3 research outputs found
Ultralight Graphene Foam/Conductive Polymer Composites for Exceptional Electromagnetic Interference Shielding
Ultralight,
high-performance electromagnetic interference (EMI) shielding graphene
foam (GF)/polyÂ(3,4-ethylenedioxythiophene):polyÂ(styrenesulfonate)
(PEDOT:PSS) composites are developed by drop coating of PEDOT:PSS
on cellular-structured, freestanding GFs. To enhance the wettability
and the interfacial bonds with PEDOT:PSS, GFs are functionalized with
4-dodecylbenzenesulfonic acid. The GF/PEDOT:PSS composites possess
an ultralow density of 18.2 × 10<sup>–3</sup> g/cm<sup>3</sup> and a high porosity of 98.8%, as well as an enhanced electrical
conductivity by almost 4 folds from 11.8 to 43.2 S/cm after the incorporation
of the conductive PEDOT:PSS. Benefiting from the excellent electrical
conductivity, ultralight porous structure, and effective charge delocalization,
the composites deliver remarkable EMI shielding performance with a
shielding effectiveness (SE) of 91.9 dB and a specific SE (SSE) of
3124 dB·cm<sup>3</sup>/g, both of which are the highest among
those reported in the literature for carbon-based polymer composites.
The excellent electrical conductivities of composites arising from
both the GFs with three-dimensionally interconnected conductive networks
and the conductive polymer coating, as well as the left-handed composites
with absolute permittivity and/or permeability larger than one give
rise to significant microwave attenuation by absorption
Graphene/Boron Nitride–Polyurethane Microlaminates for Exceptional Dielectric Properties and High Energy Densities
Hexagonal boron nitride
(h-BN) has tremendous potential for dielectric
energy storage by rationally assembling with graphene. We report the
fabrication of microlaminate composites consisting of alternating
reduced graphene oxide (rGO) and h-BN nanosheets embedded in a polyurethane
(PU) matrix using a novel, two-step bidirectional freeze casting process.
Porous, highly-aligned rGO–PU aerogels having ultrahigh dielectric
constants with relatively high dielectric losses and low dielectric
strengths are fabricated by initial freeze casting. The losses are
suppressed, whereas the dielectric strengths are restored by assembling
the porous rGO–PU skeleton with electrically insulating BN–PU
tunneling barrier layers in the second freeze casting routine. The
ligaments bridging the conductive rGO–PU layers are effectively
removed by the BN–PU barrier layers, eliminating the current
leakage in the transverse direction. The resultant rGO–PU/BN–PU
microlaminate composites deliver a remarkable dielectric constant
of 1084 with a low dielectric loss of 0.091 at 1 kHz. By virtue of
synergy arising from both the rGO–PU layers with a high dielectric
constant and the BN–PU barrier layers with a high dielectric
strength, the microlaminate composites present a maximum energy density
of 22.7 J/cm<sup>3</sup>, 44 folds of the neat rGO–PU composite
acting alone. The promising overall dielectric performance based on
a microlaminate structure offers a new insight into the development
of next-generation dielectric materials
Graphene Size-Dependent Multifunctional Properties of Unidirectional Graphene Aerogel/Epoxy Nanocomposites
Unidirectional
graphene aerogels (UGAs) with tunable densities, degrees of alignment,
and electrical conductivities are prepared by varying the average
size of precursor graphene oxide (GO) sheets between 1.1 and 1596
μm<sup>2</sup>. UGAs prepared using ultralarge GO (UL-UGA) outperform
those made from small GO in these properties. The UL-UGA/epoxy composites
prepared by infiltrating liquid epoxy resin into the porous UGA structure
exhibit an excellent electrical conductivity of 0.135 S/cm, along
with an ultralow percolation threshold of 0.0066 vol %, which is one
of the lowest values ever reported for all graphene-based composites.
Owing to their three-dimensional interconnected network, a high degree
of alignment, and effective reduction, UL-UGAs effectively enhance
the fracture toughness of epoxy by 69% at 0.11 vol % graphene content
through unique toughening mechanisms, such as crack pinning, crack
deflection, interfacial debonding, and graphene rupture. These aerogels
and composites can be mass-produced thanks to the facile, scalable,
and cost-efficient fabrication process, which will find various multifunctional
applications