Polarity formation microscopy

The starting system is achiral (plates at 90° with isotropic fluid between), but leads to the formation of a chiral TN structure when the fluid becomes nematic. In this case, enantiomeric domains must be formed with equal likelihood and this is precisely what happens. The size of these domains is determined by the geometry and physics of the system, but they are macroscopic. Though the output polarization is identical for a pair of heterochiral domains, domain walls between them can be easily observed by polarized light microscopy. This system represents a type of spontaneous reflection symmetry breaking, leading to formation of a conglomerate of chiral domains. 

The structure (e.g., number, size, distribution) of fat crystals is difficult to analyze by common microscopy techniques (i.e., electron, polarized light), due to their dense and interconnected microstructure. Images of the internal structures of lipid-based foods can only be obtained by special manipulation of the sample. However, formation of thin sections (polarized light microscopy) or fractured planes (electron microscopy) still typically does not provide adequate resolution of the crystalline phase. Confocal laserscanning microscopy (CLSM), which is based on the detection of fluorescence produced by a dye system when a sample is illuminated with a krypton/argon mixed-gas laser, overcomes these problems. Bulk specimens can be used with CLSM to obtain high-resolution images of lipid crystalline structure in intricate detail. 

The structure of hard gels is best elucidated using SAXS or SANS because the periods of the ordered structures are on the scale 10-100nm. In addition to tube inversion and rolling ball viscometry, which are sensitive to yield stress, the formation of a hard gel can be identified by other techniques. These include DSC (gelation is an endothermic process), NMR (via transverse relaxation time, T2, measurements), polarized light microscopy and rheometry. 

On the basis of this discussion, the mechanisms of mesophase carbon fiber formation are closely related to those of needle coke, the principal differences being the extent to which the deformation and relaxation mechanisms are able to act. Because delayed coking involves relatively gentle but random deformation processes by bubble percolation and the long dwell times in the coke drum afford opportunity for extensive disclination annihilation and micro-structural relaxation, the structure of needle coke can be well defined by polarized-light microscopy (2,36). 

It is well known that pitch, solvent-refined coal (SRC), and coking coal produce various kinds of mesophase at the early stages of carbonization (3y 4y 5). The mechanisms of many chemical reactions and physical transformations relating to mesophase formation are studied by quenching techniques. Such research techniques as polarized-light microscopy can be extremely fruitful. On the other hand, observation of phenomena at reaction temperatures may yield more easily interpretable or more relevant results. 

The formation of surfactant crystals (i.e. liquid crystals) at the oil-aqueous interface can be easily determined by the use of polarized light microscopy (35). 

The mesophase microstructure was examined using polarized light microscopy. It was found that organic sulfur compounds have less effect on mesophase microstructure than elemental sulfur but some organometallic compounds greatly inhibit mesophase formation. 

Figure 13.4. SEM images (left column) and polarized light microscopy (PLM) images (right column) of BSUA solids formatted under different conditions.

Menyhard et al. [9] reported the generation of polymer blends based on the P-modification of polypropylene. The authors studied the melting and crystallization characteristics as well as the structure and polymorphic composition of the blends by polarized light microscopy (PLM) and differential scaiming calorimetry (DSC). It was observed that the most important factor of the formation of the blend with P-crystalline phase when semicrystalline polymers were added to isotactic polypropylene (iPP) was the a-nucleation... 

Fig. 4 Structure and properties of nanocellulose, (a) Hierarchical assembly of cellulose molecules into cellulosic fibers. Adapted, with permission, from [131]. Copyright 2012 Elsevier, (b) Proposed mechanism of formation of CNF cross-linked with metal cations. Reproduced, with permission, from [132]. Copyright 2013 American Chtanical Society, (c) Effect of the type of metal cation on the frequency-dependent storage modulus of CNF hydrogels, probed by dynamic frequency sweeps (25 °C) at a strain rate of 0.5 %. Adapted, with permission, from [132]. Copyright 2013 American Chemical Society, (d) Polarization optical microscopy photograph of a biphasic 8.78 % (w/w) CNC suspension. Adapted, with permission, from [133]. Copyright 1996 American Chemical Society, (e) Polarization optical microscopy photograph of a CNC suspension. Scale bar. 200 pm. Reproduced, with permission, from [134]. Copyright 2000 Amaiean Chemical Society...

It has been shown that CNTs seed the formation of oriented domains in a liquid crystalline polymer [82]. Using polarized light microscopy it was observed that the molecular alignment in large domains was homogeneous and controlled by the direction of the nanombes nucleus. CNT films have been generated by deposition... 

Cubic phases (Cub) are mesophases of cubic symmetry (Diele, 2002). Because of their high symmetry, their physical properties are no Imiger anisotropic. No defect texture is observed by polarizing optical microscopy (POM vide infra) and the image between crossed polarizers remains black. The cubic mesophases are very viscous and often their formation kinetics is very slow. Although cubic mesophases are very common for lyotropic LCs, where a cubic phase is possible between any pair of phases, there are only relatively few examples of cubic mesophases in thermotropic LCs. Whereas a cubic mesophase can be relatively easily detected when it is present between two anisotmpic mesophases, it is difficult to observe the formation of the cubic phase when it is formed by cooling an isotropic liquid. In this case, a deformatirMi of air bubbles in the melt is observed, as well as a sharp increase in the viscosity of the liquid. 

Another property of semi-flexible polymer chains is the formation of nematic phases in concentrated solution. According to the theories of On-sager [73] and Flory [74], polymer chains with Zp/dh > 6 should form a liquid crystalline phase above a critical concentration. We were able to show the presence of such a liquid crystalline phase by polarized optical microscopy for PS-PCEMA nanofibers dissolved in bromoform at concentrations above 25 wt. % [75] Furthermore, we observed that these hquid crystalline phases disappeared when these solutions were heated to a temperature above a well-defined liquid-crystalline-to-disorder transition temperature, Tij. Such observations suggest nanofibers have concentrated solution properties similar to those of semi-flexible polymers. 

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