RF heating of carbon nanotubes enables local welding and increased strength between 3D-printed thermoplastic layers.

Here, we give the first-ever report of radio frequency (RF) electromagnetic heating of polymer nanocomposite materials via direct-contact and capacitively coupled electric field applicators. Notably, RF heating allows nanocomposite materials to be resistively heated with electric fields. We highlight our novel RF heating technique for multiwalled carbon nanotube (MWCNT) thermoplastic composites and measure their broadband dielectric properties. We also demonstrate three different electric field applicator configurations and discuss their practical use in an industrial setting. We demonstrate the use of RF heating to cure an automotive-grade epoxy loaded with MWCNTs. Our results show that lap shear joints cured faster with the RF method compared with control samples cured in an oven because of the heat-transfer advantages of directly heating the epoxy composite. Finally, we implement our RF curing technique to assemble an automotive structure by locally curing an epoxy adhesive applied to a truck chassis.

In this report, we investigate the rapid heating ability of laser-induced graphene (LIG) in response to radio frequency (RF) fields. Graphitic structures were produced from various industrially prevalent thermoplastics via laser irradiation of the polymer surface. We find that RF responsive, graphitic structures may be produced from Kapton, polyether imide (PEI), polyether sulfone (PESU), polyether ether ketone (PEEK), and polycarbonate (PC) using a conventional laser cutting machine. The graphitic structures are also electrically conductive in addition to being RF responsive. Exposure of LIG to RF fields resulted in the rapid heating of LIG with remarkable heating rates up to 126 °C/s. Finite-element simulations for these systems show similar heating trends. This heating response may be used in advanced manufacturing as a means to rapidly weld polymer–polymer interfaces, as will be demonstrated in this report. Our technique uses RF fields to induce localized heating in contrast to uniform bulk heating from external sources such as ovens or furnaces. The methods detailed in this paper provide a polymer processing pathway that may be used to generate RF responsive filler in situ. Finally, we aim to show that LIG–polymer composites may function in an industrial setting, with particular application to additive manufacturing and functional coatings.

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A Landau-de Gennes formulation was implemented in dynamic finite element simulations to compare with postshear relaxation experiments that were conducted on cholesteric cellulose nanocrystal (CNC) dispersions. Our study focused on the microstructural reassembly of CNCs in lyotropic dispersions as parameters such as chiral strength and gap confinement were varied. Our simulation results show that homeotropic and/or more complicated three-dimensional helical configurations are possible, depending on the choice of these parameters. We also observed how dynamic banding patterns develop into the hierarchical microstructures that are characterized by an equilibrium pitch length in both the experiments and simulations. This work has immediate relevance for cellulose nanocrystal dispersion processing and provides new insight into fluid phase ordering for tailorable optical properties.

The SEM imaging discussed in this thesis was performed by Aniruddh Vashisth.Materials for sample preparation, temperature and strength data for the IR lamp heating process, and additional knowledge and guidance were all provided by Tyler Auvil and Dan Sophiea, from the Dow Chemical Company.

Material extrusion (ME) 3D printing is a revolutionary technique for manufacturing thermoplastic parts; however, the printed parts typically suffer from poor interlayer bonding, which causes weak tensile strength in the build direction. Many methods have been proposed to address the mechanical deficiencies of 3D-printed parts, but most fall short of a production-ready solution. Here we report the use of a dielectric barrier discharge (DBD) plasma electrode mounted concentrically around the nozzle of an ME 3D printer for in situ welding of thermoplastic parts. This is the first report of a DBD being used as a non-contact means to induce Joule heating in resistive composite materials. The polymer welding process is accomplished by coupling the DBD with the carbon nanotube-loaded interfaces between the 3D-printed layers. The current passing through the part results in rapid resistive heating of the nanotubes and thermal welding of the interfaces. We show that parts printed with this method have isotropic strength and are equivalent to their injection-molded counterparts.

A Landau-de Gennes formulation coupled with a mass-transfer equation was used to track the evaporation front and the development of chiral microstructures during the casting of sulfuric acid-hydrolyzed cellulose nanocrystal (CNC) films. These simulations are compared to thin-film casting experiments that used analogous processing parameters and environments. The results show that the initial concentration, chiral strength, surface anchoring, speed of drying, and the influence of initial shear alignment all affect the uniformity of the microstructure and the orientation of the chiral director. In this report, we aim to show that under optimal casting conditions, the lateral size of planar microstructural domains that exhibit uniform selective reflection can be achieved on the order of millimeters.