Colloidal crystals fabrication

Hydrogel-based colloidal crystals were designed for sensing applications. Asher and co-workers polymerized NIPAM in the colloidal crystal fabricated from PS particles. The ther-moresponsivity of the PNIPAM chains allows regulating the interparticle distance in the colloidal crystal and the position of Bragg peak. 

The method for selective chemical sensing using colloidal crystal films is depicted in Fig. 4.1. The steps for the fabrication of the colloidal crystal films and determination of selective chemical sensing response are summarized in Table 4.2. 

Fig. 4.1 Diagram of the method for selective vapor detection that includes fabrication of core (1) and core shell (2) materials, their assembly into a colloidal crystal film (3), exposure of the film to different vapors (4), measurements of the spectral response of the film (5), and multivariate analysis of the spectra (6) to obtain a vapor selective response of the colloidal crystal film...

Fabrication of composite colloidal spheres involves two steps submicron particles are fabricated from a material preferentially responsive to one class of chemicals followed by a step in which the submicron spheres are coated with a shell that is preferentially responsive to another class of chemicals. A colloidal crystal array is subsequently self-assembled into a 3D ordered film. 

As an example of composite core/shell submicron particles, we made colloidal spheres with a polystyrene core and a silica shell. The polar vapors preferentially affect the silica shell of the composite nanospheres by sorbing into the mesoscale pores of the shell surface. This vapor sorption follows two mechanisms physical adsorption and capillary condensation of condensable vapors17. Similar vapor adsorption mechanisms have been observed in porous silicon20 and colloidal crystal films fabricated from silica submicron particles32, however, with lack of selectivity in vapor response. The nonpolar vapors preferentially affect the properties of the polystyrene core. Sorption of vapors of good solvents for a glassy polymer leads to the increase in polymer free volume and polymer plasticization32. 

Fabrication of Core-Shell Colloidal Crystal Films for Selective Chemical Sensing... 

Fig. 4.2 TEM images of fabricated nanoparticles, (a) Isolated composite core/shell submicron particles, (b) Hollow silica submicron particles prepared by removing the polystyrene core to demonstrate the high quality of the formed sol gel shell of the composite nanospheres employed to prepare sensing colloidal crystal films...

Yamada, Y. Nakamura, T. Ishi, M. Yano, K., Reversible control of light reflection of a colloidal crystal film fabricated from monodisperse mesoporous silica spheres, Langmuir. 2006, 22, 2444 2446... 

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. 

Another important method for photonic crystal fabrication employs colloidal particle self-assembly. A colloidal system consists of two separate phases a dispersed phase and a continuous phase (dispersion medium). The dispersed phase particles are small solid nanoparticles with a typical size of 1-1000 nanometers. Colloidal crystals are three-dimensional periodic lattices assembled from monodispersed spherical colloids. The opals are a natural example of colloidal photonic crystals that diffract light in the visible and near-infrared (IR) spectral regions due to periodic modulation of the refractive index between the ordered monodispersed silica spheres and the surrounding matrix. 

The purpose of this chapter is to provide an overview of ceramic materials used for photonic crystals, their synthesis, and macroscopic structures and architectures. Particularly close attention is given to the fabrication of silica colloidal crystals, since these forms are the most commonly studied. Initial efforts into devices are discussed, as are newer ceramic photonic crystal structures, including an overview of work in photonic crystal optical fibers. For completeness, nonoxide and organic photonic crystals also are included briefly. 

Subramania, G. et al.. Optical photonic crystals fabricated from colloidal systems, Appl. Phys. Lett., 74, 3933, 1999. 

Zhong et al. [64] have shown that the cell designed for fabricating colloidal crystals and their metal oxide inverse can also be used for the formation of... 

Recently, inqjortant efforts have been made to fabricate photonic crystals by colloidal crystal templating [1-5], Colloidal crystals are self-organized arrays of silica or latex spheres, having the periodicity required for photonic band gaps. The basic idea is to use a colloidal crystal as a template, infiltrate the interstitial spaces between the spheres with another material and, then, remove the spheres by chemical etching or combustion. Since the resulting macroporous structures have a complete photonic bandgap [6,7], these materials have many applications in photonics. 

The application of widespread standard polymer processing techniques to the formation of colloidal crystals was introduced by Ruhl et al. [60]. They demonstrated the fabrication of a large colloidal crystal film, which comprises core-shell latex particles. Upon coagulation the soft shell of the particles causes the formation of a rubbery mass, which can be uniaxially compressed. The radial horizontal flow during the compression induces crystallization of the particles from the surface of the plates inward. The soft shell constitutes the matrix in which the hard spheres are embedded. This technique is promising for efficient application to other polymer processing methods like extrusion or injection molding. 

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. 

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. 

Burkert K, Neumann T, Wang JJ, Jonas U, Knoll W, Ottleben H (2007) Automated preparation method for colloidal crystal arrays of monodisperse and binary colloid mixtures by contact printing with a pintool plotter. Langmuir 23 3478 Park J, Moon J, Shin H, Wang D, Park M (2006) Direct-write fabrication of colloidal photonic crystal microarrays by ink-jet printing. J Colloid Interface Sci 298 713 Gu ZZ, Kubo S, Fujishima A, Sato O (2002) Infiltration of colloidal crystal with nanoparticles using capillary forces a simple technique for the fabrication of films with an ordered porous structime. Appl Phys A 74 127... 

If the colloidal crystal is to be used directly for electrophoresis, it can be sealed on the sides and then covered with a PDMS lid with holes bored for the reservoirs [21]. Similar to the magnetic bead system, a colloidal crystal is a simple method of fabricating a regular nanoscale stationary phase for electrophoresis. 

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