Multifunctional Structural Carbon Fiber Composites Using Macropore-Infused Nanocomposite Emulsion Thermosets (MINETs)

<b>Acknowledgement: ONR N00014-21-1-2605</b><br/>Macropore-infused nanocomposite emulsion thermosets (MINET) are a new class of nanocomposites made from epoxy, nanoparticles, a liquid porogen, and a small quantity of surfactant. These ingredients form an intermediate between a conventional surfactant and a Pickering emulsion to create a bicontinuous network of oil and epoxy composite throughout the processing. After a room temperature cure and usage of different functional nanoparticles, selected based on the performance requirements of a given application, it is possible to design a composite with a range of functionalities, including flexibility, inertness, and electrical/thermal conductivity. By further extraction of the oil phase through rinsing, MINETs can be converted into porous (30~60% open volume) structures without considerable volume shrinkage (~1~5%). The pore size (between 100~10,000 nm) and chemical functionality of the pores is tunable by the constituent nanoparticles, allowing for, for example, hydrophilic or hydrophobic pore surfaces or the incorporation of antimicrobial particles. Simultaneously, the matrix resin can change mechanical properties and use of silicone nanoparticles as a filler can establish flexible behavior. These novel thermosets molded into centimeter to micrometer scale structures that possess interconnected pore networks through the entire component.<br/>Here, we explore the integration of MINETs into carbon fiber composite (CFC) structures. CFCs are widely used in aerial vehicles due to their low density and high strength. We have developed carbon fiber composites with MINET as a replacement for the resin matrix. Multiple functionalities can be introduced on the same part due to the viscosity of MINET materials and through use of a common resin backbone, which allows the spatial selection of particulate function. Using these MINET materials in combination with CFCs will allow for the selection of desired multifunctionality. Each target functionality requires co-optimization of the mechanical properties of the resulting composite along with the target additional functionality. This process necessitates new fundamental understanding of each component of the MINET blend along with their interaction with each other and with the CFC. As one example, MINETs created with graphene particles can possess electrical conductivities of up to ~10 S/m, which is promising for RF shielding and energy storage applications; however, the co-optimization of processability requires that the samples also have favorable viscosity for molding with carbon fiber, leading to usable conductivities of ~1 S/m. The net outcome of this combination of materials will be a new platform for incorporating multifunctionality in future aerospace structures.