Pressure-dependent variable resistors based on porous polymeric foams with conducting polymer thin films in situ coated on the interior surfaces

Pressure-dependent variable resistors were fabricated by coating conducting polymer thin films on the interior surfaces of porous polyurethane (PU) foams with thickness ranging from 1 mm to 5 mm. To coat conducting polymer thin films on the interior surfaces of the porous PU foams, the PU foams were first immersed in 1 M aqueous camphorsulfonic acid (HCSA) solution containing 0.44 M of aniline (monomer solution) and then transferred to another 1 M aqueous camphorsulfonic acid solution containing 0.1 M of ammonium peroxydisulfate (oxidant solution). After the polyaniline (PANI) deposition process by in situ oxidative chemical polymerization of aniline on the interior surfaces of the porous PU foams, the non-conductive PU foams became all-polymer conductive composites. The formation of PANI thin films on the interior surfaces of the porous PU foams was confirmed by optical microscopy and scanning election microscopy (SEM) studies, which showed that no bulk PANI was found to block the porous interstitial space of PU foams after the PANI deposition process. When a PANI-treated conductive PU foam was sandwiched between two pieces of plastic electrodes based on poly(ethyleneterephthalate) (PET) substrates coated with commercially available poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS), the whole assembly could act as an all-polymer pressure sensor. By varying the size and thickness of the all-polymer PU-based pressure devices, the responsive ranges can be adjusted for different applications with different applied pressure ranges. With the incorporation of a polymeric cushion as the mechanical buffer layer around the conductive PU composite, the dynamic pressure-responsive range could be further increased. Compared to our previous work, the all-polymer pressure sensors described in the present work showed greater reproducibility when subject to repetitive cycling tests and exhibited greater continuous linear response range.