Cai Jiang

3D Bridged Carbon Nanoring/Graphene Hybrid Paper as a High‐Performance Lateral Heat Spreader

Graphene paper (GP) has attracted great attention as a heat dissipation material due to its unique thermal transfer property exceeding the limit of graphite. However, the relatively poor thermal transfer properties in the normal direction of GP restricts its wider applications in thermal management. In this work, a 3D bridged carbon nanoring (CNR)/graphene hybrid paper is constructed by the intercalation of polymer carbon source and metal catalyst particles, and the subsequent in situ growth of CNRs in the confined intergallery spaces between graphene sheets through thermal annealing. Further investigation demonstrates that the CNRs are covalently bonded to the graphene sheets and highly improve the thermal transport in the normal direction of the CNR/graphene hybrid paper. This full-carbon architecture shows excellent heat dissipation ability and is much more efficient in removing hot spots than the reduced GP without CNR bridges. This highly thermally conductive CNR/graphene hybrid paper can be easily integrated into next generation commercial high-power electronics and stretchable/foldable devices as high-performance lateral heat spreader materials. This full-carbon architecture also has a great potential in acting as electrodes in supercapacitors or hydrogen storage devices due to the high surface area.

Nano-engineering thermal transport performance of carbon nanotube networks with polymer intercalation: a molecular dynamics study

Based on polymer perfusion behaviour inside carbon nanotube (CNT) networks, the thermal transport performances of the CNT networks with various extents of polymer intercalation are studied by dividing them into two parts: thermal transport at the tube contact interfaces of CNT junctions and along the tube axis. The thermal transport performance at the tube contact interfaces of CNT junctions is similar to that in the transverse direction of graphene layers. Hence, to obtain a fundamental understanding of thermal transport performance at the tube contact interfaces, thermal conductance along the z-axis direction of graphene layers with and without polymer intercalation is investigated using a non-equilibrium molecular dynamics (MD) simulation method. Thermal conductivity along the tube axis direction of the polymer wrapped CNT is also calculated using the same method. The simulation results show that a low extent of polymer aggregation at the tube contact interfaces can significantly improve the interfacial thermal conductance. However, when the polymer content at the tube contact interfaces exceeds a critical fraction, the interfacial thermal conductance is decreased. The results also indicate that the polymer molecules wrapping around the CNT walls have a strong negative influence on the bulk thermal conductivity of the CNT along its axis direction.

Influence of Carbon Nanotube Aspect Ratio on Glass Transition Temperature of Polymers: A Molecular Dynamics Simulation Study

Molecular dynamics (MD) simulations on three single walled carbon nanotube (SWCNT) reinforced epoxy resin composites were conducted to study the influence of SWCNT type on the glass transition temperature (Tg) of the composites. The composite matrix is cross-linked epoxy resin based on the epoxy monomers bisphenol A diglycidyl ether (DGEBA) cured by diaminodiphenylmethane (DDM). MD simulations of NPT (constant number of particles, constant pressure and constant temperature) dynamics were carried out to obtain density as a function of temperature for each composite system. The Tg was determined as the temperature corresponding to the discontinuity of plot slopes of the density vs the temperature. In order to understand the motion of polymer chain segments above and below the Tg, various energy components and the MSD at various temperatures of the composites were investigated and their roles played in the glass transition process were analyzed. The results show that the Tg of the composites increases with increasing aspect ratio of the embedded SWCNT

Diffusion of Epoxy Molecules on the Chemically Modified Graphene: A Molecular Dynamics Simulation Study

Buckypaper based polymer composites provides a new technical approach toward realizing conductive/structural multifunctional composites. Resin infiltration in the buckypaper is critical for the fabrication of buckypaper/polymer composites. To investigate the micro-infusion process of the polymer inside the paper, molecular dynamics (MD) simulations are conducted to study the diffusion behavior of epoxy molecules on the modified graphene and between graphene layers. The graphene molecular structures are constructed to represent the wall structures of the carbon nanotubes. Diffusion coefficients of the epoxy molecules on the graphene modified with different functionalization densities and interlayer distances are calculated. The results indicate that the functional groups increase the interfacial interactions between the epoxy molecules and graphene, however, largely decrease the diffusion speeds of the epoxy molecule. The simulations on the graphene layer systems indicate that, the viscous resistance of the resin is the main factor for retarding the diffusion of the epoxy molecules for the unmodified graphene layers; while for the modified graphene layers, functional groups are the main factor for retarding the resin diffusion

Influence of Surface Chemical Groups and Content of Carbon Nanotubes on Electrical Property of Epoxy Resin Composites

In this study, electrical properties of multi-walled carbon nanotubes (MWCNTs) reinforced epoxy resin composites were investigated, with respect to the method of dispersion, surfactants, content and chemical groups of CNTs. Experimental results show that chemical functionalization and surfactants improved the dispersion of CNTs in epoxy resin. Electrical conductivity of epoxy increased by two orders of magnitude with 0.5 wt% MWCNTs, while seven orders of magnitude with 2.0 wt% MWCNTs-NH2. The results also indicated that an effective electron transport channels formed in the composites with 0.5 wt% CNTs approximately.