Enhancement of Isotropic Heat Dissipation of Polymer Composites by Using Ternary Filler Systems Consisting of Boron Nitride Nanotubes, h-BN, and Al2O3.

In this research article, a poly(dimethylsiloxane) (PDMS)-based composite was postulated adapting an interactive ternary filler system consisting of Al2O3, hexagonal boron nitride (h-BN), and boron nitride nanotubes (BNNT) to construct a continuous three-dimensional (3D) structure for thermal attenuation. Al2O3 was imposed as a main filler, while h-BN and BNNT were assimilated to form interconnected heat conduction pathways for effective thermal dissipation. The structured framework articulates a profound improvement in isotropic thermal conductivity considering both axial and radial heat dissipation. The presence of h-BN entails uniform heat distribution in a planar mode, eliminating the occurrence of hotspots, while BNNT constructed a connecting phonon pathway in various directions, which insinuates effective overall thermal transport. The generated ternary filler composites attained an isotropic ratio of 1.35 and a thermal conductivity of 7.50 W/mK, which is a 36-fold (∼3650%) increase compared to neat PDMS resin and almost 3-fold (∼297%) that of the Al2O3 unary filler composite and ∼53% that of its binary counterpart, partaking interfacial thermal gaps of ∼36.15 and ∼62.24% on practical heating performance relative to its counterparts. Moreover, the incorporation of BNNT on a traditional spherical and planar filler offers an advantage not only in thermal conductivity but also in thermal and structural stability. Improvement in thermal stability is stipulated due to a melting point (Tm) shift of ∼11 °C upon the assimilation of BNNT. Mechanical permeance reinforcement was also observed with the presence of BNNT, showcasing a 31.5% increase in tensile strength and a 53% increase in Young's modulus relative to the singular filler composite. This exploration administers a new insight into heat dissipation phenomena in polymeric composites and proposes a simple approach to their design and assembly.

Two-Dimensional rGO-MoS2 Hybrid Additives for High-Performance Magnetorheological Fluid.

Magnetorheological fluids (MRF) that undergo a change in their viscoelastic properties under the magnetic fields have been considered as one of most important smart functional materials for vibration dampers and shock absorbers in several engineering applications. However, the use of magnetorheological fluids in practical applications has been limited by poor sedimentation ratio and on-state yield stress. Herein, we report hybrid rGO-MoS2 additives for a high-performance magnetorheological fluid. Two different kinds of hybrid additives, which are called non-magnetic rGO-MoS2 and magnetic Fe-rGO-MoS2, were synthesized by using a hydrothermal method. The rGO-MoS2 added suspensions remained stable for the first 90 min whereas the CIP MRFs settled down quickly (65%) in the first 10 minutes. The Fe-rGO-MoS2 additives showed a 24% higher on-state shear stress as compared to CIP MRFs. On the other hand, an increase of 60% in the on-state yield stress for Fe-rGO-MoS2 MRF can be attributed to the gap-filling by the hybrid additives during columnar-structure formation. Among two-dimensional (2D) materials, Molybdenum Disulphide (MoS2) is a member of transition metal dichalcogenides (TMDCs), traditionally used as solid lubricant, while reduced graphene-oxide (rGO) is a well-known 2D material with supreme mechanical properties. We believe that this study will blaze the new way for developing a high-performance magnetorheological fluids based on various 2D material hybrids.

Microwave-Assisted Synthesis of Boron and Nitrogen co-doped Reduced Graphene Oxide for the Protection of Electromagnetic Radiation in Ku-Band.

The electromagnetic interference (EMI) shielding of reduced graphene oxide (MRG), B-doped MRG (B-MRG), N-doped MRG (N-MRG), and B-N co-doped MRG (B-N-MRG) have been studied in the Ku-band frequency range (12.8-18 GHz). We have developed a green, fast, and cost-effective microwave assisted route for synthesis of doped MRG. B-N-MRG shows high electrical conductivity in comparison to MRG, B-MRG and N-MRG, which results better electromagnetic interference (EMI) shielding ability. The co-doping of B and N significantly enhances the electrical conductivity of MRG from 21.4 to 124.4 Sm(-1) because N introduces electrons and B provides holes in the system and may form a nanojunction inside the material. Their temperature-dependent electrical conductivity follows 2D-variable range hopping (2D-VRH) and Efros-Shklovskii-VRH (ES-VRH) conduction model in a low temperature range (T<50 K). The spatial configuration of MRG after doping of B and N enhances the space charge polarization, natural resonance, dielectric polarization, and trapping of EM waves by internal reflection leading to a high EMI shielding of -42 dB (∼99.99% attenuation) compared to undoped MRG (-28 dB) at a critical thickness of 1.2 mm. Results suggest that the B-N-MRG has great potential as a candidate for a new type of EMI shielding material useful in aircraft, defense industries, communication systems, and stealth technology.

Nanohole-Structured and Palladium-Embedded 3D Porous Graphene for Ultrahigh Hydrogen Storage and CO Oxidation Multifunctionalities.

Atomic-scale defects on carbon nanostructures have been considered as detrimental factors and critical problems to be eliminated in order to fully utilize their intrinsic material properties such as ultrahigh mechanical stiffness and electrical conductivity. However, defects that can be intentionally controlled through chemical and physical treatments are reasonably expected to bring benefits in various practical engineering applications such as desalination thin membranes, photochemical catalysts, and energy storage materials. Herein, we report a defect-engineered self-assembly procedure to produce a three-dimensionally nanohole-structured and palladium-embedded porous graphene hetero-nanostructure having ultrahigh hydrogen storage and CO oxidation multifunctionalities. Under multistep microwave reactions, agglomerated palladium nanoparticles having diameters of ∼10 nm produce physical nanoholes in the basal-plane structure of graphene sheets, while much smaller palladium nanoparticles are readily impregnated inside graphene layers and bonded on graphene surfaces. The present results show that the defect-engineered hetero-nanostructure has a ∼5.4 wt % hydrogen storage capacity under 7.5 MPa and CO oxidation catalytic activity at 190 °C. The defect-laden graphene can be highly functionalized for multipurpose applications such as molecule absorption, electrochemical energy storage, and catalytic activity, resulting in a pathway to nanoengineering based on underlying atomic scale and physical defects.

3D networked graphene-ferromagnetic hybrids for fast shape memory polymers with enhanced mechanical stiffness and thermal conductivity.

A novel 3D networked graphene-ferromagnetic hybrid can be easily fabricated using one-step microwave irradiation. By incorporating this hybrid material into shape memory polymers, the synergistic effects of fast speed and the enhancement of thermal conductivity and mechanical stiffness can be achieved. This can be broadly applicable to designing magneto-responsive shape memory polymers for multifunction applications.

Graphene--nanotube--iron hierarchical nanostructure as lithium ion battery anode.

In this study, we report a novel route via microwave irradiation to synthesize a bio-inspired hierarchical graphene--nanotube--iron three-dimensional nanostructure as an anode material in lithium-ion batteries. The nanostructure comprises vertically aligned carbon nanotubes grown directly on graphene sheets along with shorter branches of carbon nanotubes stemming out from both the graphene sheets and the vertically aligned carbon nanotubes. This bio-inspired hierarchical structure provides a three-dimensional conductive network for efficient charge-transfer and prevents the agglomeration and restacking of the graphene sheets enabling Li-ions to have greater access to the electrode material. In addition, functional iron-oxide nanoparticles decorated within the three-dimensional hierarchical structure provides outstanding lithium storage characteristics, resulting in very high specific capacities. The anode material delivers a reversible capacity of ~1024 mA · h · g(-1) even after prolonged cycling along with a Coulombic efficiency in excess of 99%, which reflects the ability of the hierarchical network to prevent agglomeration of the iron-oxide nanoparticles.

Defect-engineered three-dimensional graphene-nanotube-palladium nanostructures with ultrahigh capacitance.

The development of three-dimensional carbon-based nanostructures is the next step forward for boosting industrial applications of carbon nanomaterials such as graphenes and carbon nanotubes. Some defects, which have been considered as detrimental factors for maintaining exceptional materials properties of two-dimensional graphene, can be actively used to synthesize three-dimensional graphene-based carbon nanostructures. Here we describe a fast and heretofore unreported defect-engineered method to synthesize three-dimensional carbon nanohybrid structures with strong bonding between graphene nanoplatelets and carbon nanotubes using simple microwave irradiation and an ionic liquid. Our one-pot method utilizes defect-engineered sequential processes: microwave-based defect generation on graphene nanoplatelets, anchoring of palladium nanoparticles on these defects, and subsequent growth of carbon nanotubes by use of an ionic liquid. The unique three-dimensional nanostructures showed an ultrahigh redox capacitance due to high porosity, a high surface-to-volume ratio from the spacer role of vertically standing one-dimensional carbon nanotubes on graphene sheets, and capacitance-like redox response of the palladium nanoparticles. The proposed defect-engineered method could lead to novel routes to synthesizing three-dimensional graphene-based nanostructures with exceptionally high performance in energy storage systems.