A novel polypyrrole and natural rubber based flexible large strain sensor

A novel strain sensor for the measurement of large strains has been developed. The strain sensor was fabricated on natural rubber substrate coated with a very thin layer of the conducting polymer, polypyrrole, using vapour phase polymerisation technique in a vacuum environment. This process involves depositing a layer of FeCl3 oxidant onto the natural rubber strips which is then exposed to pyrrole monomer vapour to produce a very thin layer of conducting polymer. Various deposition parameters were experimented to determine the optimal process leading to the best strain sensing performance. Pre-straining the rubber substrate prior to deposition resulted in better stability and consistency of the sensing performance. Oxygen plasma exposure of 200 W for 40 s produced the highest reduction in water contact angle on the rubber's surface to improve the hydrophilicity without sacrificing the rubber's elasticity and flexibility. High concentration of FeCl3 oxidant prove beneficial for the polymer coating to form as well as having monomer pyrrole diluted in acetonitrile that formed the polymer coating with the best strain sensing performance. A gauge factor of up to 1.86 was achieved. The sensor has the potential to detect large mechanical strains. The developed strain sensor was successfully implemented on an air muscle where the extension and contraction of the muscle can be accurately controlled. It also has a capability to measure large bending strains and hence be used as a rotary sensor.