Nanocomposites of organically modified clay nanoparticles and a polyisoprene (PI) matrix were
prepared by solution-mediated intercalation, and their dynamics were investigated over a broad range of frequency
and temperature by dielectric relaxation spectroscopy (DRS) and dynamic mechanical spectroscopy (DMS). The
principal goal was to address the effect of geometric confinement and elucidate how the dynamics vary as a
function of the type and concentration of clay and the molecular weight of PI. Dielectric spectra of nanocomposites
with low-molecular-weight PI reveal no effect of clay loading on the average relaxation time for segmental and
normal mode relaxation, but dc conductivity and interfacial polarization are affected. In nanocomposites with
high molecular weight PI (in the entangled regime), however, a clear effect of clay loading on the average relaxation
time for the normal mode process is observed. Most interestingly, it is found that the normal mode becomes
faster with increasing clay content, and an explanation is offered in terms of the preferential suppression of the
longer scale (lower frequency) portion of the normal mode spectrum. The average relaxation times for segmental
and normal mode calculated from dielectric and viscoelastic measurements are in excellent agreement. DMS
measurements also reveal an increase in the magnitude of storage and loss modulus with increasing clay loading
up to the threshold value of 8 wt %. The observed increase originates from the “filler effect”.
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