Self-assembled Monolayers as Tailored Functional Surfaces in Two and Three Dimensions

Self-assembled Monolayers as Tailored Functional Surfaces in Two and Three Dimensions 

Specific, surface confined reactions not only directly involve catalysis but also the built-up of sdf-assembled multilayers (see Fig. 9.1 (3)) with co-functionalities for more complex (bio-) catalytic systems such as proteins or the directed deposition of active metals. Furthermore, SAM on flat substrates can be used for the study and development of e.g. catalytic systems, but are not useful for large scale applications because they have very limited specific surface. Here, nanoparticle systems covered with 3D-SAMs are the ideal solution of combining the advantages of high surface area, defined surface composition and accessibility of proximal active catalytic centers. 

Auer et al. [134] presented an example for multilayer formation and controlled deposition of functionalized nanoparticles on SAM of mercaptohexadecanoic acid (MHA) using electrostatic interactions. As a pH-sensitive switchable linker between the SAM of MHA and negatively charged gold nanoparticles, bis-benzami-dine bolaamphiphiles having different alkyl spacers were used [135]. This strategy resulted in a potentially tunable and switchable property of the entire assembly. For example, the kinetics of adsorption as well as the final particle layer thickness can be controlled by the kind of bis-benzamidine used as the linker (Fig. 9.16). 

Nanoparticles bearing a so-called three-dimensional self-assembled monolayer (3D-SAM) [136] coating or shell are ideal construction units for programmed, hierarchical self-assembly of larger objects [137]. Several research groups have successfully assembled functionalized nanoparticles into large nanocrystalline arrays 

The preparation and study of nanoparticles has attracted a remarkable academic and industrial research effort because of their potential applications, ranging from fundamental studies in quantum physics, fabrication of composite materials, information storage/optoelectronics, immunoassays, to catalysts. The precise control of size and chemical behavior (stabihty and reactivity) by means of the synthesis itself is still one of the main targets because the direct correlation of the new intriguing properties with the particle size which is just between a molecule and a bulk material [140]. 

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