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With the increasing development of multifunction liquid crystal displays (LCDs), multifunction optical diffusers have attracted more attention. In this work, switchable optical diffusers based on the transient polymer balls-networks in polymer/nematic liquid crystal composite films have been prepared and investigated, and the effects of thiol conte...
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... illustrate the role of changes to polymer morphologies on the optical properties, the curing times of samples A6-A10 are presented in Table 2. The curing time has greatly affected the microstructures of optical diffusers, when the curing time is relatively short, the average diameter size of the dispersed LC droplets in diffuser A6 is divided into the larger (9.10 µm) and the smaller (0.90 µm) as described in Figure 4. When extending the curing time, the size difference between larger LC droplets (1.80 µm) and smaller LC droplets (0.80 µm) in diffuser A7 turns smaller. ...
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Integrating the promising waveguide or lightguide optical combiners to head-mounted lightfield display (LF-HMD) systems offers a great opportunity to achieve both a compact optical see-through capability required for augmented or mixed reality applications and true 3D scene with correct focus cues required for mitigating the well-known vergence-acc...
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... The surface anchoring energy can also be increased by the polymer network that contains the fixed DEAPA. 40 Thus, sample A3's τ R is less than sample A4, while sample A3's τ D is greater than sample A4's. When the τ R is raised in Fig. 3, τ D continuously declines. ...
... Our understanding is that the V th is a linear function of the reciprocal size of the droplets R as shown in where d, K, ω, ε 0 , and Δε denote the film thickness, elastic constant, aspect ratio, vacuum permittivity, and dielectric anisotropy of the LC, respectively. 39,40 In general, when the size of the LC droplet decreases, the threshold voltage V th rises; thus, the saturation voltage V sat also changes. Figure 4 displays the values of samples A1-A4 in term of voltage-transmittance. ...
... The ratios of the materials' composition and LC types, together with physical elements like viscosity, rate of diffusion, and the solubility of LCs in the polymer, are all important determinants of LC droplet size. 40 Figure 6 demonstrates how the LC droplet size decreases as TMPTGE heat-curable monomer concentrations increase. The tri-and penta-functional monomers often have higher viscosity than the curable flexible chain segment monomers. ...
The goal of the current study was to develop a method for producing polymer-dispersed liquid crystal (PDLC) films for smart glasses that are thin and use a nematic liquid crystal system, epoxy resin monomers, hardeners, and epoxy resin. The performance of optical and electro-optical display panels is directly impacted by the techniques employed to refine smart PDLC films to increase their stability and characteristics. In this investigation, we set up the polymerization-induced phase separation heat curing method to use thermosetting resin 3-(diethylamino)propylamine as a primary functional heat curing agent and hardener, cross-linking agent poly(propylene glycol) diglycidyl ether, tri-functional trimethylolpropane triglycidyl ether, and tetra-functional pentaerythritol tetraglycidyl ether epoxy resin. Investigations were carried out using a liquid crystal device parameter tester, scanning electron microscope, UV–Vis–NIR spectrophotometer, and the generated smart glass panel sheets. The interaction between the monomer and the 3-(diethylamino)propylamine, a primary functional hardener, was confirmed using the liquid crystal device method and Scanning electron microscopy. Experiments were conducted on epoxy resins cured with 3-(diethylamino)propylamine to determine the feed ratio of epoxy monomers, the amount of curing agent, active diluents, and curing temperature. Moreover, the methyl groups of the trimethylolpropane triglycidyl ether, pentaerythritol tetraglycidyl ether, and 3-(diethylamino)propylamine were shown to play the main role in reducing the domain size of PDLC thin films in all samples. This smart glass technology will serve to create a barrier between the patient with COVID-19 and the doctor, as well as in healthcare center buildings, affected patient isolation rooms, hospitals, and smart helmets, enabling social distancing and eco-friendly environments for flexible electronics.
... Once the electric field is applied, the films become transparent and this phenomenon is attributed to the alignment of LC droplets along the direction of electric field, provided that the ordinary refractive index n o of LC precisely matches with the refractive index n p of polymer matrix [4][5][6][7]. The electric field-controlled scattering of the PDLC films is the root application that holds significant promise for many optoelectronic devices, such as switchable windows [8,9], digital optical memory devices [10], micro-lenses [11,12], optical diffusers [13,14], reflective displays [15], multicolor displays [16], light shutters [17], anti-peeping films [18] and so on. ...
Keywords: Oxygen heterocyclic acrylate Chain length High contrast ratio Low driving voltage Polymer dispersed liquid crystal A B S T R A C T The current work aimed to fabricate polymer dispersed liquid crystal (PDLC) films using het-erocyclic acrylate monomers containing oxygen atoms. The incorporation of oxygen heterocycles into the host polymer matrix significantly improved the electro-optical properties of PDLC films. Particularly, the high contrast ratio 330.0 was realized for the monomer Trimethylolpropane formal acrylate (TFA). Further, the excellent electro-optical properties, including low driving voltage (10.0 V), moderately high contrast ratio (64.0) and short response time (<8.0 ms) were obtained when the liquid crystals/polymer composite film thickness decreased from 20 μm to 8 μm. This work has provided a novel materials system to promote the application of PDLC films in the thin-layer liquid crystal display.
... Additionally, the electrically switchable property is realised only if the refractive index (RI) of the polymer matrix precisely matches with the ordinary RI of the LC by applying an electric field [7][8][9][10]. This electric field-controlled scattering of the PDLC films is the root application that holds significant promise for many optoelectronic devices, such as switchable windows [11], displays [12], diffuser film [13,14], anti-peeping film [15], quantum dots (QDs) film [16], and components of organic light-emitting diode (OLEDs) [17], field effect transistor (FET) [18], energy storage [19] and solar-energy harvesting [20]. ...
2021): Effects of multifunctional acrylates and thiols on the morphology and electro-optical properties of polymer-dispersed liquid crystal films, Liquid Crystals, ABSTRACT In the present paper, influence of the functionality of thiol monomers and acrylate crosslinkers, as well as crosslinker chain length on the polymer morphologies and electro-optical properties of the PDLC films, were systematically investigated. Results revealed that increasing the functionality of thiol monomers, both threshold voltage (V th) and saturation voltage (V sat) were increased due to the dense microstructures resulting from higher reactivity of thiol monomers. However, with increasing the functionality of acrylate monomers, V th was increased evidently, but a relatively small rise of V sat was found with moderate functionality monomer. Additionally, the increase in the chain length of flexible crosslinker resulted in an increase in the average size of LC droplets with a corresponding decrease in V th and V sat. On the whole, polymer morphology and electro-optical properties of the PDLC films can be artificially manipulated by adjusting the molecular structure of polymer matrix. A PDLC film exhibiting low driving voltage (24.0 V), moderately high contrast ratio (97.0) and fast response time (<8.0 ms), was found by employing the Pentaerythritol tetrakis (2-mercaptoacetate) (4SH), trimethylolpropane triacrylate (TMPTA) and polyethylene glycol diacry-late (PEGD 600). ARTICLE HISTORY
... Additionally, optical diffusers are a key optical component in light-emitting diodes (LEDs), which can spread the point light source uniformly without high intensity spots. In our group Zhou et al. [7,[123][124][125][126] designed optical diffusers with very high efficiency. Recently, an optical diffuser was prepared via a thiol ene click reaction comprising of 1:1 of ene and thiol and exhibited high transmission (98.49%) and high haze (91.77%). ...
Polymer dispersed liquid crystals (PDLCs) have kindled a spark of interest because of their unique characteristic of electrically controlled switching. However, some issues including high operating voltage, low contrast ratio and poor mechanical properties are hindering their practical applications. To overcome these drawbacks, some measures were taken such as molecular structure optimization of the monomers and liquid crystals, modification of PDLC and doping of nanoparticles and dyes. This review aims at detailing the recent advances in the process, preparations and applications of PDLCs over the past six years.
... As the average size of uniform spherical polymer balls is about 3.3 µm, optical diffuser with ultrahigh transmission (>94.0%) and haze (>94.0%) was fabricated [29]. For fabricating a switchable optical diffuser, we have fabricated a special polymer microstructure of transient polymer balls-networks, which has achieved high transmission (96.4%) and high haze (90.5%), at off state, the viewing angle of switchable optical diffuser is 150° (from −75° to 75°) and at on state (the voltage of applied electric field is 40.0 V), the viewing angle of switchable optical diffuser is 120° (from −60° to 60°) [30]. In order to investigate the effect of polymer microstructures on the light diffusing properties of polymer/LCs composite films, we have fabricated optical diffusers comprising uniformly distributed nano-sized polymer balls/nematic LCs, when the average diameter of nano-sized polymer balls is about 900 nm, optical transmission and haze with 89.0% and 94.5% have been reached, as the average diameter of nano-sized polymer balls is about 810 nm, optical transmission and haze with 98.5% and 91.8% have been yielded [31]. ...
Optical diffusers with high transmission, high haze and excellent diffusing ability are widely needed in backlight unit (BLU) of liquid crystal displays (LCDs). However, there are still drawbacks in the particles-doped optical diffusers, including the distribution of the scattered particles due to agglomeration of particles and complex coating process. In this paper, polymer/liquid crystal (LC) composite films which are based on the epoxy resins, polyamine (PA) and varied thiol monomers were firstly prepared by thermally initiated polymerisation. The morphologies and optical properties of the composite films were systematically investigated. By controlling the functionality of thiol in the system of epoxy resins/thiol/PA/LCs, as the light scattering of anisotropic LCs and isotropic polymer framework is both achieved in the optical diffusers, good diffusing ability and high visible transmission (total transmission >96.0% and transmission haze > 95.0%) are obtained.
... Once the electric field of sufficient strength is applied, these films become transparent and this phenomenon is attributed to the alignment of LC droplets along the direction of electric field, provided that the ordinary refractive index n o of LC precisely matches with the refractive index n p of polymer matrix [6][7][8]. Recently, PDLC films have gained significant attraction in the context of their promising applications in the electro-optical devices such as optical diffusers, biosensors, energy-saving smart windows, optical shutters, anti-peeping films, and flexible largearea display devices [9][10][11][12][13]. ...
This contribution investigates the preparation of polymer-dispersed liquid crystal (PDLC) films based on meth(acrylate) monomers containing rigid structures. The current study specifically focuses on comparison of the monomers on the basis of meth(acrylate) side group, flexible/rigid structures and rigidity. We find that methacrylate monomers exhibit more preferable electro-optic properties than that of the acrylate monomers. Furthermore, through the systematic variation of rigidity, composition of the monomers and chain length of crosslinking agents, both the morphologies and electro-optic properties of these films are found to be adjustable. A composite film is demonstrated by employing moderately rigid monomer (tetrahydrofurfuryl methacrylate) with low driving voltage (21.0 V) and high contrast ratio (87.5). Therefore, the studies here provide a new approach to optimize the electro-optical properties of the PDLC films by introducing monomers with rigid structures.
... Based on a transient polymer morphology of polymer ballsnetworks in the polymer/LCs composite film, we have fabricated a switchable optical diffuser that achieving high transmission (>96.0%), high haze (>90.0%) and wide viewing angle (from −75°to 75°) at its off state, when applied a voltage of 40.0 V, its viewing angle changes to be from −60°to 60°, which has widened the applications of optical diffusers [30]. With the development of polymer nanocomposites, nanoparticles whose diameters are below 40 nm are added into the polymer matrix to obtain high transmission [31]. ...
Optical diffusers are promising diffusing materials in the optical devices such as monitors, projectors, fibre optics, light-emitting diode (LED) systems and liquid crystal displays (LCDs). We report optical diffusers comprising uniformly distributed nano-sized polymer balls/nematic liquid crystals (LCs) by ultraviolet (UV) click reaction of ene monomer and thiol monomer. By optimising the mass ratio 1:1 of ene and thiol, of which the average diameter of the corresponding nano-sized polymer balls is about 900 nm, relatively high optical transmission and haze with 88.99% and 94.49% are yielded, respectively. Furthermore, by controlling the curing time, the average diameter of nano-sized polymer balls can be reduced to 810 nm, and the developed film exhibits high transmission (98.49%) without sacrificing the high haze (91.77%). This paper demonstrates that UV click reaction is an economical approach to fabricate optical diffusers in a controllable manner.
Recently, there has been a great deal of interest in devices which effectively shield near-infrared light with an additional feature of external field tunability, particularly for energy-saving applications. This article...
Bistable cholesteric liquid crystals have promising application prospects in various fields, such as smart windows and displays. However, the long-term stability of two individual states is not easy to achieve, hindering their practical use. In this research, the bistable feature was enhanced by constructing a microsphere-type polymer with a liquid-crystalline epoxy/thiol monomer in negative dielectric anisotropic cholesteric liquid crystals. Spectroscopic and optical examinations revealed that either the transparent planar state or the opaque focal conic state can be maintained without the aid of an external field. Moreover, they can be switched to each other by applying a high- or low-frequency electric field. Further, factors such as the chemical structure of thiol compounds, curing temperature and curing time were investigated to explore their influences on the micro morphology of the polymer and thereby the electro-optical properties. In addition, the frequency-dependent driving scheme was analysed. Finally, bistable switching was demonstrated using an optimized sample. This energy-efficient bistable film shines light on future applications in smart windows, photonic paper and other electro-optical devices.
Optical diffusers made of polymer composite materials are vital for many photonic and optoelectronic applictions such as backlight unit (BLU) in liquid crystal displays (LCDs), light extraction unit of organic light emitting diodes (OLEDs), and solar cells. We have described the types of optical diffusers, the theory and measurement of light scattering, some common approaches for fabricating optical diffusers, the potential applications and recent developments of optical diffusers containing optical physical unclonable functions (PUFs), optical random number generators, passive stretchable radiative coolers, diffuser -based deep neural networks, lensless cameras or imaging systems, and three dimensinonal (3D) displays including two dimensional (2D)/3D switchable displays, which provide effective ways for designing high-performance optical films in the applications of optical devices. To satisfy the requirements for applications in stretchable optoelectronics and optomechanics, tunable optical diffusers stimulated by electric field, heat, light, mechanical field, or ultrasound attract much attention. Polymer/liquid crystal (LC) composite films with tunable light transmittance, haze, and diffusing intensity have been firstly provided and set a great foundation for the next generation of flexible and switchable optical diffusers.
