Processing Approaches to Realize Electrically Conductive Surface-Localized Nanocomposites
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Ryan, Emily A.
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Abstract
The development of physically robust, environmentally stable, electrically conductive polymer films is critical for a wide range of future space exploration applications, including inflatable habitats and flexible robotics. In this work, melt infiltration was explored as a method to produce polymer films with integrated, thick, and durable surface-localized nanocomposite (SLNC) coatings with nanoparticle loadings well beyond the percolation threshold. A generalized method for identifying melt infiltration temperatures in semi-crystalline substrates, based on their melting regime, was developed. This approach was used to produce electrically conductive SLNCs from reduced graphene oxide (rGO) nanoparticles and a variety of semi-crystalline polymer substrates. By varying the infiltration temperature within the melt regime controllable levels of infiltration and related surface roughness and porosity were demonstrated. Thermal analysis modeling of the infiltration procedure also revealed that infiltration proceeded through mixed solid-liquid flow due to the partially melted state of the infiltrating matrix in contrast to the fully liquid infiltration observed in amorphous polymer systems.
To investigate the influence of particle chemistry on infiltration dynamics and SLNC properties, a post-reduction method was developed to synthesize fluoro-alkyl functionalization of rGO (rGO-f). Despite a low degree of functionalization (~0.1 at.% F), rGO-f exhibited significant changes in surface energy and dispersion behavior, compared to unfunctionalized rGO, while maintaining a high level of conductivity. The infiltration behavior was compared across rGO-f, unfunctionalized rGO, and a previously developed alkyl functionalized rGO (rGO-dd). Functionalization had a minimal impact on infiltration progression or SLNC conductivity. Mechanical reinforcement of the SLNCs was found to depend on compatibility between the rGO functionality and the infiltrating matrix with rGO-dd/polyethylene SLNCs showing higher reinforcement (140% increase in modulus), than rGO-f/polyethylene SLNCs (64% increase).
The piezoresistive behavior of fully infiltrated SLNCs was characterized under quasi-static and cyclic tension to understand the origin of piezoresistivity in these SLNCs. Creep-driven network reconfiguration governed the low-strain response, while crack formation dominated at higher strains. To assess durability in potential wear conditions, the conductivity of SLNCs was track during film bending and abrasion with lunar dust simulant. Fully infiltrated SLNCs maintained sufficient conductivity at >1000 cycles of lunar simulant abrasion and at sharp bend radii, indicating robustness to mechanical deformation and wear.
Finally, SLNCs were integrated into a planar electrodynamic dust shield (EDS) architecture by adapting the particle deposition and infiltration process to produce patterned devices. These EDS devices effectively removed lunar dust simulant in high vacuum conditions. Altogether, this work established a generalized processing approach for SLNCs in semi-crystalline materials and demonstrated key attributes for their use as multifunctional surface coatings in space-relevant environments.
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2025-07-29
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Dissertation