Structure formation colloidal crystals

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. 

Any study of colloidal crystals requires the preparation of monodisperse colloidal particles that are uniform in size, shape, composition, and surface properties. Monodisperse spherical colloids of various sizes, composition, and surface properties have been prepared via numerous synthetic strategies [67]. However, the direct preparation of crystal phases from spherical particles usually leads to a rather limited set of close-packed structures (hexagonal close packed, face-centered cubic, or body-centered cubic structures). Relatively few studies exist on the preparation of monodisperse nonspherical colloids. In general, direct synthetic methods are restricted to particles with simple shapes such as rods, spheroids, or plates [68]. An alternative route for the preparation of uniform particles with a more complex structure might consist of the formation of discrete uniform aggregates of self-organized spherical particles. The use of colloidal clusters with a given number of particles, with controlled shape and dimension, could lead to colloidal crystals with unusual symmetries [69]. 

Owing to the simphcity and versatility of surface-initiated ATRP, the above-mentioned AuNP work may be extended to other particles for their two- or three-dimensionally ordered assemblies with a wide controllabiUty of lattice parameters. In fact, a dispersion of monodisperse SiPs coated with high-density PMMA brushes showed an iridescent color, in organic solvents (e.g., toluene), suggesting the formation of a colloidal crystal [108]. To clarify this phenomenon, the direct observation of the concentrated dispersion of a rhodamine-labeled SiP coated with a high-density polymer brush was carried out by confocal laser scanning microscopy. As shown in Fig. 23, the experiment revealed that the hybrid particles formed a wide range of three-dimensional array with a periodic structure. This will open up a new route to the fabrication of colloidal crystals. 

In summary, for solid-type materials, molecules can form regular arrays leading to crystals, and this also may occur with colloidal-scale particles. For liquid-type materials, molecules may be dispersed on a molecular scale (i.e., dissolved) in a liquid, or they may cluster together into a separate and homogeneous phase (i.e., show phase separation). Colloidal-scale particles may also exist as separate particles in a liquid, but these particles may also cluster into a dense phase. Whether the size of the building blocks is molecular or colloidal, the phenomena of phase separation, clustering and structure formation show many similarities. 

The above features of a sheared colloidal crystal appear to be similar in both BCC and FCC structures. However, there are differences in details, and perhaps even within a given symmetry the flow behavior might vary with particle concentration or charge density. For example, Chen et al. (1994) have shown that between the strained crystal and sliding-layer microstructures there can be a polycrystalline structure, the formation of which produces a discontinuous drop in shear stress (see Fig. 6-33). Ackerson and coworkers gave a detailed description of the fascinating shear-induced microstructures of these systems (Ackerson and Clark 1984 Ackerson et al. 1986 Chen et al. 1992, 1994). 

Clay minerals have been used for a long time in various fields of application (e.g., paper coating) because of their platelike crystal habit in colloidal dimensions and the ability to bond to one another. These phenomena of structure formation are predominantly controlled by Coulombic forces between the negative charges on the basal planes and the positive charges around the edges. 

In summary, the formation of colloid crystal structure and the corresponding positive structural component of the disjoining pressure in-... 

Structural hierarchy can also be obtained by direct modification of a single body crystal. In principle both a colloidal crystal or its inverse opal can be patterned after their homogeneous formation. Techniques to achieve this are electron-beam hthography or photopolymerization via a confocal microscope, for instance. 

Other attempts follow the dual micellular templating approach involving a combination of block copolymers, surfactants, and alcohols [208]. The colloidal templating method produces three-dimensionally ordered macrostructures (3DOM-structures) [208]. However, even for the colloidal templating, the routes include besides the formation of the three-dimensionally arranged colloidal crystal always a second... 

Kubo N, Homma T, Hondo Y et al (2005) Fabrication of patterned nanostmctures with various metal species on Si wafer surfaces by maskless and electroless process. Electrochim Acta 51 834-837 Lee C, Tsuru S, Kanda Y et al (2009) Formation of 100 micrometer deep vertical pores in Si wafers by wet etching and Cu electrodeposition. J Electrochem Soc 156 D543-D547 Munoz-Noval A, Fukami K, Martin-Palma RJ et al (2013) Surface plasmon resonance study of Au nanorod structures templated in mesoporous silicon. Plasmonics 8 35-40 Ono S, Oide A, Asoh H (2007) Nanopatteming of silicon with use of self-organized porous alumina and colloidal crystals as mask. Electrochim Acta 52 2898-2904... 

The formation of open and porous structures with extremely large surface area is of high technological significance, because this structure type is very suitable for electrodes in many electrochemical devices, such as fuel cells, batteries and sensors [1,2], and in catalysis applications [3]. The template-directed synthesis method is most commonly used for the preparation of such electrodes. This method is based on a deposition of desired materials in interstitial spaces of disposable hard template. When interstitial spaces of template are filled by deposited material, the template is removed by combustion or etching, and then the deposited material with the replica structure of the template is obtained [4, 5]. The most often used hard templates are porous polycarbonate membranes [6, 7], anodic alumina membrane [8-10], colloidal crystals [11, 12], echinoid skeletal stractures [13], and polystyrene spheres [14, 15]. 

---