Molecular Self-Assembling

Templates or SDAs formed by a single molecule or ion can be used in hydro-thermal methods to shape the final products. An assembly of molecules can also act as a template to direct the formation of new materials. The well-known silica MCM-41, with a unidimensional structure of hexagonal pores, is a good example. A surfectant (e.g., NR4 cations) is used as SDA, TEOS or a similar compound as a silicon source, and water as a solvent a catalyst (acid or basic) is also added. At concentrations above the critical micellar concentration, the surfactant molecules are ordered in micelles (layers, spheres, cylinders, etc.), where the molecules are weakly bonded by van der Waals or hydrogen bonds. Supramicel-lar interactions lead to a liquid crystal (LC) structure, on whose walls the inorganic species are formed, oligomerized, and finally polymerized [44]. 

Formation of the LC structure has been discarded by Davis and coworkers [45], who claimed that siUcate species form a few layers of silica on the surface of the randomly oriented cylindrical micelles condensation of the particles thus formed leads to the characteristic hexagonal structure of MCM-41. 

Other Methods Starting from Liquid Reactants or Solutions 

Preparation of Ti02 has been taken as an example in all cases [46]. 

Ionic liquids have been used to prepare piu-e anatase by mixing [BMIM] [PF5] and tetra-M-butyl titanate [47] addition of water and stirring at 80 °C produced nanoparticles of anatase with a size close to 5 run. 

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The types of molecules synthesized by biotechnological techniques are restricted to those biomolecules whose stmctures can be encoded in the DNA of organisms capable of translating them into functional nanomaterials. Other types of molecules and nanomaterials can be synthesized by chemical synthetic approaches, such as covalent syntheses and molecular self-assembly of molecular units. 

Since multiple electrical and optical functionality must be combined in the fabrication of an OLED, many workers have turned to the techniques of molecular self-assembly in order to optimize the microstructure of the materials used. In turn, such approaches necessitate the incorporation of additional chemical functionality into the molecules. For example, the successive dipping of a substrate into solutions of polyanion and polycation leads to the deposition of poly-ionic bilayers [59, 60]. Since the precursor form of PPV is cationic, this is a very appealing way to tailor its properties. Anionic polymers that have been studied include sulfonatcd polystyrene [59] and sulfonatcd polyanilinc 159, 60]. Thermal conversion of the precursor PPV then results in an electroluminescent blended polymer film. 

Fabricating and repairing complex materials systems. Mechanical methods currently in use (e g., riveting of metals) cannot be applied reliably to the composite materials of the future. Chemical methods (e g., adhesion and molecular self-assembly) will come to the fore. 

The work reviewed here demonstrates the tremendous versatility, promise and importance of peptides as building blocks in molecular self-assembly. However, in order to fully harness their potential in nanotechnology, more systematic work... 

Zhang SG (2002) Emerging biological materials through molecular self-assembly. Biotechnol Adv 20 321-339... 

The phase transition boundaries (phase envelope) of adamantane need to be investigated and constmcted. Predictable and diverse geometries are important features for molecular self-assembly and pharmacophore-based dmg design. Incorporation of higher diamondoids in solid-state systems and polymers should provide high-temperature stability, a property already found in polymers synthesized from lower diamondoids. 

Whitesides, G. M., Mathias, J. P. and Seto, C. T. (1991) Molecular self-assembly and nanochemistry a chemical strategy for the synthesis of nanostructures. Science, 254, 1312-1319. 

Nuzzo RG, Zegarski BR, Dubois LH (1987) Fundamental studies of the chemisorption of organosulfur compounds on Au(lll). Implications for molecular self-assembly on gold surfaces. J Am Chem Soc 109 733-740... 

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