Three-Dimensional Microstructures of Epoxy-Carbon Nanotube Nanocomposites

RÉSUMÉ Dans les dernières décennies, la communauté scientifique a réalisé des efforts considérables dans le but d’avancer dans les domaines de la micro- et nanotechnologies. Cela est dû au grand potentiel de ces technologies dans une large variété d'applications, allant des composites structuraux jusqu’aux systèmes microélectromécaniques (MEMS) et à l'électronique organique. Pour de telles applications, les nanocomposites à base de polymères renforcés par des nanotubes de carbone (CNTs), plus spécifiquement les nanotubes de carbone à paroi simple, représentent un matériau prometteur grâce à ses propriétés mécaniques et électriques lorsque comparé aux résines conventionnelles. Toutefois, plusieurs défis quant au traitement et à la fabrication du nanomcomposite doivent être adressés dans l'objectif d'augmenter l'efficacité de ces nanocomposites. La production de nanotubes de carbone de haute qualité ayant un grand rapport de forme, leur dispersion dans la matrice polymère ainsi que l'amélioration de l'adhésion à l’interface sont tous des paramètres importants dans le comportement mécanique et électrique des nanocomposites. Ces paramètres pourraient être ingénieusement établis afin d'obtenir des propriétés optimales pour les micro- et macro- applications du nanocomposite. Cependant, la miniaturisation et l'optimisation des formes tridimensionnelles des systèmes en nanocomposite sont loin de leur plein potentiel, partiellement à cause du manque des techniques de fabrication adéquates. Cette thèse présente le développement des matériaux nanocomposites pour la fabrication de microstructures tridimensionnelles (3D) en utilisant les techniques de l'écriture-directe (DW), la micro-infiltration et l'écriture directe assistée par rayonnement UV (UV-DW). La thèse adresse deux parties principales: la préparation du nanocomposite et la fabrication des structures 3D de nanocomposites.----------ABSTRACT Over the last few decades, worldwide increasing effort has been directed towards achieving advances in micro- and nanotechnologies. This is motivated by their high potential for a wide variety of technological applications, ranging from structural composites to micro electromechanical systems (MEMS) and organic electronics. For such applications, polymer nanocomposites reinforced with carbon nanotubes (CNTs), and more specifically single-walled carbon nanotubes (SWCNTs), are promising materials compared to conventional resins due to their interesting mechanical and electrical properties. However, several fundamental processing and fabrication challenges have to be addressed in order to effectively use these nanocomposites. Production of high quality carbon nanotubes (CNTs) having large aspect ratio, their proper dispersion in polymer matrices as well as the improvement of interfacial bonding are the main parameters affecting their mechanical and electrical performance. Moreover, these materials can be engineered to deliver optimal properties for micro- and macro-devices. However, device miniaturization and three-dimensional shape optimization have not reached their full potential, partly because of the lack of suitable manufacturing techniques. This thesis reports the development of nanocomposite materials for the fabrication of three-dimensional (3D) microstructures with direct-write (DW), micro-infiltration and UV-assisted direct-write (UV-DW) techniques. The thesis focuses on two main parts; nanocomposite preparation and nanocomposite-based 3D microstructures fabrication. High-quality SWCNTs were produced by the UV-laser ablation method and then subjected to a chemical purification. A non-covalent functionalization with a surfactant was performed for additional interaction with the matrix

Three-dimensional printing of freeform helical microstructures: a review

Three-dimensional (3D) printing is a fabrication method that enables creation of structures from digital models. Among the different structures fabricated by 3D printing methods, helical microstructures attracted the attention of the researchers due to their potential in different fields such as MEMS, lab-on-a-chip systems, microelectronics and telecommunications. Here we review different types of 3D printing methods capable of fabricating 3D freeform helical microstructures. The techniques including two more common microfabrication methods (i.e., focused ion beam chemical vapour deposition and microstereolithography) and also five methods based on computer-controlled robotic direct deposition of ink filament (i.e., fused deposition modeling, meniscus-confined electrodeposition, conformal printing on a rotating mandrel, UV-assisted and solvent-cast 3D printings) and their advantages and disadvantages regarding their utilization for the fabrication of helical microstructures are discussed. Focused ion beam chemical vapour deposition and microstereolithography techniques enable the fabrication of very precise shapes with a resolution down to ∼100 nm. However, these techniques may have material constraints (e.g., low viscosity) and/or may need special process conditions (e.g., vacuum chamber) and expensive equipment. The five other techniques based on robotic extrusion of materials through a nozzle are relatively cost-effective, however show lower resolution and less precise features. The popular fused deposition modeling method offers a wide variety of printable materials but the helical microstructures manufactured featured a less precise geometry compared to the other printing methods discussed in this review. The UV-assisted and the solvent-cast 3D printing methods both demonstrated high performance for the printing of 3D freeform structures such as the helix shape. However, the compatible materials used in these methods were limited to UV-curable polymers and polylactic acid (PLA), respectively. Meniscus-confined electrodeposition is a flexible, low cost technique that is capable of fabricating 3D structures both in nano- and microscales including freeform helical microstructures (down to few microns) under room conditions using metals. However, the metals suitable for this technique are limited to those that can be electrochemically deposited with the use of an electrolyte solution. The highest precision on the helix geometry was achieved using the conformal printing on a rotating mandrel. This method offers the lowest shape deformation after printing but requires more tools (e.g., mandrel, motor) and the printed structure must be separated from the mandrel. Helical microstructures made of multifunctional materials (e.g., carbon nanotube nanocomposites, metallic coated polymer template) were used in different technological applications such as strain/load sensors, cell separators and micro-antennas. These innovative 3D microsystems exploiting the unique helix shape demonstrated their potential for better performance and more compact microsystems

Three-dimensional printing of multifunctional nanocomposites: Manufacturing techniques and applications

The integration of nanotechnology into three-dimensional printing (3DP) offers huge potential and opportunities for the manufacturing of 3D engineered materials exhibiting optimized properties and multifunctionality. The literature relating to different 3DP techniques used to fabricate 3D structures at the macro- and microscale made of nanocomposite materials is reviewed here. The current state-of-the-art fabrication methods, their main characteristics (e.g., resolutions, advantages, limitations), the process parameters, and materials requirements are discussed. A comprehensive review is carried out on the use of metal- and carbon-based nanomaterials incorporated into polymers or hydrogels for the manufacturing of 3D structures, mostly at the microscale, using different 3D-printing techniques. Several methods, including but not limited to micro-stereolithography, extrusion-based direct-write technologies, inkjet-printing techniques, and popular powder-bed technology, are discussed. Various examples of 3D nanocomposite macro- and microstructures manufactured using different 3D-printing technologies for a wide range of domains such as microelectromechanical systems (MEMS), lab-on-a-chip, microfluidics, engineered materials and composites, microelectronics, tissue engineering, and biosystems are reviewed. Parallel advances on materials and techniques are still required in order to employ the full potential of 3D printing of multifunctional nanocomposites

Processing parameters investigation for the fabrication of self-supported and freeform polymeric microstructures using ultraviolet-assisted three-dimensional printing

The ultraviolet-assisted 3D printing (UV-3DP) was used to manufacture photopolymer-based microdevices with 3D self-supported and freeform features. The UV-3DP technique consists of the robotized deposition of extruded filaments, which are rapidly photopolymerized under UV illumination during the deposition process. This paper systematically studies the processing parameters of the UV-3DP technique using two photo-curable polymers and their associated nanocomposite materials. The main processing parameters including materials’ rheological behavior, deposition speed and extrusion pressure, and UV illumination conditions were thoroughly investigated. A processing map was then defined in order to help choosing the proper parameters for the UV-3D printing of microstructures with various geometries. Compared to self-supported features, the accurate fabrication of 3D freeform structures was found to take place in a narrower processing region since a higher rigidity of the extruded filament was required for structural stability. Finally, various 3D self-supported and freeform microstructures with high potential in micro electromechanical systems, micro-systems and organic electronics were fabricated to show the capability of the technique

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

Preparation of Highly Exfoliated Polyester–Clay Nanocomposites: Process–Property Correlations

A large number of polyester nanocomposite batches featuring different kinds of nanoclay surface modifiers and up to 6 wt.% nanoclay were manufactured using a solvent-based technique. Montmorillonite platelets modified with ammonium ions of different chemical architectures were examined in order to study the effect of ammonium ions on the extent of surface reactions with long chain fatty acids. The ammonium montmorillonite was first dispersed and suspended in acetone. This suspension was further esterificated with dotriacontanoic (lacceroic) acid to form high density brushes on the clay surface. This led to achieving higher basal plane spacing of the montmorillonite platelets owing to the reduction of electrostatic interactions holding them. The outcome of the surface esterification was analyzed by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The esterificated ammonium modified clays were then mixed by five different mixing strategies based on the use of a three-roll mill mixer (TRM) and/or ultrasonication (US) in order to obtain the desired polyester-nanoclay dispersion, intercalation, and exfoliation. The dispersion states of the modified nanoclay in polymer were characterized from XRD, scanning electron microscopy (SEM), and low and high magnification transmission electron microscopy (TEM). Mechanical, thermal and barrier properties of the resulting composites were experimentally characterized. The Mori-Tanaka method along with an orientation distribution function was used to verify the experimental effective stiffness of the polyester nanocomposite systems. The aspect ratio of nanoclays and their level of intercalation and/or exfoliation after mixing were also confirmed by the comparison of the experimental diffusivity results with those of Fick’s diffusion model. Systems having 4 and 6 wt.% esterificated ammonium nanoclay and prepared according to a combined TRM/US mixing procedure showed optimal performance with balanced properties and processing ease, thereby showing potential for use in automotive, transportation and packaging industry

Micro-infiltration of three-dimensional porous networks with carbon nanotube-based nanocomposite for material design

Epoxy composite beams reinforced with a complex three-dimensional (3D) skeleton structure of nanocomposite microfibers were fabricated via micro-infiltration of 3D porous microfluidic networks with carbon nanotube nanocomposites. The effectiveness of this manufacturing approach to design composites microstructures was systematically studied by using different epoxy resins. The temperature-dependent mechanical properties of these multifunctional beams showed different features which cannot be obtained for those of their individual components bulks. The microfibers 3D pattern was adapted to offer better performance under flexural solicitation by the positioning most of the reinforcing microfibers at higher stress regions. This led to an increase of 49% in flexural modulus of a reinforced-epoxy beam in comparison to that of the epoxy bulk. The flexibility of this method enables the utilization of different thermosetting materials and nanofillers in order to design multifunctional composites for a wide variety of applications such as structural composites and components for micro electromechanical systems

Micromechanical characterization of single-walled carbon nanotube reinforced ethylidene norbornene nanocomposites for self-healing applications

We report on the fabrication of self healing nanocomposite materials, consisting of single-walled carbon nanotube (SWCNT) reinforced 5-Ethylidene-2-norbornene (5E2N) healing agent -reacted with Ruthenium Grubbs catalyst- by means of ultrasonication, followed by a three-roll mixing mill process. The kinetics of the 5E2N ring opening metathesis polymerization (ROMP) was studied as a function of the reaction temperature and the SWCNT loads. Our results demonstrated that the ROMP reaction still effective in a large temperature domain (-15 to 45 ºC), occurring at very short time scales (less than one minute at 40 ºC). On the other hand, the micro-indentation analysis performed on the SWCNT/5E2N nanocomposite materials after its ROMP polymerization were shown a clear increase in both the hardness and the Young modulus -up to nine times higher than that of the virgin polymer- when SWCNT loads range only from 0.1 to 2 wt. %. This approach demonstrated here opens new prospects for using carbon nanotube and healing agent nanocomposite materials for self-repair functionality, especially in space environment

Manufacturing composite beams reinforced with three-dimensionally patterned-oriented carbon nanotubes through microfluidic infiltration

Functionalized single-walled carbon nanotubes (SWCNTs)/epoxy nanocomposite suspensions were prepared and injected into three-dimensional (3D) interconnected microfluidic networks in order to fabricate composite beams reinforced with patterned-oriented nanotubes. The microfluidic networks were fabricated by the robotized direct deposition of fugitive ink filaments in a layer-by-layer sequence onto substrates, followed by their epoxy encapsulation and the ink removal. Then, the nanocomposite suspensions prepared by ultrasonication and three-roll mill mixing methods were injected into the empty networks under two different controlled and constant pressures in order to subject the suspensions to different shear conditions in the microchannels. Morphological studies revealed that the SWCNTs were preferentially aligned in the microchannels along the flow direction at the higher injection pressure. The improvement of Young’s modulus of the manufactured 3D-reinforced rectangular beams prepared at the high injection pressure was almost doubled when compared to that of beams prepared at the low injection pressure. Finally, the stiffness of the 3D-reinforced beams was compared with the theoretically predicted values obtained from a micromechanical model. The analytical predictions give a close estimation of the stiffness at different micro-injection conditions. Based on the experimental and theoretical results, the present manufacturing technique enables the spatial orientation of nanotube in the final product by taking advantage of shear flow combined with dimensional constraining inside the microfluidic channels

Reinforcing epoxy nanocomposites with functionalized carbon nanotubes via biotin–streptavidin interactions

We report on the preparation of nanocomposites consisting of biofunctionalized single-walled carbon nanotubes (BF-SWCNTs) reinforcing an ultraviolet curable epoxy polymer by means of biotin–streptavidin interactions. The as-produced laser ablation SWCNTs are biofunctionalized via acid oxidization based purification process and non-covalent functionalization using surfactant, followed by grafting the resulting nanotubes with biomolecules. The biotin-grafted nanotubes are capable of interacting with epoxy groups in presence of streptavidin molecules by which chemical bridges between BF-SWCNTs and epoxy matrix are formed. The biomolecules grafted to the nanotubes surface not only facilitate the load transfer, but also improve the nanotube dispersion into the epoxy matrix, as observed by optical imaging and scanning electron microscopy. Mechanical characterization on the nanocomposite microfibers demonstrates considerable enhancement in both strength (by 76%) and modulus (by 93%) with the addition of only 1 wt.% of BF-SWCNTs. The electrical measurements reveal a clear change in electrical conductivity of nanocomposite microfibers reinforced with 1 wt.% of BF-SWCNTs in comparison to the microfibers containing solely purified carbon nanotubes. These multifunctional nanocomposite materials could be used to fabricate macro and microstructures for a wide variety of applications such as high strength polymer nanocomposite and potential easily-manipulated biosensors