Chuck Zhang

Lithium-Air Batteries Using SWNT/CNF Buckypapers as Air Electrodes

Li-air cells based on Li foil as an anode electrode, freestanding carbon nanotube/nanofiber mixed buckypaper as an air (cathode) electrode, and organic electrolyte were assembled. The air electrode was made with single-wall carbon nanotube (SWNT) and carbon nanofiber (CNF) without any binder. The discharge capacity was strongly dependent on both the discharge current density and the thickness of the air electrode. A discharge capacity as high as 2500 mAh/g was obtained for an air electrode at a thickness of 20 μm with a discharge current density of 0.1 mA/cm 2 ; however, it was reduced to 400 mAh/g when the thickness of the air electrode was increased to 220 μm. For a 66 μm thick air electrode, the discharge capacity decreased from 1600 to 340 mAh/g when the discharge current density increased from 0.1 to 0.5 mA/cm 2 . The scanning electron microscope images on surfaces of the air electrode from a fully discharged cell showed that the voids at the air side were almost fully filled by the solid deposition; however, the voids at the membrane side were still wide open.

Carbon nanotube integrated multifunctional multiscale composites

Carbon nanotubes (CNTs) demonstrate extraordinary properties and show great promise in enhancing out-of-plane properties of traditional polymer composites and enabling functionality, but current manufacturing challenges hinder the realization of their potential. This paper presents a method to fabricate multifunctional multiscale composites through an effective infiltration-based vacuum-assisted resin transfer moulding (VARTM) process. Multi-walled carbon nanotubes (MWNTs) were infused through and between glass-fibre tows along the through-thickness direction. Both pristine and functionalized MWNTs were used in fabricating multiscale glass-fibre-reinforced epoxy composites. It was demonstrated that the mechanical properties of multiscale composites were remarkably enhanced, especially in the functionalized MWNT multiscale composites. With only 1?wt% loading of functionalized MWNTs, tensile strength was increased by 14% and Youngs modulus by 20%, in comparison with conventional fibre-reinforced composites. Moreover, the shear strength and short-beam modulus were increased by 5% and 8%, respectively, indicating the improved inter-laminar properties. The strain?stress tests also suggested noticeable enhancement in toughness. Scanning electron microscopy (SEM) characterization confirmed an enhanced interfacial bonding when functionalized MWNTs were integrated into epoxy/glass-fibre composites. The coefficient thermal expansion (CTE) of functionalized nanocomposites indicated a reduction of 25.2% compared with epoxy/glass-fibre composites. The desired improvement of electrical conductivities was also achieved. The multiscale composites indicated a way to leverage the benefits of CNTs and opened up new opportunities for high-performance multifunctional multiscale composites.

A Strong Integrated Strength and Toughness Artificial Nacre Based on Dopamine Cross-Linked Graphene Oxide

Demands of the strong integrated materials have substantially increased across various industries. Inspired by the relationship of excellent integration of mechanical properties and hierarchical nano/microscale structure of the natural nacre, we have developed a strategy for fabricating the strong integrated artificial nacre based on graphene oxide (GO) sheets by dopamine cross-linking via evaporation-induced assembly process. The tensile strength and toughness simultaneously show 1.5 and 2 times higher than that of natural nacre. Meanwhile, the artificial nacre shows high electrical conductivity. This type of strong integrated artificial nacre has great potential applications in aerospace, flexible supercapacitor electrodes, artificial muscle, and tissue engineering.

Functionalized Carbon‐Nanotube Sheet/Bismaleimide Nanocomposites: Mechanical and Electrical Performance Beyond Carbon‐Fiber Composites

Since their discovery in 1991, carbon nanotubes (CNTs) have been considered as the next-generation reinforcement materials to potentially replace conventional carbon fibers for producing super-high-performance lightweight composites. Herein, it is reported that sheets of millimeter-long multi-walled CNTs with stretch alignment and epoxidation functionalization reinforce bismaleimide resin, which results in composites with an unprecedentedly high tensile strength of 3081 MPa and modulus of 350 GPa, well exceeding those of state-of-the-art unidirectional carbon-fiber-reinforced composites. The results also provide important experimental evidence of the impact of functionalization and the effect of alignment reported previously on the mechanical performance and electrical conductivity of the nanocomposites.

α-MnO2/Carbon Nanotube/Carbon Nanofiber Composite Catalytic Air Electrodes for Rechargeable Lithium-air Batteries

Air electrodes, made with a mixture of carbon nanotube (CNT)/carbon nanofiber (CNF) and with/without α-MnO2 nano-rods, were prepared for Li-air cells. The charge capacity and cyclability were found to increase largely for the cells made with the α-MnO2 catalyst; however, the first cycle discharge capacities were no different for the cells made with and without the α-MnO2 catalyst. It was found that the discharge capacity of the Li-air cell was mainly due to oxygen deficiency from the pinch-off of the diffusion channel by the deposition product at the air side of the air electrode. Electrochemical impedance spectra at different cycles demonstrated that the charge transfer resistance was increased and decreased during discharge and charge processes, respectively, due to the change of porosity, oxygen concentration, and rate of coefficient of chemical reaction in the air electrode.

Electromagnetic interference shielding properties of carbon nanotube buckypaper composites

Preformed carbon nanotube thin films (10-20 microm), or buckypapers (BPs), consist of dense and entangled nanotube networks, which demonstrate high electrical conductivity and provide potential lightweight electromagnetic interference (EMI) solutions for composite structures. Nanocomposite laminates consisting of various proportions of single-walled and multi-walled carbon nanotubes, having different conductivity, and with different stacking structures, were studied. Single-layer BP composites showed shielding effectiveness (SE) of 20-60 dB, depending on the BP conductivity within a 2-18 GHz frequency range. The effects on EMI SE performance of composite laminate structures made with BPs of different conductivity values and epoxy or polyethylene insulating layer stacking sequences were studied. The results were also compared against the predictions from a modified EMI SE model. The predicted trends of SE value and frequency dependence were consistent with the experimental results, revealing that adjusting the number of BP layers and appropriate arrangement of the BP conducting layers and insulators can increase the EMI SE from 45 dB to close to 100 dB owing to the utilization of the double-shielding effect.

Flow modeling and simulation of SCRIMP for composites manufacturing

Abstract As for the environmental protection, relatively inexpensive tooling and the ability to fabricate large parts with complex geometry, the vacuum bag molding (VBM) process and its variations such as SCRIMP might be the best choice to replace the traditional open molding processes. Since SCRIMP is often used to fabricate large size composites with a complex geometry, it is difficult to reach an acceptable design by the trial and error. Considerable expenses and time are compiled this way and obstruct the widespread use of VBM. Computer aided design and computer aided manufacturing (CAD/CAM), with its ability to simulate resin flowing through fiber mat, would be the best way to solve this problem. Many 2 1 2 -dimensional ( 2 1 2 D ) flow models have been developed to simulate the mold filling processes in resin transfer molding (RTM). The resin infusion processes in VBM are similar to the mold filling process in RTM, but the following two issues must be considered: the resin flow from the channels or grooves to the fiber mats, and the compressibility of fiber mats. A hybrid 2 1 2 D and 3D flow model to simulate the SCRIMP processes is proposed in the paper. According to the simulated results, sub-scale composite hulls (4′) were fabricated. The simulated results agree well with the experimental results.

Statistical characterization of single-wall carbon nanotube length distribution

This paper describes an effective method for quantifying the length and length distribution of large populations of single-wall carbon nanotubes using atomic force microscopy and SIMAGIS software. The results of the measurements were modelled with the Weibull distribution, resulting in a statistically confirmed fit. The fitted Weibull distribution was used to predict the length effect factor and elastic modulus as functions of nanotube properties in composite materials. The prediction shows that the length factor for the elastic modulus tends to increase with enhanced loading but decrease with rising rope diameter. The statistical characterization presented indicates a pathway for the future theoretical modelling and related experimental investigation of carbon nanotube application.

Controlled nanostructure and high loading of single-walled carbon nanotubes reinforced polycarbonate composite

This paper presents an effective technique to fabricate thermoplastic nanocomposites with high loading of well-dispersed single-walled carbon nanotubes (SWNTs). SWNT membranes were made from a multi-step dispersion and filtration method, and then impregnated with polycarbonate solution to make thermoplastic nanocomposites. High loading of nanotubes was achieved by controlling the viscosity of polycarbonate solution. SEM and AFM characterization results revealed the controlled nanostructure in the resultant nanocomposites. Dynamic mechanical property tests indicated that the storage modulus of the resulting nanocomposites at 20 wt% nanotubes loading was improved by a factor of 3.4 compared with neat polycarbonate material. These results suggest the developed approach is an effective way to fabricate thermoplastic nanocomposites with good dispersion and high SWNT loading.

Effects of surfactants and alignment on the physical properties of single-walled carbon nanotube buckypaper

Single-walled carbon nanotubes were dispersed in an aqueous medium using surfactants and filtered to make entangled networks, called buckypaper (BP), and the Raman spectra of BP samples revealed the degree of entanglement and residual surfactant content. The temperature dependence of the G-band peak shift in the BP was found to depend on the reduction in residual surfactant and nanotube oxidation. The electrical conductivity was improved after removing the surfactant and increasing the nanotube alignment, although the temperature dependence of electrical resistivity still followed a variable range hopping conduction behavior. The mechanical properties were affected by the degree of entanglement, alignment, and residual surfactant content, and tensile properties were found to improve with the reduction in surfactant and enhancement of alignment.