Jesse Smithyman

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.

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.

Energy harvesting from humidity changes with a flexible coaxial electrode solid-state cell

The response to humidity changes from the open-circuit potential (OCP) of a coaxial electrode polymer electrolyte cell was characterized. The OCP response showed a dependency on both the rate of change of the humidity and on the rate of water diffusion within the electrolyte, suggesting the Gibbs free energy due to ionic concentration gradients as the source of the OCP response. This is supported through the estimation of the membrane potential using the Nernst equation and the good agreement between the experimental and theoretical results. The method exploits the hygroscopic properties of the polymer electrolyte and utilizes changes in the relative humidity (RH) of the surrounding environment to induce a concentration gradient between the electrodes. The establishment of the concentration gradient is achieved through the use of a solid-state electrochemical cell with a coaxial electrode structure, enabling the exposure of only one of the electrodes to the environment. These results have implications for applications such as energy harvesting and self-powered sensors and additionally may provide a novel approach to studying the thermodynamic properties of polymer electrolytes.