Vat Photopolymerization 3D Printing of Conductive Nanocomposites

Abstract

Recent years have witnessed a surge in efforts to integrate electrically conductive nanomaterials into photopolymer-based additive manufacturing (AM), driven by the growing demand for multifunctional 3D-printing. While several AM techniques have been adapted to process conductive composites, Digital Light Processing (DLP) stands out for its high-resolution and fast-curing capabilities. However, it poses a central limitation: the requirement for optical transparency in the printing resin, which is compromised by the incorporation of conventional conductive fillers. This Account highlights the advances in overcoming three fundamental challenges in the field: (i) How can conductive nanocomposites be printed by DLP without compromising resolution? (ii) How can high electrical conductivity be achieved at low filler content? (iii) What is the origin of anisotropic conductivity in printed objects, and how can it be mitigated?

To address the first question, the authors introduced a strategy based on UV-transparent precursors, specifically monolayer graphene oxide (GO). GO’s minimal UV absorption allows its use as a printable nanofiller at weight fractions up to 0.35 vol %, preserving the curing depth and optical clarity required for DLP. Postprinting thermal reduction of GO into reduced graphene oxide (rGO) yields nanocomposites with conductivities up to 10^–2 S m^–1─comparable to conventional carbon nanotube (CNT) systems but achieved without high UV attenuation. To tackle the second question, the authors explored the use of single-walled carbon nanotubes (SWCNTs), which, due to their high aspect ratio and intrinsic conductivity, exhibit ultralow percolation thresholds (<0.01 vol %). At these concentrations, UV interference is negligible. However, the need for surfactant-assisted dispersion introduces contact resistance, limiting conductivity. To overcome this, this Account presents a hybrid formulation in which GO serves as both dispersant and conductive additive, enhancing internanotube contacts upon reduction. This approach achieves conductivities up to 0.3 S m^–1, with a total filler content below 0.15 vol %, representing a significant leap in performance without sacrificing resolution. To resolve the third question regarding electrical anisotropy, the study employs polarized Raman spectroscopy, conclusively showing that nanotube alignment is not responsible for the observed directional conductivity differences. Instead, the anisotropy arises from interfacial contact resistance between printed layers, an intrinsic artifact of the layer-by-layer DLP process. Mitigation strategies such as delayed UV curing and temperature-controlled printing were shown to significantly reduce this resistance and improve isotropy.

Beyond addressing these scientific questions, this Account highlights the practical impact of these materials. Notably, hybrid nanocomposites exhibited strong potential in microwave absorption, reaching broadband reflection losses below −10 dB at low filler loadings, due to combined ohmic and dielectric losses. These outcomes demonstrate that high-resolution, fast DLP printing of conductive materials is not only feasible but also tunable and scalable for applications in sensors, soft robotics, and electromagnetic shielding. By answering these key questions, the work establishes a foundation for the rational design of printable conductive nanocomposites, balancing optical compatibility, conductivity, and mechanical precision─paving the way for next-generation functional devices fabricated through vat photopolymerization.