Evaluation of Direct-Ink-Writing (DIW) of PDMS Hybrid Nanocomposite Ink for Piezoresistive Sensor Applications

Abstract

Direct-Ink-Writing (DIW) provides unprecedented flexibility in regulating the different compositions and fabricating complex geometry when compared with traditional manufacturing methods. In this paper, polydimethylsiloxane (PDMS) polymer is modified with a thixotropic filler, such as silica and conducting additives, such as carbon nanotubes (CNT) and carbon black (CB) to investigate the viscoelastic ink for the DIW printing. Different amounts of silica in the range from 10-20% are considered. Based on the percolation threshold (1.5% for CNT and 15% for CB), hybrid conducting additives of CB in the amount 1-2wt% are considered to fine-tune the viscosity and rheology of the ink which eventually transform the ink into an electrically conductive while exhibiting shear thinning characteristics. The resulting inks are used to print different cross-sectional geometries and further optimized for further use as piezoresistive sensors. It is found that silica filler in the amount beyond 15% puts a limit in the 3D printer as it takes a significant amount of force to extrude. It is found that the addition of inhibitor greatly decouples the curing process, which indeed assists in printing more complex structures over a few hours. Mechanical and piezoresistive data of some selected inks shown potential as sensor applications in soft robotics and pressure sensing.