Disinclination points

As remarked in chapter 1, the nematic state is named for the threads that can be seen within the fluid under a microscope (fig. 1.1.6(a)). In thin films sandwiched between glass plates these threads can be seen end on. A typical example of the texture in a plane film of thickness about 10 /tm between crossed polarizers - the structures a noyaux or schlieren textures - is given in fig. 1.1.6(6). The black brushes originating from the points are due to line singularities perpendicular to the layer. In analogy with dislocations in crystals, Frank proposed the term disinclinations , which has since been modified to disclinations in current usage. 

In Fig. 8.11 an example is given of a Schlieren texture in the nematic phase observed under a polarisation microscope. The polariser and analyser are always crossed and their positions with respect to photos (a) and (b) differ by 45° as shown by small crosses. On both photos characteristic brushes (threads) are seen originated and terminated at some points. The points are linear singularities (disinclinations or just disclinations) to be discussed below. Note the difference between a number of brushes originated or terminated in different points only two brushes in points 1 and 5 and four brushes in points 2, 3 and 4. It is evident that the pictures discussed are related to the local orientation of the director, i.e. to the structure of... 

By Ivan s requirement, the AA contract included rather punitive damages for the consequences of design error. The AA team were totally disinclined to make any assumptions that might accelerate the project, but rather dissipated their ingenuity in writing clever letters to their client, pointing out how the client team was alone responsible for all the delays and re-work. 

There is an important point. The Br ion cannot bond to the molecule if it approaches from the side to which the first Br atom is attached because that atom shields the C atoms. The only side from which it can approach is the side opposite to the resident Br atom. Therefore, instead of getting a mixture of products with the two Br atoms attached on either face of the molecule, there is only one with the atoms attached on opposite sides. (This is the reason why I chose cyclohexene it can t twist into a different shape, so the distinction between the products is preserved.) Once again, you see that it is possible to achieve subtle control of molecular architecture. Put another way Nature forbids the achievement of what she is disinclined to allow. 

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