Polarized light crystallization process

The solid-state properties like crystallinity, polymorphism (crystal structure), shape (morphology), and particle size of drugs are important in the stability, dissolution, and processibility of drugs. Some commonly used methods in solid-state studies include microscopy, hot stage microscopy with polarized light, x-ray powder diffraction (XRPD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infrared FTIR/Raman, and solid-state NMR. 

In polymers crystallized from the melt, in most cases spherulitic structures are observed spherical agglomerates of crystals and amorphous regions, grown from a primary nucleus via successive secondary nucleation (Figure 4.18). The dimensions of the spherulites are commonly between 5 pm and 1 mm. When spherulites grow during the crystallization process, they touch each other and are separated by planes. In a microtome slice they show a very attractive coloured appearance in polarized light. 

The optical texture of mesophase and resultant carbons is observed readily by means of a reflected polarized light microscope and may be classified according to the shape and size of the isochromatic units. Such a classification is useful to evaluate the properties of mesophase and carbons such as needle cokes. The mesophase has been defined as the intermediate state which shows optical anisotropy and is quinoline-insoluble at room temperature (5,51) (liquid crystal glass), although it is a viscous liquid crystal during the carbonization process (6). ... 

The configuration of natural amino acids has led to studies on the possibility that homochirality emerged at a prebiotic stage, which may be supported by the presence of amino acids as non-racemic mixtures in meteorites (32). This enantiomeric excess may have resulted from the exposition of extraterrestrial matter to circularly polarized light (42). Whatever the origin of this enantiomeric excess, it may have initiated stereoselective processes through different catalytic pathways (7). Symmetry breaking may also have resulted from reactivity in connection with other processes such as crystallization or interfacial chemistry (43, 44) and polymerization of amino acids (45). 

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