Nanoporous metals are a distinct class of materials suitable for electrolysis, energetics, and energy materials because of their high surface area, diffusivity, and electrical conductivity. With the advent of additive manufacturing, this work attempts to elucidate the role of rheology in the printability of these materials via freeform filament fabrication. To fabricate dense nanocomposite for additive manufacturing, rigorous mixing of porous metals and thermoplastic is necessary, which requires intricate control on the capillary-driven infiltration of the polymeric phase into the nanoscale metal pores. Our project sheds light on the control and modulation of polymers (dissolved in solvent) into the sub-nanometer metal pores by examining the wetting characteristics of polymeric solution as a function of different molecular weights (chain length ranging from 5 to 35 nm) and different surface functionalization of the host metal nano-powders (by acidic and basic base chemical dealloying). The molecular weight and the solvent’s transient concentration regulate its wettability and scale its viscosity, which consequentially inhibits capillary-driven imbibition and densification. In our study, nanocomposites with different molecular weight thermoplastics and surface functionalization were prepared by solution mixing and cast before being dried to evaluate their density, dynamic viscosity, and microstructure. Subsequently, the results were correlated with its wettability characteristics. Using Lucus-Washburn equation and experimental data, a direct interdependence of density and rheology scaling was established with the degree of capillary infiltration. Additionally, segmental dynamics of polymers chains were found vividly different while transitioning from macroscopic behavior to nano-confinement (in composite), exhibiting exceptional thermal transition compared to the bulk polymer. Our study aims to understand the complex science of capillary infiltration of polymers in this bi-continuous and tortuous nanoporous metal network and its impact on rheology and density, which can eventually widen the door for achieving a scalable materials design approach for the 3D printing of conductive nanoporous metal tracks.

Scalable design of polymeric nanocomposites driven by capillary infiltration and surface functionalization for 3D printed electronics

ACS Spring 2022

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