5.D.1 Introduction

Liquid crystals are certainly one of the nicest examples of crossed fertilization between basic and applied research. The first theoretical introduction of the notion of an organized state of matter in the case of liquids and the first experimental observations were made by Reinitzer in 1888, the expression liquid crystal was introduced for the first time by O. Lehmann in 1890. At that time scientists were merely concerned in studying a phase transition between two states of matter and surely didn't think of display or of signal processing devices.

Once the high technological potentialities of liquid crystals were identified, it became necessary to identify and understand the physical mechanisms responsible for their behavior. This necessitated a large research effort, in both applied and basic research. The French Physics Nobel Prizewinner, P.G. de Gennes, was among those who, as early as 1960, had anticipated the importance of liquid crystals in technology and who has largely contributed in developing the physics of the related phenomena.

One purpose of liquid crystal devices is to compete with cathode ray tubes, their main advantage is their extremely low-energy consumption which has allowed them to take an overwhelming position on the market of small-size display devices (watch, pocket computer and, more recently, personal computer screens).

5.D.2 Physical-Chemistry of Liquid Crystals

From a thermodynamic point of view a liquid crystal is intermediate between a crystal where a quasi-perfect order is found and a liquid where no long-range order remains. A crystal is a regular...