Chemistry Reference
In-Depth Information
can behave as an elastomeric phase because the glass transition tem-
perature of PDMS is far below room temperature.
134-136
When the mate-
rial is subjected to an impact test, the PDMS component absorbs energy
by motion of the PDMS chains, thus ameliorating the growth of cracks
and fracture. Therefore, considerable toughening of the glass can be
achieved by increasing the amount of PDMS. The impact resistance was
also observed to increase with increasing PDMS molecular weight, pos-
sibly due to an increase in the phase separation that leads to the energy-
absorbing domains
403
as was found by introducing PDMS domains into a
polyamide.
404
For composites having relatively low PDMS content, microscopy of
fracture typically shows smooth fracture surfaces,
405
with little evidence
of effective resistance to either initiation or propagation of cracks. In con-
trast, samples with high PDMS contents had fracture surfaces showing
some degree of “whitening” or shearing,
403
implying a ductile, energy-
absorbing response to the impacts, with increased resistance to crack
propagation.
REFERENCES
1. Hench, L. L.; West, J. K., The Sol-Gel Process.
Chem. Rev
.
1990
,
90
, 33-72.
2. Schaefer, D. W.; Mark, J. E.,
Polymer-Based Molecular Composites
. Materials
Research Society: Pittsburgh, PA, 1990; Vol. 171.
3. Brinker, C. J.; Scherer, G. W.,
Sol-Gel Science. The Physics and Chemistry of Sol-
Gel Processing
. Academic Press: New York, 1990.
4. Keefer, K. D., Structure and Growth of Silica Condensation Polymers. In
Sili-
con-Based Polymer Science. A Comprehensive Resource
, Zeigler, J. M.; Fearon,
F. W. G., Eds. American Chemical Society: Washington, DC, 1990; Vol. 224,
pp 227-240.
5. Doughty, D. H.; Assink, R. A.; Kay, B. D., Hydrolysis and Condensation Kinet-
ics of Dimeric Sol-Gel Species by 29Si NMR Spectroscopy. In
Silicon-Based Poly-
mer Science. A Comprehensive Resource
, Zeigler, J. M.; Fearon, F. W. G., Eds.
American Chemical Society: Washington, DC, 1990; Vol. 224, p 241.
6. Ulrich, D. R., Special Report—Chemical-Processing of Ceramics.
Chem. Eng.
News
1990
,
68
(1), 28-40.
7. Holmes, R. R., The Stereochemistry of Nucleophilic Substitution of Tetracoor-
dinated Silicon.
Chem. Rev.
1990
,
90
, 17- 31.
8. Coltrain, B. K.; Sanchez, C.; Schaefer, D. W.; Wilkes, G. L.,
Better Ceramics
Through Chemistry VII: Organic/Inorganic Hybrid Materials
. Materials Research
Society: Pittsburgh, PA, 1996; Vol. 435.
9. Brinker, C. J.; Giannelis, E. P.; Laine, R. M.; Sanchez, C.,
Better Ceramics
Through Chemistry VIII: Hybrid Materials
. Materials Research Society: Warren-
dale, PA, 1998; Vol. 519.
