Self-Assembled Functional Materials

Having discussed self-assembly strategies toward noncovalently functionalized side chain supramolecular polymers as well as studies toward the orthogonahty of using multiple noncovalent interactions in the same system, this section presents some of the potential applications of these systems as reported in the literature. The apphcations based on these systems can be broadly classified into two areas 1) self-assembled functional materials and 2) functionalized reversible network formation. 

Network Formation Using Side Chain Supramolecular Polymers 

Self-Associative Polymer Network. In self-associative polymer networks (often called one component systems), the hydrogen bonding recognition units that are covalently attached to the polymer backbone have an appreciable tendency for self-association, that is, self-dimerize, which leads to interchain cross-linking of the polymers. As a result, the system is inherently cross-linked and does not require any external cross-linking agents for network formation (Fig. 5.11a). Because the cross-linking is based on dimerization phenomena, to achieve effective 

The network strength of these systems can also be altered by varying the stability of the hydrogen bonded complex formation between the cross-linking agent and the 

They demonstrated that the linker length influenced the median diameter of the spherical aggregate that was formed, resulting in good control over the aggregate dimension. 

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Woolfson and Mahmoud have classified the routes to preparation of decorated self-assembling peptide materials [53] as (1) co-assembly, where the functional part is already attached to a self-assembling component prior to assembly, and (2) postassembly, where a non-functionahsed self-assembled structure is modified by covalent or non-covalent means. This discussion adheres to this classification. A third route, beyond the scope of this review, is the use of structured peptides as templates for inorganic materials. Section 4.1 discusses functionalised self-assemblies formed from co-assembly-type approaches, while post-assembly modifications of self-assembled structures are considered in Sect. 4.2. 

Although much of the interest in biological nanostructures has focused on relatively complex functionality, cells and organisms themselves can be considered as a collection of self-assembled materials lipid bilayers, the extracellular matrix, tendon and connective tissue, skin, spider silk, cotton fiber, wood, and bone are all self-assembled biological materials, with an internal structure hierarchically ordered from the molecular to the macroscopic scale. 

I. Honma and H.S. Zhou, Self-assembling Functional Molecules in Mesoporous Silicate Materials Optical Properties and Mesophase of Dye-doped M41S. Adv. Mater., 1998, 10, 1532-1536. 

De Luca, G., Romeo, A., Villari, V., Micali, N., Foltran, L, Foresti, E., Lesci, I.G., Roveri, N., Zuccheri, T. Scolaro, L.M. (2009) Self-organizing functional materials via ionic self assembly Porphyrins h- and j-aggregates on synthetic chrysotile nanotubes. Journal of the American Chemical Society, 131, 6920-6921. 

Bernhard Rieger obtained his PhD in chemistry at the Ludwig-Maximilians-Universitat, Munich in 1988. After a postdoctoral research at the University of Massachusetts in Amherst, Department of Polymer Science and Engineering from 1988 till 1989, he joined the BASF Company for research about metallocene polymerizations, from 1989 till 1991. After his habilitation from 1991 till 1995 at the Eberhard-Karls-University in Tubingen, he was a Professor at the University of Ulm from 1995 on, as well as Head of the Department of Materials and Catal) until 2006. Since thea he has been head ofthe WACKER Chair of Macromolecular Science at the Technische Universitat Miinchen. His main research interests are homogeneous polymerization catalysis, where numerous publications concern the alkene/CO copolymerizatioa as well as silicon-containing polymers and self-assembled functional surface structures. 

A second class of monolayers based on van der Waal s interactions within the monolayer and chemisorption (in contrast with physisorption in the case of LB films) on a soHd substrate are self-assembled monolayers (SAMs). SAMs are well-ordered layers, one molecule thick, that form spontaneously by the reaction of molecules, typically substituted-alkyl chains, with the surface of soHd materials (193—195). A wide variety of SAM-based supramolecular stmctures have been generated and used as functional components of materials systems in a wide range of technological appHcations ranging from nanoHthography (196,197) to chemical sensing (198—201). 

Functional supramolecular materials, formation by self-assembly of phthalocyanins and porphyrazines 96CC2385. 

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. 

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