The well-known three states of matter are solid, liquid and gas. When cooled, gas condenses to form a liquid as you see in a warm room in winter where water vapor forms dew on glass windows cooled by the cold air outside. In the gas state, molecules are free to move around pretty much independent from each other except for occasional collisions. Molecules in the liquid state are less mobile and closer to each other. Frequent collisions between molecules make the liquid more viscous, yet it can still flow like "liquid." As the liquid is further cooled, say at the freezing point of water 0℃ (32℉), it is transformed to a solid, which is rigid; water freezes to become ice at 0℃ (32℉). Until two scientists in Europe, Friedrich Reinitzer and Otto Lehmann, discovered liquid crystals in the late 19th century, these three are the only states of matter that humans have ever known.
Liquid crystal is the fourth state of matter that occurs between solid and liquid. While studying the function of cholesterol in plants, Friedrich Reinitzer, an Austrian botanist, found an unusual melting that was always accompanied by the presence of cloudy liquid state before the clear liquid appears. This cloudy liquid is what is now known as "liquid crystal." Intrigued by this usual observation, Reinitzer sent the sample1 to a renowned German crystallographer, Otto Lehmann. Through his careful observations of the melting of the substance using his state-of-the-art microscope with a gas heating stage, Lehmann was convinced that the cloudy state is truly a new state of matter that differs from solid, liquid and gas. The year 1888 Reinitzer found this double melting phenomenon is officially recognized as the year of discovery of liquid crystals.
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