Biomedical Engineering Reference
In-Depth Information
Schematic illustration of optical nanocomposite.
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3.1
exceptionally high aspect ratio. Nanocomposite materials show great
promise as they can provide the necessary stability and processability for
many important applications. Due to their nanoscale constituents they also
exhibit optical and electronic properties that differ from the corresponding
macroscopic properties. There is a wide range of potential applications of
nanocomposite materials. Among them are electrical and optical sensors,
dispersions, coatings and novel optical glasses.
The applications of optical materials and the need for novel optically
functional and transparent materials are expanding. In addition to optical
needs such as switching and amplification, the materials must be integrated
into existing structures such as waveguides and optical fibers.
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In general,
the principle in the construction of an optical composite involves the
intimate mixing of optically functional materials within a processable
matrix. This type of composite is schematically shown in Fig. 3.1, where the
enclosing matrix imparts processability in film or fiber forms and the small
particles possess the desirable optical properties.
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Examples of incorporated phases include quantum-confined semiconduc-
tors, solid-state lasers, small molecules and polymers. Matrix materials can
be polymers, copolymers, polymer blends, glasses or ceramics. Using such a
composite structure, nanocomposites have been formed with non-linear
optical and laser amplification properties, among others.
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In these types of
composites, optical scattering must be avoided; this results from a mismatch
between the refractive index of the matrix and that of the particles.
Refractive index mismatch is not so important in the case of small particles
(typically
25 nm), but for larger particles the refractive index of the matrix
and the particles must be carefully matched to avoid scattering.
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Since the 1970s there has been considerable progress in the sol-gel
technique for the manufacture of glasses, glass-ceramics and ceramics. This
method has been successfully used for a variety of products ranging from
bulk glasses
4, 15
and optical fibers, to special coatings, ultra-pure powders
and multifunctional materials. The sol-gel processed transparent porous
matrix also offers an exciting potential as a host matrix for doping optically
active organic molecules.
6
This matrix exhibits many properties of inorganic
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