ma402220j_si_001.pdf (485.57 kB)
Enhanced Polymeric Dielectrics through Incorporation of Hydroxyl Groups
journal contribution
posted on 2014-02-11, 00:00 authored by Mayank Misra, Manish Agarwal, Daniel
W. Sinkovits, Sanat K. Kumar, Chenchen Wang, Ghanshyam Pilania, Ramamurthy Ramprasad, Robert
A. Weiss, Xuepei Yuan, T. C. Mike ChungWe use simulations and experiments
to delineate the mechanism by
which the addition of a small number of polar −OH groups to
a nonpolar polymer increases the static relative permittivity (or
dielectric constant) by a factor of 2, but more importantly while
keeping the dielectric loss in the frequency regime of interest to
power electronics to less than 1%. Dielectric properties obtained
from experiments on functionalized polyethylenes and polypropylenes
as a function of −OH doping are in quantitative agreement with
one another. Molecular dynamics simulations for the static relative
permittivity of “dry” −OH functionalized polyethylene
(in the absence of water) are apparently in quantitative agreement
with experiments. However, these simulation results would further
imply that there should be considerable dielectric loss beyond simulation
time scales (>0.1 μs). Since there are minimal experimentally
observed dielectric losses for times as short as a microsecond, we
believe that a small amount of adsorbed water plays a critical role
in this attenuated loss. We use simulations to derive the water concentration
at saturation, and our results for this quantity are also in good
agreement with experiments. Simulations of the static relative permittivity
of PE–OH incorporating this quantity of hydration water are
found to be in quantitative agreement with experiments when it is
assumed that all the dipolar relaxations occur at time scales faster
than 0.1 μs. These results suggest that improved
polymeric dielectric materials can be designed by including −OH
groups on the chain, but the mechanism requires the presence of a
stoichiometric quantity of hydration water.