Colloidal assembly method

A number of techniques have been used for producing nanoparticles, including vapour phase techniques [72], sol-gel methods [73], sputtering [74], coprecipitation [75] etc. Two main methods can be employed for the preparation of metal nanoparticles coprecipitation and chemical reduction. In both cases, the presence of surfactant is required to govern the growth process. Typically, the coprecipitation reactions involve the thermal decomposition of organometallic precursors [76 ]. The chemical reduction occurring in colloidal assemblies... 

Fig. 12.7 Schematic diagram describing hollow capsule production by exploiting colloidal templating and self-assembly methods [12.8). Explanation see text.

M. A. Hayat. Colloidal Gold Methods and Applications. Academic, San Diego, CA, 1989 C. D. Keating, M. D. Musick, M. H. Keefe, and M. J. Natan. Kinetics and thermodynamics of Au colloid monolayer self-assembly - undergraduate experiments in surface and nanomaterials chemistry. J. Chem. Education, 76 949-955, 1999... 

D arrays of colloidal spheres formation 2 Colloidal lithography 4 Nanostructuration of thin films and surfaces 4 Polymer colloid 1 Self-assembly of nanospheres 1 Supramolecular self-assembly methods 2... 

In contrast to the first approach of utilizing the polymer as the template and growing the nanoparticles in isolated compartments, the second approach to the formation of MNP-polymer assemblies involves synthesizing the MNP prior to its assembly into a composite. This strategy takes advantage of advances in colloidal synthetic methods. 

A number of assembly methods employ self-assembly of nanoparticles at the air-water interface. Monolayers (and subsequent multilayers) can be formed at the interface due particle interaction and transferred to a solid substrate by controlled dip-coating and vertical deposition methods similar to Langmuir-Blodgett film deposition [81-86]. Regular monolayers of polymer colloids can also be assembled via an electrohydrodynamic route, whereby electrophoretically deposited particles between two electrodes can be manipulated to cluster in the presence of an electric field. On application of an AC or DC field, contrary to electrostatic norms, the like-charged particles are observed to coalesce producing large close-packed 2D crystalline domains [87]. 

Monodispersed particles can form close packed assemblies on nanostructured blend surfaces because of van der Waals interactions. The particle assemblies provide roughness to the underlying substrates. Further treatment, such as plasma etching [77] can also be applied to improve the surface roughness of blends. The colloidal particles can vary from polymer blends to inorganic spheres. Colloidal assembly is cost effective, since no expensive lithographic technique is required. This method is easy to master and to apply under laboratory conditions. 

Fabricating 3D colloidal crystals with a PEG lying in the visible range is another option for mimicking natural structural color. Inspired by natural photonic crystals (Figure 7.7), researchers have fabricated colloidal crystals with tunable structural colors [108-110]. One of the most commonly used techniques to fabricate colloidal crystals is the evaporation-induced self-assembly method, which enables... 

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