Louis Laberge Lebel

Ultraviolet‐Assisted Direct‐Write Fabrication of Carbon Nanotube/Polymer Nanocomposite Microcoils

[*] Prof. D. Therriault, L. L. Lebel Laboratory of Multi-scale Mechanics, Center for Applied Research on Polymers (CREPEC) École Polytechnique of Montreal C.P. 6079, succ. Centre-Ville, Montreal, QC H3C 3A7 (Canada) E-mail: daniel.therriault@polymtl.ca B. Aissa, Prof. M. A. E. Khakani Institut National de la Recherche Scientifique, INRS-Énergie, Matériaux et Télécommunications 1650 Blvd. Lionel-Boulet, Varennes, QC J3X 1S2 (Canada)

Electrical transport properties of single wall carbon nanotube/polyurethane composite based field effect transistors fabricated by UV-assisted direct-writing technology

We report on the fabrication and transport properties of single-walled carbon nanotube (SWCNT)/polyurethane (PU) nanocomposite microfiber-based field effect transistors (FETs). UV-assisted direct-writing technology was used, and microfibers consisting of cylindrical micro-rods, having different diameters and various SWCNT loads, were fabricated directly onto SiO₂/Si substrates in a FET scheme. The room temperature dc electrical conductivities of these microfibers were shown to increase with respect to the SWCNT concentrations in the nanocomposite, and were about ten orders of magnitude higher than that of the pure polyurethane, when the SWCNT load ranged from 0.1 to 2.5 wt% only. Our results show that for SWCNT loads ≤ 1.5 wt%, all the microfibers behave as a FET with p-type transport. The resulting FET exhibited excellent performance, with an I(on)/I(off) ratio of 10⁵ and a maximum on-state current (I(on)) exceeding 70 µA. Correlations between the FET performance, SWCNTs concentration, and the microfiber diameters are also discussed.

Three-dimensional micro structured nanocomposite beams by microfluidic infiltration

Three-dimensional (3D) micro structured beams reinforced with a single-walled carbon nanotube (C-SWNT)/polymer nanocomposite were fabricated using an approach based on the infiltration of 3D microfluidic networks. The 3D microfluidic network was first fabricated by the direct-write assembly method, which consists of the robotized deposition of fugitive ink filaments on an epoxy substrate, forming thereby a 3D micro structured scaffold. After encapsulating the 3D micro-scaffold structure with an epoxy resin, the fugitive ink was liquefied and removed, resulting in a 3D network of interconnected microchannels. This microfluidic network was then infiltrated by a polymer loaded with C-SWNTs and subsequently cured. Prior to their incorporation in the polymer matrix, the UV-laser synthesized C-SWNTs were purified, functionalized and dispersed into the matrix using a three-roll mixing mill. The final samples consist of rectangular beams having a complex 3D skeleton structure of C-SWNT/polymer nanocomposite fibers, adapted to offer better performance under flexural solicitation. Dynamic mechanical analysis in flexion showed an increase of 12.5% in the storage modulus compared to the resin infiltrated beams. The nanocomposite infiltration of microfluidic networks demonstrated here opens new prospects for the achievement of 3D reinforced micro structures.

Solvent-cast based metal 3D printing and secondary metallic infiltration

Affordable 3D printing methods are needed for the development of high performance metallic structures and devices. We develop a method to fabricate dense metallic structures by combining a room temperature 3D printing and subsequent heat-treatments: sintering and secondary metallic infiltration. The high flexibility of this method enables the fabrication of customized 3D structures, such as fully-filled, porous, interlocked and overhung structures. These geometries are printed using a highly concentrated metallic ink (metallic load up to 98 wt%) consisting of highly alloyed steel (HAS) microparticles, polylactic acid (PLA) and dichloromethane (DCM). In order to improve the mechanical properties and the electrical conductivity, the as-printed structures are sintered and infiltrated by copper in a furnace protected by a mixture of H2 and Ar. The filament porosity of the copper infiltrated samples is as low as 0.2%. Mechanical testing and electrical conductivity measurement on the copper infiltrated structures reveal that the Youngs modulus reaches up to ∼195 GPa and the electrical conductivity is as high as 1.42 × 106 S m−1. Our method enables the simple fabrication of high performance metallic structures which could open up new technological applications where cost is an important factor.

Manufacturing of three-dimensionally microstructured nanocomposites through microfluidic infiltration.

Microstructured composite beams reinforced with complex three-dimensionally (3D) patterned nanocomposite microfilaments are fabricated via nanocomposite infiltration of 3D interconnected microfluidic networks. The manufacturing of the reinforced beams begins with the fabrication of microfluidic networks, which involves layer-by-layer deposition of fugitive ink filaments using a dispensing robot, filling the empty space between filaments using a low viscosity resin, curing the resin and finally removing the ink. Self-supported 3D structures with other geometries and many layers (e.g. a few hundreds layers) could be built using this method. The resulting tubular microfluidic networks are then infiltrated with thermosetting nanocomposite suspensions containing nanofillers (e.g. single-walled carbon nanotubes), and subsequently cured. The infiltration is done by applying a pressure gradient between two ends of the empty network (either by applying a vacuum or vacuum-assisted microinjection). Prior to the infiltration, the nanocomposite suspensions are prepared by dispersing nanofillers into polymer matrices using ultrasonication and three-roll mixing methods. The nanocomposites (i.e. materials infiltrated) are then solidified under UV exposure/heat cure, resulting in a 3D-reinforced composite structure. The technique presented here enables the design of functional nanocomposite macroscopic products for microengineering applications such as actuators and sensors.

Effect of stamp-forming parameters and bend radius on the mechanical performance of curved beam carbon fiber/polyphenylene sulfide specimens

The stamp-forming process is used to manufacture S-shape parts made of carbon fiber/polyphenylene sulfide thermoplastic composites. The processing parameters and part layup, thickness, and bend radius are varied in order to investigate their effects on the parts’ quality and mechanical performance. The interlaminar tensile strength of the formed parts is measured using the results of curved beam four-point bending tests and recommended analytical equations. A nonlinear finite element model of the tested coupons is developed, taking into account the contact between the loading bars and the coupon as well as the plies’ interface properties. The results of the model are used to verify the precision of the analytical equations for various bend radii and part layup and thickness. Conclusions as to the optimum set of processing parameters that should be used for the stamp forming of carbon fiber/polyphenylene sulfide are drawn.

Multiscale Manufacturing of Three-Dimensional Polymer-Based Nanocomposite Structures

There is currently a worldwide effort for advances in micro and nanotechnologies due to their high potential for technological applications in fields such as microelectromechanical systems (MEMS), organic electronics and high-performance structures for aerospace. In these fields, nanoparticle-filled composites, i.e. nanocomposites, represent an interesting material option compared to conventional resins due to their enhanced properties and multi-functional potential. However, several significant scientific and technological challenges must be first overcome in order to fabricate nanocomposite-based structures and devices rapidly and cost-effectively. Various fabrication techniques of one or twodimensional (1D/2D) nanocomposite structures have been developed, but few techniques are available for three-dimensional (3D) nanocomposite structures. The capability to manufacture complex 3D structures will greatly expand the practical applications of nanocomposite materials and enable the development of novel devices such as a 3D nanocomposite micro-coil spring. This chapter will present an overview of the challenges in multiscale fabrication and the current manufacturing techniques available to create 3D structures of polymer-based nanocomposites.