Electromechanical Properties of Novel Carbon-Nanofiber/Polypyrrole Composite Bending Sensors and Actuators

An electrochemical polymerization method has been developed newly to fabricate a single layer polypyrrole (PPy) film and some single layer carbon-nanofiber (CNF)/PPy films with several different weight ratios of CNF such as 3%, 5%, 7%, and 10%. The CNF/PPy composite material was newly fabricated first time for this research. PPy was fabricated by oxidation of pyrrole monomer in a mixed solution of propylene carbonate and LiTFSI (Bis(trifluoromethane)sulfonamide lithium salt). Ni sheets were used as working and counter electrodes during polymerization. SEM images were taken on surfaces and cross-sections of the CNF/PPy composite samples. Conductivity is shown to be improved much from 77.93S/cm to 124.3S/cm due to the high conductivity of CNF. Experimental results show that conductivity increases approximately linearly. Actuation strain was measured. The strain of a PPy film was 12.6% and for a 10% CNF/PPy film, the strain was 8.6%. It was noticed from experiments as the strain of samples was reduced as CNF weight ratio increased. Bending motions were observed for both PPy and CNF/PPy films when subjected to electric currents. The tip deflections of the films varied from 0.5mm to 2mm. Mechanical properties such as Young’s modulus and strength were tested and it was shown that the CNF enhanced the strength of the composite samples greatly. The CNF/PPy films show a great potential to be a good candidate for good sensor and actuator material.