Crystalline microstructure

Given these conditions, the final crystalline microstructure is essentially the same as that produced from the bulk process. 

Understanding the factors that govern the formation of mesogens will assist in determining the processing conditions for the production of materials with specified amounts, sizes, and distribution of such crystalline microstructures. Mesophases can be local or permeate the entire structure. They can be large or small, and present in a random or more ordered arrangement. 

There are three key variables in the design of a glass-ceramic the glass composition, the glass-ceramic phase assemblage, and the nature of the crystalline microstructure. 

Finally, the nature of the crystalline microstructure, ie, crystal size and morphology and the textural relationship among the crystals and glass, is the key to many mechanical and optical properties, including transparency/opacity, strength and fracture toughness, and machinability. These microstructures can be quite complex and often are distinct from conventional ceramic microstructures (6). 

From the snap, gloss and texture of chocolate to the shelf life of frozen foods, crystalline microstructure plays a very important role in the texture, appearance, shelf life and overall quality of many foods. The total amount of crystaUine phase in a food, as well as the size distribution and shape of the crystals within the food, can affect the physical properties of the product. Furthermore, some mataials in food can crystallize in different polymorphic forms so that control of polymorphic transformations may also be necessary. 

Depending on conditions during processing and storage, a crystalline microstructure develops in many foods that can significantly impact food propaties. Some important characteristics of the crystalline dispersion include the crystalline phase volume, mean size and size distribution of crystals, shape and surface characteristics of the particles, polymorphic characteristics, and any network structure that forms between... 

In some foods, the crystalline microstructure forms networks between individual crystals. These network structures may also interact with other elements of the food matrix, including emulsion droplets and air cells. The nature and strength of these... 

The next area of future development is microstructure analysis. Although numerous attempts have been made to connect crystal stmcture to food texture, a long road still remains ahead before it can be said that a certain type of stmcture leads definitively to certain mechanical properties. Development of methodologies for structure analysis and further developments in analytical modeling of crystalline microstructure are needed. Further, the connection between these microstructural models and food properties related to the crystalline microstructure are important. 

Finally, the crystalline microstructure in many foods is not the only microstructural element of interest. Often crystal dispersions are found alongside other structures, such as air cells, fat globules, protein micelles, liquid crystals, and others. The interactions among these structural elements will be the focus of future studies in complex foods. 

Looking at the structure of these crack tip plastic zones in more detail, it is found that the individual crazes are less straight compared to the low temperature crazes (Fig. 21). This indicates a more pronounced influence of the crystalline microstructure on craze formation. Figure 21a and b demonstrate for fine spherulitic, highly isotactic PP the interaction between the crazes and the microstructural features. Most of the... 

Proper control of the crystalline microstructure leads to products with the desired textural properties and physical characteristics. For example, tempering of chocolate prior to molding or enrobing is designed to control crystallization of the cocoa butter into a large number of very small crystals that are aU in the desired polymorphic form. When controlled properly, the cocoa butter crystals in chocolate contribute to the desired appearance (shine or gloss), snap, flavor release, meltdown rate upon consumption, and stability during shelf life (fat bloom). Similar... 

To truly control crystallization to give the desired crystalline microstructure requires an advanced knowledge of both the equilibrium phase behavior and the kinetics of nucleation and growth. The phase behavior of the particular mixture of TAG in a lipid system controls both the driving force for crystallization and the ultimate phase volume (solid fat content) of the solidified fat. The crystallization kinetics determines the number, size, polymorph, and shape of crystals that are formed as well as the network interactions among the various crystalline elements. There are numerous factors that influence both the phase behavior and the crystallization kinetics, and the effects of these parameters must be understood to control lipid crystallization. 

In the case of semi-crystalline PET, comparing the TEM photographs and the measured spherulite sizes, it can be assumed that the individual reactive particles should be distributed in within the spherulitic structure. Concerning the non-reactive one it is highly probable, knowing the small size of the semi-crystalline microstructure, that the modifier clusters remain outside the spherulites. 

Finally, crystalline microstructure of PET is not significantly modified by the blending if one except a small nucleating effect of the non-reactive additive that can be observed in laboratory conditions. However, this nucleating effect is not due to the nodule itself [20] as no transcrystallisation can be observed on particles. Additionally, this nucleating effect does not lead to significant evolution in mean spherulite diameter in injection moulded parts. 

Although the so-called a-phase of the fatty alcohols—a thermotropic type smectic B liquid crystal with hexagonal arrangement of molecules within the double layers—is initially formed from the melt during the manufacturing process, it normally transforms into a crystalline modification as it cools. However, the crystallization of the gel matrix can be avoided if the ot-phase can be kept stable as it cools to room temperature. This can be achieved by combining appropriate surfactants such as myristyl or lauryl alcohol and cholesterol, a mixture of which forms a lamellar liquid crystal at room temperature. Due to depression of the melting point, the phase transition temperature of crystalline to liquid crystalline as well as liquid crystalline to isotropic decreases. Therefore, a liquid crystalline microstructure is obtained at room temperature. 

The green material from both sides must contain malachite. The XRD results of the sample from side B are verified by the characteristic nodular outer structure and the slender, almost needlelike prism crystalline microstructure (11) that both malachite and the green nodule exhibit (Figure 2). Although restricted from forming a nodular outer structure by the physical shape of the silk filament, the inner micro-... 

Rheinberg differential color contrast (22.231. in which the normal and oblique illuminating rays have different colors. Fine detail in the image of the specimen appears with a color different to that of the coarse detail. This technique maximizes illumination, and is useful when attempting to highlight disclinations without loss of intermediate detail. It appears to be a novel technique in the context of liquid crystalline microstructures. 

Emulsifiers stabilize emulsions in various ways. They reduce interfacial tension and may form an interfacial film that prevents coalescence of droplets. In addition, ionic emulsifiers provide charged groups on the surface of the emulsion droplets and thus increase repulsive forces between droplets. Emulsifiers can also form liquid crystalline microstructures such as micelles at the interface of emulsion droplets. These are formed only at emulsifier concentrations larger than the critical micelle-forming concentration. These microstructures have a stabilizing effect. 

On the computation of crystalline microstructure by Mitchell Luskin, Acta Numerica, pg. 191, Cambridge University lYess, Cambridge England, 1996. Luskin s article covers many similar issues to those found in the article of... 

Luskin M., On the Computation of Crystalline Microstructure, Acta Numerica, 191 (1996). 

Crystallization from an oriented melt may occur during extrusion and injection molding processes of crystallizable polymers. The crystalline microstructure which results is... 

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