Simultaneous realization of conductive segregation network microstructure and minimal surface porous macrostructure by SLS 3D printing

A general strategy, i.e. simultaneous realization of the conductive segregation network microstructure and minimal surface porous macrostructure by means of selective laser sintering (SLS) 3D printing is proposed for devices fabrication. For the purpose of strategy demonstration, a flexible piezoresistive sensor is fabricated by SLS 3D printing with the use of self-made single-walled carbon nanotubes (SWCNTs) wrapped thermoplastic polyurethane (TPU) powders. The SLS-printed TPU/SWCNTs composite possesses an ultra-low conductive percolation threshold and excellent mechanical strength due to the construction of electrically conductive segregation network microstructure in polymer matrix, what is a prerequisite to a flexible piezoresistive sensor. The minimal surfaces including the Schwarz, Gyroid- and Diamond-structures have been used to design a 3D-ordered porous macrostructure of the sensor. The Schwarz structure has been found to be capable of producing the best piezoresistive properties of the SWCNTs/TPU composite sensor with a gauge factor (GF) much higher than that for the Gyroid- and Diamond-structures. This phenomenon is well understood by the relationship between the piezoresistive sensitivity and the localized strain distribution revealed by Finite Element Modeling. Keywords: 3D printing, SLS, Piezoresistive sensor, Segregation network, Minimal surface