Polymer Dispersed Liquid Crystal Films Research Articles

Combined effect of hydroxylated and fluorinated acrylate monomers on improving the electro-optical and mechanical performances of PDLC-films

ABSTRACT In this work, we prepared polymer-dispersed liquid crystal (PDLC) films with good mechanical properties, high contrast ratio (CR), and low driving voltage (Vdr). These PDLC films included two different monomers, which were hydroxyl methacrylate monomers and fluorinated methacrylate monomers. The electro-optical properties, micro-structures and mechanical properties of these films were also characterised. It was found that the hydroxyl methacrylate monomers could improve the adhesion force of the PDLC film, while fluorinated methacrylate monomers could reduce the driving voltage. In this way, the PDLC films with excellent comprehensive performance could be obtained. Compared with the original sample, the adhesion force was improved approximately 200% to 180 N/cm2. The driving voltage threshold was reduced about 140% to 18.5 V. The contrast ratio was increased about 150% to 51.9. This work enlightened a novel way to improve the mechanical properties of PDLC films and promised a broader application of PDLC.

Polymer Dispersed Liquid Crystal Film as a Functional and Aesthetic Second Skin Barrier

Polymer films, which reproduce the functional properties of human skin, are emerging as innovative solutions to many skin problems. These films, referred to as second skins, not only serve as a physical barrier to environmental insults but also impart an aesthetic appearance to the skin. Despite being essential components in the cutaneous barrier, lipids have never been included in the second skin films. Here we show that wearable and transparent second skin can be prepared as a polymer dispersed liquid crystal (PDLC) film, where lipid materials are contained as a lamellar liquid crystalline (LC) phase. The lipid materials are mixtures of phytosterol, stearic acid, and lecithin or ceramide, which can be dispersed as lyotropic LC microdroplets in a polymer matrix. The PDLC film can be topically applied as a cosmetic cream (PDLC emulsion), and consequently forms on human skin as a substrate. Structural (X-ray diffraction, XRD), thermal (differential scanning calorimetry, DSC), and surface (atomic force microscopy, AFM) characterizations reveal that our PDLC film has human skin-like features. Notably, the PDLC film can act as an effective barrier against evaporative water loss and carbon pollutants. In a human study (n=10), we have demonstrated that the hydration, adhesion, mechanical, and aesthetic properties of the PDLC film are superior to those of control polymer films. We mainly attribute this in vivo performance to a unique hydration mechanism, whereby the lamellar LC dispersion generates a water concentration gradient and regulates the water content in the PDLC film. Taken together, our beauty film prepared by the PDLC approach is a highly functional cosmetic and potentially serves as a second skin barrier.

Enhancing morphological, electro-optical and dielectric properties of polymer-dispersed liquid crystal by doping of disperse Orange 25 dye in LC E7

ABSTRACT In this work, we have investigated morphological, electro-optical and dielectric properties of disperse orange 25 dye-doped polymer-dispersed liquid crystal (DPDLC) films. The DPDLC film composed of monomer Norland optical adhesive (NOA 65), nematic liquid crystal (E7), and disperse orange 25 dye was prepared through the polymerisation-induced phase separation (PIPS) method. The polarising optical microscope (POM) has been utilised to observe the effect of dye concentration and voltage on liquid crystal (LC) droplet morphology. The electro-optical properties of such DPDLC films were studied at a fixed frequency of 200 Hz and different voltage and temperature conditions (0–100 V, 25–50°C). The change in absorbance value with varying dye concentration and the electric field was monitored through a UV-Vis spectrophotometer. Dielectric relaxation characteristics of DPDLC films were examined using a precision impedance analyser in the frequency range 20 Hz–20 MHz and temperature range 25–60°C. Debye and Cole-Cole fitting techniques were used to describe the dielectric properties of DPDLC films.

Spatially Patterned Polymer Dispersed Liquid Crystals for Image‐Integrated Smart Windows

AbstractConventional polymer dispersed liquid crystal (PDLC) films have been successful as electrically‐switchable screens for privacy applications. However, spatial patterning of the films so as to generate a visually appealing design, logo, or image typically requires intricate fabrication processes, such as the use of prefabricated photomasks that do not allow for on‐demand designs. Herein is reported on the fabrication and characterization of spatially patterned PDLC “pixels” using drop‐on‐demand inkjet printing, and it is demonstrated how these materials can be used to form a new generation of smart windows that consist of embedded images or company logos, which can be made to disappear with the application of a voltage. Following refinements to the material rheology and the subsequent successful deposition of individual PDLC droplets, arrays of PDLC pixels are printed at a resolution of 250 pixels per inch with an individual pixel size of 130 µm operating at an electric field strength (E) of E = 1.4 V μm−1. Finally, using the approach developed herein, these printed PDLC pixels are arranged to form a college emblem that is embedded within a smart window that can be made to disappear with the application of a voltage.

Aligned polymer dispersed liquid crystal film for light enhancement of quantum dot backlight

Quantum dots (QDs) have been used to make backlight, which provides a superior color gamut, for liquid crystal flat panel displays. In the backlight system, quantum dots, embedded in a polymer film and illuminated by blue light, emit red and green light with narrow bandwidths. There is, however, a problem with the system in that the quantum dots emit light in all directions, and most of the emitted light is in directions with large incident angles and cannot exit the film due to the total internal reflection at the film-air interface and is wasted. We propose to use an aligned polymer dispersed liquid crystal (APDLC) film to reduce the total internal reflection in the QD backlight and thus improve the light efficiency. A regular PDLC film, where the embedded liquid crystal droplets are randomly oriented, exhibits isotropic scattering and is not a good candidate for the enhancement of light efficiency of QD backlight. Through a two-step polymerization, we successfully developed an aligned polymer dispersed liquid crystal (APDLC) film where the liquid crystal droplets are permanently unidirectionally aligned in the film’s normal direction. It exhibits selective scattering: it scatters light with large incident angles but not light with small incident angles. When the APDLC film is laminated on the QD backlight film, a significant enhancement of the light efficiency of the QD backlight is achieved. The APDLC film can also be used to increase the light efficiency of other flat panel displays, such as organic light emitting diode (OLED) display and micro-light emitting diode (MLED) display.

Study on electro-optical and adhesion properties of polymer dispersed liquid crystal films from thiol-ene click reaction

ABSTRACT In this work, polymer dispersed liquid crystal (PDLC) films, with good electro-optical and adhesion properties, were obtained by phase separation induced through thiol-ene click chemistry. The effects of liquid crystal content, thiol content and thiol functionality on the electro-optical and adhesion properties of the PDLC films were systematically investigated. It is found that adding an appropriate proportion of high-molecular-weight polymer thiol, Capcure 3–800 as the curing agent can effectively decrease the saturation voltage of the PDLC films. And when the content of Capcure 3–800 is 5.5 wt.%, the PDLC films can show the optimised electro-optical performance. Moreover, the adhesion properties between the two pieces of substrates and the PDLC films are related to the density of the polymer network.

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.

High dielectric properties, TiO2 nanoparticles doped PDLC devices for lower switching voltage

ABSTRACT Polymer dispersed liquid crystal (PDLC) films were prepared using a nematic liquid crystal, photo-curable polymer and TiO2 nanoparticles by polymerisation-induced phase separation (PIPS) method. Electro-optical properties of doped and undoped samples including transmittance, driving voltage, contrast ratio and response time of the transmittance-voltage were measured, compared and analysed. The morphology of polymer network has been investigated by means of SEM. The phase separation of LC droplets was found to be dependent on the content of prepolymer, LC and nanoparticles used. The high dielectric properties and high refractive index of TiO2 nanoparticles make PDLC have low driving voltage and high contrast. In particular, the nanoparticles concentration can be optimised to obtain promising electronic materials with minimum threshold and high contrast for display applications.

Polymer dispersed liquid crystals doped with low concentration γ-Fe2O3 nanoparticles

ABSTRACT The polymer dispersed liquid crystal films doped with the low concentration γ-Fe2O3 nanoparticles coated with oleic acid were inverstigatited. The experimental results showed that the doped and un-doped polymer dispersed liquid crystal films were the similar surface morphologies, however their evolving curves of the capacitance with the applied voltage were different, as well as the transmission rate. The interpretations based on these differences were proposed, i.e. those came from the adsorbed free ions by the γ-Fe2O3 nanoparticles, instead of the electromagnetic properties of the γ-Fe2O3 nanoparticles. The effect of the free ions is equivalent to the negative dielectric constant and refractive index. Furthermore, the reduction of the free ion concentration due to the absorption in the doped polymer dispersed liquid crystal films can decrease the negative dielectric constant and refractive index, i.e. the effective dielectric constant and refractive index were increased. As a result, the contrast ratio increased significantly, and the driving and threshold voltages decreased distinctly. These results may be useful for electro-optics devices.

Effects of dye doping on electro-optical, thermo-electro-optical and dielectric properties of polymer dispersed liquid crystal films

In this study, polymer dispersed liquid crystal (PDLC) films comprising a phase separated low molecular weight thermotropic liquid crystal (LC) and high molecular weight polymer were, prepared using the polymer–induced phase separation method. In order to enhance the optical efficiency of the PDLC films, LC was doped with dichroic azo dye. Various characterization techniques were employed to determine the properties of the components and, the operating principles of the dye–doped PDLC (DPDLC) films. Morphological studies using polarizing optical microscopy and scanning electron microscopy indicated that the LC droplet configuration changed with various dye concentrations and voltages. Electro-optical analysis showed that the performance of the DPDLC film with a low dye concentration (0.007%) was excellent, with a high contrast ratio (241) and transmittance difference (ΔT = 98.57%), low threshold (VTH = 0.85 V/μm) and saturation voltages (VSAT = 1.45 V/μm), and a minimum hysteresis effect. The effects of temperature on the electro-optical properties of the DPDLC films were studied. Absorbance analyses were conducted using ultraviolet–visible spectrophotometry to complement the transmittance analyses. Dielectric relaxation spectroscopy was employed to measure relaxation frequency/time of DPDLC films. Debye and Cole – Cole modeling were conducted to understand nature of the relaxation process. The zero values of the distribution parameter (α) for all of the DPDLC composite films confirmed their Debye type relaxation process.

Organic Solvent Sensors Using Polymer-Dispersed Liquid Crystal Films with a Pillar Pattern.

An organic solvent sensor of polymer-dispersed liquid crystals (PDLCs) film is fabricated by a combination of tri-functional monomers and LCs. When the patterned PDLC film comes into contact with the organic solvent, the organic solvent will penetrate into the film to induce the orientation of the liquid crystals, which will change from an ordered to a disordered state, which causes the PDLC film to scatter incident light. The experiment used acetone and ethanol as the organic solvents of interest. The results show that the patterned PDLC film has a stronger response to acetone than to ethanol. Based on the difference in the intensity of light scattering and the response time of the patterned PDLC film to different organic solvents, the results can be used to identify and recognize different types of organic solvents.

Photoinitiator release improves PDLC electro-optical performance

In this paper, polymer-dispersed liquid crystal (PDLC) films of acrylate polymer systems were fabricated by polymerization-induced phase separation. It was a complex process involving simultaneous curing and phase separation to form nematic microdomains. We also have examined the morphology of PDLC films, which show great potential for electro-optic applications. Here we used the adsorbability of white carbon black and loaded the photoinitiator (IRG651) in it to prepare PDLC films. Electrooptic devices based on the PDLC films were constructed by using indium-tin-oxide transparent electrodes, and the electro-optic responsivity was also explored.

The regulation of electric-optical properties of polymer-dispersed liquid crystals via implantation of polyhedral oligomeric silsesquioxane (POSS) microstructure

ABSTRACT In this paper, we report a simple and effective technique to improve the electro-optical performance of polymer-dispersed liquid crystal (PDLC) films via the implantation of polyhedral oligomeric silsesquioxane (POSS) microstructure into the polymer matrix. The measurement results of the electro-optical properties indicated that the electro-optical performances of PDLC films have been regulated successfully via the implantation of POSS microstructure into the polymer matrix. SEM results suggested that the size of polymer meshes was broadened with the increase in the content of POSS microstructure, while the static water contact angles of the polymers increased after the implantation of POSS microstructure. Because of the lower surface energy as well as the increased steric repulsions between liquid crystal molecules and polymer surfaces, the anchoring effect of the polymer matrix containing POSS microstructure was concluded to be weakened, which was the dominant factor in achieving the dramatic regulation effect of the electro-optical properties of the PDLC films. This work could provide a creative approach for the fabrication of low voltage-driven PDLC films for their practical applications.

Viewing-angle-switching film based on polymer dispersed liquid crystals for smart anti-peeping liquid crystal display

ABSTRACT In this paper, the viewing-angle-switching (VAS) films based on polymer dispersed liquid crystals (PDLCs) were fabricated and the optical properties of the VAS films were studied. The VAS films based on PDLC films can exhibit electrically switchable viewing-angle properties, and the films showed a narrow viewing angle under no electric field and presented a wide viewing angle under electric field (24 V). Furthermore, the smart anti-peeping liquid crystal display (LCD) containing the VAS film based on PDLC film also displayed the electrically switchable viewing-angle performance and the corresponding mechanism was discussed. The results demonstrated both the anti-peeping effect and electrically switchable view-angle effect of the as-fabricated VAS film, promising potential applications in intelligent optical films and novel information displays.

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.

Effects of terpene alcohol dopant on the morphology and electro‐optical properties of polymer‐dispersed liquid‐crystal composite films

AbstractTerpenes are a large class of hydrocarbon compounds derived from isoprene, which can be produced by plants or emitted by insects. Terpene alcohols contain double bonds that may affect the addition polymerization, and hydroxyl groups that can promote the network crosslinking density during the formation of polymer‐dispersed liquid‐crystal (PDLC) composite films. In this work, effects of different terpene alcohol dopant on the morphology and electro‐optical properties of PDLC films are systematically investigated. It is found that the appropriate dopant amount of geraniol (GOL) has the superior effect to improve the electro‐optical performance. The optimum addition amount is at 3 wt%, where the transmittance vs. voltage curve gets steeper, the driving voltage of PDLC film reduces from 74 to 32 V and meanwhile the contrast ratio maintains at a relatively high level (123). Thus, this work not only broadens the application scope of the natural spices but also provides a new strategy to reduce the driving voltage of PDLC films for practical applications.

Polymer dispersed liquid crystals doped with CeO2 nanoparticles for the smart window

ABSTRACT 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.

Study on the electro-optical properties of epoxy resin based polymer dispersed liquid crystal films

Abstrat Polymer dispersed liquid crystal (PDLC) films have been extensively studied for their ability to control the attitude of aircraft by varying the reflectivity of solar sails. However, most of the polymeric matrix of PDLC films are based on polyacrylates, which comprehensive properties such as thermal stability, chemical stability, mechanical strength and radiation resistance can not meet the requirements of the harsh environment in space. In order to improve the radiation resistance of PDLC films, polyimide-epoxy resin PDLC films were prepared by thermal polymerization using Kapton polyimide film as conductive film and two kinds of epoxy resin as monomer in this paper. The electro-optic properties of PDLC films prepared by flexible chain and rigid chain epoxy resin monomers in different ratios were studied and the microscopic morphology of the polymer network of the polyimide PDLC films was observed by scanning electron microscopy (SEM) and the relationship between them was studied.

The Electro-Optical Properties and Adhesion Strength of Epoxy-Polymercaptan-Based Polymer Dispersed Liquid Crystal Films

Polymer dispersed liquid crystal (PDLC) films were prepared by thermal polymerization-induced phase separation in epoxy/polymercaptan/liquid crystal (LC)/accelerator mixtures. The effects of the concentration of LC and accelerator, the curing temperature, and the structure of epoxy monomer on the electro-optical (E-O) properties and adhesion strength of the PDLC films were studied systematically via E-O, peel strength, DSC, IR, and gel measurements. It showed that different polymer structures and the properties of the polymer can be obtained by changing the compositions and the curing temperature, which had significant impacts on the E-O properties of the PDLC films. Meanwhile, the polymer matrix with high glass-transition temperature (Tg) and small pore size will improve the adhesion strength of the PDLC film, and these kinds of epoxy-polymercaptan-based PDLC films have better performance than traditional acrylate-based PDLC in the aspect of the adhesion strength. This work may provide some inspiration in preparing epoxy-polymercaptan-based PDLC films, which both have excellent E-O performance and good adhesion strength, towards roll-to-roll processes and large-scale flexible applications.

The relationship between crosslinker, liquid crystal, and magnetic nanomaterial doping on electro-optical properties of PDLC

ABSTRACT Polymer-dispersed liquid crystal (PDLC) is a striking material that has a great role in optoelectronic display devices. In this paper, PDLC films were prepared by the polymerisation-induced phase separation (PIPS) process under the same curing temperature, UV intensity, and photo-initiator dosage. The morphology and electro-optical properties of PDLC with crosslinker content, the liquid crystal content, and magnetic nanomaterial doping were comprehensively investigated. Different crosslinker and liquid crystal contents changed the crosslinker degree and free radical content in the blends, which changed the polymer network size while changing the electro-optical properties of PDLC. The magnetic nanomaterials dispersed in PDLC established the intrinsic potential and reduced the threshold voltage (24.1 V) and saturation voltage (54.5 V) were obtained at a Fe3O4 NPs doping concentration of 1.0 wt%, which led to a CR of 89.9 and a toff of 14.1 ms. This work provides a feasible method to optimise the electro-optical properties of PDLC and provides the possibility for the wide application of PDLC.