In
the recent times, multifunctional materials have attracted immense
interest. Self-healing polymers are in great demand in almost every
coating application. With an increase in electromagnetic (EM) pollution,
curbing the same has become an urgent necessity. Lightweight coatings
and conducting polymeric materials are being highly researched upon
in this regard, and combining these properties with self-healing systems
would open new avenues in EM interference (EMI) shielding (specifically
in the microwave frequency domain) applications. In the current study,
a novel approach toward the development of microwave shielding materials
capable of self-healing through microwave heating has been attempted.
A covalently cross-linked material was developed using Diels–Alder
(DA) chemistry, which shows self-healing properties when stimulated
by heating. Herein, reduced graphene oxide grafted with magnetite
nanoparticles (rGO/Fe
3
O
4
) was covalently cross-linked
to thermoplastic polyurethane using DA chemistry. The addition of
multiwalled carbon nanotubes into these nanocomposites led to exceptional
EM wave shielding and self-healing properties through a synergistic
effect. The synergism led to exceptional EMI shielding of −36
dB, primarily through absorption in the microwave region of the EM
spectrum. When used in the form of thin coatings of about 1 mm in
thickness, the shielding value reached −28 dB, manifesting
in more than 99% attenuation of EM waves through absorption. The material
was also found to be capable of healing scratches or cuts through
microwave irradiation.
The recent surge
in the usage of electronics has led to a new kind
of problem; electromagnetic interference which necessitates finding
alternate materials that offer ease of processing, design flexibility,
light weight, and ease of embedding and integrating with the existing
systems in place as shields to protect the precise electronic circuitry.
Herein, lightweight polycarbonate (PC)-based nanocomposites using
doped graphene derivatives and multiwalled carbon nanotubes (MWCNT)
has been explored for effective shielding of EM radiation in X- and
Ku-band. To get a mechanistic insight as to how the dopant in graphene
derivatives influences the EM shielding properties, two dopants have
been explored here: ferrimagnetic (ferrite, Fe3O4) and the other one as paramagnetic (gadolinium oxide, Gd2O3). The doped graphene derivatives when composited with
PC and MWCNTs resulted in materials that can shield the incoming EM
radiation through magnetic and dielectric losses. This strategy of
doping improves the state of dispersion of these dopants in the nanocomposites,
besides enhancing the shielding effectiveness. The PC-based nanocomposites
illustrated a total shielding effectiveness (SET) of −28
and −33 dB at 18 GHz for a given concentration of Gd2O3 and Fe3O4 hybrid, respectively.
A closer look into the mechanism of shielding reveals that irrespective
of the dopant, various losses (magnetic and dielectric) decide the
shielding effectiveness in polymeric nanocomposites facilitated by
multiple internal reflections. Taken together, this study brings in
new insight as to how the losses contribute toward effective shielding
rather than the choice of the dopant and will help guide researchers
working in this area from both industrial as well as academic perspective.
Recent advancements in electronics and telecommunication require materials with excellent resiliency and sustainability in order to extend their lifetime. Keeping this in mind, we developed a sustainable multifunctional nanocomposite by combining the shape memory assisted selfhealing (SMASH) capability of "mussel-inspired" dopamine functionalized polyurethane (PU) with synergistic electromagnetic interference (EMI) shielding capabilities from multiwalled carbon nanotubes (MWNTs) and ferrite doped with MoS 2 (Fe 3 O 4 @MoS 2 ). The self-healing ability in the polymer was driven by the reversible dynamic coordination bonds, between Fe 3+ ions and hydroxyl functional groups of dopamine. The modified PU was also found to be capable of undergoing SMASH by heating it to 50 °C, whereby no manual intervention was required to bring the damaged ends together to trigger healing ability. The developed polymer and its nanocomposites performed quite well in terms of restoration of up to 75% and 56% of its original tensile strength, respectively. The nanocomposite showed outstanding EMI shielding capability of up to −36.6 dB manifesting in up to 96% absorption of EM waves. This strategy aims to shed some light on the design and development of sustainable and resilient materials for EMI shielding applications.
In this critical review, we have enlisted a comprehensive summary of different approaches that have been used over the past decade to synthesize self-healing polyurethanes including “close then heal” and “shape memory assisted self-healing” concept.
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