Nanoparticles self-assembly process

Biological systems provide numerous examples of self-assembled objects. Owing to the relatively weak interactions involved, a self-assembled structure is much more sensitive and responsive to its environment than a more rigid structure held together by covalent bonds. Unlike processes involving simple surfactants, polymers, and nanoparticles, self-assembly processes in biological systems are usually directional and functional and often lead to the formation of extremely complex structures. For example, the three-dimensional structure adopted by a protein in solution is critical to the protein s function, and this structure is determined by both strong (covalent) and weak... 

Figure 8. TEM images of (a) 6.1 + 0.6 nm Fe36Pt64, (b) 5.8 + 0.7 nm Fe44Pt56, and 5.1+ 0.7 nm Fe49Pt5i nanoparticles formed by a self-assembly process of hexane solution on an amorphous carbon substrate. (Reprinted from Ref [23], 2006, American Chemical Society.)...

Figure 6.9 A schematic representation of orthogonal process for nanoparticles self-assembly (a) a patterned sihcon wafer with Thy-PS and PVMP polymers fabricated through photolithography and (b) orthogonal surface functionahzation through Thy-PS/DP-PS recognition and PVMP/acid-nanoparticle electrostatic interaction. Reprinted with permission from Xu et al. (2006). Copyright 2006 American Chemical Society.

Polymer-mediated self-assembly of nanoparticles provides a versatile and effective approach for the fabrication of new materials. This bottom-up strategy builds up nanocomposite materials from diverse nanosized building blocks by incorporation of molecular-level recognition sites. The flexibility and reversibUity of self-assembly processes imparted by specific molecular interactions facilitates the formation of defect-free superstmctures, and it can be further explored in fields ranging from electronics to molecular biology. 

Photoelectrochemical assemblies consisting of gold nanoparticles and a tris (2,2 -bipyridine)ruthenium(II)-viologen -disulfide derivative ([RuVS]2) were obtained at gold electrodes by virtue of combination of the salting-out effect and self-assembly process [172]. 

One assembly example is polyethylenamine (PEI)-mediated self-assembly of FePt nanoparticles [56]. PEI is an all -NH-based polymer that can replace oleate/oleylamine molecules around FePt nanoparticles and attach to hydrophilic glass or silicon oxide surface through ionic interactions [52], A PEI/FePt assembly is readily fabricated by dipping the substrate alternately into PEI solution and FePt nanoparticle dispersion. Figure 10 shows the assembly process and TEM images of the 4 nm Fes8Pt42 nanoparticle self-assemblies on silicon oxide surfaces. Characterizations of the layered structures with X-ray reflectivity and AFM indicate that PEI-mediated FePt assemblies have controlled thickness and the surfaces of the assemblies are smooth with root mean square roughness less than 2 nm. 

Colloidal zeolites have been used as building blocks to fabricate hierarchical porous materials. Infiltrating ethanol sol of zeolite nanoparticles into an ordered array of polystyrene spheres resulted in macroporous zeolites, which involves a self-assembly process. After ethanol evaporation, zeolite nanoparticles were aggregated by capillary forces. High concentration of external silanol groups favored the formation of hydrogen bonds between particles and eventually Si-O-Si bonds after calcination. The method has been further developed to produce transparent and self-standing zeolite membranes with controlled mesoporosity. Concurrently, the preformed zeolite-coated polystyrene spheres have been... 

Vlckova et al. demonstrated single-molecule SERS in self-assembled dimers of silver nanoparticles [161]. The self-assembly process was driven by nanoparticle functionalization with a bifunctional molecular linker (4,4 -diaminoazobenzene) which forms a molecular bridge between the particles. Molecules forming the molecular bridge are then precisely positioned within the hot spot with the molecular population being controlled by careful optimization of the linker to... 

The self-assembly process in these studies was driven by strongly interacting groups which bind covalently to the metal surface [159]. However, several protocols for the dynamic formation of SERS hot spots using self-assembly have been developed based on DNA hybridization or n-n interactions [159, 163, 164]. As a result, a wide range of options for the controlled aggregation of silver and gold nanoparticles are now available. 

Multiscale ordering of functional colloidal nanoparticles is a powerful technique for the creation of macroscopic devices. This can be performed via selective polymerization, self-assembly processes, or through controlled molecular recognition processes (Fig. 4). Further assembly between NBB is addressed following three main strategies, namely, electrostatic coupling, covalent, or self-assembly-based noncovalent binding. 

A broad view of principal findings and processes utilized for the development of oriented polymer morphologies has been presented. New trends toward the advancement of this topic are being developed within the realm of multidisciplinary research. Studies of order development in polymers have—for a few years already—transcended beyond traditional disciplines in chemistry and engineering. Genetically engineered polymers, nanoparticles, self-assembled molecules, supercritical fluids, and hybrids are some of the few areas that are now an integral part of macromolecular structural property relationship studies. 

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