Ultralight Graphene Foam/Conductive Polymer Composites for Exceptional Electromagnetic Interference Shielding

Ultralight, high-performance electromagnetic interference (EMI) shielding graphene foam (GF)/poly­(3,4-ethylenedioxythiophene):poly­(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^–3 g/cm³ 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·cm³/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/cm³, 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 μm². 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