colloidal crystal (rus. коллоидный кристалл) — spatially ordered system of similar submicron size objects, whose properties are determined not only by the size of individual elements, but also by specifics of their mutual arrangement.

Description

Most colloidal systems are polydisperse, i.e. they are characterised by the fairly broad size distribution of the dispersed phase. The colloidal crystallisation observed in monodisperse colloidal systems, consisting of particles having similar shape, size and nature of interaction, is not characteristic of polydisperse systems. This process of spontaneous arrangement of particles into spatially periodic structures is very similar to the process of forming atomic or molecular crystals. The lower size limit of the particles involved in this process is determined by the high intensity of the Brownian motion of particles, whose size is below several nanometres, which prevents the stabilisation of extended ordered structures; the higher size limit is determined by the very low mobility of micron-sized particles, which prevents the healing of defects in the structure formed.

The main method of obtaining colloidal crystals is the self-assembly of colloidal size microspheres in the process of gravity sedimentation, vertical deposition, electrophoresis, application of particle suspensions on a rotating substrate, etc. At the same time great attention is paid to the nature (type) of particle arrangement and perfection of the resulting spatial structure, which is especially important when using these crystals in optics. The main types of spontaneous arrangement are face-centred cubic packing and hexagonal close packing; although special synthetic methods, in particular, the use of templates, allow mixed structures, structures with loose packing, textured colloidal crystals, etc. to be obtained. Along with bulk colloidal crystals, it is possible to obtain two-dimensional (2D) crystals (films) on various surfaces including complex shapes.

Photonic crystals form a special group of colloidal crystals, related to their main application. Their specificity is determined by the high requirements of optical applications to perfection and length of spatial structures. Photonic crystals can be formed either by controlled self-assembly of particles, or by high-precision formation of topography of thin films by means of traditional and modern technologies of micro- and nanoelectronics. The ordered pore space of colloidal crystals can be used as a template for filling with other components with further removal of the matrix by calcination or selective dissolution. The best-known natural colloidal crystals are opals, in which the pore space of an ordered array of silica microspheres is filled with hydrated silicon oxide. Colloidal crystals also form in concentrated suspensions of some viruses.

Author

  • Shlyakhtin Oleg A.

Sources

  1. Concise Encyclopedia of Physics. — McGraw-Hill Professional, 2004. — 500 p.
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  4. Colloidal crystal // Wikipedia, the free Encyclopedia. — http://en.wikipedia.org/wiki/Colloidal_crystal (reference date: 12.12.2011).
  5. The amazing ability of matter to “self assemble” ... // The School of Physics and Astronomy, The University of Edinburgh, 2009. — http://www2.ph.ed.ac.uk/~wckp/ (reference date: 12.12.2011).

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