Colloidal assemblies, applications

Landfester, K. Antonietti, M. Miniemulsions for the convenient synthesis of organic and inorganic nanoparticles and single molecule applications in materials chemistry. Colloids Colloid. Assembl., 175-215 (2004). 

In THE PAST DECADE, IMPROVEMENTS IN infrared spectroscopic instrumentation have contributed to significant advances in the traditional analytical applications of the technique. Progress in the application of Fourier transform infrared spectroscopy to physiochemical studies of colloidal assemblies and interfaces has been more uneven, however. While much Fourier transform infrared spectroscopic work has been generated about the structure of lipid bilayers and vesicles, considerably less is available on the subjects of micelles, liquid crystals, or other structures adopted by synthetic surfactants in water. In the area of interfacial chemistry, much of the infrared spectroscopic work, both on the adsorption of polymers or proteins and on the adsorption of surfactants forming so called "self-assembled" mono- and multilayers, has transpired only in the last five years or so. 

Shipway, A. N., Katz. E. and Willner, I. (2000) Nanoparticles Arrays on Surface for Eelectronic, Optical, and Sensor Applications. Chem. Phys. Chem., 1,18-52. Liz-Marzan, L. M. (2003) Colloids and Colloid Assemblies, ed. Caruso, E, Wiley, Weinheim, ch. 7,216-45. 

The last section provides a concise overview on current and potential application possibilities of block or graft copolymer colloidal assemblies as nanoreservoirs in, among others, controlled drug delivery and gene therapy. 

The variety of strategies available to assemble colloidal polymer particles and the manifold applications of particle assemblies has lead to the design of a large range of setups to fabricate colloidal polymer patterns. The fabrication setups can be divided into two main groups setups to produce bulk colloidal assemblies and setups to deposit thin two-dimensional (2D) arrays of particles. 

The foregoing results demonstrate that the thickness of the capsule wall can be controlled at the nanometer level by varying the number of deposition cycles, while the shell size and shape are predetermined by the dimensions of the templating colloid employed. This approach has recently been used to produce hollow iron oxide, magnetic, and heterocomposite capsules [108], The fabrication of these and related capsules is expected to open up new areas of applications, particularly since the technology of self-assembly and colloidal templating allows unprecedented control over the geometry, size, diameter, wall thickness, and composition of the hollow capsules. This provides a means to tailor then-properties to meet the criteria of certain applications. 

The reviews collected in this book convey some of the themes recurrent in nano-colloid science self-assembly, constraction of supramolecular architecture, nanoconfmement and compartmentalization, measurement and control of interfacial forces, novel synthetic materials, and computer simulation. They also reveal the interaction of a spectrum of disciplines in which physics, chemistry, biology, and materials science intersect. Not only is the vast range of industrial and technological applications depicted, but it is also shown how this new way of thinking has generated exciting developments in fundamental science. Some of the chapters also skirt the frontiers, where there are still unanswered questions. 

There are very many papers in the literature that address some aspect of gold nanospheres. In particular, their plasmon response (see Section 7.3.1.1) has been well studied, as has their agglomeration [50-52] and the manner in which they can be assembled into highly ordered colloidal crystals [50, 53, 54]. The latter are interesting and will be further discussed in Section 7.3.8.2. Conjugation of gold nanospheres with proteins and antibodies, for use as a stain in microscopy [55] or possibly, in medical applications [23], is another rich field. 

The benefit of the LbL technique is that the properties of the assemblies, such as thickness, composition, and function, can be tuned by varying the layer number, the species deposited, and the assembly conditions. Further, this technique can be readily transferred from planar substrates (e.g., silicon and quartz slides) [53,54] to three-dimensional substrates with various morphologies and structures, such as colloids [55] and biological cells [56]. Application of the LbL technique to colloids provides a simple and effective method to prepare core-shell particles, and hollow capsules, after removal of the sacrificial core template particles. The properties of the capsules prepared by the LbL procedure, such as diameter, shell thickness and permeability, can be readily adjusted through selection of the core size, the layer number, and the nature of the species deposited [57]. Such capsules are ideal candidates for applications in the areas of drug delivery, sensing, and catalysis [48-51,57]. 

Finally, we have designed and synthesized a series of block copolymer surfactants for C02 applications. It was anticipated that these materials would self-assemble in a C02 continuous phase to form micelles with a C02-phobic core and a C02-philic corona. For example, fluorocarbon-hydrocarbon block copolymers of PFOA and PS were synthesized utilizing controlled free radical methods [104]. Small angle neutron scattering studies have demonstrated that block copolymers of this type do indeed self-assemble in solution to form multimolecular micelles [117]. Figure 5 depicts a schematic representation of the micelles formed by these amphiphilic diblock copolymers in C02. Another block copolymer which has proven useful in the stabilization of colloidal particles is the siloxane based stabilizer PS-fr-PDMS [118,119]. Chemical... 

A number of diblock copolymers of NIPAM and hydrophobic comonomers have been prepared by various groups and assessed in terms of micellar structure, thermosensitivity, and applications. For example, PS-fo-PNIPAM was shown to form either micelles consisting of a PS core and a PNIPAM corona, or vesicles. The assemblies were colloidally stable at elevated temperature [262-266]. 

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