The cloudy liquid reported by Reinitzer is now known to be a liquid crystal phase. Upon further heating, a second melting point occurred at 178.5☌, at which the cholesteryl benzoate turned into a transparent liquid. The first of the melting points occurred at 145.5☌ and led to the formation of a cloudy liquid. Liquid crystals were first discovered in 1888 by the chemist Friedrich Reinitzer, who observed that heating a sample of cholesteryl benzoate (a solid at room temperature) led to two melting points. In classic liquids, the molecules have no positional or orientational ordering. The orientational ordering and fluid flow in liquid crystal materials are coupled to each other, where molecular rotation can cause flow and vice versa. In liquid crystal materials, the molecules lose the positional ordering found in solids, but not their orientational ordering (i.e., how the molecules are aligned in a sample). They can therefore be thought of as an intermediate state of matter, existing between the solid and liquid phases (see Figure 1). What are liquid crystals and why are they important?Īs the name suggests, liquid crystals are materials which share some structural properties that are found in solid crystals (e.g., diamond), while at the same time displaying flow behaviour observed in classic liquids (e.g., water).
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