Polymer Dispersed Liquid Crystal Samples Research Articles

Dielectric characterization of polymer dispersed liquid crystal film with chitosan biopolymer

Polymer Dispersed Liquid Crystals (PDLC) systems were obtained using chitosan as a biopolymer matrix and the nematic liquid crystal (LC) mixture E7 in various concentrations (30, 40 and 50% E7 in chitosan). Several techniques were used to analyze the obtained films: polarizing optical microscopy (POM), IR spectroscopy (FTIR), differential scanning calorimetry (DSC) and dielectric spectroscopy (DS). FTIR spectroscopy revealed minor changes for all PDLC films, suggesting weak interactions between LC and chitosan matrix. For each sample a clear segregation of the nematic droplets could be observed by POM. DSC measurements show that the phase transitions have shifted to lower temperature values for PDLC samples with approximately 2.7 °C compare to pure E7. The values of α (fraction of LC in the droplets) for compositions of 30, 40 and 50 wt% E7 in Chitosan were 0.48, 0.55 and 0.61 respectively, that are lower than for E7/PMMA system.The qualitative and quantitative analysis of the permittivity spectra obtained by DS reveals the fact that there are no significant changes in the molecular dynamics attributed to pure LC E7 compared to the PDLC composites, leading to the conclusion of the existence of a weak interaction between the two components, fact confirmed by the findings from the FTIR results.

High-Throughput Preparation and High-Throughput Detection of Polymer-Dispersed Liquid Crystals Based on Ink-Jet Printing and Grayscale Value Analysis.

In this paper, based on high-throughput technology, polymer dispersed liquid crystals (PDLC) composed of pentaerythritol tetra (2-mercaptoacetic acid) (PETMP), trimethylolpropane triacrylate (TMPTA), and polyethylene glycol diacrylate (PEGD 600) were investigated in detail. A total of 125 PDLC samples with different ratios were quickly prepared using ink-jet printing. Based on the method of machine vision to identify the grayscale level of samples, as far as we know, it is the first time to realize high-throughput detection of the electro-optical performance of PDLC samples, which can quickly screen out the lowest saturation voltage of batch samples. Additionally, we compared the electro-optical test results of manual and high-throughput preparation PDLC samples and discovered that they had very similar electro-optical characteristics and morphologies. This demonstrated the viability of PDLC sample high-throughput preparation and detection, as well as promising application prospects, and significantly increased the efficiency of PDLC sample preparation and detection. The results of this study will contribute to the research and application of PDLC composites in the future.

Liquid crystal droplet design by using pseudopeptidic bottlebrush polymer additives.

Liquid crystal (LC) droplets are promising candidates for sensing applications due to their high sensitivity to surface anchoring changes, resulting in readily detectable optical effects. Herein, we have designed and synthesized amino acid-based bottlebrush polymers and investigated their impact on LC director configurations in the droplets. The pseudopeptidic bottlebrush polymers with an aromatic (phenyl) and aliphatic appendages are synthesized using ring-opening metathesis polymerization (ROMP). Polymer dispersed liquid crystal (PDLC) samples are prepared by employing pseudopeptidic bottlebrush polymers and 4-cyano-4'-pentylbiphenyl (5CB) LC via solvent-induced phase separation (SIPS) technique. Due to π-π stacking, the phenyl group favours radial configuration, whereas the repulsion between 5CB and aliphatic groups induces molecular alignment leading to bipolar droplet arrangement. The impact of various pendant groups attached to the polymer on the prepared PDLC sample's surface characteristics and free energy components is illustrated. The sensing capability of 5CB dispersed in pseudopeptidic bottlebrush polymers for various pH solutions is investigated using polarizing optical microscopy (POM). The PDLC samples are moderately permeable to water and sensitive to different pH solutions. The results demonstrate a simplified and straightforward approach for preparing LC-based biosensors and chemical sensors.

The regulation of contrast ratio of polymer-dispersed liquid crystals (PDLCs) via polyvinyl alcohol (PVA) nanofibers

In this study, a method to regulate the visible transmittance in off-state (T off) and the contrast ratio (CR) for polymer-dispersed liquid crystals (PDLCs) via electrospinning polyvinyl alcohol (PVA) nanofibers on ITO surfaces in liquid crystal cells was reported. The PDLC samples were prepared in the conventional liquid crystal cells and in the nanofiber cells. The results indicated that the sample in the nanofiber cell presented a lower T off and a larger CR in comparison with the sample in the conventional cell if the samples were prepared under the same UV light.

Effect of preparation conditions on the electro-optical performance and the polymer morphology of polymer-dispersed liquid crystals with polyhedral oligomeric silsesquioxane (POSS) microstructure

In this work, the effects of the preparation conditions on the electro-optical performance and the polymer morphology of the polymer dispersed liquid crystal (PDLC) samples in which the polymer matrix contained polyhedral oligomeric silsesquioxane (POSS) microstructure were studied. The results confirmed the dramatic improvement effect of POSS microstructure for the electro-optical properties of PDLC. Moreover, the electro-optical performance and the polymer morphology of the PDLC samples with POSS microstructure can be regulated successfully by the preparation conditions, such as UV light intensity and polymerization temperatures. This work can provide a way for regulating methods for PDLC films.

The Electro-optical study of Al2O3 nanoparticles doped polymer dispersed liquid crystal films

ABSTRACT 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.

Studies on electro‐optical properties of polymer matrix/LC/ITO nanoparticles composites

In this paper, polymer‐dispersed liquid crystal (PDLC) films consisting of liquid crystal (LC)/monomers/indium tin oxide (ITO) nanoparticles with good near‐infrared absorption property had been fabricated, and the influence of the ITO nanoparticles modified with 3‐methacryloxypropyltrimethoxysilane (KH570) on the PDLC films was systematically studied. First, different liquid crystal content was studied to obtain PDLC films with good electro‐optical properties. And then, various weight ratio of ITO nanoparticles was added to samples. While the content of ITO nanoparticles was increased, the saturation voltage increased and the CR decreased. Though the electro‐optical properties of PDLC samples reduced with the addition ITO nanoparticles, the near‐infrared absorption property of films was enhanced.

Droplet configuration control with orange azo dichroic dye in polymer dispersed liquid crystal for advanced electro-optic characteristics

Orange azo dichroic dye dependent droplet configuration and electro-optic (EO) characteristics of polymer dispersed liquid crystals (PDLCs) were studied. PDLCs were prepared using a nematic liquid crystal (LC) and UV-curable liquid photopolymer in equal ratio by polymerization induced phase separation (PIPS) technique. Orange azo dichroic dye was taken in different concentrations (wt./wt. ratio) particularly 0.0625, 0.125, 0.25, 0.5 and 1% of the LC mixture to prepare different PDLC samples. In OFF state, bipolar configuration of LC droplets in polymer matrix was observed predominantly for each concentration of dye. In ON state, LC molecules align along the direction of applied electric field and LC droplets configuration shifted to vertical radial configuration in orange azo dichroic dye doped PDLCs at electric field (~3V/μm). Experimental results showed radically improved transmission value (~25.4a. u.) and contrast (~1058) at relatively lower operating electric field (3.13V/μm) with consistent average droplet size ~4.0μm, at lowest (0.0625%) orange azo dichroic dye concentration among all.

Enhanced Photorefractive and Third-Order Nonlinear Optical Properties of 5CB-Based Polymer-Dispersed Liquid Crystals by Graphene Doping

The enhanced photorefractive and third-order nonlinear optical properties of graphene/graphene oxide (GO)-doped polymer-dispersed liquid crystals (PDLC) were studied by two-beam coupling and z-scan methods. A higher interior electric field will be produced according to the photorefractive performance because of the high electrical conductivity of graphene. The doping of graphene also improved the uniformity of alignments of 4-cyano-4′-pentylbiphenyl (5CB) in PDLC because the rod-shaped liquid crystals tended to align along the surface of sheet structures and the alternate positions of the hexagons on the graphene surface matched well with the alkyl chains of 5CB molecules. Higher third-order nonlinear refraction and absorption coefficient can be attributed to the geometric relationship between graphene and 5CB. The GO-doped samples exhibited higher photorefractive efficiency, third-order nonlinear refraction, and absorption coefficient than undoped PDLC samples, but lower values than the graphene-doped sa...

Polymer Matrix on Polymer Dispersed Liquid Crystals Electro-Optical Properties

Polymer dispersed liquid crystal (PDLC) films are fabricated with various compositions of E7 liquid crystal (LC), 2-Hydroxy ethyl methacrylate (HEMA), Methyl methacrylate (MMA), n-butyl methacrylate (nBMA), Ethyl methacrylate (EMA), Tetraethylene glycol diacrylate (TEGDA), and Benzoin. The results show that the refractive index of the PDLC films is insensitive to the monomer side groups. The effects of different monomers addition on the microstructure, the corresponding polymer matrix motion and electro-optical properties of the PDLC samples are examined using Dynamic Mechanical Analyzers (DMA) and UV-Vis spectroscopy, respectively. The experimental results reveal that the addition of HEMA and TEGDA yields a considerable improvement in the electro-optical properties and the contrast ratio. Overall, the results show that a PDLC comprising 40wt% E7 liquid crystals, 50mol% TeGDA and 50mol% HEMA has both a high contrast ratio (12.75:1) and a low driving voltage (16 V), and is therefore a suitable candidate for smart window and a wide variety of intelligent photoelectric applications.

Preparation and electro‐optical properties of polymer dispersed liquid crystal films with relatively low liquid crystal content

In this paper, polymer dispersed liquid crystals (PDLC) films with LC content as low as 40 wt% were prepared, and the electro‐optical properties were carefully investigated. To accomplish this, different (meth)acrylate copolymerizaiton monomers have been used. The electro‐optical properties and morphologies of the PDLC films were strongly influenced by the chemical structure of copolymerization monomers (hydroxypropyl methacrylate (HPMA), glycidyl methacrylate, hydroxypropyl acrylate) and their feed ratio. Lower driven voltage and higher contrast ratio were achieved when the PDLC films showed a morphology with suitably LC domain size. At high HPMA content, a thin polymer film was formed on the surface of PDLC samples, which is beneficial to decrease the total LC content in PDLC devices. Copyright © 2013 John Wiley & Sons, Ltd.

Dichroic Dye Induced Nonlinearity in Polymer Dispersed Liquid Crystal Materials for Display Devices

The electro-optical characteristics of dye-doped polymer dispersed liquid crystals (PDLCs) have been investigated for display applications. The PDLC samples were obtained by polymerization induced phase separation of the nematic liquid crystal (LC)-dye-prepolymer mixtures under UV illumination with a constant intensity. The optimum conditions for the scattering characteristics of the dye-doped PDLC films as function of the dye concentration have been examined. It was seen that the phase separation and segregation of LC droplets is dependent on the amount of dye used. LC droplets in dye-doped PDLC films exhibit various configurations at lower and higher applied electric field when observed in situ under polarizing optical microscope. The effects of morphology on the electro-optical properties were examined. Experimental results indicate that the driving voltage and contrast ratio were affected considerably by the amount of dye. UV-VIS spectroscopy results showed that the molecular orientation of dye in LC droplets can be controlled to induce nonlinearity in these materials. The results showed that the dye concentration can be optimized to obtain promising electronic materials with minimum threshold and high contrast for display applications.

Comparison of optical diffraction gratings fabricated using in-plane switching cells

In this work, we compare the optical properties of diffraction gratings fabricated using in-plane switching cells. For this purpose, we constructed three different grating cells while varying the preparation process (E7 100%, E7 50% + glycerol 50%, polymer dispersed liquid crystal (PDLC)). Interestingly, the diffraction efficiency of various diffraction orders of the bulk liquid crystal (LC) samples, measured as a function of the applied voltage, showed several maxima and minima. Microscopic studies of these samples showed a zigzag structure consisting of many rod-like segments connected to each other. Our results showed that the first-order diffraction efficiency for the PDLC sample was 5 times larger than that of the bulk LC sample.

聚合物分散液晶的电场诱导定向聚合实验研究

The field induced stereo regular polymerization of polymer dispersed nematic liquid crystal both positive and negative dielectric character are experimentally studied,the picture in kind and polarizing microscope photograph of samples are given.The experiment results show that there are obvious distinguish with in different area of electric field applied or not,the electric field has the induced stereo regular polymerization action under the polymer dispersed liquid crystal sample preparation process.The experiment results are useful to understand the influence of polymer border condition to liquid crystal micro drop configuration,and are in a sense of gaining a good deal to design a new type liquid crystal display device.

Thermotropic and optical behaviour of new PDLC systems based on a polysulfone matrix and a cyanoazomethine liquid crystal

The thermotropic and optical characterisations of a novel polymer dispersed liquid crystal (PDLC) system based on polysulfone UDEL P-1700 as polymer matrix and a low molecular weight liquid crystal compound containing a mesogenic azomethine core and a cyano-substituent were investigated. The PDLC samples were prepared by solvent-induced phase separation (SIPS) and thermally induced phase separation (TIPS) methods using various compositions in the two components. Information on the morphology and phase structure was obtained by polarising optical microscopy, differential scanning calorimetry and X-ray diffraction measurements. PDLC systems with well-defined droplets were obtained for the composite with medium content of liquid crystal compound. The optical characterisation of these materials was performed by analysing their UV–visible absorption and photoluminescence emission as a function of the liquid crystal aggregation degree.

A Wide-Range Controlling of Optical and Morphological Parameters of PDLC Samples via the Intensity of Curing Light

The phase separation kinetics and morphology of polymer dispersed liquid crystals (PDLCs) formed from the nematic liquid crystal (LC) E7 and pre-polymeric composition NOA65 via the photoinduced phase separation in a wide intensity range of actinic UV light (I = 0.5–40 mW/cm2) are investigated. The phase separation process was monitored by measuring transmittance kinetics of the composite layers, while the morphology was observed by polarized optical microscopy. Increase of curing light intensity dramatically influenced the phase separation kinetics and final structure of PDLC samples. Reduction of light intensity below 2 mWcm−2 resulted in transition from the conventional PDLC morphology of fine monodispersed LC droplets (with a droplet diameter d ∼ 1 μm) to the morphology of large LC domains (d ∼ 10 μm) of irregular shape. The realized transition extends the field of PDLC morphologies of E7-NOA65 composites and thus the field of their potential applications.

Control of phase separation and morphology of thiol–ene based PDLCs by curing light intensity

Polymer dispersed liquid crystals (PDLCs) based on nematic liquid crystal (LC) E7 and pre-polymeric composition NOA65 were formed via the photoinduced phase separation in a wide intensity range of the actinic UV light ( I = 0.5–40 mW cm −2). The phase separation process was monitored by measuring transmittance kinetics of the composite layers. Increase of curing light intensity accelerates the phase separation and drastically influences the final structure of PDLC samples. Reduction of light intensity below 2 mW cm −2 results in transition from the conventional PDLC morphology of fine monodispersed LC droplets (with a droplets’ diameter d ∼ 1 μm) to the more complex morphology combining fine droplets ( d ∼ 1 μm) with the large LC domains ( d ∼ 10 μm) of irregular shape. The dual-size morphology is explained by essential contribution of both liquid–liquid and liquid–gel demixing processes at low intensities of curing light. This morphology causes unusual electro-optic response characterized by non-monotonic dependence of optical transmittance on the applied voltage, low driving voltage and high initial transmittance. It extends range of potential applications of thiol–ene based PDLCs.

Quantification of Liquid Crystal Concentrations in Periodically Stratified Polymer-Dispersed Liquid Crystal Films by Dynamic Secondary Ion Mass Spectrometry and Multivariate Statistical Analysis

Liquid crystal (LC) concentrations in stratified holographic polymer-dispersed liquid crystal (PDLC) films have been quantified from depth profiles obtained by time-of-flight secondary ion mass spectrometry (SIMS). The volatile nature of the LCs was hindered during SIMS analysis by capping the PDLC samples with poly(vinyl alcohol) and cooling to cryogenic temperatures. It remains difficult to gain quantitative results from SIMS analysis due to matrix effects yielding complex SIMS fingerprint spectra. With the multivariate statistical method discriminant function analysis the LC contents in the stratified holographic PDLC films were quantified. The concentration of the LC-rich layers was determined to be 32.9 ± 3.4 wt % LC, and for the polymer-rich layers it was 28.8 ± 2.7 wt % LC. The low concentration difference was supported by imaging analysis and modeling results.

Light‐scattering liquid‐crystal composites with reduced off‐axis haze

Abstract— The majority of liquid‐crystal (LC) composites operating in a light‐scattering mode suffer from scattering of the obliquely incident light in the field on‐state (off‐axis haze effect). This is evident in the angularly selective viewing‐angle characteristic with a maximal transmittance corresponding to the normally incident light. We consider methods to control the viewing‐angle characteristic of polymer‐dispersed LC (PDLC) and filled LC. For PDLC samples, this control is realized by modification of the refractive index of the polymer matrix with highly refractive nanoparticles (NP) having a low rate of aggregation in the polymer. By proper optimization of NP concentration, one can bring the refractive index of the polymer matrix in the range needed to reduce the haze problem. In filled LC, the viewing‐angle curve depends on the refractive‐index mismatch between the LC and NP. By optimization of this parameter, one can flatten the angular characteristic or obtain selectable viewing angles in the desirable range. These results allow for the construction of optical shutters and a scattering‐type LCD with controllable viewing‐angle characteristics, particularly with low off‐axis haze.

Electrically switchable spatial filter based on polymer-dispersed liquid crystal film

This work demonstrates the feasibility of using polymer-dispersed liquid crystal (PDLC) films as electrically switchable spatial filters in the optical signal process. The fabrication relies on the fact that the size of the liquid crystal droplet formed in a PDLC film is inversely proportional to the intensity of curing. Controlling the driving voltage on the PDLC sample can filter particular spatial frequencies in the Fourier optical signal process. A simulation is also performed, and the results are highly consistent with those of experiments.