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Thermal Conductivity of Polyacrylamide Hydrogels at the Nanoscale
journal contribution
posted on 2018-09-25, 00:00 authored by Shuai Xu, Shengqiang Cai, Zishun LiuA polymer
network can imbibe copious amounts of water and swell,
and the resulting state is known as a hydrogel. In many potential
applications of hydrogels, such as stretchable conductors, ionic cables,
and neuroprostheses, the thermal conductivities of hydrogels should
be understood clearly. In the present work, we build molecular dynamics
(MD) models of random cross-linked polyacrylamide hydrogels with different
water volume fractions through a reaction method. On the basis of
these models, thermal conductivities of hydrogels at the nanoscale
are investigated by a none-equilibrium MD method. This work reveals
that when the water fraction of hydrogels is under 85%, the thermal
conductivity increases with the water fraction, and can be even higher
than the thermal conductivities of both pure polymer networks and
pure water because of the influence of the interface between polymer
networks and water. However, when the water fraction in hydrogels
is bigger than 85%, its thermal conductivity will decrease and get
close to the water’s conductivity. Accordingly, to explain
this abnormal phenomenon, a 2-order-3-phase theoretical model is proposed
by considering hydrogel as a 3-phase composite. It can be found that
the proposed theory can predict results which agree quite well with
our simulated results.