Template colloidal nanoparticle

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). 

Fig. 11 Process of the DNA-based colloidal nanoparticle assembly, a Base-pairing interactions induced assembly in ID template, b Immobilization by DNA hybridization onto 2D surface, c 3D assembly by duplex DNA interconnects...

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. 

Use of the LbL technique is not restricted to the preparation of planar thin films. One of the most outstanding strategy modifications of the LbL technique involves assembly on colloidal particles followed by hollow capsule formation. For example, Caruso and co-workers reported the formation of hollow silica vesicles through LbL assembly on colloidal nanoparticle templates (Fig. 14). Polyelectrolytes and smaller silica particles were initially formed on a larger colloidal core, which was subsequently selectively destroyed. Calcination of the hybrid vesicles resulted in a hollow vesicle composed of silica. Formation of controlled organic-inorganic layer structures on colloidal particles by LbL assembly also provides media appropriate for investigation of fundamental phenomena. 

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. 

Another approach is to use the LB film as a template to limit the size of growing colloids such as the Q-state semiconductors that have applications in nonlinear optical devices. Furlong and co-workers have successfully synthesized CdSe [186] and CdS [187] nanoparticles (<5 nm in radius) in Cd arachidate LB films. Finally, as a low-temperature ceramic process, LB films can be converted to oxide layers by UV and ozone treatment examples are polydimethylsiloxane films to make SiO [188] and Cd arachidate to make CdOjt [189]. 

A scaled-up version of this central template-concentric sphere surface assembly approach has been demonstrated for the growth of multi-layer core-shell nano- and microparticles, based upon the repeated layer-by-layer deposition of linear polymers and silica nanoparticles onto a colloidal particle template (Figure 6.8) [60]. In this case, the regioselective chemistry occurs via electrostatic interactions, as opposed to the covalent bond formation of most of the examples in this chapter. The central colloidal seed particle dictates the final particle... 

Figure 6.8 Illustration of colloid-templated nanoparticle assemblies. The process involves the layer-by-layer adsorption of charged polymers and oppositely charged nanoparticles onto the surfaces of the colloidal template. The colloidal core particles may then be removed to generate a hollow sphere of nanoparticles, held together by electrostatic interactions with the linear polymer glue ...

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]. 

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