Effect of Contact Pressure on the Performance of Carbon Nanotube Arrays Thermal Interface Material

Hybrid carbon thermal interface materials for thermoelectric generator devices

Thermal interface materials (TIMs) are extensively used in electronic devices as efficient heat transfer materials. We fabricated all-carbon TIMs by hybridizing single-wall carbon nanotubes (SWCNTs) with graphite and demonstrated their performance by applying them to a thermoelectric generator (TEG) device. The hybrid carbon TIM exhibited maximum thermal conductivity when the SWCNT content was near 10 wt%. The TIM thermal contact resistance measured by a home-made calorimeter setup was 2.19 × 10⁻⁴ m²K/W, which did not vary with temperature but decreased with applied pressure. Post-treatment of the TIM with a silane coupling agent further reduced the TIM thermal contact resistance by 30%. When the TIM was placed between a TEG device and a copper heat reservoir, the TEG output power increased with the temperature difference across the TEG and applied pressure. Moreover, the post-treatment of the TIM enhanced the output power of the TEG device by up to 18.5%. This work provides a simple and effective pathway towards a carbon-based TIM that can be applied to a high temperature TEG.

Investigation of the relationship between adhesion force and mechanical behavior of vertically aligned carbon nanotube arrays

The mechanical behavior of vertically aligned carbon nanotube (VACNT) arrays can largely impact their adhesion performance. In this paper, we fabricated various VACNT arrays to investigate the relationship between adhesion force and their mechanical behavior. High-volume fraction (3.4%) CNT arrays did not exhibit the applicable adhesion effect due to their intrinsic elastic property. Adhesion measurements on several low-density (less than 0.5%) VACNT arrays demonstrated that the adhesion performance is strongly related to the plastic deformation of the carbon nanotubes at the contact surface. Due to the nature of the growth of CNT arrays, the top region of the as-grown CNT arrays is denser and stiffer than the bottom region of the arrays. Therefore, compared with as-grown CNT arrays, the flipped CNT arrays reached higher adhesion efficiency (the ratio of adhesion force to preload) with lower preload due to the higher compliance at the top surface of the arrays. With cyclic loading under micro mechanical tests, stiffening of the surface and declining of adhesion force were also observed. These results illustrated that the mechanical compliance at the region near the contact interface is the dominant factor for the adhesion performance of VACNT arrays.

Applying Aluminum⁻Vertically-Aligned Carbon Nanotube Forests Composites for Heat Dissipation

Vertically-aligned carbon nanotube forests (VACNTs) with excellent axial heat dissipation properties were formed on aluminum foil to dissipate heat. In addition, the heat dissipation efficiency of aluminum-VACNTs composites in this work was compared with that of commercially available mainstream thermal sheets under the same natural cooling conditions. Chemical vapor deposition (CVD) was employed as a synthesis method using a three-segment high-temperature furnace. Subsequently, the temperature changes in a heating body with the aluminum-VACNTs composites was measured over time subject to natural cooling. In addition, the performance was compared with copper and pyrolytic graphite sheets. The experimental results revealed that the heat dissipation efficiency of the flexible aluminum-VACNTs composites was higher than that of clean aluminum foil, a copper sheet, and a pyrolytic graphite sheet by up to 56%, 40%, and 20%, respectively. Moreover, this work also verified the height of the carbon nanotube (CNT) did not influence the heat dissipation efficiency, indicating that the time cost of synthesis could be reduced.

Wave Propagation of Porous Nanoshells

This study aims at investigating the wave propagation of porous nanoshells. The Bi-Helmholtz non-local strain gradient theory is employed in conjunction with a higher-order shear deformation shell theory, in order to include the size-dependent effects. The nanoshells are made of a porous functionally graded material (P-FGM), whose properties vary continuously along the thickness direction. A variational approach is here applied to handle the governing equations of the problem, which are solved analytically to compute the wave frequencies and phase velocities as function of the wave numbers. The sensitivity of the wave response is analyzed for a varying porosity volume fraction, material properties, non-local parameters, strain gradient length scales, temperature, humidity, and wave numbers. Based on the results, it is verified that the size-dependence of the response is almost the same to the one of plates, beams and tubes.