Environmental Engineering Reference
In-Depth Information
nanocomposites, which are able to quantify and/or identify microorgan-
isms based on their gas emissions. Sensors based on conducting polymers
(or electroactive conjugated polymers) consist of conducting particles
embedded into an insulating polymer matrix [18]. h e resistance changes
of the sensors produce a pattern corresponding to the gas under investi-
gation. Conducting polymers are very important because of their electri-
cal, electronic, magnetic and optical properties, which are related to their
conjugated π electron backbones. Polyene and polyaromatic conducting
polymers, such as polyaniline, polyacetylene and polypyrrole, have been
widely studied. Electrochemically polymerized conducting polymers have
a remarkable ability to switch between conducting oxidized (doped) and
insulating reduced (undoped) states, which is the basis for several appli-
cations. Nanosensors containing carbon black and polyaniline have been
developed which have been demonstrated to be able to detect and identify
three foodborne pathogens by producing a specii c response pattern for
each microorganism.
13.4.4 Dif erent Fillers for Nanocomposites
13.4.4.1
Nanoclay as Fillers
Nanoclays have been the most studied nanoi llers due to their high avail-
ability, low cost, good performance and good processability. h e clays for
nanocomposites usually are bidimensional platelets with very tiny thick-
nesses (frequently around 1 nm) and several micrometers in length. In con-
trast with the typical tactoid structure of microcomposites (conventional
composites), in which the polymer and the clay tactoids remain immis-
cible, the interaction between layered silicates and polymers may produce
two types of nanoscale composites, namely: intercalated nanocomposites,
which result from penetration of polymer chains into the interlayer region
of the clay, producing an ordered multilayer structure with alternating
polymer/inorganic layers, and exfoliated nanocomposites, which involve
extensive polymer penetration, with the clay layers delaminated and ran-
domly dispersed in the polymer matrix. Exfoliated nanocomposites have
been reported to exhibit the best properties due to their optimal clay-
polymer interactions.
h e hydrophilicity of the surface of most clays make their dispersion in
organic matrices dii cult. Organoclays, produced by interactions of clays
and organic compounds, have found an important application in polymer
nanocomposites. An adequate organophilization is essencial for successful
exfoliation of clays in most polymeric matrices, since organophilization
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