POLYMER COMPOSITES FOR SENSING AND ACTUATION

Abstract

This thesis concerns materials for polymer actuators and mechanical sensors. Polymer actuators are a class of artificial muscle with promising actuation performance; however, they are currently limited by the materials used in their fabrication. The metal-foil type mechanical strain gauges are commercially available and well understood; however, typically have gauge factors less than 5.5 [1], cannot be patterned into custom shapes, and only monitor small areas. New materials provide opportunities to improve the performance of both polymer actuators and mechanical sensors. The aim of this research was to develop, characterize, and implement such materials. Specifically, this thesis describes novel composites of exfoliated graphite (EG) blended with elastomeric hosts. The mechanical and electrical properties of these composites were tailored for two specific applications by modifying the EG loading and the elastomer host: compliant electrodes and strain gauges. Compliant electrodes were demonstrated that had ultimate tensile strains greater than 300% and that could withstand more than 106 strain cycles. Composites fabricated with polydimethylsiloxane (PDMS) exhibited conductivities up to 0.2 S/cm, and having tangent moduli less than 1.4 MPa. This modulus is the lowest reported for loaded elastomers above the percolation threshold. Conductivity was increased to more than 12.5 S/cm by fabricating composites with polyisoprene (latex) elastomers, and the tangent moduli remained less than 5 MPa. Actuation strains of polymer actuators were increased 3 fold using the composites as electrodes, compared to using carbon-grease electrodes. This was due to the composites ability to be spincoated with thin insulating layers of PDMS, allowing 30% higher electric fields to be applied. Strain gauges fabricated with these composites exhibited gauge factors (GFs) > 27,000, to the authors knowledge this is the highest GF ever reported. The effects of humidity, temperature and strain were investigated.