities for liquid crystal elastomers to control light enabling new application in textiles, optics, and architecture.
关键词： liquid crystals,bioinspired,shape transformation
更新于2025-09-23 15:22:29
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Self-assembly of fractal liquid crystal colloids
摘要： Nematic liquid crystals are anisotropic fluids that self-assemble into vector fields, which are governed by geometrical and topological laws. Consequently, particulate or droplet inclusions self-assemble in nematic domains through a balance of topological defects. Here, we use double emulsions of water droplets inside radial nematic liquid crystal droplets to form various structures, ranging from linear chains to three-dimensional fractal structures. The system is modeled as a formation of satellite droplets, distributed around a larger, central core droplet and we extend the problem to explain the formation of fractal structures. We show that a distribution of droplet sizes plays a key role in determining the symmetry properties of the resulting geometric structures. The results are relevant to a variety of inclusions, ranging from colloids suspensions to multi-emulsion systems. Such systems have potential applications for novel switchable photonic structures as well as providing wider insights into the packing of self-assembled structures.
关键词： Self-assembly,Fractal structures,Topological defects,Colloids,Liquid crystals
更新于2025-09-23 15:22:29