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.
Abstract. We detail on a continuous colloidal pattern replication by using contact photolithography. Chrome 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 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 photolithography exposure and processing. In turn, the presence of an air-gap in between has been found to affect the projected image onto the photoresist layer, strongly dependent on the mask feature size and air-gap height. Pattern replication, inversion and hybridization was achieved for 980 nm-period mask; no hybridization for the 620 nm; and only pattern replication for the 480 nm. These results are interpreted in the framework of a "Talbot-Fabry-Perot" effect. Numerical simulations corroborate with the experimental findings providing insight into the involved processes highlighting the important parameters affecting the exposure pattern. The approach allows complex subwavelength patterning and is relevant for a 3D layer-by-layer printing.
High-power electronics in the transportation and aerospace sectors need size and weight reduction. Multifunctional and multistructured materials are currently being 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 electromagnetic response of the CNT array is expected to be sensitive to the micro-structured pattern etched in the CNT brush.
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