Here we introduce the electromagnetic shielding effectiveness (SE) of reduced graphene oxide (RGO) sheets interleaved between polyetherimide (PEI) films fabricated by electrophoretic deposition (EPD). Incorporating only 0.66 vol % of RGO, the developed PEI/RGO composite films exhibited an electromagnetic interference shielding effectiveness (EMI SE) at 6.37 dB corresponding to ∼50% shielding of incident waves. Excellent flexibility and optical transparency up to 62% of visible light was demonstrated. It was achieved by placing the RGO sheets in the localized area as a thin film (ca. 20 nm in thickness) between the PEI films (ca. 2 μm) to be an interleaved and alternating structure. This unique interleaved structure without any delamination areas was fabricated by a successive application of cathodic and anodic EPD of both RGO and PEI layers. The EPD fabrication process was ensured by an alternating deposition of the quarternized-PEI drops and RGO, each taking positive and negative charges, respectively, in the water medium. We believe that the developed facile fabrication method of RGO interleaved structure with such low volume fraction has great potential to be used as a transparent EMI shielding material.
A new synthesis route of a solution-processed highly
conductive
self-standing graphite membrane from reassembled graphene oxide (GO)
has become one of the intensive research focus, because of its immense
application opportunities. Previously demonstrated techniques were
limited by the unstable reduced graphene oxide (RGO) dispersion and
agglomeration during chemical reduction without any surfactant. This
results in poor packing morphology and low electrical conductivity
of the RGO membrane. Here, we report a novel synthesis route of a
highly concentrated RGO solution from exfoliated GO, which results
highly conductive and self-standing RGO membrane without using any
binders or organic solvents. Our low-temperature reduction method
is significantly different from previous investigations in which controlling
the reduction rate by lowering the reduction temperature of the GO
solution and collision probability was the key factor in preventing
random agglomeration. Further high-temperature reduction of the RGO
membrane gave rise to a reassembled graphite structure containing
negligible oxygen content (O 1s/C 1s = 0.005), and high electrical
conductivity (up to 1.6 × 105 S/m) without disintegration
of its self-standing feature. This result is better than any previously
reported value. Developed RGO membrane could be mass-produced for
various flexible device applications. The in-plane alignment and through-thickness
consolidation of GO and RGO membranes using vacuum-filtration and
thermal treatment successfully ensured the synthesis of highly conductive,
mechanically robust RGO and graphite membranes.
A large-area, conductive, and flexible membrane made from the stabilized aqueous solution of reduced graphene oxide (RGO) is successfully fabricated using an electrophoretic deposition (EPD) method. A low-voltage operation of EPD (∼3 volts) allows a robust consolidation of RGO layers desirably aligned in the in-plane direction through the cohesive electrophoretic squeezing force near the current collector. Transferring the deposited RGO layers to arbitrary substrates or achieving as a free-standing form, two methods of "chemical etching" and "electrochemical etching" are developed to detach the RGO layers from the EPD current collector without damaging the deposited RGO. Further reducing the free-standing RGO membrane by thermal annealing up to 1000 °C, a graphite-like architecture is restored (d-spacing at 3.42 Å with C/O ratio at 16.66) and the electrical conductivity increases as high as 5.51 × 10(5) S/m. The tightly-consolidated and securely-detached RGO membrane allows the free-standing and flexible features and highly conductive characteristics, which are further developed during thermal treatment. Because of the facile scale-up nature of the EPD process and RGO solution, the developed methodology has a considerable potential to be applied to various energy storage devices, flexible conductive coatings, and other electrochemical systems.
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