liquid crystals
Materials in nature can be divided into different phases, also called states of matter, depending on the mobility of the individual atoms or molecules. The obvious states of matter are the solid, the fluid and the gaseous state. In the solid state, intermolecular forces keep the molecules close together at a fixed position and orientation, so the material remains in a definite shape. In the fluid state, the molecules are still packed closely together, but they are able to move around. Hence a fluid does not have a rigid shape, but adapts to the contours of the container that holds it. Like a liquid a gas has no fixed shape, but it has little resistance to compression because there is enough empty space for the molecules to move closer. Whereas a liquid placed in a container will form a puddle at the bottom of the container, a gas will expand to fill the container.
Although the three categories seem very well defined, the borders between the different states are not always clear. Apart from the three familiar states, there exist a large number of other intermediate phases. A simple example is a gel. A gel is not quite solid, neither is it a liquid. Liquid crystals are another important intermediate phase which exhibits features from both the solid and the fluid state. Liquid crystals have the ordering properties of solids but they flow like liquids. Liquid crystalline materials have been observed for over a century but were not recognized as such until 1880s. In 1888, Friedrich Reinitzer (picture) is credited for the first systematic description of the liquid crystal phase and reported his observations when he prepared cholesteryl benzoate, the first liquid crystal.
Ordinary fluids are isotropic in nature: they appear optically, magnetically, electrically, etc. to be the same from any direction in space. Although the molecules which comprise the fluid are generally anisometric in shape, this anisometry generally plays little role in macroscopic behavior.
Although the three categories seem very well defined, the borders between the different states are not always clear. Apart from the three familiar states, there exist a large number of other intermediate phases. A simple example is a gel. A gel is not quite solid, neither is it a liquid. Liquid crystals are another important intermediate phase which exhibits features from both the solid and the fluid state. Liquid crystals have the ordering properties of solids but they flow like liquids. Liquid crystalline materials have been observed for over a century but were not recognized as such until 1880s. In 1888, Friedrich Reinitzer (picture) is credited for the first systematic description of the liquid crystal phase and reported his observations when he prepared cholesteryl benzoate, the first liquid crystal.
Ordinary fluids are isotropic in nature: they appear optically, magnetically, electrically, etc. to be the same from any direction in space. Although the molecules which comprise the fluid are generally anisometric in shape, this anisometry generally plays little role in macroscopic behavior.