Templates colloidal ‘opal

Similarly to the codeposition procedure above, the metal can also be delivered as nanoparticles to the colloidal crystal template, but in this case after preparation of the template. This was demonstrated for gold nanoparticles, which were filled into the interstitial sites of a polymer opal by filtering a gold nanoparticle suspension through the preassembled opal with a filter small enough to hold back the nanoparticles [33]. The templating opal was prepared before in very much the same way by filtration of a PS latex suspension. 

In principle, the morphology of macroporous carbon materials is largely dependent on the degree of void infiltration of the opal template. In order to maximise the filling of the interstitial voids of the colloid crystal with carbon precursors, liquid phase carbon precursors such as phenolic resin and sucrose solution are usually used to achieve better replication.1 2 -194] variety of carbon precursors, including propylene gas, benzene and divinylbenzene can also be successfully utilised to make three-dimensional macroporous carbon materials using colloid crystals as hard templates. The... 

The colloidal-crystal-templating approach offers yet another new approach to preparing 3-D macroporous solid materials [6,17]. Spherical colloidal particles of submicrometer size can self-organize themselves into a colloidal crystal, the so-called opal [64], which can be utilized as an endotemplate to fabricate ordered macroporous carbons of two types volume-templated carbon, which is an exact inverse replica of the opal template, and surface-templated carbon, which is formed by coating the colloidal spheres. Zakhidov et al. [64] were the first to use colloidal crystals as templates to prepare highly ordered 3-D macroporous carbon of both types. As schematically illustrated in Figure 2.39, for the volume-templat-ing approach, a carbon precursor is infiltrated into interstitial spaces between colloidal spheres. Carbonization and removal of the opal template leave behind a 3-D periodic carbon structure (i.e., an inverse carbon). With this approach, macroporous carbon structures with a wide range of pore sizes have been produced. 

Inverse Opal Sensors. Colloidal crystals are ordered crystalline structure obtained via the self-assembly of monodispersed colloidal particles. Dried colloidal crystals can be used to template the polymerization of infiltrated monomer precursors. After polymerization, the colloidal template is removed by chemical etching, yielding a bicontinuous polymer/solvent mesostructure, i.e., inverse opal. Because of its periodically ordered structure inherited from the colloidal crystal template, inverse opal also shows structural color as a result of light diffraction. This property has also been used to design optical glucose sensors (Scheme 10.5f). 

Compared with the various templating methods, some advantages associated with the colloidal silica templating method are the commercial availability of colloidal particles of various sizes, and of carbon precursors, such as mesophase pitches, organic monomers, polymers, and phenolic resins. Hence, the colloidal silica and opal templating approach are attractive for the possible large-scale production of nanoporous carbons. 

Figure 6.1 SEM images of (a) colloidal crystal (opal structure) of PMMA spheres and (b and c) 3D0M LaFeOa prepared by the colloidal crystal template method.

DOM materials are prepared using colloidal crystal templates [2-8]. The colloidal crystal (opal structure) templates consist of monodispersed spheres with face-centered closed (fee) packing. When 3D network of voids in colloidal crystals is filled by targeted materials and subsequentiy the colloidal crystals are removed, a replica of the colloidal crystal (inverse opal structure) is produced (Figure 6.2). 

Stein, A., Wilson, B.E., and Rudisill, S.G. (2013) Design and functionality of colloidal-crystal-templated materials - chemical applications of inverse opals. Chem. Soc. Rev., 42, 2763-2803. 

Stein, A., Li, F., and Denny, N.R. (2008) Morphological control in colloidal crystal templating of inverse opals, hierarchical structures, and shaped particles. Chem, Mater., 20, 649-666. 

D. Wang, V. Salgueiriiio-Maceira, L.M. Liz-Maizan, and F. Caniso, Gold-silica inverse opals by colloidal crystal templating, Adv. Mater. 14,908-912 (2002). 

An interesting variation on template deposition is to self-assanble ordered nanostructures (e.g., surfactants) and microstructures (e.g., polystyrene or Si02 beads) on the surface of an electrode and then electrodeposit into the self-assembled pores. The order in the resulting nanostructure is imposed by the self-assembled layer, not by the substrate. Schwartz and coworkers have extended this idea to the use of crystalline protein masks to produce ordered nanostructures of metals (such as Ni, Pt, Pd, and Co) and metal oxides (such as Cu20). Braun and coworkers have used the electrodeposition of materials into self-assembled colloidal crystals or silica or polymer opals. The template is then removed (see Figure 17.11) to produce an inverse opal. This type of templating produces periodic microstructures that can be used to produce functional photonics. Figure 17.11 shows the production of CdSe and Ni inverse opals by electrodeposition into a colloidal crystal with subsequent removal of the colloidal crystal template. ... 

Lytle JC, Stein A (2006) Recent progress in syntheses and applications of inverse opals and related macroporous materials prepared by colloidal crystal templating. Annu Rev Anal... 

The porous membrane templates described above do exhibit three-dimensionality, but with limited interconnectedness between the discrete tubelike structures. Porous structures with more integrated pore—solid architectures can be designed using templates assembled from discrete solid objects or su-pramolecular structures. One class of such structures are three-dimensionally ordered macroporous (or 3-DOM) solids, which are a class of inverse opal structures. The design of 3-DOM structures is based on the initial formation of a colloidal crystal composed of monodisperse polymer or silica spheres assembled in a close-packed arrangement. The interconnected void spaces of the template, 26 vol % for a face-centered-cubic array, are subsequently infiltrated with the desired material. 

CVD, and electrodeposition, depending on the desired composition. Removal of the colloidal templating spheres renders a negative replica (the inverse opal) structure of the active material, with an interconnected, 3-D array of pores, typically sized in the hundreds of nanometers. 

Figure 41. The SEM micrograph images of an Er 1 Ti()2 inverse-opal structure templated using a colloidal crystal of 466-nm polystyrene beads by filling the interstitial volumes with colloidal 50-nm diameter Lr 1 Ti()2 nanocrystals followed by calcination to remove the poylystyrene. (a) Low magnification. (b) High magnification. [Adapted from (187).]...

F. Caruso uses monodisperse polymer spheres and their colloidal crystals only as templates to create hollow capsules or extended opal arrays with the layer-by-layer technique. Again this is a typical colloid chemistry tool which is unparalleled in low molecular weight organic chemistry, and hollow mesostruc-tures systems with astonishingly high complexity and chemical function can be generated. 

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