Advances in methodologies to characterize complex carbon-based materials by sub-GHz and MID-THz spectroscopies

Functional and structured materials are currently developed for high power electronics in transportation and aerospace sectors facing size and weight constraints. In this thesis, we develop the EM absorption study concerning the isotropic and anisotropic structures (composites and CNT brushes). These structures show high absorption as a function of frequency, CNT load charge, morphology, and thickness. The optimal values are highly correlated to these parameters. The modification of one parameter will have consequences on the overall absorption, reflection and transmission. As example, a matrix containing 2%CNT in 2mm thickness sample has the best absorption (from 20% to 80%) for PC nanocomposites. Anisotropic structures such as the CNT coating or CNT brushes are considered for anisotropic electromagnetic properties. The laser-machined micro patterns of CNT brushes is an alternative to metallic structures for simultaneously driving EM and heat propagation. The thermal response of the CNT array is observed to be sensitive to the microstructured pattern etched in the CNT brush, and to the mechanical stress induced by an incident air flux. The measurement of additional thermal parameters (emissivity and thermal diffusivity) show that the thermal diffusivity of the PC nanocomposite decreases when the CNT loading rate increases from 5%, 10%, to 15%wt. This behavior can be explained by the thermal barriers, added by the CNT inside the PC.(FSA - Sciences de l'ingénieur) -- UCL, 201

STUDY OF ABSORPTION IN CARBON NANOTUBE COMPOSITES FROM 1HZ TO 40GHZ

Absorption performances in High Density Polyethylene (HDPE) and polycarbonate (PC) polymer matrices containing various loads of carbon nanotubes were analysed. It depends on electrical conductivity, dielectric constant and thickness of the polymer composites. These parameters can be easily controlled. Significant absorption, which can reach between 60 and 90%, hence occurs at particular combinations of these last parameters (in a frequency range from 1Hz to GHz). These new results are really useful in various applications, and are considered in low scale systems as a major technological solution against electromagnetic interferences

Multifunctional material structures based on laser etched carbon nanotubes arrays

High power electronics in transportation and aerospace sectors needs size and weight reduction. Multifunctional and multistructured materials are currently developed to couple electromagnetic (EM) and thermal properties, i.e. shielding against electromagnetic impulsions, and thermal management across the thermal interface material (TIM). In this work, we investigate laser-machined patterned carbon nanotube (CNT) micro-brushes as an alternative to metallic structures for driving simultaneously EM and heat propagation. The thermal and the electromagnetic response of the CNT array is expected to be sensitive to the micro-structured pattern etched in the CNT brush

Colloidal pattern replication through contact photolithography operated in a 'Talbot–Fabry–Perot' regime

We describe a method for continuous colloidal pattern replication using contact photolithography. Cr-on-quartz masks are fabricated using colloidal nanosphere lithography and subsequently used as photolithography stamps. Hexagonal pattern arrangements with different dimensions (980, 620 and 480 nm, using colloidal particles with these respective diameters) have been studied. When the mask and the imaged resist layer were in intimate contact, a high fidelity pattern replica was obtained after photolithographic exposure and processing. In turn, the presence of an air gap in between was found to affect the projected image on the photoresist layer, with a strong dependence on the mask feature size and height of the air gap. Pattern replication, inversion and hybridization were achieved for the 980 nm period mask; no hybridization for the 620 nm one; and only pattern replication for the 480 nm one. These results are interpreted in the framework of a 'Talbot–Fabry–Perot' effect. Numerical simulations corroborate the experimental findings, providing insight into the processes involved and highlighting the important parameters affecting the exposure pattern. This approach allows complex subwavelength patterning and is relevant for three-dimensional layer-by-layer printing

Polypropylene Carbon Nanotubes Nanocomposites: Combined Influence of Block Copolymer Compatibilizer and Melt Annealing on Electrical Properties

We study the influence of melt annealing and the presence of a block copolymer compatibilizer on the electrical properties of polypropylene carbon nanotubes (CNT) nanocomposites from the DC limit to microwave frequencies and link it to the morphological details. We show that the compatibilizer concentration controls three types of morphologies: separate CNT agglomerates, a network of well dispersed but interconnected CNT, and individualized but separate nanotubes. This explains why conductivity reaches an optimum over the whole frequency range at a low compatibilizer concentration. We model the corresponding structures by a semiquantitative schematic equivalent electrical circuit. A key outcome of the work is the understanding and control of dispersion mechanisms in order to optimize the electrical performances for efficient EMI shielding depending on the targeted frequency range

Mid-infrared Near-Field Nanoscopy of organic and inorganic samples

Mid-infrared near-field nanoscopy is a new technique that allows to extract interesting informations at the nanoscale. After a short presentation of the technique, some electromagnetic simulations are showed and some examples of images obtained in two different cases are presented