Chemistry Reference
In-Depth Information
and could also find applications as elastomeric bearings and vibration
absorbers.
269
The types of particles seem endless and new applications appear regu-
larly. Iron particles have been used to modify the dielectric properties of
polyoxides
272
and alumina particles to increase thermal conductivity.
273
PDMS composites with Al
2
O
3
-NbC have also been prepared.
274
Also, gold
nanoparticles can serve as catalysts for the polymerization of polysilox-
anes into nanowires, filaments, and tubes.
275
Another catalytic applica-
tion involves gold nanoparticles mimicking the catalytic activity of a
polysiloxane-synthesizing enzyme.
276
One novel aspect of such gold-
polysiloxane nanocomposites is the ability to switch between several
colors by swelling.
277
It is also possible to form striped patterns on a gold
film deposited on a stretched polysiloxane film
278
and silica-coated gold
particles have also been used to make polysiloxane films with unusual
optical properties.
279
9.2.6 Polyhedral Oligomeric Silsesquioxanes
Polyhedral silsesquioxanes fillers are cage-like silicon-oxygen structures,
and have been called the smallest possible silica particles.
280-285
he most
common structure has eight silicon atoms, each carrying an organic
group. The particles on which none of the groups are functionally reac-
tive can be simply blended into elastomers such as PDMS using mixing or
compounding techniques. In this case, the inert groups are chosen to im-
prove miscibility with the elastomeric host matrix. Polyhedral oligomeric
silsesquioxanes (POSS) molecules having one reactive functional group
can be attached to a polymer as side chains.
286
Those with two reactive
groups can be incorporated into polymer backbones by copolymeriza-
tion, and those with more than two can be used for forming cross links.
As opposed to particulate fillers where interfacial bonding is of second-
ary importance,
287,
288
bonding polyhedral silsesquioxanes to the elasto-
meric network is critical to effective reinforcement. Bonding is not the
source of reinforcement, but rather it aids in dispersion of the cage
structures.
285
POSS particles have been extensively used to reinforce polysilox-
anes.
285,
289-291
In some cases, the surfaces of the nanoparticles were made
strongly hydrophobic by fluorination.292
292
C
60
fullerene particles have also
been used to improve the mechanical properties of PDMS.
293
The polymer
had been functionalized and the particles were either monofunctional-
ized or multifunctionalized with complementary groups.
