Development of flexible piezoresistive pressure sensors via direct ink writing of MWCNT/PDMS nanocomposite inks: rheological and electromechanical characterization

The integration of nanoscience and 3D printing has given rise to the emerging field of printable and flexible electronics. Direct ink writing (DIW) has transformed the field of 3D printing by using viscoelastic inks, ensuring design, intricacy, and flexibility. This study presents the fabrication of flexible piezoresistive pressure sensors using multiwalled carbon nanotubes (MWCNTs)/polydimethylsiloxane (PDMS) based conductive inks via the DIW method. Three ink formulations were prepared with MWCNT concentrations of 2 wt%, 4 wt%, and 6 wt% to investigate their rheological and printability characteristics. Rheological analysis revealed that MWCNT loading concentrations above 4 wt% impart shear-thinning behavior and solid-like viscoelastic properties essential for DIW printing. Among the formulations, the 6 wt% MWCNT/PDMS ink exhibited the best printability and structural integrity for porous woodpile architectures. Morphological analysis confirmed the dispersion of MWCNTs within the PDMS matrix, indicating an effective filler distribution and network formation throughout the composite. Mechanical testing demonstrated that 6 wt% MWCNT/PDMS exhibited a threefold increase in Young's modulus (3.61 MPa) and a higher tensile strength (2.44 MPa) compared to pristine PDMS, owing to effective stress transfer and nanotube reinforcement. Cyclic tensile fatigue tests confirmed the CNT-6 composite's mechanical stability and low stress softening at lower strains, underscoring its durability for flexible pressure sensor applications. The fabricated pressure sensor demonstrated a pronounced piezoresistive response with a high sensitivity of 0.047 kPa-1, along with excellent repeatability and stability under both static and dynamic loading conditions, establishing its potential for precision pressure monitoring in flexible and wearable sensing applications.