Polymer Dispersed Liquid Crystal Research Articles

Studies of the structure and properties of polymer dispersed liquid crystal films to create a polarizer

A novel composite material based on polymers (polyvinyl alcohol, polyvinyl butyral) and liquid crystal (4-n-pentyl-4’-cyanobiphenyl) has been developed and studied. Configuration transformations of point defects in nematic droplets under the influence of an electric field, caused by localized changes in the concentration of NLC within the polymer matrix, have been discovered and analyzed. The boundary conditions necessary for achieving a nematic structure with homogeneous alignment of the director both within the droplet and at its surface have been established, optimizing the anisotropy of light transmission in polymer-dispersed liquid crystal (PDLC) films. Additionally, polarization effects inside nematic droplets under the application of an electric field have been identified.

Phenyl group-based fluorinated polymer dispersed liquid crystal composite films with high contrast ratio and low driving voltage

Polymer dispersed liquid crystal (PDLC) is a type of composite materials which is usually obtained by the phase separation during polymerization of liquid crystal/monomer mixtures, and it has shown potential applications in smart windows. In this work, the rigidity and flexibility of phenyl acrylate monomers were regulated by varying the number of benzene rings and their influences on the morphology and electro-optical properties of PDLC were discussed. The results showed that the PDLC films formed by monomers with one benzene ring possessed better performance. In addition, fluorination of monomers with a benzene ring could further enhance overall performance. The contrast ratio was significantly improved from 138 to 175, but the driving voltage is maintained at a lower value (6.9 V). This work provides a choice for optimizing electro-optical properties of PDLC films.

Heteroatom-Terminated Acrylate-Based Polymer-Dispersed Liquid Crystal Composite Films with High Contrast Ratio and Low Driving Voltage.

A series of polymer-dispersed liquid crystal (PDLC) films were prepared by using acrylate monomers containing heteroatom-terminated groups. The microscopic morphology and electro-optical properties reveal that these monomers effectively reduce the switching voltage and improve the contrast ratio at the same time. The saturation voltage of the best sample was reduced by 47%, and the contrast ratio was improved by 74%. In addition, the introduction of various heteroatoms endows the PDLC films with a variety of functionalities. Sulfur atoms effectively increase the refractive index of the polymer matrix (np). By adjustment of the match between np and the ordinary refractive index of the LC, films with large contrast ratio and diminutive switching voltage were manufactured for display applications. Besides, chlorine atoms can help reduce the surface anchoring energy of the polymer matrix to LCs and reduce the impedance. Meanwhile, the abundant C-H, C-O, C═O, and C-Cl groups endow the films with solar modulation functions.

Assessing energy savings and visual comfort with PDLC-based smart window in an Istanbul office building: A case study

Lighting applications in architectural structures have a high share in energy consumption. Inefficient lighting applications and technologies will increase energy consumption and do not guarantee the visual comfort desired by users. Recognizing the importance of user comfort, this study takes a deeply user-centric approach in proposing feasible lighting control methods that can improve energy efficiency in smart and carbon-neutral future buildings and change daylight's benefits in favor of the user. Smart glass technology, which can adjust the color and transmittance of the light in response to external stimuli (applied voltage) and can be dynamically modulated, changing window and door characteristics, has high potential in the market for modern societies. This paper develops an innovative lighting control method to improve energy efficiency and visual comfort and reduce energy consumption. The daily performance of the proposed control methods regarding illuminance, uniformity factor, and energy consumption is experimentally analyzed in a test bench modeling an office environment with IG80 glass (for comparison), artificial lighting source (LED lamp), and polymer-dispersed liquid-crystal (PDLC)-based smart window. The research methodology involved a detailed analysis of the relationship between performance metrics and dimmer percentages and comparing the energy consumption performance of the lighting methods with other design parameters and technological advances. This algorithm prioritizes user comfort and considers the PDLC-based smart window light transmittance and LED lamp dimmer control depending on daylight. The results show that the proposed algorithm can increase energy savings by up to 22 %. While efficient lighting control is closely related to weather conditions and indoor specifications, it has similar energy consumption performance compared to research into design parameters and technological advances, eliminating further efforts.

Nanostructured Polymer-Dispersed Liquid Crystals Using a Ferroelectric Smectic A Liquid Crystal.

Nanostructured polymer-dispersed liquid crystals (nano-PDLCs) are transparent and optically isotropic materials in which submicron-sized liquid crystal (LC) domains are dispersed within a polymer matrix. Nano-PDLCs can induce birefringence by applying an electric field (E-field) based on the reorientation of the LC molecules. If nano-PDLCs are utilized as light-scattering-less birefringence memory materials, it is necessary to suppress the relaxation of the LC molecule orientation after the removal of the E-field. We focused on the ferroelectric smectic A (SmA) phase to suppress the relaxation of LC molecules, owing to its layered structure and high viscosity. Although nano-PDLCs require a strong E-field to reorient their LC molecules because of the anchoring effect at the LC/polymer interface, the required field strength can be reduced using a ferroelectric smectic A (SmAF) LC with a large dielectric constant. In this study, we fabricated a nano-PDLC by shining an ultraviolet light on a mixture comprised an SmAF LC, photocurable monomers, and a photo-initiator. The electro-birefringence effect was evaluated using polarizing optical microscopy. After the removal of the E-field, an enhanced memory effect was observed in the sample using SmAF LC compared with nematic LC-based nano-PDLCs.

Dielectric analysis of unpolymerized and photopolymerized NOA65 in a parallel-plate cell

The flourishing development of liquid crystal research in recent decades has highlighted the importance of polymer materials in enhancing liquid–crystal material and device properties, demonstrating tremendous potential in a wide range of industries. One of the polymer materials widely used in polymer-dispersed liquid crystal is Norland UV-curable optical adhesive (NOA65). This study focuses on the dielectric behavior of the optical adhesive in a parallel-plate cell. Given the broadness and asymmetry of the dielectric dispersion curve, the two-relaxation Havriliak–Negami model was employed to analyze the complex dielectric spectra of NOA65 before and after photocuring. Experimental results indicate that as temperature rises, the dielectric relaxation of NOA65 undergoes a blue shift, leading to an eventual overlap with pseudo-dielectric relaxation at a higher frequency. This brings about an increase in the obtained signal in the dielectric loss spectrum, implying that the observed feature of pseudo-dielectric relaxation is actually superposed or contributed by the intrinsic relaxation signal. Furthermore, as temperature continues to rise, the intrinsic dielectric loss signal of NOA65 becomes untraceable beyond the frequency span within which the pseudo-dielectric relaxation signal lies.

Low-voltage and high-contrast polymer dispersed liquid crystals enabled by ferroelectric fluoro-copolymer doped polyimide film

Smart windows incorporating polymer dispersed liquid crystal (PDLC) technology provide user-friendly operation and play a significant role in intelligent buildings and building energy conservation. Long standing issues of the PDLCs such as high driving voltage, low contrast ratio, and narrow viewing angle hinder their applications. Here PDLCs are sandwiched between the hybrid substrates composed of the ferroelectric polyvinylidene fluoride trifluoroethylene (P(VDF-TrFE)) copolymer and the homogeneous polyimide. The high dielectric constant and ion-trapping ability of ferroelectric copolymers increase the effective voltage drop in the PDLCs. Concurrently, the local electric field created by large dipole moment of ferroelectric copolymers triggers the alignment of liquid crystals (LCs) along the applied field. These synergistic effects contribute to a substantial decrease in the driving voltage of PDLCs. In the opaque state, the random dipole moments in ferroelectric copolymers disrupt the LC orientations near hybrid substrates, thereby increasing the light scattering and reducing the transmission of PDLCs. Consequently, the proposed PDLCs exhibit a contrast ratio ∼2× higher compared to the conventional PDLCs at normal incident. Moreover, the proposed PDLCs demonstrate a wider viewing angle in the transparent state compared to conventional PDLCs. This development promises energy-efficient, eco-friendly, and cost-effective smart windows.

Assessing the Potential of Smart Windows for Energy Efficiency in Tropical Buildings: A Review of Current Research and Future Directions

Abstract Smart windows have energy-saving potential in buildings in tropical climates. Characterized by high solar radiation, humidity, and temperature, tropical climates demand innovative solutions for energy-efficient building design. Smart windows, which can regulate the transmission of light and heat through different thermochromic, photochromic, or electrochromic technologies, are promising to reduce energy consumption in such buildings. Several emerging window technologies, such as gasochromic, hydrochromic, polymer-dispersed liquid crystal, and suspended particle device technologies, also have promising energy-saving potential. However, their high initial costs, durability, and reliability of these technologies limit their applicability. Prospects for smart windows in buildings in tropical climates include advancements in materials science, cost reduction, and integration of smart window technology with other building systems, such as lighting and heating, ventilation, and air conditioning systems. The potential benefits of smart windows for energy-saving s in buildings in tropical climates are substantial, up to 37%. Thus, further research and development in this area would lead to significant advancements in sustainable building design for a better future.

Enhanced electro-optical properties of polymer dispersed liquid crystals doped with functional nanofibers for applications of efficient smart windows and advanced anti-counterfeiting

The development of polymer-dispersed liquid crystal (PDLC) capable of infrared smart tuning and displaying distinct information under ultraviolet, visible, and infrared light presents significant challenges. These challenges include the tuning of electro-optical properties and IR reflectivity, the preparation of complex patterns, and the display of different display states under various stimuli. In this work, nanofibers doped with alumina-zinc oxide nanoparticles (AZO NPs) and loaded with cesium tungstate nanoparticles (Cs0.33WO3 NPs) into PDLC not only enhanced their electro-optical properties but also added infrared shielding. Temperature regulation tests demonstrate that PDLC films can intelligently modulate infrared light reflection, offering superior shading and temperature regulation capabilities. PDLC smart windows integrated with nanofibers achieve a temperature coordination function, maintaining a temperature differential of 12.1 °C compared to standard PDLC. This significant enhancement underscores their potential for applications in thermally regulated smart windows. In addition, a full-wavelength anti-counterfeiting mode for PDLC was developed using a screen-printing strategy to display different information under various wavelengths of light. Noteworthily, the anti-counterfeiting system exhibits a bright fluorescent pattern under UV light, a scattering pattern under visible light, and an infrared-modulated pattern when viewed with an infrared detector. Furthermore, an advanced dynamic anti-counterfeiting mode with time response was created using nanofibers loaded with different concentrations of Cs0.33WO3 NPs. This advanced anti-counterfeiting material can be used as multimodal and dynamic anti-counterfeiting label, which greatly facilitates the development of novel anti-counterfeiting and optical sensing materials.

Optical characterization and thermal performance of a novel solar dryer with dynamic control of solar radiation

In this study, a novel adaptive solar dryer with a coating of polymer-dispersed liquid crystals (PDLC) was designed, built, and characterized to evaluate its optical properties and thermal performance by modulating the transmission of solar radiation toward the drying chamber. PDLC films can electrically switch between opaque and transparent states, making them ideal for controlling solar radiation. Unlike conventional direct dryers, the proposed solar drying system takes advantage of direct solar radiation, known for its rapid drying process, while minimizing the impact on product properties. The results show that the PDLC coating exhibited a significant difference in transmittance between the “on” and “off” states under ambient conditions. At 400 nm, the transmittance varied by 20 %, increasing to 30 % at 450 nm. The solar dryer with dynamic control of solar irradiance constantly maintained a temperature range of 52.19 °C–57 °C. Lower relative humidity values were achieved compared to the uncontrolled solar dryer, resulting in a uniform irradiance distribution within the drying cabinet. The solar dryer with dynamic control of solar irradiance (acrylic and PDLC film) presents a total thermal resistance (0.02817 mK/W) exhibiting better heat permanence inside the drying cabinet compared to polycarbonate (one of the materials most used for drying systems). The system's thermal efficiency ensures reliable operation regardless of weather conditions, efficiently capturing and converting solar energy into heat.

Preparation of polymer dispersed liquid crystal doped with bilayer nanofiber membranes and phase‐change microcapsule coating for enhanced infrared modulation

AbstractThe effective manipulation and regulation of infrared (IR) radiation represent significant advancements in the realm of liquid crystal applications. In this investigation, the synergistic integration of nanofiber membranes and phase change microencapsulated film with polymer dispersed liquid crystal (PDLC) layers was employed for IR modulation. To obtain the excellent electro‐optical properties of PDLC composite films, the ratio of the PDLC system, the thickness of the nanofiber membrane, and the concentration of phase‐change microcapsules were meticulously regulated, and the polymer network morphology of the PDLC films was analyzed to achieve a high contrast ratio (162.72) of PDLC composite films. The fabricated PDLC composite devices show excellent IR shielding efficiency of 15% in the presence of doped nanofiber membranes and phase change microencapsulated films. Notably, patterned nanofiber layers and phase‐change microcapsule coating were obtained by template electrospinning, resulting in patternable PDLC composite film devices.

A flexible colored polymer-dispersed liquid crystal smart windows with excellent near-infrared shielding performance

A flexible colored polymer-dispersed liquid crystal smart windows with excellent near-infrared shielding performance

The electrically controlled dimming film of thiol-vinyl ether system with low-voltage and high contrast ratio for smart windows

As a type of smart window, polymer dispersed liquid crystal (PDLC) electrically controlled dimming film can respond to external electrical stimuli to regulate the optical flux of sunlight, reducing energy consumption. Herein, a PDLC film was prepared by systematically studying the functionalities and structural compatibility of vinyl ether and thiol compounds, and the optimal PDLC film possesses a superior contrast ratio (CR) of 196.9. When the film thickness is adjusted to 8 μm, the film saturation voltage is reduced to 6.7 V, still maintaining a high CR of 48.4. The well-designed PDLC films exhibited excellent modulation of light. The temperature difference between PDLC film and bare ITO glass can reach 4 °C under the simulated sunlight test, demonstrating the good thermal insulation performance. This smart films with low power consumption and high CR can meet the demand for active regulation of optical flux on smart windows.

The role of sub-regional electrostatic spinning nanofiber loaded with WO3 nanoparticle in modulating electro-optic performance and stepwise display of polymer dispersed liquid crystal

ABSTRACT The advancement of multi-functional displays with outstanding electro-optical properties is particularly essential at present. However, conventional integral all-area driven transparent displays are gradually failing to meet current demands. Herein, sub-regional electrostatic spinning of nanofibers as a novel fabrication method was introduced into polymer-dispersed liquid crystal (PDLC) to achieve stepwise display in concert with loaded WO3 nanoparticles, addressing the aforementioned drawback. The use of nanofibers played a crucial role in ensuring fine dispersion of nanoparticles, resulting in a reduction of the saturation voltage of the PDLC film from 28.9 V to 19.7 V and an increase in contrast ratio from 105.7 to 194.3. Meanwhile, experimental findings and theoretical considerations have revealed that variations in microscopic pore size can significantly influence the electro-optical behaviour of PDLC film. Next, the stepwise PDLC film was prepared by electrostatically spinning nanofibers onto half of the LC cell region, leading to different voltage-transmittance responses between the two regions. Consequently, under appropriate driving voltages, the PDLC film can realise three different optical states: total scatter, half-transparency, and total transparency. In addition, the PDLC film exhibited excellent anti-thermal ageing performance, allowing it to excel in various advanced display applications.

Electro-optical effect of unpolarized light modulation in homeoplanar structures of ferroelectric and ferrielectric liquid crystals.

A clearly expressed effect of unpolarized light electro-optical modulation by homeoplanar structures of a smectic C* ferroelectric liquid crystal (FLC) and a ferrielectric liquid crystal (FerriLC) was discovered and investigated for the first time to our knowledge. This effect of electrically controlled light scattering is insensitive to the applied voltage sign, as for polymer-dispersed nematic liquid crystals (PDLCs), but the electro-optical modulation frequency reaches the kilohertz range. Occurrence conditions and essential features of the effect, as well as its physical origin, are discussed.

Tuning the morphology and electro-optical properties of reverse mode PDLCs using multifunctional acrylates

ABSTRACT Reverse-mode Polymer Dispersed Liquid Crystals (rev-PDLCs) are composite materials generally obtained by the phase separation of dispersions of liquid crystal/monomer mixtures and characterised by the possibility to change on-demand their transmittance in a continuous manner from an initial transparent state to an opaque one by application of an electric field. Rev-PDLCs have found applications in many fields, including large-area smart windows, automotive, and bifunctional devices. In this work, acrylate monomers with different functionality (from 3 to 6) and weight ratios (from 5 to 15%) were used to finely adjust the morphology and electro-optical properties of the rev-PDLCs obtained by photo-polymerisation of an aligned LC/LC monomer mixture. The doping of nematic liquid crystalline monomers with acrylate monomers allowed to finely tune the morphology of rev-PDLC films, which were characterised by highly transparent OFF-states (TOFF always larger than 60%), strongly opaque ON-states (TON always around or lower than 1%), but with contrast ratios, transmittance slopes, threshold and switching fields dependent on the amount and functionality of used monomers. Such results could represent a valid method to overcome the drawback of relatively low materials to be used as starting components in the fabrication of reverse mode dimming films.

A recyclable, interchangeable optical switch with a PDLC-PVA-PSCLC structure and a low-voltage drive system

ABSTRACT Polymer dispersed liquid crystals (PDLC) and polymer stabilised cholesteric liquid crystals (PSCLC) are an indispensable class of electrically switchable materials, which have been widely applied in the fabrication of efficient and systematic smart windows. And doping nanoparticles in PDLC films can greatly improve their properties. In this study, PDLC films doped with zirconia nanoparticles were prepared by polymerisation-induced phase separation (PIPS) method, PSCLC films with nematic liquid crystals as the main part (reflecting wavelengths in the range of 400–600 nm) were prepared by UV curing method, and a novel optical switch was developed by combining these two liquid crystal films. The optimal bilayer sample was developed through a comparative analysis of properties among samples with varying formulations for each liquid crystal layer. This study represents a novel advancement in PSCLC and nanoparticle-doped PDLC bilayer structures, showcasing fully actuatable properties in the visible wavelength range. These structures exhibit excellent electro-optical properties and demonstrate stable, sustainable performance that can be regenerated. The findings underscore the potential of PDLC and PSCLC for applications in smart curtains and flexible materials, opening up new avenues for innovative technological applications.

Molecular engineering controlled electric-optical performance of polymer dispersed liquid crystals

ABSTRACT In this work, the methods of doping different fluorine-containing monomers and fluorine-containing nanoparticles into the mixture were adopted to boost the electro-optical performance of PDLC films. The electro-optical measurements indicate the improved electro-optical performance of PDLCs through the introduction of MX-3 monomer, and the corresponded SEM results demonstrate the successful adjustment of surface morphology. Further doping F-Si@SiO2 nanoparticles into MX-3 monomer-modified PDLC system, the Vth and Vsat values are greatly reduced and reach lowest when F-Si@SiO2 content is 5 wt.%. The enhanced electro-optical property is due to the combined control of fluorine-containing MX-3 monomer and F-Si@SiO2 nanoparticles, the fluorine functional group can promote the uniform dispersion of nanoparticles; the existence of F-Si@SiO2 nanoparticles can regulate the anchoring effect on liquid crystal molecules in the polymer matrix, thus electric-optic characteristics of the PDLC materials are greatly enhanced.

Low-threshold distributed feedback laser based on holographic polymer dispersed liquid crystals through the oriented organic semiconductor films

A specific optimized configuration for low threshold organic semiconductor laser based on a holographic polymer dispersed liquid crystal (HPDLC) transmission grating was demonstrated. Here the organic semiconductor films and phase separated liquid crystal (LC) molecules were oriented along the direction of the HPDLC grating grooves. The influence of the organic semiconductor chain orientation and the excitation polarization on the optical properties of the materials has been investigated. Especially, when polymer chain orientation, LC molecules and pump light polarization are consistent with the direction of the grating grooves, the performance of the outgoing laser is greatly improved. Up to 9.78% conversion efficiency with a threshold lower to 0.12 μJ/pulse can be obtained, indicating their potential for high-performance organic optoelectronics.

New graphene oxide doped polymer dispersed liquid crystal nanocomposites targeted to eco-friendly and energy-efficient smart windows

Graphene oxide-polymer dispersed liquid crystal (GO-PDLC) composites are proposed as a solution for energy-efficient switchable windows. These composites were prepared by incorporating varying concentrations of graphene oxide (GO) into a mixture of nematic liquid crystal (E7) and a UV–Vis curable resin using the polymerization-induced phase separation technique. The results indicate that the dispersion of GO at an optimum concentration of 0.005 wt% significantly affects the morphology, phase transition temperatures, and electro-optic properties of polymer dispersed liquid crystal (PDLC). In particular, the GO-PDLC composites exhibit a transition from an opaque to a transparent state at a remarkably low voltage (∼11.5 V) compared to pure PDLC cell. Dielectric analysis reveals that adding GO increases the permittivity, conductivity, and dielectric strength of PDLC composites. Moreover, the Cole-Cole plot indicates a non-Debye type relaxation in a higher frequency region. Furthermore, a blue shift in emission wavelength and enhanced photoluminescence intensity suggest alterations in electronic transitions within the composites. This comprehensive study provides valuable insights into optimizing the properties of PDLCs through the dispersion of GO, thereby offering promising prospects for their utilization in various optoelectronic applications.