We have demonstrated that the piezoelectric performance of polyvinylidene fluoride (PVDF) can be doubled through the controlled incorporation of carbon nanomaterials. Specifically, PVDF composites containing carbon fullerenes (C60) and single walled nanotubes (SWNT) are fabricated over a range of compositions and optimized for their Young’s modulus, dielectric constant, and d31 piezoelectric coefficient. Thermally stimulated current measurements show a large increase in internal charge and polarization in the composites over pure PVDF. The electromechanical coupling coefficients (k31) at optimal loading levels are found to be 1.84 and 2 times greater than pure PVDF for the PVDF-C60 and PVDF-SWNT composites, respectively. Such property-enhanced nanocomposites bring significant advances to electromechanical systems employed for structural sensing, energy scavenging, sonar, and biomedical devices. In this work, we employ PVDF-C60 composites (the highest piezoelectric value of any polymer composite) in a yarn structure to produce large-displacement, electrically driven artificial muscles. Polymer composite fibers of 1 mm in diameter are drawn through core shell extrusion, with a soft metal conductive core that acts as an inner electrode. Fibers are gold coated and twisted into a yarn-like structure. Through extensive twisting, tight coils are formed in the structure which, upon applying a voltage between the inner and outer electrodes of the yarn, expands and contracts across the length and the width of the structure. Torsional strain allows for the coils to be “unravelled” which greatly increases the elongation of the muscles. Alternately, the application of long strains enable this material to be a long-stroke energy harvesting device. Many piezoelectric energy harvesting material are only able to endure small strains before undergoing catastrophic degradation. The development of large strain energy harvesters presents manifold applications where large deformations/movements are anticipated.

Piezoelectric polymer composites: From energy harvesting to artificial muscles

249th National Meeting (2015)

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