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Biomimetic Reversible Heat-Stiffening Polymer Nanocomposites
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posted on 2017-07-26, 00:00 authored by Elvis Cudjoe, Shaghayegh Khani, Amanda E. Way, Michael J. A. Hore, Joao Maia, Stuart J. RowanInspired by the ability of the sea
cucumber to (reversibly) increase
the stiffness of its dermis upon exposure to a stimulus, we herein
report a stimuli-responsive nanocomposite that can reversibly increase
its stiffness upon exposure to warm water. Nanocomposites composed
of cellulose nanocrystals (CNCs) that are grafted with a lower critical
solution temperature (LCST) polymer embedded within a poly(vinyl acetate)
(PVAc) matrix show a dramatic increase in modulus, for example, from
1 to 350 MPa upon exposure to warm water, the hypothesis being that
grafting the polymers from the CNCs disrupts the interactions between
the nanofibers and minimizes the mechanical reinforcement of the film.
However, exposure to water above the LCST leads to the collapse of
the polymer chains and subsequent stiffening of the nanocomposite
as a result of the enhanced CNC interactions. Backing up this hypothesis
are energy conserving dissipative particle dynamics (EDPD) simulations
which show that the attractive interactions between CNCs are switched
on upon the temperature-induced collapse of the grafted polymer chains,
resulting in the formation of a percolating reinforcing network.