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3.3.3. Temperature Ramp
Varying the temperature for a constant frequency, constant strain test is
perhaps the most powerful technique in DMA. Temperature-Dependent behavior
can be used to observe subtle nuances in a polymer's structure, such as its cross-link
density, degree of crystallinity, and thermal stability.
In Figure 3.8 we observe that for a 2 Hz, .3% strain amplitude test, there is no
obvious difference in the glass transition between the composite and the neat
polymer. The similarly-shaped and поп-shifted tangent delta peak drives the
conclusion that the structure of the polymer in the composite is similar to that of the
neat polymer. The peak appears to be slightly lower than the neat polymer, which
may indicate less amorphous content, but the shift is within error and, so far,
inconclusive.
The point of thermal degradation tells a different story, as the composite
shows much greater thermal stability. This polymer is rated to 200 0C, so it is not
unexpected that the neat PDMS will show signs of degradation when heated past
this temperature. However, it is clear that the composite is much less susceptible to
such temperatures, indicating its superior thermal robustness. This resistance to
failure may support the observation that CNTs may serve as radical scavengers [50],
as the neutralization of any free radicals created above 200 oC would serve to
preserve the mechanical integrity up until the temperature at which the polymer
backbones begin to degrade. Otherwise, the introduction of free radicals will serve
to initiate the escalating degradation of the polymer.