Colloidal templating

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. 

Increasingly chemists are contributing to the synthesis of advanced materials with enhanced or novel properties by using colloidal assemblies as templates. Colloid chemistry is particularly well suited to this objective since nanoparticles, by definition, are colloidal and since processing of advanced materials involve reactions at solid-solid, solid-liquid or solid-gas interfaces (3-5). 

Wang, D., and Caruso, R, Lithium niobate inverse opals prepared by templating colloidal crystals of polyelectrolyte-coated spheres, Adv. Mater., 15, 205, 2003. 

Moreover, the isolation of self-assembled LiNbOj powders using this route has added credibility to the methodology they were otherwise prepared by templating colloidal crystals of polyelectrolyte-coated spheres. The interest in LiNb03 inverse opals stems from the fact that they have a constant refractive index, but a spatially periodic second-order nonlinear susceptibility. Such nonlinear periodic structures allow for efficient qnasi-phase-matched second-order harmonic generation, which conld find applications where simultaneous conversion of multiple wavelengths is reqnired. Thns, in this chapter we will focus our... 

A.N., Zancanela, D.C., Simao, A.M.S., Ciancaglini, P., and Ramos, A.P. (2014) Formation of carbonated hydroxyapatite films on metallic surfaces using dihex-adecyl phosphate-LB films as template. Colloids Surf, B Biointerfaces, 118, 31-40. 

Codeposition, which represents the concurrent processes of colloidal crystal template formation and simultaneous filling of the interstitial sites with the desired framework material, is usually achieved by the deposition of a mixture of the templating colloids with the matrix material precursor (for example, a sol-gel precursor or nanoparticles). For this purpose, a dispersion of large particles, which will constitute the template, is mixed with nanoparticles of the framework material, which have to be small enough to easily fit into the interstitial space without interfering with crystal formation. By this method porous silica [25,32,35] and titania [32] were fabricated. 

Y. Zhao, M. Chen, T. Xu, and W. Liu, Electrochemical synthesis and electrochemical behavior of highly ordered polyaniUne nanofibrils through AAO templates. Colloids Surf. A, 257-258, 363 368 (2005). 

Kumar A, Kumar V Self-assemblies from RNA-templated colloidal CdS nanostructures. J Phys Chem C 2008, 112(10) 3633—3640. 

Zhao, M. Zheng, L. Bai, X. Li, N. Yu, L. (2009). Fabrication of silica nanoparticles and hollow spheres using ionic liquid microemulsion droplets as templates. Colloids and Surfaces A Physicochemical and Engineering Aspects 346(1-3), 229-236. 

Having succeeded in coating colloids, there is an obvious next step to template colloids by dissolving the core and thus obtaining hollow capsules. This route is discussed in the following, including the interesting properties and possible applications of these capsules. 

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