In the exploration of circularly polarized luminescence(CPL)materials,doping cholesteric liquid crystals(CLCs)with achiral dyes is a common strategy.Conjugated polymers are favored as achiral dyes for their superior l...In the exploration of circularly polarized luminescence(CPL)materials,doping cholesteric liquid crystals(CLCs)with achiral dyes is a common strategy.Conjugated polymers are favored as achiral dyes for their superior luminescent properties.In this study,a series of oligomers(M1-M3)and the conjugated polymer F8BT were synthesized to systematically assess the impact of the length of the conjugated backbone on CPL signals of CLCs doped with conjugated polymers.As the length rose from M1 to M3,CPL intensity concurrently increased(|g_(lum)|increased from 0.35 to 0.84),attributable to enhanced dichroism(order parameter,SFincreased from 0.20 to 0.56).In contrast,F8BT polymer resulted in diminished CPL intensity(|g_(lum)|=0.64)due to the reduced compatibility.Achieving a balance between dichroism and compatibility is crucial for optimizing CPL in conjugated polymer-doped CLCs.The guiding principle established here may have broad applicability in other CPL assemblies,offering a strategic avenue to engineer highperformance CPL materials with conjugated polymer.展开更多
Liquid crystals （LCs） and polymers are extensively used in various electro-optical applications. In this paper, normal mode polymer stabilized cholesteric LC film is prepared and studied. The effects of chiral dopan...Liquid crystals （LCs） and polymers are extensively used in various electro-optical applications. In this paper, normal mode polymer stabilized cholesteric LC film is prepared and studied. The effects of chiral dopant and monomer concentrations on the electro-optical properties, such as contrast ratio, driving voltage, hysteresis width and response time, are investigated. The reasons of electro-optical properties influenced by the concentrations of the materials are discussed. Through the proper material recipe, the electro-optical properties of polymer stabilized cholesteric LC film can be optimized.展开更多
In this study, a novel H-bonded cholesteric polymer film responding to temperature and pH by changing the reflection color was fabricated. The H-bonded cholesteric polymer film was achieved by UV-photopolymerizing a c...In this study, a novel H-bonded cholesteric polymer film responding to temperature and pH by changing the reflection color was fabricated. The H-bonded cholesteric polymer film was achieved by UV-photopolymerizing a cholesteric liquid crystal （Ch-LC） monomers mixture containing a photopolymerizable chiral H-bonded assembly （PCHA）. The cholesteric polymer film based on PCHA can be thermally switched to reflect red color from the initial green/yellow color as temperature is increased, which is due to a change in helical pitch induced by the weakening of H-bonded interaction in the polymer film. Additionally, the selective reflection band （SRB） of the cholesteric polymer film in solution with pH 〉 7 showed an obvious red shift with increasing pH values. While the SRB of the cholesteric polymer film in solutions with pH = 7 and pH 〈 7 hardly changed. This pH sensitivity in solutions with pH 〉 7 could be explained by the breakage of H-bonds in the cholesteric polymer film and the structure changes induced by --OH- and --K＋ ions in the alkaline solution. In contrast, it couldn＇t happen in the neutral and acidic solutions. The cholesteric polymer film in this study can be used as optical/photonic papers, optical sensors and LCs displays, etc.展开更多
Cholesteric liquid crystals（CLCs） have recently sparked an enormous amount of interest in the development of soft matter materials due to their unique ability to self-organize into a helical supra-molecular architec...Cholesteric liquid crystals（CLCs） have recently sparked an enormous amount of interest in the development of soft matter materials due to their unique ability to self-organize into a helical supra-molecular architecture and their excellent selective reflection of light based on the Bragg relationship.Nowadays,by the virtue of building the self-organized nanostructures with pitch gradient or non-uniform pitch distribution,extensive work has already been performed to obtain CLC films with a broad reflection band.Based on authors＇ many years＇ research experience,this critical review systematically summarizes the physical and optical background of the CLCs with broadband reflection characteristics,methods to obtain broadband reflection of CLCs,as well as the application in the field of intelligent optical modulation materials.Combined with the research status and the advantages in the field,the important basic and applied scientific problems in the research direction are also introduced.展开更多
The planar texture of glassy cholesteric siloxane cyclic side-chain liquid crystals was fixed by quenching initially. Then the polymer network formed by the optically active polymerizable monomers imposed additional c...The planar texture of glassy cholesteric siloxane cyclic side-chain liquid crystals was fixed by quenching initially. Then the polymer network formed by the optically active polymerizable monomers imposed additional constraints on the motion of chain segments of the glassy liquid crystal and then further stabilized the molecule arrangement. A cholesteric liquid crystal film with stable optical properties was developed by this method.展开更多
The cholesteric liquid crystalline structure in chitosan/polyacrylic acid composite films was studied by surface techniques. A periodical lamellar-like structure was observed in the permanganic acid etched film surfac...The cholesteric liquid crystalline structure in chitosan/polyacrylic acid composite films was studied by surface techniques. A periodical lamellar-like structure was observed in the permanganic acid etched film surface by both scanning electron microscopy (SEM) and atomic force microscopy (AFM), instead of the thumb-print texture which can be detected with polarized optical microscopy. It is suggested that the periodical lamellar-like structure is induced by the etching selectivity between cholesteric layers due to different molecular arrangement on the film surface. Four kinds of perpendicular disclinations, i.e. chi --> tau (-) + lambda (+), chi --> lambda (-) + tau (+), chi --> tau (-) + tau (+) and chi --> lambda (-) + lambda (+) were found in the composite films from SEM observations. The smallest periodicity of lamellar-like structure (equals to half pitch) is 20 similar to 40 nm measured with AFM.展开更多
The kinetics of mesophase formation of a thermotropic hydroxyethyl cellulose acetate from isotropic phase to cholesteric mesophase has been studied by means of depolarizing transmittance method. Avrami type analysis o...The kinetics of mesophase formation of a thermotropic hydroxyethyl cellulose acetate from isotropic phase to cholesteric mesophase has been studied by means of depolarizing transmittance method. Avrami type analysis of the data gives an exponent n close to 1, which suggests the nucleation followed by rod-like growth. It means that the kinetic behavior of phase transition from isotropic to cholesteric mesophase is very similar to that of the mesophase formation from isotropic to nematic mesophase.展开更多
Photo-responsive cholesteric liquid crystals(CLCs)have attracted much attention in recent years due to their wide applications in filters,tun able optical lasers,dyn amic display devices,etc.However,UV light is usuall...Photo-responsive cholesteric liquid crystals(CLCs)have attracted much attention in recent years due to their wide applications in filters,tun able optical lasers,dyn amic display devices,etc.However,UV light is usually used as the exter nal stimulus source,which is not envir on ment-frie ndly enough.On the other hand,the mecha nical properties of CLCs are not strong eno ugh for these practical applications.Therefore,it still remains a challenge to endow the CLCs with visible light response and high mechanical properties at the same time.Herein,an axially chiral tetra-fluorinated binaphthyl azobenzene gelator(S-4F-AG)is synthesized.Upon 550 and 450 nm light irradiations,S-4F-AG exhibits excellent photo-switchable behaviors.Notably,the maximum con tent of c/s-isomer and its half-life are as high as 35%and 89 h in acet on itrile,respectively.A self-supporting CLC physical gel with a storage modulus around 104 Pa can be obtained when 3wt%S-4F-AG and 12wt%binaphthyl azobenzene derivative(dopant 2)are co-doped into a nematic LC host P0616A.This CLC physical gel exhibits a temperature-driven blue,green,and red reflection colors reversibly.Importantly,such three primary RGB colors can also be realized by adjusting the exposure time of 550 nm green light.This work lays a solid foundation for the applications ranging from information storage to high-tech anticounterfeit.展开更多
Optical filters with different configurations based on cholesteric liquid crystals （CLCs） are designed. The central wavelength from CLCs can be tuned by the electric field or temperature. For the electric field tuni...Optical filters with different configurations based on cholesteric liquid crystals （CLCs） are designed. The central wavelength from CLCs can be tuned by the electric field or temperature. For the electric field tuning, the ITO is designed with circular patterns, which can make the tunable range 18 nm. For the temperature tuning, two-layer- CLC configurations are used. The experimental results indicate that a deepened or broadened bandgap from the CLC can be achieved by different handedness or concentrations of chiral dopants. The spectrum study is carried out.展开更多
Five aza-crown-ethers were synthesized and four of them shown to have cholesteric liquid crystalline properties. Their properties relevant to cholesteric liquid crystal were determined by DSC and the textures. The typ...Five aza-crown-ethers were synthesized and four of them shown to have cholesteric liquid crystalline properties. Their properties relevant to cholesteric liquid crystal were determined by DSC and the textures. The type of cholesteric mesomorphic azacrown ether have not been reported so far.展开更多
Cholesteric liquid crystal(Ch-LC)exhibits many remarkable optical properties due to formation of a macroscopic helical structure.A low amount of monomer(5wt.%)is dispersed into cholesteric liquid crystal and get polym...Cholesteric liquid crystal(Ch-LC)exhibits many remarkable optical properties due to formation of a macroscopic helical structure.A low amount of monomer(5wt.%)is dispersed into cholesteric liquid crystal and get polymerized under UV radiations to form polymer stabilized cholesteric texture(PSCT).The thermo-chromic response made this device suitable for the developing applications in thermal imaging.Temperature based measurements of PSCT exploits the key property of some polymer stabilized cholesteric liquid crystals(PSCLC)to reflect definite colors at specific temperatures.The selective color of PSCT texture shifts with raise in temperature from 30oC to 85oC,which can be utilized in thermal imaging applications.展开更多
The composite materials based on nanopowder dispersed liquid crystals are important both from fundamental research and device applications due to their unique properties such as improvement in various properties like ...The composite materials based on nanopowder dispersed liquid crystals are important both from fundamental research and device applications due to their unique properties such as improvement in various properties like electrical,optical,thermal,energy storage and spontaneous polarization etc.The proper selection of nanoparticle and its size which to be dispersed in particular liquid crystals is very important for a particular application.In the present study,a ferroelectric nanopowder of Barium Titanate(BaTiO3)was dispersed in cholesteric liquid crystal and the same was confirmed by Fourier Transform Infrared(FTIR)Spectroscopy.The various acoustical properties like ultrasonic velocity,density,Adiabatic Compressibility,Rao Constant,Wada Constant and Acoustic Impedance were investigated by ultrasonic interferometer at room temperature at fixed frequency.The dielectric constant was determined by Precision Impedance Analyzer.In addition to these investigations,particle size and surface area were also measured.Our investigation shows enhanced in dielectric and acoustical properties which may be useful for device applications extensively in microelectronics,low cost-photovoltaic devices,and custom-shaped containers possibly applied as a coating.展开更多
BACKGROUND: Generally main chain cholesteric thermotropic liquid crystalline polymers are prepared form chiral diacid or diol monomer. But these monomers are costly. Isosorbide is chiral cycloaliphatic diol accessible...BACKGROUND: Generally main chain cholesteric thermotropic liquid crystalline polymers are prepared form chiral diacid or diol monomer. But these monomers are costly. Isosorbide is chiral cycloaliphatic diol accessible from renewable resources in the form of pure enantiomers. Thus it is used to synthesize main chain cholesteric thermotropic liquid crystalline polymers. Incorporation of phenyl hydroquinone into the backbone of the main chain frustrates chain packing, thus lowering the crystallinity and depressing the melting point below the degradation temperature, also improves the solubility due to disruption of packing and maintains the mechanical and thermal performance. RESULTS: Optical microscopy study reveals that more than 50% of isosorbide content with phenyl hydroquinone and terephthalic acid showed “yellow iridescent oily streaks” with a background of mosaic/marble texture. These are the typical textures of cholesteric liquid crystalline phase. Copolyesters based on phenyl hydroquinone, isosorbide and terephthalic acid are soluble in aprotic solvents like N,N-dimethylacetamide (DMAC), dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), and N-methyl-2-pyrrolidone (NMP). Solubility increases with the content of isosorbide percent. Thermal stability of all copolyesters was more than 300?C on the basis of 10% wt loss. CONCLUSIONS: It was found that main chain cholesteric thermotropic liquid crystalline polymers can be prepared form chiral cycloaliphatic diol such as isosorbide. Main chain cholesteric thermotropic liquid crystalline polyesters are prepared from phenyl hydroquinone, isosorbide and terephthalic acid showed thermal stability more than 300?C. Main chain cholesteric thermotropic liquid crystalline polymers are soluble in aprotic solvents like DMAC, DMSO, DMF and NMP.展开更多
Polymer fibers are attracting increasing attention as a type of fundamental material for a wide range of products.However,to incorporate novel functionality,a crucial challenge is to simultaneously manipulate their st...Polymer fibers are attracting increasing attention as a type of fundamental material for a wide range of products.However,to incorporate novel functionality,a crucial challenge is to simultaneously manipulate their structuring across multiple length scales.In this research,a facile and universal approach is proposed by directly drawing a pre-gel feedstock embedding a cellulose cholesteric liquid crystal(CLC).An in situ photo-polymerization process is applied,which not only allows for the continuous drawing of the filaments without breakup but also makes the final CLC fibers a colored appearance.More importantly,the multiscale properties of the fibers,such as their diameter,morphology,and the internal liquid crystalline ordering of the molecules(and thus structural color),can be manipulated by several controlling parameters.Combining this cross-scale tunability with a smart functional hydrogel system results in the formation of fibers with structural coloration,self-healing,electrical conduction,and thermal-sensing abilities.We believe that this platform can be extended to other hydrogel systems and will help unlock a wide variety of real-life applications.展开更多
In this Letter,by exploiting the spin-to-orbital angular momentum conversion capability and the polarization selectivity characteristic of cholesteric liquid crystal planar optical elements,an approach of combing two ...In this Letter,by exploiting the spin-to-orbital angular momentum conversion capability and the polarization selectivity characteristic of cholesteric liquid crystal planar optical elements,an approach of combing two cholesteric liquid crystal layers with opposite handedness and independent surface patterns is proposed and investigated for generating arbitrary vector vortex beams on the hybrid-order Poincarésphere.Furthermore,the intensity profiles and polarization distributions of typical vector vortex beams are experimentally demonstrated and analyzed,which shows good agreement with the theoretical prediction.The approach also suggests its advantages of operating light in the polychromatic spectral region of Bragg reflection.Our method presents a simple and direct way of phase and polarization manipulation,which also provides promising opportunities for developing advanced applications in structured light,high-resolution imaging,and information processing.展开更多
Solid materials with dynamically tunable circularly polarized luminescence(CPL) feature higher security levels and devicefriendly characteristics, showing great superiority in the field of information technology and a...Solid materials with dynamically tunable circularly polarized luminescence(CPL) feature higher security levels and devicefriendly characteristics, showing great superiority in the field of information technology and anti-counterfeiting. To address the limited photoisomerization of fluorescent photoswitch in CPL-active solid materials, here a cholesteric liquid crystal elastomer(CLCE) containing a hydrogen-bonded(H-bonded) polymerizable fluorescent switch AHBA-PSD is prepared. Owing to the good flexibility and low glass-transition temperature of CLCE, AHBA-PSD shows a fast and fully reversible photocyclization/cycloreversion with fluorochromic behavior in CLCE. Further, by controlling the spectral overlapping area between the emission and reflection bands, the CLCE exhibits a strong CPL with a g_(lum) value of up to 0.76 accompanied by a reversible phototunable CPL signal. Meanwhile, the H-bond helps to stabilize the mechanical property, and the force-induced switching-off of CPL signal could be achieved due to the destroyed helical structures by external force. Finally, an automatically-recognized identification card with abundant chiroptical information is demonstrated.展开更多
The key to high-level encryption and anti-counterfeiting techniques is the storage of multiple levels of distinct information that can be individually and precisely addressed by certain stimuli.This continues to be a ...The key to high-level encryption and anti-counterfeiting techniques is the storage of multiple levels of distinct information that can be individually and precisely addressed by certain stimuli.This continues to be a formidable challenge as the concealed images or codes must be read with fast response and high resolution without cross-talk to the first layer of information.Here,we report a non-fluorescencebased strategy to establish responsive encryption labels taking advantage of solely tuning multiple optical patterns of cholesteric liquid crystal(CLC)microdroplets doped with light-driven molecular motors.The photo-triggered unidirectional rotation of the motor induced not only changes in the helical twist power value but the opposite helical orientation of the superstructure in CLCs as well,resulting in changes in both the structural color and the selective reflection of circularly polar light.The designed labels,which featured highly selective addressability of dual-level distinct information,good reversibility,and viewing angle-independence,were applied to build devices for daily practical use,demonstrating great potential in anti-counterfeiting technology and provide a versatile platform for enhanced data protection and encryption of authentic information.展开更多
Smart beams play a vital role in modern intelligent vehicles and have recently attracted significant attention.A spatial light modulator with high optical efficiency,low cost,and compact size is crucial for designing ...Smart beams play a vital role in modern intelligent vehicles and have recently attracted significant attention.A spatial light modulator with high optical efficiency,low cost,and compact size is crucial for designing smart beams.Here,we mix cholesteric liquid crystals with dichroic black dye and a monomer.After UV polymerization,the sample exhibits a low driving voltage of 26 V,a high transmittance of over 70%,and an On-off ratio over 280,thanks to the joint contribution of both the absorption and the scattering effect.A smart beam device is demonstrated by electrically addressing the dye-doped and polymer-stabilized cholesteric liquid crystal with pixelated electrodes.Light patterns with arbitrary designs are projected dynamically.The switching time reaches several tens of milliseconds.This strategy brings new designs to intelligent vehicles and may also inspire applications in public information displays,advertising,and even AR/VR displays.展开更多
Versatile stimuli-responsive circularly polarized luminescent(CPL)materials have potential applications in information storage,security encryption,and intelligent displays.In this study,the Z/E isomerization of ultrav...Versatile stimuli-responsive circularly polarized luminescent(CPL)materials have potential applications in information storage,security encryption,and intelligent displays.In this study,the Z/E isomerization of ultraviolet(UV)-photosensitive achiralα-cyanostilbene derivative was used as an achiral dichroic dye(Switch)to drive the controllable CPL-active response in cholesteric liquid crystals(CLCs).Under irradiation by 365 nm UV light,the resulting CLCs-Z-Switch underwent a Z-to-E configuration isomerization as CLCs-E-Switch,accompanied by a decrease in its dichroic order parameter(SFvalue)from 0.15to 0.07.Although the quantum yield(QY)of CLCs-E-Switch increased from 8.1%(CLCs-Z-Switch)to 16.8%,the corresponding glumvalues of CPL emission decreased from+0.55/-0.57 to+0.37/-0.39 due to a decrease in the order of helical arrangement of E-Switch in E7 media.This study enables photosensitive CLCs-Switch to be applied for optical information storage devices.展开更多
Cholesteric liquid crystals(CLCs)exhibit unique helical superstructures that selectively reflect circularly polarized light,enabling them to dynamically respond to environmental changes with tunable structural colors....Cholesteric liquid crystals(CLCs)exhibit unique helical superstructures that selectively reflect circularly polarized light,enabling them to dynamically respond to environmental changes with tunable structural colors.This dynamic color-changing capability is crucial for applications that require adaptable optical properties,positioning CLCs as key materials in advanced photonic technologies.This review focuses on the mechanisms of dynamic color tuning in CLCs across various forms,including small molecules,cholesteric liquid crystal elastomers(CLCEs),and cholesteric liquid crystal networks(CLCNs),and emphasizes the distinct responsive coloration each structure provides.Key developments in photochromic mechanisms based on azobenzene,dithienylethene,and molecular motor switches,are discussed for their roles in enhancing the stability and tuning range of CLCs.We examine the color-changing behaviors of CLCEs under mechanical stimuli and CLCNs under swelling,highlighting the advantages of each form.Following this,applications of dynamic color-tuning CLCs in information encryption,adaptive camouflage,and smart sensing technologies are explored.The review concludes with an outlook on current challenges and future directions in CLC research,particularly in biomimetic systems and dynamic photonic devices,aiming to broaden their functional applications and impact.展开更多
基金supported by the National Natural Science Foundation of China(Nos.21975118,92156014,52373188)。
文摘In the exploration of circularly polarized luminescence(CPL)materials,doping cholesteric liquid crystals(CLCs)with achiral dyes is a common strategy.Conjugated polymers are favored as achiral dyes for their superior luminescent properties.In this study,a series of oligomers(M1-M3)and the conjugated polymer F8BT were synthesized to systematically assess the impact of the length of the conjugated backbone on CPL signals of CLCs doped with conjugated polymers.As the length rose from M1 to M3,CPL intensity concurrently increased(|g_(lum)|increased from 0.35 to 0.84),attributable to enhanced dichroism(order parameter,SFincreased from 0.20 to 0.56).In contrast,F8BT polymer resulted in diminished CPL intensity(|g_(lum)|=0.64)due to the reduced compatibility.Achieving a balance between dichroism and compatibility is crucial for optimizing CPL in conjugated polymer-doped CLCs.The guiding principle established here may have broad applicability in other CPL assemblies,offering a strategic avenue to engineer highperformance CPL materials with conjugated polymer.
基金Project partially supported by the National Natural Science Foundation of China （Grant Nos. 60736042, 60578035 and 50703039） and the Science Foundation of Jilin Province of China （Grant Nos. 20050520 and 20050321-2）.
文摘Liquid crystals （LCs） and polymers are extensively used in various electro-optical applications. In this paper, normal mode polymer stabilized cholesteric LC film is prepared and studied. The effects of chiral dopant and monomer concentrations on the electro-optical properties, such as contrast ratio, driving voltage, hysteresis width and response time, are investigated. The reasons of electro-optical properties influenced by the concentrations of the materials are discussed. Through the proper material recipe, the electro-optical properties of polymer stabilized cholesteric LC film can be optimized.
基金supported by the National Natural Science Foundation of China (No. 50903004)
文摘In this study, a novel H-bonded cholesteric polymer film responding to temperature and pH by changing the reflection color was fabricated. The H-bonded cholesteric polymer film was achieved by UV-photopolymerizing a cholesteric liquid crystal （Ch-LC） monomers mixture containing a photopolymerizable chiral H-bonded assembly （PCHA）. The cholesteric polymer film based on PCHA can be thermally switched to reflect red color from the initial green/yellow color as temperature is increased, which is due to a change in helical pitch induced by the weakening of H-bonded interaction in the polymer film. Additionally, the selective reflection band （SRB） of the cholesteric polymer film in solution with pH 〉 7 showed an obvious red shift with increasing pH values. While the SRB of the cholesteric polymer film in solutions with pH = 7 and pH 〈 7 hardly changed. This pH sensitivity in solutions with pH 〉 7 could be explained by the breakage of H-bonds in the cholesteric polymer film and the structure changes induced by --OH- and --K＋ ions in the alkaline solution. In contrast, it couldn＇t happen in the neutral and acidic solutions. The cholesteric polymer film in this study can be used as optical/photonic papers, optical sensors and LCs displays, etc.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51573006,51573003,51203003,51303008,51302006,51402006,51272026,and 51273022)the Major Project of Beijing Science and Technology Program,China(Grant Nos.Z151100003315023 and Z141100003814011)the Fok Ying Tung Education Foundation,China(Grant No.142009)
文摘Cholesteric liquid crystals（CLCs） have recently sparked an enormous amount of interest in the development of soft matter materials due to their unique ability to self-organize into a helical supra-molecular architecture and their excellent selective reflection of light based on the Bragg relationship.Nowadays,by the virtue of building the self-organized nanostructures with pitch gradient or non-uniform pitch distribution,extensive work has already been performed to obtain CLC films with a broad reflection band.Based on authors＇ many years＇ research experience,this critical review systematically summarizes the physical and optical background of the CLCs with broadband reflection characteristics,methods to obtain broadband reflection of CLCs,as well as the application in the field of intelligent optical modulation materials.Combined with the research status and the advantages in the field,the important basic and applied scientific problems in the research direction are also introduced.
基金This work was financially supported by the National High-Tech Research and Development Program of China (No. 2003AA327050).
文摘The planar texture of glassy cholesteric siloxane cyclic side-chain liquid crystals was fixed by quenching initially. Then the polymer network formed by the optically active polymerizable monomers imposed additional constraints on the motion of chain segments of the glassy liquid crystal and then further stabilized the molecule arrangement. A cholesteric liquid crystal film with stable optical properties was developed by this method.
基金This work was supported by the National Natural Science Foundation of China (No. 29974023) and Natural Science Foundation of Fujian (No.29910006).
文摘The cholesteric liquid crystalline structure in chitosan/polyacrylic acid composite films was studied by surface techniques. A periodical lamellar-like structure was observed in the permanganic acid etched film surface by both scanning electron microscopy (SEM) and atomic force microscopy (AFM), instead of the thumb-print texture which can be detected with polarized optical microscopy. It is suggested that the periodical lamellar-like structure is induced by the etching selectivity between cholesteric layers due to different molecular arrangement on the film surface. Four kinds of perpendicular disclinations, i.e. chi --> tau (-) + lambda (+), chi --> lambda (-) + tau (+), chi --> tau (-) + tau (+) and chi --> lambda (-) + lambda (+) were found in the composite films from SEM observations. The smallest periodicity of lamellar-like structure (equals to half pitch) is 20 similar to 40 nm measured with AFM.
基金This work supported by the National Basic Research Project-Macromolecular Condensed State
文摘The kinetics of mesophase formation of a thermotropic hydroxyethyl cellulose acetate from isotropic phase to cholesteric mesophase has been studied by means of depolarizing transmittance method. Avrami type analysis of the data gives an exponent n close to 1, which suggests the nucleation followed by rod-like growth. It means that the kinetic behavior of phase transition from isotropic to cholesteric mesophase is very similar to that of the mesophase formation from isotropic to nematic mesophase.
文摘Photo-responsive cholesteric liquid crystals(CLCs)have attracted much attention in recent years due to their wide applications in filters,tun able optical lasers,dyn amic display devices,etc.However,UV light is usually used as the exter nal stimulus source,which is not envir on ment-frie ndly enough.On the other hand,the mecha nical properties of CLCs are not strong eno ugh for these practical applications.Therefore,it still remains a challenge to endow the CLCs with visible light response and high mechanical properties at the same time.Herein,an axially chiral tetra-fluorinated binaphthyl azobenzene gelator(S-4F-AG)is synthesized.Upon 550 and 450 nm light irradiations,S-4F-AG exhibits excellent photo-switchable behaviors.Notably,the maximum con tent of c/s-isomer and its half-life are as high as 35%and 89 h in acet on itrile,respectively.A self-supporting CLC physical gel with a storage modulus around 104 Pa can be obtained when 3wt%S-4F-AG and 12wt%binaphthyl azobenzene derivative(dopant 2)are co-doped into a nematic LC host P0616A.This CLC physical gel exhibits a temperature-driven blue,green,and red reflection colors reversibly.Importantly,such three primary RGB colors can also be realized by adjusting the exposure time of 550 nm green light.This work lays a solid foundation for the applications ranging from information storage to high-tech anticounterfeit.
基金Supported by the National Natural Science Foundation of China under Grant Nos 61107059,61308052 and 61077047the Fundamental Research Funds for the Central Universitiesthe 111 Project of the Harbin Engineering University under Grant No B13015
文摘Optical filters with different configurations based on cholesteric liquid crystals （CLCs） are designed. The central wavelength from CLCs can be tuned by the electric field or temperature. For the electric field tuning, the ITO is designed with circular patterns, which can make the tunable range 18 nm. For the temperature tuning, two-layer- CLC configurations are used. The experimental results indicate that a deepened or broadened bandgap from the CLC can be achieved by different handedness or concentrations of chiral dopants. The spectrum study is carried out.
文摘Five aza-crown-ethers were synthesized and four of them shown to have cholesteric liquid crystalline properties. Their properties relevant to cholesteric liquid crystal were determined by DSC and the textures. The type of cholesteric mesomorphic azacrown ether have not been reported so far.
文摘Cholesteric liquid crystal(Ch-LC)exhibits many remarkable optical properties due to formation of a macroscopic helical structure.A low amount of monomer(5wt.%)is dispersed into cholesteric liquid crystal and get polymerized under UV radiations to form polymer stabilized cholesteric texture(PSCT).The thermo-chromic response made this device suitable for the developing applications in thermal imaging.Temperature based measurements of PSCT exploits the key property of some polymer stabilized cholesteric liquid crystals(PSCLC)to reflect definite colors at specific temperatures.The selective color of PSCT texture shifts with raise in temperature from 30oC to 85oC,which can be utilized in thermal imaging applications.
文摘The composite materials based on nanopowder dispersed liquid crystals are important both from fundamental research and device applications due to their unique properties such as improvement in various properties like electrical,optical,thermal,energy storage and spontaneous polarization etc.The proper selection of nanoparticle and its size which to be dispersed in particular liquid crystals is very important for a particular application.In the present study,a ferroelectric nanopowder of Barium Titanate(BaTiO3)was dispersed in cholesteric liquid crystal and the same was confirmed by Fourier Transform Infrared(FTIR)Spectroscopy.The various acoustical properties like ultrasonic velocity,density,Adiabatic Compressibility,Rao Constant,Wada Constant and Acoustic Impedance were investigated by ultrasonic interferometer at room temperature at fixed frequency.The dielectric constant was determined by Precision Impedance Analyzer.In addition to these investigations,particle size and surface area were also measured.Our investigation shows enhanced in dielectric and acoustical properties which may be useful for device applications extensively in microelectronics,low cost-photovoltaic devices,and custom-shaped containers possibly applied as a coating.
文摘BACKGROUND: Generally main chain cholesteric thermotropic liquid crystalline polymers are prepared form chiral diacid or diol monomer. But these monomers are costly. Isosorbide is chiral cycloaliphatic diol accessible from renewable resources in the form of pure enantiomers. Thus it is used to synthesize main chain cholesteric thermotropic liquid crystalline polymers. Incorporation of phenyl hydroquinone into the backbone of the main chain frustrates chain packing, thus lowering the crystallinity and depressing the melting point below the degradation temperature, also improves the solubility due to disruption of packing and maintains the mechanical and thermal performance. RESULTS: Optical microscopy study reveals that more than 50% of isosorbide content with phenyl hydroquinone and terephthalic acid showed “yellow iridescent oily streaks” with a background of mosaic/marble texture. These are the typical textures of cholesteric liquid crystalline phase. Copolyesters based on phenyl hydroquinone, isosorbide and terephthalic acid are soluble in aprotic solvents like N,N-dimethylacetamide (DMAC), dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), and N-methyl-2-pyrrolidone (NMP). Solubility increases with the content of isosorbide percent. Thermal stability of all copolyesters was more than 300?C on the basis of 10% wt loss. CONCLUSIONS: It was found that main chain cholesteric thermotropic liquid crystalline polymers can be prepared form chiral cycloaliphatic diol such as isosorbide. Main chain cholesteric thermotropic liquid crystalline polyesters are prepared from phenyl hydroquinone, isosorbide and terephthalic acid showed thermal stability more than 300?C. Main chain cholesteric thermotropic liquid crystalline polymers are soluble in aprotic solvents like DMAC, DMSO, DMF and NMP.
基金supported by the National Natural Science Foundation of China(grant no.32271383).
文摘Polymer fibers are attracting increasing attention as a type of fundamental material for a wide range of products.However,to incorporate novel functionality,a crucial challenge is to simultaneously manipulate their structuring across multiple length scales.In this research,a facile and universal approach is proposed by directly drawing a pre-gel feedstock embedding a cellulose cholesteric liquid crystal(CLC).An in situ photo-polymerization process is applied,which not only allows for the continuous drawing of the filaments without breakup but also makes the final CLC fibers a colored appearance.More importantly,the multiscale properties of the fibers,such as their diameter,morphology,and the internal liquid crystalline ordering of the molecules(and thus structural color),can be manipulated by several controlling parameters.Combining this cross-scale tunability with a smart functional hydrogel system results in the formation of fibers with structural coloration,self-healing,electrical conduction,and thermal-sensing abilities.We believe that this platform can be extended to other hydrogel systems and will help unlock a wide variety of real-life applications.
基金supported by the National Natural Science Foundation of China(No.U23A20377)the Natural Science Foundation of Henan Province(No.232300421389)。
文摘In this Letter,by exploiting the spin-to-orbital angular momentum conversion capability and the polarization selectivity characteristic of cholesteric liquid crystal planar optical elements,an approach of combing two cholesteric liquid crystal layers with opposite handedness and independent surface patterns is proposed and investigated for generating arbitrary vector vortex beams on the hybrid-order Poincarésphere.Furthermore,the intensity profiles and polarization distributions of typical vector vortex beams are experimentally demonstrated and analyzed,which shows good agreement with the theoretical prediction.The approach also suggests its advantages of operating light in the polychromatic spectral region of Bragg reflection.Our method presents a simple and direct way of phase and polarization manipulation,which also provides promising opportunities for developing advanced applications in structured light,high-resolution imaging,and information processing.
基金supported by the National Natural Science Foundation of China (52073017, 51773009)the High Performance Computing Platform of Beijing University of Chemical Technology。
文摘Solid materials with dynamically tunable circularly polarized luminescence(CPL) feature higher security levels and devicefriendly characteristics, showing great superiority in the field of information technology and anti-counterfeiting. To address the limited photoisomerization of fluorescent photoswitch in CPL-active solid materials, here a cholesteric liquid crystal elastomer(CLCE) containing a hydrogen-bonded(H-bonded) polymerizable fluorescent switch AHBA-PSD is prepared. Owing to the good flexibility and low glass-transition temperature of CLCE, AHBA-PSD shows a fast and fully reversible photocyclization/cycloreversion with fluorochromic behavior in CLCE. Further, by controlling the spectral overlapping area between the emission and reflection bands, the CLCE exhibits a strong CPL with a g_(lum) value of up to 0.76 accompanied by a reversible phototunable CPL signal. Meanwhile, the H-bond helps to stabilize the mechanical property, and the force-induced switching-off of CPL signal could be achieved due to the destroyed helical structures by external force. Finally, an automatically-recognized identification card with abundant chiroptical information is demonstrated.
基金supported financially by the National Key R&D Program of China(grant no.2020YFE0100200)Science and Technology Projects in Guangzhou(grant no.202201000008)+2 种基金Guangdong Provincial Key Laboratory of Optical Information Materials and Technology(grant no.2017B030301007)the Netherlands Ministry of Education,Culture and Science(Gravitation Program 024.001.035 to B.L.F.)S.X.acknowledges the fellowship of China Postdoctoral Science Foundation(grant no.2022M711224).
文摘The key to high-level encryption and anti-counterfeiting techniques is the storage of multiple levels of distinct information that can be individually and precisely addressed by certain stimuli.This continues to be a formidable challenge as the concealed images or codes must be read with fast response and high resolution without cross-talk to the first layer of information.Here,we report a non-fluorescencebased strategy to establish responsive encryption labels taking advantage of solely tuning multiple optical patterns of cholesteric liquid crystal(CLC)microdroplets doped with light-driven molecular motors.The photo-triggered unidirectional rotation of the motor induced not only changes in the helical twist power value but the opposite helical orientation of the superstructure in CLCs as well,resulting in changes in both the structural color and the selective reflection of circularly polar light.The designed labels,which featured highly selective addressability of dual-level distinct information,good reversibility,and viewing angle-independence,were applied to build devices for daily practical use,demonstrating great potential in anti-counterfeiting technology and provide a versatile platform for enhanced data protection and encryption of authentic information.
基金This work was supported by the National Key Research and Development Program of China(No.2022YFA1203703)the National Natural Science Foundation of China(NSFC)(No.62035008)the Fundamental Research Funds for the Central Universities(No.021314380233).
文摘Smart beams play a vital role in modern intelligent vehicles and have recently attracted significant attention.A spatial light modulator with high optical efficiency,low cost,and compact size is crucial for designing smart beams.Here,we mix cholesteric liquid crystals with dichroic black dye and a monomer.After UV polymerization,the sample exhibits a low driving voltage of 26 V,a high transmittance of over 70%,and an On-off ratio over 280,thanks to the joint contribution of both the absorption and the scattering effect.A smart beam device is demonstrated by electrically addressing the dye-doped and polymer-stabilized cholesteric liquid crystal with pixelated electrodes.Light patterns with arbitrary designs are projected dynamically.The switching time reaches several tens of milliseconds.This strategy brings new designs to intelligent vehicles and may also inspire applications in public information displays,advertising,and even AR/VR displays.
基金supported by the National Natural Science Foundation of China(21975118,92156014,52373188)。
文摘Versatile stimuli-responsive circularly polarized luminescent(CPL)materials have potential applications in information storage,security encryption,and intelligent displays.In this study,the Z/E isomerization of ultraviolet(UV)-photosensitive achiralα-cyanostilbene derivative was used as an achiral dichroic dye(Switch)to drive the controllable CPL-active response in cholesteric liquid crystals(CLCs).Under irradiation by 365 nm UV light,the resulting CLCs-Z-Switch underwent a Z-to-E configuration isomerization as CLCs-E-Switch,accompanied by a decrease in its dichroic order parameter(SFvalue)from 0.15to 0.07.Although the quantum yield(QY)of CLCs-E-Switch increased from 8.1%(CLCs-Z-Switch)to 16.8%,the corresponding glumvalues of CPL emission decreased from+0.55/-0.57 to+0.37/-0.39 due to a decrease in the order of helical arrangement of E-Switch in E7 media.This study enables photosensitive CLCs-Switch to be applied for optical information storage devices.
基金financially supported by the National Natural Science Foundation of China(Nos.52233001,51927805,and 52173110)the Innovation Program of Shanghai Municipal Education Commission(No.2023ZKZD07)the Shanghai Rising-Star Program(No.22QA1401200)。
文摘Cholesteric liquid crystals(CLCs)exhibit unique helical superstructures that selectively reflect circularly polarized light,enabling them to dynamically respond to environmental changes with tunable structural colors.This dynamic color-changing capability is crucial for applications that require adaptable optical properties,positioning CLCs as key materials in advanced photonic technologies.This review focuses on the mechanisms of dynamic color tuning in CLCs across various forms,including small molecules,cholesteric liquid crystal elastomers(CLCEs),and cholesteric liquid crystal networks(CLCNs),and emphasizes the distinct responsive coloration each structure provides.Key developments in photochromic mechanisms based on azobenzene,dithienylethene,and molecular motor switches,are discussed for their roles in enhancing the stability and tuning range of CLCs.We examine the color-changing behaviors of CLCEs under mechanical stimuli and CLCNs under swelling,highlighting the advantages of each form.Following this,applications of dynamic color-tuning CLCs in information encryption,adaptive camouflage,and smart sensing technologies are explored.The review concludes with an outlook on current challenges and future directions in CLC research,particularly in biomimetic systems and dynamic photonic devices,aiming to broaden their functional applications and impact.
