Reverse Mode Polymer Dispersed Liquid Research Articles

Reverse Mode Polymer Dispersed Liquid Crystal-based Smart Windows: A Progress Report

The reverse mode polymer dispersed liquid crystal (PDLC) is an emerging smart window technology. Unlike traditional PDLCs, a reverse mode PDLC can be transparent and opaque in the absence and presence of an external electric field. This report provides a brief introduction to several reverse modes PDLC smart window technologies, focusing on polymer-stabilized liquid crystals (PSLCs). The systems based on electrohydrodynamic instability (EHDI) of liquid crystals have also been discussed. The working principles, mode of material design, and recent developments are presented for each technology. The current obstacles have also been pointed out. The prospects of smart windows have also been presented.

Preparation and electrooptic study of reverse mode polymer dispersed liquid crystal: Performance augmentation with the doping of nanoparticles and dichroic dye

ABSTRACTReported herein, the preparation, morphological, and electrooptic (EO) characterization of reverse mode polymer dispersed liquid crystals (PDLCs) with nematic liquid crystal (LC) and UV curable polymer optical adhesive using polymerization induced phase separation method. The PDLCs are switchable between transparent and opaque states due to the homeotropic and planar alignment of LC in their OFF and ON states of applied voltage, respectively. Further, effect of doping of a fixed concentration of azo dye and silica nanoparticles (NPs) on morphological, EO and response characteristics of same PDLC sample was also analyzed. Experimental results showed that doped reverse mode PDLCs have the higher OFF state optical transmission and boost up in the scattering ON state compared with pristine reverse mode PDLC. The phenomenon is also supported by extinction coefficient and absorption study based on Beer's law. The threshold and operating voltages were found reduced ~1.56 and ~1.73 times for NPs and (NPs + dye) doped reverse mode PDLCs, respectively, along with better contrasts to the pristine reverse mode PDLC. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48745.

2D/3D switchable displays through PDLC reverse mode parallax barrier

ABSTRACTIn this paper, we present a new type of parallax barrier, for switchable 2D/3D display vision, obtained by using a Reverse Mode Polymer Dispersed Liquid Crystal display (RV-PDLC). The parallax barrier was prepared by sandwiching the RV-PDLC film between two ITO conductive glass supports. Strips of ITO were removed from one of the supports, in order to alternate conductive to not conductive strips. In this way the RV-PDLC films could be electrically switched in a parallax barrier able to turn a 2D image in a 3D one. The RV-PDLC barrier was obtained in tree steps: (1) a nematic diacrylate monomer (NDM) was dissolved in a nematic liquid crystal (NLC) in the presence of a small quantity of radical polymerisation initiator; (2) the mixture was homeotropically aligned between the glass conductive supports, previously treated with an aligning chemical; (3) the liquid crystal monomer was polymerised by UV curing. A 2D/3D switchable device was finally obtained by coupling the parallax barrier with a 2D tablet display.

Surfactant-doped reverse-mode polymer-dispersed liquid crystal display with enhanced properties

ABSTRACTIn this article, a nonionic surfactant Brij30 has been used to vertical align the negative anisotropic liquid crystal. The surfactant is further used in reverse-mode polymer-dispersed liquid crystal display to enhance the electro-optical properties. This work shows an enhancement of contrast ratio simply with the addition of surfactant. In addition, contact angle and surface free energies have been determined to judge the role of surfactant in control of surface orientation of liquid crystal molecules.

Physicochemical properties of long-hydrocarbon-chain-silane-coated indium tin oxide glass for reverse-mode polymer-dispersed liquid crystals

We prepared silane-coated indium tin oxide (ITO) glass having different surface energies and topologies by using dipping and evaporation methods with the silane solution. The silane-coated ITO glass samples were analysed using contact angles and atomic force microscopy. Liquid crystal (LC) cells with positive and negative dielectric LCs and a mixture of negative dielectric LCs and liquid crystalline monomers were viewed between crossed polarisers. The ITO glass prepared using the dipping method showed a rougher topology and higher surface energy than the ITO glass prepared using the evaporation method. LCs having positive and negative dielectric anisotropy showed vertical alignment on the silane-coated ITO glass samples as viewed between crossed polarisers. However, the mixture of negative dielectric LCs and liquid crystalline monomers showed vertical alignment only for the ITO glass prepared using the evaporation method. The evaporation method was used for fabrication of reverse-mode polymer-dispersed liquid crystals, and the crystals showed well-aligned vertical polymer networks, good reverse operational mode and a double-U-shaped graph around each 40° by the crystal rotation method.

Effect of cetyltrimethylammonium bromide coatings on indium tin oxide surfaces in reverse mode polymer dispersed liquid crystal films

The vertical alignment of liquid crystals (LCs) on cetyltrimethylammonium bromide-coated (CTAB-coated)indium tin oxide (ITO) glass is the consequence of specific interactions between the LCs, CTAB and ITO surface. The CTAB concentration influences the LC orientation, which changes the ITO surface energy. Changes in the surface energy of CTAB-coated ITO glass are investigated by the Owens–Wendt method. Both polar- and dispersive-component energies on the ITO surface decrease as the CTAB concentration increases, and reach saturation around 0.002% CTAB. The physico-chemical interaction between the LCs and the ITO surface was diminished by the presence of the CTAB layer, which induced the vertical alignment of LCs having positive or negative dielectric anisotropy. Vertical alignment is confirmed using crossed polarisers and the crystal rotation method. The electro-optical properties of fabricated reverse mode polymer dispersed liquid crystal films display transmittance of Ton: 29.7%, Toff: 85% and a response time of τon: 33 ms, τoff: 107 ms.

High Contrast Reverse Mode PDLC Films: A Morphologic and Electro-Optical Analysis

Reverse Mode Polymer Dispersed Liquid Crystal films obtained by the photo polymerization of homeotropically aligned Liquid crystal solutions, have been investigated in order to optimise their optical contrast with the aim of their application as windows able to be switched from an high transparent state into a very opaque state by an appropriate electric field. An excellent optical contrast has been obtained by varying the amounts of two different liquid crystal diacrylate monomers in the starting solutions as precursors of the final polymer matrix. Morphology of the film has been investigated to account for the electric threshold field needed to operate the film. A simple model has been proposed to describe the threshold field and the behaviours of the dynamic response times as a function of the polymer composition. A novel type of morphology which opens the field for deeper investigation, has been found, where two different segregations of the liquid crystal into the polymer matrix coexist.

Preparation of Newly Designed Reverse Mode Polymer Dispersed Liquid Crystals and its Electro-Optic Characteristics

Polymer Dispersed Liquid Crystal (PDLC) films, of which the liquid crystal has negative dielectric anisotropy, were prepared from the phase separation between liquid crystal (MJ001317) and the various compositions of resins by common polymerization induced phase separation method. In this work, the effects of resin compositions have been systematically investigated. It was found that the morphology and size of droplets related to electro-optic properties mainly depend on the rate of polymerization and cross-linking density for each resin composition. A reverse mode PDLC films developed from a new formulation containing TPGDA/EHA/HMPPO showed the good off-state transmittance, contrast ratio (19:1), and relatively low driving voltage (10 V).

Anisometric, non-mesogenic, tailor-made monomer for reverse-mode shutters

Reverse-mode operation films can be achieved with polymer dispersed liquid crystals by many methods. One method consists in the use of either rough or polyimide treated supports in order to induce homeotropic alignment of the initial mixture that will separate in liquid crystal and polymer rich phases. The major disadvantage is the need for mesogenic monomers to keep a good alignment of the liquid crystal after the polymerization process. In this paper we present results concerning the use of an anisometric, non-mesogenic, tailor-made monomer for the preparation of excellent reverse-mode polymer dispersed liquid crystal shutters cast on rough surfaces. The combined use of rough surfaces and non-mesogenic monomers allows us to exceed earlier limits in physical and chemical properties, cost, and device dimensions by the use of a wider class of monomer molecules.

Morphology and electro-optical properties of reverse mode polymer dispersed liquid crystals

We have investigated the morphology and electro-optical properties of reverse mode polymer dispersed liquid crystals as a function of liquid crystal loading. Reverse mode shutters have been obtained by a polymerization-induced phase separation of mixtures, consisting of a liquid crystalline monomer and a non-reactive nematic liquid crystal, placed between rough conductive surfaces. Such surfaces are able to keep the photopolymerizable mixtures homeotropically aligned without the use of any aligning polymer substrate. OFF state transmittances are always larger than 80% and the switching fields decrease if the non-reactive liquid crystal percentage is increased. Both rise and decay times are always lower than 10 ms. The electro-optical properties have been related to the sample morphology and a simple mode is proposed.

Rough surfaces for orientation control in reverse mode polymer dispersed liquid crystal films

Reverse mode operation shutters have been achieved with polymer dispersed liquid crystals by means of polymerization-induced phase separation of nematic mixtures consisting of a low molecular mass liquid crystal and a liquid crystalline monomer. Fluid mixtures were homeotropically aligned by rough surfaces and transparent films were obtained after polymerization. Transmittance in the OFF state can be larger than 80% and decreases to less than 1% when an electric field of about 2 V μm-1 at 1 kHz is applied (ON state). Both rise and decay times can be lower than 10 ms and the drop in the OFF state normal transmittance is drastically reduced with respect to conventional polymer dispersed liquid crystals since samples exhibit a reverse morphology. The role played by surface roughness is also discussed.

Normal and reverse mode polymer dispersed liquid crystal devices

Polymer dispersed liquid crystal (PDLC) devices are an interesting new use of liquid crystals which could allow liquid crystals to be used in large areas and as flexible films. The topic is now very diverse. It ranges from the traditional PDLC/ nematic curvilinear aligned phase films, characterized by the liquid crystal being in discrete or fairly discrete droplets embedded in a polymer matrix, to networks or gels in which the liquid crystal content in somewhat higher and exists as a continuum within a web of polymer. This article aims to provide an insight into some of the practical features associated with traditional PDLC, which are important for its use in the more commercially advanced areas, while also providing some basic information on other, newer areas.

Preparation and Optical Properties of a Reverse-Mode Polymer Dispersed Liquid Crystal Film

ABSTRACTTwo new types of reverse-mode polymer-dispersed liquid crystal films have been developed and successfully produced. The first was produced by UV-curing of a mixture of dual frequency addressable liquid crystal (DFALC) and UV-curable polymers under an applied voltage at a frequency lower than the crossover frequency (fc) of the DFALC. This first type is referred to as a dual frequency type. The second type was produced by injecting a liquid crystal having negative dielectric anisotropy into a specially prepared porous polymer film from which liquid crystal having positive dielectric anisotropy had previously been extracted. The type thus produced through such “negative-for-positive” substitution is referred to as a substitution type. While the dual frequency type can not be driven at a low frequency, substitution type can, which gives it a distinct advantage. Other electro-optic characteristics of the two types of films, including alignment properties of the liquid crystal molecules, are also discussed.