Chemistry Reference
In-Depth Information
There are endless variations of the in situ filler generation method.
Polysiloxane can be made rod-like by cationic charges from ammonium
groups.
155
Epoxies have also been studied for coating applications.
156
In
some cases, the particles can give an elastomer “self-healing” proper-
ties.
157
Particles have been introduced in emulsions,
158
or in the curing
agent to provide reinforcement as well as cross linking.
159
In one set of
studies, hyperbranched poly(ethoxysiloxane) was used to reinforce or-
ganic polymers, including poly(ethylene terephthalate), isotactic polypro-
pylene, and high-density polyethylene.
160
9.2.3 Ex Situ and Modified Silicas
Separately prepared silica has long been used to reinforce polysiloxanes
by blending them into the polymer prior to its cross linking. The tech-
nology of this ex situ method is well developed, including the charac-
terization of the resulting composites.
128,
161-169
Mesoporous silica
particles have also been used to improve reinforcement of polysiloxane
elastomers.
170
Theory and simulations have also been carried out on
these materials.
63,
171-173
One goal is to modify the surfaces of silica particles to improve
bonding with PDMS, for example, with vinylethoxysilane
174
or by si-
lanization.
175
Similarly, tetraphenyl-modified fumed silica has been
used to increase PDMS radiation resistance.
176
Such materials can be
difficult to characterize quantitatively. For example, in some cases
fumed silica particles in PDMS formed secondary domain structures
that made it difficult to characterize nanoparticle formation by tap-
ping-mode atomic force microscopy.
177
Ultra small angle x-ray
91
and
neutron scattering
178
are useful for characterization of such complex
morphologies.
More novel structures have also been produced. Biogenic opaline silica
short fibers modified with vinyltrimethoxysilane, for example, are good
alternative reinforcing fillers for PDMS.
179
Other materials in this cate-
gory include mesoporous silica,
180
composites with polyindole,
181
and self-
assembled structures such as molecularly ordered phenylene-bridged
mesoporous organosilica nanofilaments.182
182
Also of interest are polysilox-
anes with quaternary ammonium salt biocidal functionality,
183
conver-
sion of hyperbranched polyethoxysiloxane,
184
and hybrid core-shell
systems based on molecular silicasols.
185
Perhaps the most novel struc-
tures are some recently developed enzyme-responsive snap-top covered
silica nanocontainers.
186
