Colloidal films/crystals, fabrication

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... 

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... 

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]. 

Many other examples include the work of Jian and co-workers [659-661], who reported colloidal Au for enhancement of the immobilisation capacity and ultimately detection limit of DNA using quartz crystal microbalance (QCM). These authors showed that Au nanoparticle films on the Au plate provide a novel means for the fabrication of DNA sensor [659-661]. 

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. 

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. 

Ordered 3D arrays of polyaniline [PANI] inverse opals can also fabricated via electrochemical methods by using colloidal crystals of polystyrene beads as sacrificial templates as shown in Fig. 1.19 [208]. Compared with films obtained by chemical synthesis, the inverse opaline samples obtained by electrochemistry had a much higher structural quality. Such PANI inverse opals were prepared... 

M. Ishii, H. Nakamura, H. Nakano, A. Tsukigase, and M. Harada, Lai e-domain colloidal crystal films fabricated using a fluidic cell, Langmuir, 21,5367-5371 (2005). 

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