Associations defects/textures

Plate 1. The defect texture of the TGBA phase, under crossed polars, formed on coohng from the isotropic hquid (xlOO). The textures show both platelets and Grandjean planar regions (associated with a helical macrostructure)... 

In addition to positive aspects, numerous flavor and textural defects may be associated with the fat phase of ice cream. Such flavor defects are usually related to either autoxidation of the fat, resulting in oxidized flavors (cardboardy, painty, metallic) or, especially in the case of milk-fat, lipolysis of free fatty acids from triglycerides by the action of lipases (referred to as hydrolytic rancidity). A significant content of free butyric acid gives rise to very undesirable rancid flavors. These defects tend to be present in the raw ingredients used in ice cream manufacture, rather than promoted by the ice cream manufacturing process itself. However, processing... 

Materials science associated with fracture mechanics has mainly been confined to composite materials such as concrete, ceramics and metals. Much of the emphasis of the research has been on preventing fatigue and failure rather than designing for it to occur. The way a structure deforms and breaks under stress is crucial for properties such as flow and fracture behaviour, sensory perception of structure, water release and the mobility and release of active compounds. In the case of foods, the ability to break down and interact with the mouth surfaces provides texture and taste attributes. The crack propagation in a complex supramolecular structure is highly dependent on the continuous matrix, interfacial properties and defects and the heterogeneity of the structure. Previous structure-fracture work has dealt with cellular plant foods, and it has been demonstrated that the fracture path differs between fresh and boiled carrots due to cellular adhesion and cell wall strength as well as cell wall porosity and fluid transport (Thiel and Donald 1998 Stoke and Donald 2000 Lillford 2000). 

Recently Ribeiro et al. [65] reported on the synthesis and characterization of a variety of tolanes that had optically active sulfinate groups. Some of these compounds, see 23, were found to possess a phase that exhibited oily-streak textures typical of chiral nematic phases and also defect pattern associated with columnar phases (the earlier photomicrograph Plate 6 for 14P1M7 is similar). 

Distinct improvement of MC in toughness was accomplished by employing the block copolymers. The typical examples are the blends of PPTA-b-nylon 6, 66/nylon 6, 66 [18] and PPTA-b-butadiene rubber (BDR)/ABS resin [19]. In the latter case, only 2.5 wt % of PPTA in MC improved the energy-to-fracture by a factor of four in comparison with that of unmodified ABS resin, while the blend employing homopolymer of PPTA was brittle. Thus, the block copolymerization of PPTA with flexible matrix polymer blocks has advantages of the removal of defects associated with heterogeneous texture in MC and the increase in the degree of dispersion of PPTA block in MC. 

LCs and LCPs exhibit similar textures, although there are differences between them. Normally, the texture of an LCP is not as distinct as that of an LC because of the higher molecular weight and defect density normally associated with polymers. 

The SmC analog nature of the lyotropic phase was demonstrated by the observation of characteristic textures associated with the thermotropic SmC phase, such as broken fan-shaped texture, schlieren texture, zigzag defects, spontaneous tilt domains in the surface-stabilized state and pitch lines. Further evidence was provided by X-ray experiments. The two-dimensional dififaction pattern of an aligned sample confirms that the phase is lamellar, tilted and fluid. 

In the fibers produced from lyotropic spinning dopes, there still appear to be limitations on the ultimate physical properties due to higher-order morphological defects (the periodic director-orientation distortions alluded to earlier) [115]. In this context, much experimental and theoretical work remains to be done to delineate those parameters that control disclination textures and director patterns created by complex shear fields encountered in processing LCPs. As is typically the case, there are natural systems wherein these difficulties appear to have been optimally minimized spiders spin nearly defect-free fibers from a mesomorphic form of silk [116]. Consequently, efforts to analyze the spinning process - the spinner draw-down geometry and its associated shear field - used by arachnids are under way. 

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