Morphological Control

In some cases it may be advantageous to deviate from the classical technology. For example, in wet-chemical preparation better chemical and morphological control may be achieved by starting from salt solutions. 

A weU-known feature of olefin polymerisation with Ziegler-Natta catalysts is the repHcation phenomenon ia which the growing polymer particle mimics the shape of the catalyst (101). This phenomenon allows morphological control of the polymer particle, particularly sise, shape, sise distribution, and compactness, which greatiy influences the polymerisation processes (102). In one example, the polymer particle has the same spherical shape as the catalyst particle, but with a diameter approximately 40 times larger (96). 

The use of interpenetrating donor-acceptor heterojunctions, such as PPVs/C60 composites, polymer/CdS composites, and interpenetrating polymer networks, substantially improves photoconductivity, and thus the quantum efficiency, of polymer-based photo-voltaics. In these devices, an exciton is photogenerated in the active material, diffuses toward the donor-acceptor interface, and dissociates via charge transfer across the interface. The internal electric field set up by the difference between the electrode energy levels, along with the donor-acceptor morphology, controls the quantum efficiency of the PV cell (Fig. 51). 

Yoshimura M, Suchanek W (1997) In situ fabrication of morphology-controlled advanced ceramic materials by Soft Solution Processing. Solid State Ionics 98 197-208 Yu S-H, Yoshimura M (2002) Feriite/metal composites fabricated by soft solution processing. Adv Funct Mater 12 9-15... 

Synthesis of Morphologically Controlled Pt Nanoparticles and Their Application in Catalytic... 

The synthesis of Pt nanocrystals with controlled morphology must have interesting applications in practice, since the catalytic activity for structure-sensitive reactions depends on the orientation of the crystalline facets. Using the obtained morphologically controlled Pt nanoparticles, Pt/Al203 catalysts were prepared and applied for a structure-sensitive reaction, i.e., NO reduction by CH4. 

Figure 8. Comparison between catalytic properties of Pt(poly-crystalline)/Al203 (Engelhard) and Pt(l 00)/Al203 (morphologically controlled Pt nanoparticles) the NO/CH4 reaction conversion (X) and yield (Y), and the reaction products at 500 °C.

By using thermosensitive poly-acrylamides, it is possible to prepare cubic Pt nanocrystals (with predominant (1 0 0) facets) and tetrahedral Pt nanocrystals (rich in (111) facets). These Pt nanocrystals can be supported on oxide (alumina) and used as a catalyst in structure-sensitive reaction, NO reduction by CH4. The results proved that morphologically controlled metal nanoparticles supported on adequate support give us a novel tool to connect the worlds of surface science with that of real catalysis. 

The potential of morphologically controlled metal nanoparticles should be expanded by further improvement of their preparation method. It is highly required to develop preparation methods to obtain a better morphological control, i.e., perfect facet control on the particles of optional size. Better morphological control of metal nanoparticles is expected to be achieved in near future and the obtained metal particles will find new exciting applications, not only in catalysis but also in other technically important fields. 

A. Fukuoka, M. Ichikawa, in Y. Waseda, A. Muramatsu (eds.) Morphology Control of Materials and Nanoparticles, Springer, Berlin, 2003, 201. 

Pach L, Duncan S, Roy R, Komameni S (1996) Morphological control of precipitated calcium carbonates and phosphates by colloidal additives. J Mater Sci 31 6565-6569... 

Cao, S.W. and Zhu, Y.J. (2009) Iron oxide hollow spheres microwave-hydrothermal ionic liquid preparation, formation mechanism, crystal phase and morphology control and properties. Acta Materialia, 57 (7), 2154-2165. 

John, G., Jung, J.-H., Minamikawa, H., Yoshida, K. and Shimizu, T. (2002) Morphological control of helical solid bilayers in high-axial-ratio nanostructures... 

In fact, such biomimetic molecules demonstrate the ability to tailor the growth of silica nanoparticles in a way that is very similar to diatom-extracted species. However, they demonstrate the same limitations in terms of morphological control of nanoparticle assembly. This is because the diatom shell architecture results not only from interactions of silica precursors with templating molecules but also benefits from a cell-driven molding of the vesicular compartment where silicification occurs [29]. Thus, it is very likely that diatom-like synthetic silica will only be achieved when such confinement/molding effects are taken into account in the design of biomimetic experiments [30]. 

Eisenberg and coworkers have pioneered the field of micellar morphology control with the so-called crew-cut micelles. Generalities about the structure and preparation of crew-cut micelles have been described in Sects. 2.2,... 

Figure 9.3 Morphology control in the preparation of arborescent copolymers (a) core-shell morphology from short side chains, and (b) star-like morphology from long side chains...

Well-defined Quantum Dots and Morphological Control of Nanomaterials... 

Y. F. Huang, C. W. Lin, Facile synthesis and morphology control of graphene oxide/polyaniline nanocomposites via in-situ polymerization process, Polymer, vol. 53, pp. 2574-2582, 2012. 

Eder, D. and A.H. Windle, Morphology control ofCNT-Ti02 hybrid materials and rutile nanotubes. Journal of Materials Chemistry, 2008.18(17) p. 2036-2043. 

Eder, D. Windle, A.H., Morphology control of CNT-Ti02 hybrid materials and rutile nanotubes. /. Mater. Chem. 2008,18 2036-2043. 

Ding, J. F, Chuy, C. and Holdcroft, S. 2002. Enhanced conductivity in morphologically controlled proton exchange membranes Synthesis of macromonomers by SFRP and their incorporation into graft polymers. Macromolecules 35 1348-1355. 

Bi, Y.P. Lu, G.X. 2008. Morphological controlled synthesis and catalytic activities of gold nanocrystals. Materials Letters, 62, 2696-2699. 

Fukuoka, A. and Ichikawa, M. (2003) Morphology Control of Materials and Nanoparticles Advanced Materials Processing and Characterization (eds Y. Waseda and A. Muramatsu), Springer-Verlag, Heidelberg, pp. 201-18. 

The use of tailor made additives holds great promise in the area of crystal growth and morphology control. The routine selection and use of these type of additives will require a fundamental understanding of the mechanism which the additives work on a molecular basis. At the same time, the effect of solvent molecules on the crystal growth process is another related and important problem. In both instances, the relationship between internal aystal structure, aystal growth rate, solvent and impurities are needed to predict the habit of a crystal and thus allow seleaion of the proper conditions and components required to obtain a desired habit... 

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