Thin polygonal patterned

A film of highly viscous PDMS can be made as thin as we wish by solvent evaporation. Once the film thickness is less than one micron, it is observed to be unstable it breaks up into a large number of droplets that arrange themselves into a polygonal pattern (see Fig. 1.28). This phenomenon can be... 

Fig. 1.3 A thin section of bulk crystallized nylon, in polarized light, reveals a bright, birefringent and spherulitic texture. In the overview (A) the spherulites range from nearly round to polygonal in shape. At higher magnifications (B, C) a classic Maltese cross pattern is seen, with black crossed arms aligned in the position of the crossed polarizers.

The distribution of defects in mesophases is often regular, owing to their fluidity, and this introduces pattern repeats. For instance, square polygonal fields are frequent in smectics and cholesteric liquids. Such repeats occur on different scales - at the level of structural units or even at the molecular level. Several types of amphiphilic mesophase can be considered as made of defects . In many examples the defect enters the architecture of a unit cell in a three-dimensional array and the mesophase forms a crystal of defects [119]. Such a situation is found in certain cubic phases in water-lipid systems [120] and in blue phases [121] (see Chap. XII of Vol. 2 of this Handbook). Several blue phases have been modeled as being cubic centred lattices of disclinations in a cholesteric matrix . Mobius disclinations are assumed to join in groups of 4x4 or 8x8, but in nematics or in large-pitch cholesterics such junctions between thin threads are unstable and correspond to brief steps in recombinations. An isotropic droplet or a Ginsburg decrease to zero of the order parameter probably stabilizes these junctions in blue phases. 

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