Liquid crystals have become an integral part of our commercial electronics world, and liquid crystal displays are a key part of most mobile, battery-powered electronic devices. Despite their success and the common usage of the term “liquid crystal,” the juxtaposition of two such contradictory terms is easily comparable with other oxymorons such as “irregular pattern” or “meaningful nonsense” and can still be a cause for pause for many engineers and scientists. Clarifying what is meant by liquid crystals up front is particularly important, as the focus of this book is on the applications of liquid crystals, in particular, those related to their optical properties.
In our everyday world, we commonly interact with three states of matter: gas, liquid, and solid. Gases such as the air we breathe have variable volumes and shape, and expand to fill their containers. Liquids have fixed volumes but they flow, and their containers impose the shape the liquid takes. Solid matter has a fixed volume and will hold its shape. These three forms of matter, while common, are not the only forms of matter. Plasma is considered a fourth form of matter and is created when a gas is ionized. In this state, the ionized gas is conductive, similar to metals, and may be the most common state of matter in the universe. Plasma is a distinct form of matter, having the properties of a gas in that it has variable volume and shape; however, unlike gases, under magnetic fields it can take on defined structures. Before we start thinking that plasmas are exotic and we seldom encounter them, consider that the Sun is mostly plasma, as are the light-emitting components of neon signs and even the common fluorescent light. There are more exotic forms of matter, but we rarely encounter them, as they require special environments, such as extreme cold or extreme mass.
The idea of matter having properties between two states is not unique to plasmas. Just before the turn of the 20th century, a unique material was discovered that appeared to have the properties of both liquids and solids. The solid form of matter had the behavior of crystals, leading to the name liquid crystals.
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