Inverse opal structure

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).]...

The opals obtained by self-assembly are mechanically unstable because there is only Van der Waals force between spheres. The subsequent infiltration process could easily destroy the ordered colloid arrays. So we annealed the opals of polymer sphere to increase their stability. As a result, there would form interconnections between spheres, which come from the slight melting of the sphere surfoces. These necks can provide the opal with necessary mechanical stability. In addition, they are important for producing inverse opal structure. After infiltration, when the samples are treated with calcinations, these necks can act as channels for the transport of the products formed during calcination like CO2. 

FIGURE 4.6 Schematic showing the approach used to produce highly ordered inverse opal structures with conducting polymers. 

Inverse opal structures have been classified into three structures, the so-called residual volume structure , shell structure and skeleton structure . The residual volume structure is a perfect inverse opal structure, which can be produced if the whole space among the opal spheres is completely filled by the product materials. If the space is incompletely filled, the surface of the sphere template is covered by the product materials, and a shell structure is generated. Most amorphous compounds tend to form a shell structure. On the other hand, crystalline compounds tend to form a skeleton structure. 

The synthesis of macroporous carbon materials was first realised by Zakhidov et al. in 1998. Macroporous carbon materials with inverse opal structures, as shown in Figure 4.14, were obtained using silica opals as hard templates and phenol resin and/or propylene gas as carbon precursor. The macroporous carbons had different structures depending... 

Stmctures with micrometer or submicrometer dimensions can be created using different templating methods [4, 5]. A large variety of approaches have been developed and employed to prepare microporous structured materials, including the use of templates such as ordered arrays of colloidal particles to produce inverse opal structures [6-9], from transformed polymeric sphere arrays [10, 11], using emulsion droplets as templates [12], employing natural biological templates [13-16], by... 

Ceramic monolithic structures made from inverted opal silicon carbonitride (see Figure 6.6) were presented by Mitchell et al. [460]. The inverse opal structure was achieved using polystyrene templates. They prepared monoliths of 74% porosity, typically 350-pm wide, 100-pm high and 3-mm long. Propane steam reforming was then successfully performed in the reactor (see Section 7.1.2). 

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). 

Structure of 3DOM Materials (Inverse Opal Structures)... 

Inverse opal structures have been classified into three structures residual volume structure, shell structure, and skeleton structure [56,57]. The... 

A well-ordered 3DOM structure was observed by SEM for all samples (Figure 6.6). Well-ordered air spheres and interconnected walls create an inverse opal structure in three dimensions, and the next layer is clearly visible. Large fiactions (more than 95% of the particles by SEM images) of all the 3DOM materials were highly ordered porous structures over a range of tens of micrometers. 

Middle-IR transmitting films, rare-earth doped snlfide films and snlfide films for other applications also need further study. According to the properties of specific sulfide compounds, one can chose the most suitable method to prepare sulfide films and bulk materials. Since sulfide glasses have high refractive index, sol-gel derived sulfides can also be used to infiltrate silica or polystyrene opals, in order to obtain inverse opal structures for photonic bandgap devices. 

Figure 9.10 Inverse opal structures in silica, templated by PMMA (a) or polystyrene (b) spheres (electron micrograph reproduced with permission from [122]. Copyright (2002) American Chemical Society.)...

Kuo and Lu coated the surfaces of the spherical voids with 10-15 nm TiOi nanoparticles by TiCU treatment to increase the surface area for dye adsorption. Figure 3.43 shows the SEM and high resolution transmission electron microscopy (HRTEM) images of the structures. The voids were 100 nm in diameter with transport channels of 30-50 nm in between. The film was 25 pm in thickness. The Voc decay when switching from AM 1.5 to dark was recorded for a 13 pm film and the calculated. The inverse opal structure was found to result in longer... 

Figure 3.88 Reflectance spectra of the (a) 400 nm polystyrene colloidal array, (b) Ti02 nanoparticle-infiltrated polystyrene colloidal array and (c) liquid-electrolyte-infiltrated Ti02 inverse opal structure. Adapted from Kwak et al., 2009 Copyright (2009) Wiley-VCH Verlag GmbH c Co. KGaA...

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