Non-covalent surface modifications

A number of nanotube surface modification approaches have been reported in the recent years. Non-covalent surface modifications aim to physically wrap polymer chains around the nanotubes or adsorb various surfactant molecules on the surface of nanotubes. Thus,... 

Much research has been eondueted in the past decade in studying surface modifieation of earbon nanotubes. These efforts basically fall into two categories covalent and non-covalent modifieation. Covalent surface modification of the reinforeing material involves a permanent ehange to the material surfaee such that it is functionalized with reaetive groups whieh ean later form a covalent bond with... 

While the previous sections have largely addressed variation of the dendrimer periphery by covalent transfunctionalisation, an alternative concept is based on modification of the dendrimer surface by non-covalent interactions [18]. Selective interactions of guest molecules with dendritic hosts depend upon the nature of both the dendrimer core and the dendrimer shell. 

Figure 3. Functionalization of CNTs (a) non-covalent interacions with polymers and biomolecules (b) covalent surface chemical modification (end-functionalization and side-wall functionalization).

Surface modification of optical fiber can be categorized into two groups (i) physical adsorption (non-covalent bonding), and (ii) covalent bonding. 

While the covalent bonding of polymers on oxide surfaces requires certain reaction conditions adapted for the particular reaction system, for example highly purified non-aqueous solvents or thermally activated surface groups, surface modification with polyelectrolytes can be carried out in aqueous environment [31-46]. Numerous parameters can be adjusted to control the conformation of the polyelectrolyte molecules, e.g. their charge density and the charge density of the metal oxide surface. In other words, the adsorption process and the surface properties of the final product can be influenced in many different ways. This diversity is a challenge for academic research to develop novel hybrid materials for technical applications. 

Hemoproteins are a broad class of redox-proteins that act as cofactors, e.g. cytochrome c, or as biocatalysts, e.g. peroxidases. Direct ET between peroxidases such as horseradish peroxidase, lactoperoxidase," or chloropcroxidasc"" and electrode surfaces, mainly carbonaceous materials, were extensively studied. The mechanistic aspects related with the immobilized peroxidases on electrode surfaces and their utilization in developing biosensor devices were reviewed in detail. The direct electrical contact of peroxidases with electrodes was attributed to the location of the heme site at the exterior of the protein that yields close contact with the electrode surface even though the biocatalyst is randomly deposited on the electrode. For example, it was reported " that non-oriented randomly deposited horseradish peroxidase on a graphite electrode resulted in 40-50% of the adsorbed biocatalyst in an electrically contacted configuration. For other hemoproteins such as cytochrome c it was found that the surface modification of the electrodes with promoter units such as pyridine units induced the binding of the hemoproteins in an orientation that facilitated direct electron transfer. By this method, the promoter sites induce a binding-ET process-desorption mechanism at the modified electrode. Alternatively, the site-specific covalent attachment of hemoproteins such as cytochrome c resulted in the orientation of the protein on the electrode surfaces and direct ET communication. ... 

In this and the following sections we describe the methods which do not need a hydrophilic solvent to retain the catalyst on the surface of the solid support. Utilization of hydrogen bonding for the non-covalent immobilization of Ru and Rh complexes on silica gel was investigated in detail [45-47]. The loading of the support was done without further covalent modification of the silica gel, and there was no need for a solvent film covering the support particles. 

The major drawback of cellulose fibers in the present context resides in their highly polar and hydrophilic character, which make them both poorly compatible with commonly used non-polar matrices, such as polyolefins, and subject to loss of mechanical properties upon atmospheric moisture absorption. That is why they should be submitted to specific surface modifications in order to obtain an efficient hydrophobic barrier and to minimize their interfacial energy with the often nonpolar polymer matrix, and thus generate optimum adhesion. Further improvement of this interfacial strength, which is a basic requirement for the optimized mechanical performance of any composite, is attained by chain entanglement between the matrix macromolecules and the long chains appended to the fiber surface (brushes) or, better still, by the establishment of a continuity of covalent bonds at the interface between the two components of the composite. 

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