Multi-walled carbon nanotubes/silicone conductive foams and their piezoresistive behaviors

Multi-walled carbon nanotubes/silicone conductive nanocomposites are of great significance because of their unique electrical and mechanical properties and are expected to open up a new field of applications as smart functional materials. Especially their noticeable piezoresistive behaviors can be utilized to produce flexible tactile sensors with large sizes but low costs. To enhance the sensitivity of the piezoresistive property, a foaming procedure was introduced to the conductive polymeric composites. A series of novel multi-walled carbon nanotubes/silicone conductive foamed nanocomposites were fabricated with different types of foaming agents to obtain a diverse porous structure. The porous structures of the foams, the distribution and orientation state of the multi-walled carbon nanotubes in the silicone matrix were both observed using a laser microscope and SEM with or without a compressive load. The influences of the porous structure and porosity on the foam were studied. It was found that a different porosity and different voids structure affected the density, elastic modulus, resistivity as well as piezoresistive property significantly. A piezoresistive model for the conductive fillers reinforced elastomeric composites was developed, the calculated results of resistive variations were used to compare to the measured values. Although the overall trends of the resistance changes matched, notable separations were found between the theoretical values and the measured values, which are thought to be caused by the viscoelasticity of the silicone matrix.