Ultrafast Synthesis of Multifunctional N‑Doped Graphene Foam in an Ethanol Flame

A hard template method to prepare N-doped graphene foams (NGF) with superfast template removal was developed through a pyrolyzing commercial polyurethane (PU) sponge coated with graphene oxide (GO) sheets in an ethanol flame. The removal of the template was fast and facile, and could be completed in less than 60 s in an open environment. The synthesized graphene foams consisted of a unique structure of 3D interconnected hollow struts with highly wrinkled surfaces, and the morphology of the hollow struts could be tuned by controlling the GO dispersion concentration. The foams showed high hydrophobicity and were used as absorbents for a variety of organic solvents and oils. The unique NGF structure afforded a high absorption rate and capacity, and a remarkable 98.7% pore volume of the foam could be utilized for absorption of hexane, exhibiting one of the highest capacity values among existing absorptive counterparts. The N-doping brought higher capacitive performance than conventional graphene foams prepared by chemical vapor deposition on nickel foam templates. The NGFs also displayed high elasticity and could recover completely after 50% compressive strain. Owing to easy availability and reduction environment of the flame, complete thermal decomposition of the PU sponge and highly porous open-cell structure, and flame resistance of the graphene foam, the present flame method was demonstrated to be a simple, effective, and ultrafast approach to fabricate ultra-low-density NGFs with good electromechanical response, excellent organic liquid absorption, and high-energy dissipation capabilities

Exceptional Electrical Conductivity and Fracture Resistance of 3D Interconnected Graphene Foam/Epoxy Composites

Cellular-structured graphene foam (GF)/epoxy composites are prepared based on a three-step fabrication process involving infiltration of epoxy into the porous GF. The three-dimensional (3D) GF is grown on a Ni foam template <i>via</i> chemical vapor deposition. The 3D interconnected graphene network serves as fast channels for charge carriers, giving rise to a remarkable electrical conductivity of the composite, 3 S/cm, with only 0.2 wt % GF. The corresponding flexural modulus and strength increase by 53 and 38%, respectively, whereas the glass transition temperature increases by a notable 31 °C, compared to the solid neat epoxy. The GF/epoxy composites with 0.1 wt % GF also deliver an excellent fracture toughness of 1.78 MPa·m^1/2, 34 and 70% enhancements against their “porous” epoxy and solid epoxy counterparts, respectively. These observations signify the unrivalled effectiveness of 3D GF relative to 1D carbon nanotubes or 2D functionalized graphene sheets as reinforcement for polymer composites without issues of nanofiller dispersion and functionalization prior to incorporation into the polymer

Ultralow-Carbon Nanotube-Toughened Epoxy: The Critical Role of a Double-Layer Interface

Understanding the chemistry and structure of interfaces within epoxy resins is important for studying the mechanical properties of nanofiller-filled nanocomposites as well as for developing high-performance polymer nanocomposites. Despite the intensive efforts to construct nanofiller/matrix interfaces, few studies have demonstrated an enhanced stress-transferring efficiency while avoiding unfavorable deformation due to undesirable interface fractures. Here, we report an optimized method to prepare epoxy-based nanocomposites whose interfaces are chemically modulated by poly­(glycidyl methacrylate)-<i>block</i>-poly­(hexyl methacrylate) (PGMA-<i>b</i>-PHMA)-functionalized multiwalled carbon nanotubes (bc@fMWNTs) and also offer a fundamental explanation of crack growth behavior and the toughening mechanism of the resulting nanocomposites. The presence of block copolymers on the surface of the MWNT results in a promising double-layered interface, in which (1) the outer-layered PGMA segment provides good dispersion in and strong interface bonding with the epoxy matrix, which enhances load transfer efficiency and debonding stress, and (2) the interlayered rubbery PHMA segment around the MWNT provides the maximum removable space for nanotubes as well as triggering cavitation while promoting local plastic matrix deformation, for example, shear banding to dissipate fracture energy. An outstanding toughening effect is achieved with only a 0.05 wt % carbon nanotube loading with the bc@fMWNT, that is, needing only a 20-times lower loading to obtain improvements in fracture toughness comparable to epoxy-based nanocomposites. The enhancements of their corresponding ultimate mode-I fracture toughnesses and fracture energies are 4 times higher than those of pristine MWNT-filled epoxy. These results demonstrate that a MWNT/epoxy interface could be optimized by changing the component structure of grafted modifiers, thereby facilitating the transfer of both mechanical load and energy dissipation across the nanofiller/matrix interface. This work provides a new route for the rational design and development of polymer nanocomposites with exceptional mechanical performance

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

Reinforcement of Polyether Polyurethane with Dopamine-Modified Clay: The Role of Interfacial Hydrogen Bonding

Dopamine-modified clay (D-clay) was successfully dispersed into polyether polyurethane (PU) by solvent blending. It is found that the incorporation of D-clay into PU gives rise to significant improvements in mechanical properties, including initial modulus, tensile strength, and ultimate elongation, at a very low clay loading. The large reinforcement could be attributed to the hydrogen bonds between the hard segments of PU and stiff D-clay layers that lead to more effective interfacial stress transfer between the polymer and D-clay. Besides, the interactions between D-clay and PU are also stronger than those between Cloisite 30B organoclay and the PU chains. Consequently, at a similar clay loading, the PU/D-clay nanocomposite has much higher storage modulus than the PU/organoclay nanocomposite at elevated temperatures

Anelastic Behavior in GaAs Semiconductor Nanowires

The mechanical behavior of vertically aligned single-crystal GaAs nanowires grown on GaAs(111)_B surface was investigated using in situ deformation transmission electron microscopy. Anelasticity was observed in nanowires with small diameters and the anelastic behavior was affected by the crystalline defects in the nanowires. The underlying mechanism for the observed anelasticity is discussed. The finding opens up the prospect of using nanowire materials for nanoscale damping applications

Hollow Carbon-Nanotube/Carbon-Nanofiber Hybrid Anodes for Li-Ion Batteries

By a novel <i>in situ</i> chemical vapor deposition, activated N-doped hollow carbon-nanotube/carbon-nanofiber composites are prepared having a superhigh specific Brunauer–Emmett–Teller (BET) surface area of 1840 m² g^–1 and a total pore volume of 1.21 m³ g^–1. As an anode, this material has a reversible capacity of ∼1150 mAh g^–1 at 0.1 A g^–1 (0.27 C) after 70 cycles. At 8 A g^–1 (21.5 C), a capacity of ∼320 mAh g^–1 fades less than 20% after 3500 cycles, which makes it a superior anode material for a Li-ion battery

Anelastic Behavior in GaAs Semiconductor Nanowires

The mechanical behavior of vertically aligned single-crystal GaAs nanowires grown on GaAs(111)_B surface was investigated using in situ deformation transmission electron microscopy. Anelasticity was observed in nanowires with small diameters and the anelastic behavior was affected by the crystalline defects in the nanowires. The underlying mechanism for the observed anelasticity is discussed. The finding opens up the prospect of using nanowire materials for nanoscale damping applications

Anelastic Behavior in GaAs Semiconductor Nanowires

The mechanical behavior of vertically aligned single-crystal GaAs nanowires grown on GaAs(111)_B surface was investigated using in situ deformation transmission electron microscopy. Anelasticity was observed in nanowires with small diameters and the anelastic behavior was affected by the crystalline defects in the nanowires. The underlying mechanism for the observed anelasticity is discussed. The finding opens up the prospect of using nanowire materials for nanoscale damping applications

Anelastic Behavior in GaAs Semiconductor Nanowires

The mechanical behavior of vertically aligned single-crystal GaAs nanowires grown on GaAs(111)_B surface was investigated using in situ deformation transmission electron microscopy. Anelasticity was observed in nanowires with small diameters and the anelastic behavior was affected by the crystalline defects in the nanowires. The underlying mechanism for the observed anelasticity is discussed. The finding opens up the prospect of using nanowire materials for nanoscale damping applications