Polymer-dispersed liquid crystals (PDLCs) refer to nematic liquid crystals, which are embedded in a polymer matrix. A conventional PDLC device is fabricated by phase separation. However, this method leads to non-uniform electro-optical characteristics of the device due to the non-uniform size distribution of the liquid crystal droplets. Moreover, the PDLC device is switched between the transparent state and the scattering state so that a full color scheme is intrinsically impossible without a color filter. In this paper, a fabrication method for a color PDLC device with uniform size and shape for liquid crystal droplets is proposed. Droplets of a fairly uniform size in large quantities can be obtained by means of membrane emulsification. Microcapsules are fabricated by complex coacervation with gelatin and gum arabic. By adding red, green, and blue pigments, color microcapsules are obtained. The electro-optical effects of the fabricated color PDLC devices are also demonstrated. The driving voltage of the device is 90 V, and the switching time is 8.3 ms. In the turn-on state, the measured hazes of red, green, and blue PDLC devices are 16.89%, 15.82%, and 18.55%, respectively, while in the turn-off state, the measured hazes of those devices are 65.21%, 67.32%, and 70.76%, respectively.Crystals 2019, 9, 364 2 of 11 substantially increase. In the guest-host mode, the color shift is caused by the anisotropic properties of the dichroic dye. Moreover, this type of device is short-lived, because the dichroic dye is vulnerable to ultraviolet light.To address both the non-uniform size distribution and the full color display, we propose a color PDLC device, which is characterized by a colored core-shell structure. The fabrication process of color PDLCs with a core-shell structure of uniform size is investigated. The electro-optical properties are also demonstrated in terms of the voltage-transmittance curve, response time, and spectroscopic properties. Materials and Methods Formation of Liquid Crystal Droplets by Membrane EmulsificationMembrane emulsification is an emulsification technique, for example, the Shirasu-porous-glass membrane emulsification method to make monodispersed emulsions developed by Nakashima et al. [13]. It is suitable for the fabrication of all types of droplets, including oil in water emulsion and water in oil emulsion. Also, membrane emulsification can form small-sized and uniform droplets. The schematic diagram of the droplet-forming process is depicted in Figure 1. The dispersed phase escapes through the porous membrane filter into the moving continuous phase. At the surface of membrane filter, the dispersed droplets, which pass though the pore of the filter, will be detached by the shear stress in the continuous phase. In this way, droplet size can be effectively controlled by the shear stress.

Cholesteric liquid crystal (CLC) has a helical structure with either of left-handedness or right-handedness. Due to the helical structure, the selective reflection occurs depending on the chrial pitch. However, the reflectance of the CLC layer is theoretically limited to 50% because only one of right-or left-handed circularly polarized light is reflected. In this paper, we demonstrate high reflectance with double layer structure for the color reflector application.

Due to the fact the conventional polymer dispersed liquid crystal (PDLC) device operates between the transparent state and the scattering sate, color realization is limited. In this paper, we propose the color PDLC device with colored core-shell structure. By the complex coacervation microencapsulation process, liquid crystal droplets are encapsulated by the aqueous solution of gelatin, arabic gum, and color pigments. The size of the color droplet can be controlled by the pore size of the membrane filter. The average diameter of the fabricated color droplets is approximately 10 µm.

Cholesteric liquid crystal (CLC) has a helical structure with either of left-handedness or right-handedness. Due to the helical structure, the selective reflection occurs depending on the chrial pitch. However, the reflectance of the CLC layer is theoretically limited to 50% because only one of right-or left-handed circularly polarized light is reflected. In this paper, we demonstrate high reflectance of CLC layer with quantum dots for the color reflector application.