Direct ink writing of conductive ultra-soft PDMS/MWCNT nanocomposites for flexible electronic applications

The field of flexible and stretchable electronics is rapidly growing, with applications in wearable electronics, soft robotics, and human-machine interfaces. These systems require ultra-soft conductive materials, but there is still a challenge in integrating high electrical conductivity, printability, and mechanical performance. In this work, direct ink writing (DIW)-printable, multi-walled carbon nanotube (MWCNT)-reinforced polydimethylsiloxane (PDMS) nanocomposites were developed and investigated. The MWCNT loading (1–5 wt%) was optimized to balance rheology, printability, and functional performance. Stable extrusion with good structural fidelity was achieved at MWCNT content of 3–4 wt%. The mechanical properties were significantly improved with the incorporation of MWCNTs, with the 4 wt% DIW sample exhibiting the maximum tensile strength (~ 68.7 kPa) and a low modulus. Electrical measurements showed that the percolation threshold was reached at 2–3 wt% and that the conductivity of the DIW-fabricated samples (~ 2.01 × 10⁻² S/m) was much greater than that of the mold-cast counterparts. The fabricated PDMS/MWCNT nanocomposites exhibit desirable printability, electrical conductivity, and mechanical compliance, making them suitable for future flexible and soft electronics applications.