Colloidal spheres

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Also see Colloidal Dispersion

Monodisperse colloidal spheres are often used in soft matter experiments as test systems to study biological structures such as proteins, macromolecules and DNA, as they can be made in almost any size between a few nm and many microns, and surface coated in a wide range of manners. The most studied and best established examples of colloidal materials are inorganic silica colloids, and polymer latexes.

Many chemical approaches are available for producing colloidal spheres that are monodispersed in size. The best established and most commonly used methods are controlled precipitation for inorganic oxides and emulsion polymerization for polymer latexes. Using these methods, inorganic oxides such as amorphous silica can been easily prepared as uniform spheres with diameter ranging from a few nm to 1 mm; polymer latexes in sizes of 20 nm to 100 mm.

The properties of colloidal spheres can be further modified by coating them with thin shells of a different chemical composition, as well as in varying thickness. It has been demonstrated that the structure, size, and com- position of these hybrid particles could be altered in a controllable way to tailor their optical, electrical, thermal, mechanical, electro-optical, magnetic, and catalytic properties over a broad range. This modification is also useful for tuning the interactions between colloidal spheres, and stabilizing dispersions of these spheres in a given medium.

Schematic illustrations of three types of representative colloidal spheres: A) a solid sphere; B) a core±shell sphere; and C) a hollow sphere. The size of the surface groups, X, has been exaggerated in (A). The polarity and density of charges on a colloidal sphere are mainly determined by the surface group. The surface of silica spheres is usually terminated in silanol groups (±Si±OH). For polymer latexes, the surface groups can span over a diverse range that includes ±NH2, ±COOH, ±SO4H, ±SO3H, ±OH, ±CONH2, ±CH2NH2, ±CH2Cl, and epoxy groups. In some cases, the bulk structure (chemical composition and substructure) and surface morphology of colloidal spheres may also play an important role, although the effect of these parameters is usually neglected in most discussions.
TEM images of two representative colloidal systems that can be readily prepared as monodispersed samples at large quantities: A) ~400 nm silica spheres; and B) ~200 nm polystyrene beads.
Manufacturers of colloidal spheres[1]

[1] Monodispersed Colloidal Spheres: Old Materials with New Applications Younan Xia, Byron Gates, Yadong Yin, and Yu Lu, Advanced Materials 12, 10, 693-713 (2000)