Reverse mode operation polymer dispersed liquid crystal with a positive dielectric anisotropy liquid crystal

Abstract

The development of electrically activated chromogenic materials is important for their potential applications in smart windows. Several previous works have reported on reverse mode operation polymer dispersed liquid crystals (PDLCs) based on negative dielectric anisotropy liquid crystals. They have a transparent OFF state, which turns opaque after the application of a suitable external electric field. Nevertheless, these devices have some limitations such as the use of large amount of expensive liquid crystals with peculiar physical‐chemical properties. In addition, a good matching between the refractive index of liquid crystal and the polymer matrix one is required. The main result of this work is the achievement of reverse mode operation devices prepared with a positive dielectric anisotropy liquid crystal and characterized by a high OFF state transmittance obtained by the onset of high intensity built‐in DC electric fields in a direct mode operation PDLC, which allows the OFF state homeotropic alignment of liquid crystal directors. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011

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

“…This is described as the random orientation of nematic liquid crystal in all directions. [18,19] The images for R-PDLC device doped with surfactant are shown in Figure 2D. Figure 2D showed the major part of the device as black.…”

“…The darker state under the polarised optical films is defined as the vertical and grey the tilted arrangement of LC molecules towards the light. [18,19] It can be stated as the R-PDLC devices filled with Brij30 has homeotropic liquid crystal molecular orientation. The reason for getting homeotropic alignment or vertical orientation in the simply surfactant-doped devices could be the decrease in surface free energy of the device filled with surfactant.…”

“…Owing to such advantageous, features the R-PDLCs have been used in large-area displays, shutters, smart windows, micro-lenses and automotive applications. [8,9] To date, several techniques have been proposed for the vertical alignment (VA) of positive and negative anisotropic LCs, such as rubbing of polyimide layer [10] photo-alignment [11] cetyltrimethylammonium bromide coatings on indium tin oxide (ITO) surfaces [12] and applying magnetic field. [13,14] Recent studies showed the vertical alignment of LC molecules is achieved just by utilizing the polysulfone polymer [15] and anionic-surfactant [16] in PDLC mixtures.…”

Reverse-mode polymer dispersed liquid crystal films prepared by patterned polymer walls

“…Several authors have reported examples of reverse-mode PDLC films obtained by modification of the polymer surface energy, [6] by functionalising the LC/polymer matrix interface, [7] by using dualfrequency addressable LC, [8] by means of rough surfaces [9,10] or by increasing the LC content. [11] Unfortunately, the existing process to prepare reverse-mode PDLC films was complex and expensive, which resulted in restricted in many fields for its further applications.…”

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

“…20 Therefore to overcome to the hitches, different techniques for getting reverse mode PDLCs with HA of LCs have been proposed using positive and negative dielectric anisotropic LCs. 21,22 Alteration of glass surface by polyvinyl butyral layer, 23 photoalignment, 24 cetyltrimethylammonium bromide coatings on indium tin oxide (ITO) surfaces, 25 rough surfaces for orientational control, 13,26 and doping of ferromagnetic nanoparticles (NPs) 27 are few other reported techniques for reverse mode PDLCs. HA of LC molecules was also achieved by utilizing the polysulfone polymer 28 and surfactant (ionic and nonionic) 7 in PDLC mixtures.…”