New operating principles for liquid-crystal displays – DISPLAY

Nematic liquid crystals are most often made of organic rod-like molecules that align parallel to each other while remaining in a fluid state. Liquid crystal displays (LCD), which are one of their most important applications, presently dominate by far the huge flat-panel display market. These electro-optic devices cleverly use the anisotropy of optic, elastic, and electric properties of nematic materials, to achieve both good contrast and high speed of the display. However, current LCD technologies are not well suited for integration in mobile devices, such as e-book readers and electronic shelf labels, because of their large energy consumption due to the fast refresh rate and the need for back- or front-light. These important segments of the display market are nowadays left to competing technologies such as the e-ink. Low energy consumption is also a crucial feature for the fast-growing market of “smart windows” the transmission of which can be tuned by applying an electric potential difference. From a more fundamental perspective, the mechanical properties of usual nematics of rod-like molecules, used in LCD, are defined by their three elastic constants for splay, twist, and bend deformations. In fact, these three constants usually do not vary much from one compound to another. However, during the last decade, a new large family of nematic compounds with a bent molecular shape has been designed by organic chemists. These new bent-shaped molecules are currently being studied extensively worldwide mainly because they exhibit original spatially-modulated nematic organizations in addition to the usual nematic state. However, it turns out that the latter drastically differs from that of the common rod-like compounds presently used in LCD because the bend elastic modulus is much lower than usual, by up to two orders of magnitude. In fact, this ultra-low bend elastic constant of the bent-shaped compounds completely transforms the context of the physical mechanisms that are at the basis of LCD technology. Here, we propose to exploit this opportunity by building two demonstrators of new LC displays combining low energy consumption with high multiplexability and good optical quality. Indeed, our preliminary experiments and numerical simulations have highlighted the great potential of these original materials for bistable nematic devices based either on classic (e.g. Twisted) or novel cell architectures and switching mechanisms. In this project, we will optimize the liquid-crystalline mixtures of bent-shaped compounds for these applications and design low-consumption devices showing bistability and operating in transmission/reflection mode, with or without polarizers. Moreover, to prove the feasibility of this new nematic technology, we will prepare two demonstrators of such devices and study their characteristics. Our consortium gathers five partners, purely academic or related to industry, who are experts in the study of structural properties and formulation of liquid-crystalline mixtures, electro-optical properties of liquid crystals, fundamental operating mechanisms of LCD, and design of LCD demonstrators.