Chemistry Reference
In-Depth Information
Carbon nanotubes are also of considerable interest with regard to
both reinforcement and possible increases in electrical conductiv-
it y.
280,
281,
283,
284,
294-306
If the goal is to reduce the percolation thresh-
old for electrical conductivity, aggregation can be helpful if it occurs
in a random way to create fractal structures.
57
There is considerable
interest in characterizing the flexibility of these nanotube structures,
in managing their tendencies to aggregate, and in maximizing their
miscibility with inorganic as well as organic polymers. Although an
enormous effort has been expended on surface functionalization to
improve coupling between the filler and the matrix, it is not clear that
functionalization does more than improve dispersion.
57
There can be a considerable advantage to using a combination of fillers of
different types, such as particles and layered sheets. One frequently ob-
tains a synergistic effect in that the improvements in properties obtained
can be larger than expected from simple additivity. In addition, the first
filler may have a solubilizing effect, making incorporation of the second
one easier. Relatively little has been done in this regard.
307-310
Some fillers such as zeolites are sufficiently porous to harbor monomers,
which can then be polymerized. This approach threads the chains through
the cavities, with unusually intimate interactions between the reinforcing
phase and the host elastomeric matrix (figure 9.12).
295,
311,
312
Good rein-
forcement is observed. Because of the constraints imposed by the cavity
walls, these confined polymers frequently show no glass transition
Figure 9.12:
Polymer chains being threaded through a porous inorganic material such as a zeolite by
polymerizing monomer that had been absorbed into one of the channels or cavities.
