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.
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.
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