Poly crystalline aggregates

Solvothermal growth of single crystals or poly crystalline aggregates from hydro-thermal or ammonothermal solution. 

Another candidate for a useful material from very high pressure synthesis is the gem material, jadeite (NaAlSi206). The natural material of Imperial quality can cost as much as 2000 per carat. Jadeite can be synthesized at about 30 kb and above in equipment similar to that used for diamond growth, and it has been made into pieces of jewelry. Since jadeite is used as a poly-crystalline aggregate, synthesis is essentially hot pressing and sintering, much simpler than if single crystals were needed. However, it does not appear to be a commercial product in competition with the natural supply. 

Figure 17. Variations of bulk properties derived from variations of the individual elastic constants of stishovite. (a) Bulk modulus (K) and shear modulus (G). Solid lines are the average of Reuss and Voigt limits the latter are shown as dotted lines (Voigt limit > Reuss limit), (b) Velocities of P (top) and S (lower) waves through a poly crystalline aggregate of stishovite. Circles indicate experimental values obtained by Li et al. (1996) at room pressure and 3GPa. After Carpenter et al. (2000a).

The use of ordered supramolecular assemblies, such as micelles, monolayers, vesicles, inverted micelles, and lyotropic liquid crystalline systems, allows for the controlled nucleation of inorganic materials on molecular templates with well-defined structure and surface chemistry. Poly(propyleneimine) dendrimers modified with long aliphatic chains are a new class of amphiphiles which display a variety of aggregation states due to their conformational flexibility [38]. In the presence of octadecylamine, poly(propyleneimine) dendrimers modified with long alkyl chains self-assemble to form remarkably rigid and well-defined aggregates. When the aggregate dispersion was injected into a supersaturated... 

M. Grell, D.D.C. Bradley, X. Long, T. Chamberlain, M. Inbasekaran, E.P. Woo, and M. Soliman, Chain geometry, solution aggregation and enhanced dichroism in the liquid-crystalline conjugated polymer poly(9,9-dioctylfluorene), Acta Polym., 49 439-444, 1998. 

For a crystalline polymer, the melting temperature (Tm) may be observed for both the cyclic and the backbone in some cases. Poly(alkylene sebacate crown ether rotaxane)s 60 have two Tm values, those of the cyclic and the backbone [19, 111]. The crystallization of the crown ether on the backbone was attributed to aggregation enabled by the mobility of the crown ether along the backbone in solution or melt states. The crystallization process is driven by the tendency for these immiscible components to form their own separate phases to minimize interfacial energy. According to an X-ray diffraction study of polystyrene rotaxane)s 26... 

It must be concluded from the results that reactions take place which change the number of active sites present, due to the different behavior of the polymers in solution. With polyethylene, crystalline insoluble globules cause break-up of the catalyst aggregates, and even crystal scission with poly( 1-butene) the chains are highly solubilized. 

Lyotropic liquid crystalline properties were observed for poly (arylamide) monodendrons derived from 1,3,5-substituted amino acid chloride hydrochlorides according to Kim [168]. These systems aggregate readily to form high molecular weight species in the absence of complexing ions. Amide solvents containing more than 40 wt.% of the dendrons exhibit nematic phase liquid crystalline texture under a polarizing microscope, whereas, 60 wt.% solutions produce a hard gel under static conditions. 

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