Reading to Learn Activity (1)

Modern Materials

What are modern materials?

Modern materials refer to the materials with properties that traditional materials do not possess.  The chemical or physical properties of these materials can be changed by external factors like temperature, light and electrical charges, so as to meet specific requirements in modern technologies. Two important modern materials, liquid crystals and nanotubes, are discussed below.

What are liquid crystals?

Liquid crystals were first discovered in 1888, by Austrian botanist Friedrich Reinitzer when he was studying a cholesterol-like substance (cholesteryl benzoate). When heated, it first became a milky liquid and then turned into a clear liquid as its temperature rose. Upon cooling, the reverse process occurred. This turbid viscous phase is called the liquid crystal phase.  Unlike solid that have very little translational freedom, liquid crystal possesses some degree of translational freedom with certain orientation preference in one or two direction.  This is also different from true liquid as the molecules in true liquid have no intrinsic order.  Liquid crystal shows unique properties of optical anisotropy and sensitivity of orientation to electromagnetic field.  This class of material generally has several characteristics such as, rod or disc like molecular structure, rigidity along the long axis and possession of strong dipoles.

Depending on the nature of the ordering, liquid crystals can be classified into three categories: nematic, smectic and cholesteric. Molecules in nematic phase have no positional order but tend to align in the same direction as the director. Molecules in smectic phase show some degree of two-dimentional order. They align towards the direction of the director and tend to arrange in layers or planes.  When compared with nematic phase, smectic phase shows a lower degree of freedom.

Join now!

Cholesteric or chiral nematic phase arises when the molecules that made up the nematic phase are chiral.  In the chiral nematic phase, the molecules line up in positions that they are slightly twisted from the molecules next to them giving rise to a helical-like arrangement. The overall arrangement of the molecules can be treated as a stack of nematic molecules twisting in a small angle for each layer.

What is the function of liquid crystal in LCD?

For a LCD to work, liquid crystals are packed between a polarizer and an analyser which are arranged ...

This is a preview of the whole essay