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Radio-frequency (RF) heating of thermosetting epoxies is an agile method to decouple the extrudability of epoxy resins from their buildability for additive manufacturing. Through this method, the resin is extruded in the liquid state at the early stages of curing. Then, an RF applicator induces a rapid and uniform increase in temperature of the resin, accelerating the solidification of the printed feature. Understanding the evolution of the resin's RF heating response as it cures is therefore critical in meeting the demands of additive manufacturing. In this work, we show that the high-frequency dielectric loss, determined using in situ rheo-dielectric measurements, of both neat and carbon nanotube (CNT) filled resins is correlated to the heating response at different temperatures throughout curing. Furthermore, we show that the presence of CNTs within the resin augments the heating response and that their dispersion quality is critical to achieving rapid heating rates during the cure. 

Abstract Porous MXene-polymer composites have gained attention due to their low density, large surface area, and high electrical conductivity, which can be used in applications such as electromagnetic interference shielding, sensing, energy storage, and catalysis. High internal phase emulsions (HIPEs) can be used to template the synthesis of porous polymer structures, and when solid particles are used as the interfacial agent, composites with pores lined with the particles can be realized. Here, we report a simple and scalable method to prepare conductive porous MXene/polyacrylamide structures via polymerization of the continuous phase in oil/water HIPEs. The HIPEs are stabilized by salt flocculated Ti 3 C 2 T x nanosheets, without the use of a co-surfactant. After polymerization, the polyHIPE structure consists of porous polymer struts and pores lined with Ti 3 C 2 T x nanosheets, as confirmed by scanning electron microscopy, energy dispersive x-ray spectroscopy, and x-ray photoelectron spectroscopy. The pore size can be tuned by varying the Ti 3 C 2 T x concentration, and the interconnected Ti 3 C 2 T x network allows for electrical percolation at low Ti 3 C 2 T x loading; further, the electrical conductivity is stable for months indicating that in these composites, the nanosheets are stable to oxidation at ambient conditions. The polyHIPEs also exhibit rapid radio frequency heating at low power (10 °C s −1 at 1 W). This work demonstrates a simple approach to accessing electrically conductive porous MXene/polymer composites with tunable pore morphology and good oxidation stability of the nanosheets.