Design of Liquid Crystalline Materials
A very large number of chemical compounds are known to exhibit one or several liquid crystalline phases. Despite significant differences in chemical composition, these molecules have some common features in chemical and physical properties. There are two types of thermotropic liquid crystals: discotics and rod-shaped molecules. Discotics are flat disc-like molecules consisting of a core of adjacent aromatic rings. This allows for two dimensional columnar ordering. Rod-shaped molecules have an elongated, anisotropic geometry which allows for preferential alignment along one spatial direction.
• The molecular shape should be relatively thin or flat, especially within rigid molecular frameworks.
• The molecular length should be at least 1.3 nm, consistent with the presence of long alkyl group on many room-temperature liquid crystals.
• The structure should not be branched or angular.
• A low melting point is preferable in order to avoid metastable, monotropic liquid crystalline phases. Low-temperature mesomorphic behavior in general is technologically more useful, and alkyl terminal groups promote this.
An extended, structurally rigid, highly anisotropic shape seems to be the main criterion for liquid crystalline behavior, and as a result many liquid crystalline materials are based on benzene rings.
Read more about this topic: Liquid Crystal
Famous quotes containing the words design of, design, liquid, crystalline and/or materials:
“Humility is often only the putting on of a submissiveness by which men hope to bring other people to submit to them; it is a more calculated sort of pride, which debases itself with a design of being exalted; and though this vice transform itself into a thousand several shapes, yet the disguise is never more effectual nor more capable of deceiving the world than when concealed under a form of humility.”
—François, Duc De La Rochefoucauld (1613–1680)
“What but design of darkness to appall?—
If design govern in a thing so small.”
—Robert Frost (1874–1963)
“Telephone poles were matchsticks, put there to be snapped off at a whim. Dogs trotting across the road were suddenly big trucks. Old ladies turned into moving—vans. Everything was too bright, but very funny and made for my delight. And about half a mile from my long liquid breakfast I turned carefully down a side street and parked, and sat beaming happily through the tannic fog for about an hour, remembering how witty we all had been, how handsome and talented ... [ellipsis in original]”
—M.F.K. Fisher (1908–1992)
“While the stars that oversprinkle
All the heavens, seem to twinkle
With a crystalline delight;
Keeping time, time, time,
In a sort of Runic rhyme,
To the tintinnabulation that so musically wells
From the bells, bells, bells, bells,”
—Edgar Allan Poe (1809–1849)
“Kicking his mother until she let go of his soul
Has given his a healthy appetite: clearly, her role
In the New Order must be
To supply and deliver his raw materials free;”
—W.H. (Wystan Hugh)