Polymer dispersed nematic liquid crystal for large area displays and light valves

Abstract

A new electro-optical material based on nematic liquid crystal dispersed in a polymer matrix has recently been introduced by Fergason. This technology (termed NCAP, for nematic curvilinear aligned phase) is suitable for making very large area (thousands of square centimeter) light valves and displays. The device consists of micron size droplets of liquid crystal dispersed in and surrounded by a polymer film. Light passing through the film in the absence of an applied field is strongly forward scattered, giving a milky, translucent film. Application of an electric field across the liquid crystal/polymer film places the film in a highly transparent state. Pleochroic dyes may be employed in the system in order to achieve controllable light absorption as well as scattering. Microscopically, it is shown that the liquid-crystal director lies preferentially parallel to the polymer wall, leading to a bipolar-like configuration of the liquid-crystal directors within the droplet. The symmetry axes of the droplets are randomly oriented in the unpowered, scattering state, but align parallel to the field in the powered, transparent state. The electric field required to reorient a given droplet varies inversely with the diameter of that droplet, and it is shown that the macroscopic electro-optical properties of the film can be modeled if the distribution of liquid-crystal droplet sizes is known.

Orientation and Solvatochromism of Dyes in Liquid Crystals

“…In particular, the alignment of the dipole moment of the dye with the director of the LC offers the prospect of a coloured liquid crystal display (LCD) that can be switched to a transparent state in an on-off fashion with an external electric field [1][2][3][4]. Additionally, it has been observed that the electro-optic response time of nematic LCs can be improved by dye dopants with large dipole moments, which is also of great interest in display applications [5].…”

Properties and Application of UV-Curable Liquid Crystals.

“…The liquid crystal displays (LCDs) with light scattering properties using nematic liquid crystals and polymers have been studied [1][2][3][4][5]. Polymer Network (PN) LCD, which contains a dispersed three dimensional polymer network in liquid crystal (PNLC), is one of the most promising light scattering displays because of the compatibility of brightness and low driving voltage.…”

Low-Power Driving Technique for 1-Pixel Display Using an External Capacitor

“…A major disadvantage of the smart glass, the need for a voltage source, can be resolved by the integration of photovoltaic (PV) devices [12], [13], which means lower power consumption is desirable. PDLCD [14], one type of smart glass, is often used to realize electrically controlled privacy glass thanks to its scattering property [15]. PDLCDs generally scatter light when they are OFF and transparent when ON, and a reverse mode PDLCD works as expected [16].…”