northanger (northanger) wrote,

Nemat Space

never fully investigated Nemat-space mentioned here until searching for more info on phenyl benzoate related to this. see it all fits together.

Liquid crystalline mesophases can be modulated by molecular engineering. Nematic liquid crystals (LCs) are used in twisted nematic displays, whereas smectic LCs are used are used to construct large-area flat panel display devices. Manipulation of mesomorphic structures therefore has strong technological implications. A. C. Small and C. Pugh* have taken a molecular engineering approach to perform such manipulations.

It is well known that phenyl benzoate mesogens tend to form nematic phases, but the authors forced low– and high–molecular-mass LCs with these mesogens to order into smectic layers by adding fluorocarbon moieties at the ends of the p-alkoxy groups on the benzene rings.

The immiscibility of the hydrocarbon and fluorocarbon segments induced the amphiphilic tails to undergo microphase separation, leading to the formation of the layered smectic structures.

The authors found that the bulk of the lateral substituent attached to the ortho or para position of the benzene rings of the mesogens affected their mesophase structure: When the lateral substituents changed from methyl (1) to norbornyl (2) to polynorbornyl (3), increasingly longer hydrocarbon or fluorocarbon tails (larger n or m values) were required to induce smectic layering. This structure–property relationship may help design new LC materials with tailored mesophase structures. (Macromolecules 2002, 35, 2105–2115; Ben Zhong Tang).

About Liquid Crystals

Normally, we consider matter to have three distinct states: solid, liquid, and gas. However, there are states of matter which do not meet the necessary requirements of any of these three categories. For example, a substances such as mayonnaise is somewhere between a liquid and a solid.

Liquid crystals are also not quite liquid and not quite solid. Physically, they are observed to flow like liquids, but they have some properties of crystalline solids. Liquid crystals can be considered to be crystals which have lost some or all of their positional order, while maintaining full orientational order. For example, imagine a large number of toothpicks put into a rectangular box and shaken. When you open the box, the toothpicks will be facing in about the same direction, but will have no definite spatial organization. They are free to move, but like to line up in about the same direction. This is a primitive model for nematic liquid crystals.

Nematics are polarizable rod-like organic molecules on the order of 20 Angstroms in length. Because of their tendency to organize themselves in a parallel fashion, they demonstrate interesting and useful optical properties; the digital watch you used to wear back in the 80's functioned using nematic liquid crystals. Today, many more useful and interesting properties of nematics are known and exploited.

Smectic Liquid crystals are different from nematics in that they have one more degree of orientational order than do the nematics. Smectics generally form layers within which there is a loss of positional order, while orientational order is still preserved. There are several different categories to describe smectics. The two best known of these are Smectic A, in which the molecules align perpendicular to the layer planes, and Smectic C, where the alignment of the molecules is at some arbitrary angle to the normal.

Liquid Crystal: Nematic phase

One of the most common LC phases is the nematic, where the molecules have no positional order, but they do have long-range orientational order. Thus, the molecules flow and are randomly distributed as in a liquid, but they all point in the same direction (within each domain). Most nematics are uniaxial: they have one axis that is longer and preferred, with the other two being equivalent (can be approximated as cylinders). Some liquid crystals are biaxial nematics, meaning that in addition to orienting their long axis, they also orient along a secondary axis.

nemato– or nemat– :: pref. Thread; threadlike: nematocyst. [New Latin nēmato-, from Greek nēma, nēmat-, thread].

smec·tic :: Of or relating to the mesomorphic phase of a liquid crystal in which molecules are closely aligned in a distinct series of layers, with the axes of the molecules lying perpendicular to the plane of the layers. [From Greek smēktos, smeared, from smēkhein, to wash off].

hendeceagram :: A hendeceagram is a star polygon that has eleven points. The {11/2} star polygon is used as a symbol for the Aleister Crowley Foundation. {11/3} Hendecagrams are on the Dome of the tomb of Shah Nemat Ollah Vali, Mahan.


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