GB1376115A - Nematogenic compositions - Google Patents

Abstract

1376115 Liquid crystal compositions MERCK PATENT GmbH 26 Jan 1973 [26 Feb 1972] 3995/73 Heading C4X A known nematogenic material contains as an additive 0À001 to 2% by weight of at least one carboxylic acid of the formula and/or ar least one salt thereof, in which Y is -R 1 or n is 0 or 1, R 1 is an alkyl or alkoxy radical with 6-18 carbon atoms or an acyloxy radical with 4-18 carbon atoms when n is 0, R 2 is an alkyl, alkoxy or acyloxy radical with up to 18 carbon atoms, R 1 =R 2 when n is 1, and X is a halogen atom (chlorine). The group A may be common to the additive and at least one of the compounds constituting the nematogenic material. The additive cation may be an alkali metal, an alkaline earth metal or a tetra-substituted ammonium or phosphonium cation. The nematic material may include an isomeric pair of compounds and/or a eutectic mixture of compounds, the compounds having the formula where A is as defined above, R 1 and R 2 are alkyl, alkoxy or acyloxy with up to 18 carbon atoms and may be the same or different. The modified nematic material readily assumes a homotropic alignment at a boundary surface, either after heating to the clear point and cooling, or often with the omission of such steps, and may be used in electro-optic, e.g. display, devices ex- hibiting dynamic scattering. In the unenergized state the homotropic alignment prevents the appearance of streaks (which lower the contrast), and reduce the visible intensity of the inherent colouring of certain nematic compounds, for example epoxybenzene derivatives. The inclusion of the carboxylic acid salts allows the conductivity of the composition to be controlled.