Hybrid silver nanoparticle–boron nitride fillers enabling high thermal conductivity in 3D-printed PDMS composites

Thermal management remains a major challenge for miniaturized and flexible electronics, where polymer composites often trade thermal conductivity for compliance and processability. Here, we present 3D-printable thermal management materials (TMMs) based on polydimethylsiloxane (PDMS) incorporating hybrid silver nanoparticle–boron nitride (AgNP–BN) fillers. Two AgNP decoration strategies were compared: a conventional route using N,N-dimethylformamide (DMF) and a greener isopropanol/water co-solvent with trisodium citrate as reducing agent. Structural analyses revealed that the DMF process induced secondary AgCN phases, whereas the citrate route yielded AgNP deposition without by-products. Hybrid fillers were formulated into shear-thinning inks suitable for direct ink writing (DIW), which enabled anisotropic filler alignment during printing. The composites achieved thermal conductivities up to 1.40 W m⁻1 K⁻1, representing nearly a 9-fold enhancement over neat PDMS and a 79 % improvement compared to BN-only systems, without increased filler loading. This work demonstrates the synergistic benefits of filler hybridization and extrusion-based additive manufacturing, establishing a sustainable pathway for lightweight, flexible, and high-performance TMMs for wearable devices, conformal electronics, and advanced packaging.