Smart and responsive flexible foams via 3D printing of polymer composites*

We will report lightweight, highly-compressible, and piezoresistive polymer composite foam structure successfully prepared by 3D printing a thixotropic ink. The structures have exhibits tailorable mechanical strength, high compressibility and remarkable robustness. Inks are composed of nanoclay and carbon black particles in an organic solution polyurethane, and are processed using direct ink writing (DIW) into wearable strain sensor devices. Removal of the clay by chemical etching yields structures with high porosity and good elasticity, which have good compressibility and stable piezoresistive sensing signals at a strain of > 90%. We illustrate these structures can be used in pressure sensing, as well as the sensing of volatile organic solvents. The conductive structures can easily be reprocessed to different shapes and have great potential for lightweight, energy-saving, flexible, highly sensitive, and stable piezoresistive sensors.