Colloidal-templated crystals

The above discussions have highlighted the utility of both magnetic arrays and colloidal-templated crystals for DNA electrophoresis. While the variety of solid supports that can be fabricated by these techniques is limited when compared to those available through micro- and nanofabrication, the ease with which these self-assembled arrays can be constmcted confers significant advantages... 

Particularly in 2D systems, control over the self-assembly of colloidal templates has offered a versatile way to produce patterned surfaces or arrays with a precision of few nanometres. Diblock copolymer micellar nanolithography (dBCML) is a versatile method that uses homopolymers or block copolymers for the production of complex surface structures with nanosized features [69], In contrast to other approaches like electron-beam lithography (EBL) and photolithography, dBCML does not require extensive equipment. In fact, it is commonly used in the fabrication of data storage devices and photonic crystals, in catalyses [70], and for the design of mesoporous films and nanoparticle arrays [71]. 

The materials which have been mentioned here so far are predominantly shaped in planar films of hierarchical order. However, the synthesis of hierarchically structured particles is also highly desirable, as they might be further processed and used for the preparation of composite porous materials. Wu et al. showed the synthesis of raspberry-like hollow silica spheres with a hierarchically structured, porous shell, using individual PS particles as sacrificial template [134]. In another intriguing approach by Li et al. [135], mesoporous cubes and near-spherical particles (Fig. 10) were formed by controlled disassembly of a hierarchically structured colloidal crystal, which itself was fabricated via PMMA latex and nonionic surfactant templating. The two different particle types concurrently generated by this method derive from the shape of the octahedral and tetrahedral voids, which are present in the template crystal with fee lattice symmetry. 

In spite of its simplicity, the long response time of the hydrogel photonic crystal materials has limited their utility as sensors. This is because of the slow diffusion of analytes in the hydrogel to influence the optical properties. New fabrication procedures of these hydrogel photonic crystal sensors were used to improve the response time. The Lee Group [96] demonstrated a mechanically robust and fast responsive photonic crystal pH sensor, which was fabricated by templated photopolymerization of hydrogel monomers within the interstitial space of a self-assembled colloidal photonic crystal, as shown in Fig. 25. 

Figure 6.7 Upper SEM surface images of (A) 2D silica colloid-carbon nanotube complex crystals, and (B) the carbon nano tube network morphology after removing the colloidal particles lower transmittance and resistivity tuning using the controlled colloidal templates.

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... 

Scheme 5.1 Preparation process of the 3 DOM titania microparticles formed by adopting colloidal polystyrene crystals as a template. Reprinted from Ref. 71, Copyright 2006, with permission from Elsevier.

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). 

Figure 7.4 Preparation of a periodically ordered interconnecting porous poly(NIPAAm-c o-Ru(bpy)3) gel using a close-packed colloidal silica crystal as a template.

Different colloidal cores can be decomposed after multilayers are assembled on their surface. If the products of core decomposition are small enough to expel out of polyelectrolyte multilayer the process of core dissolution leads to formation of hollow polyelectrolytes shells (Fig. 2.1, d-f). Up to now, various colloidal templates such as organic and inorganic cores, like MF-particles, organic crystals, carbonate particles and biological cells were used as templates for hollow capsule fabrication. Decomposition can be done by different means, such as low pH for MF- and carbonate particles [43], organic water miscible solvents for organic crystals [44] and... 

Dispersed colloidal silica particles of various sizes and colloidal silica crystals (opals) " have been used as templates of porous carbons, with spherical pores having narrow pore size distributions (PSDs). By coating monodisperse colloidal silica particles or crystals with a suitable carbon precursor, followed by carbonization and etching of the sUica, porous carbon particles can be obtained. The diameters of the mesopores are determined by the size of the silica particles. Because... 

Fig. 12 shows an experiment [31], analogous to nanoindentation of atomic crystals, in which an indenter is driven into a colloidal single crystal, grown on a (100) template, to observe the resulting dislocation dynamics by both confocal and laser diffraction microscopies. The indenter is simply a commercial sewing needle, which is produced with a hemispherical tip with a diameter of 40 pm. The ratio of the tip and particle radii is similar to that in nanoindentation experiments. The needle is attached to a piezoelectric drive and is moved at a rate of 3.4 pm/h. 

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