Constitutive model of aligned carbon nanotube/nafion nanocomposite ionic electroactive polymer actuators
Author(s)Jacobs, Douglas S. (Douglas Scott)
Massachusetts Institute of Technology. Department of Mechanical Engineering.
Brian L. Wardle.
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Research is progressing rapidly on composite nano-structured materials, including aligned carbon nanotube (A-CNT) polymer nanocomposites (PNC), and with device construction utilizing these novel materials. However, the material constitutive relations of the PNCs and tailoring of these is lagging. In this work, A-CNT and Nafion PNC electrodes are manufactured and investigated as the key active element in ionic-electroactive polymer (i- EAP) devices. i-EAP actuators are known to create relatively large strains with low input voltages, and could therefore be used for future high-strain actuation mechanisms such as synthetic muscles, microfluidic drug delivery, or low-frequency energy harvesting. Tailoring the PNC is accomplished by process control and moving to higher volume fraction (Vf) A-CNTs, in order to increase both the rate and magnitude of strain through increased nonisotropy and specific surface area for ionic transfer efficiency. This work shows methods to increase the A-CNT synthesis yield from below 50% to ~90%, while keeping quality and morphology stable. Porous A-CNT based i-EAP electrodes are synthesized with CNT and Nafion volume fractions of 10-40% and 10-25%, respectively. Key elements of the non-isotropic mechanical, electrical and electroactive constitutive law are discussed and calculated for different morphologies of the electrodes. Tailored high Vf i-EAP devices at ±3 V show ±4,130 microstrain in the transverse direction and an order of magnitude smaller strain (±420 microstrain) in the CNT axis direction, with A-CNT and Nafion Vfs of ~20% and ~15%, respectively. These large non-isotropic strains correspond to electroactive coupling coefficients of 7.1 x 10-12 m=V in the transverse direction and 7.2 x 10-13 m=V along the CNT axis. In addition, the i-EAP material's moduli are measured to be ~85 MPa in the CNT axis direction and ~50 MPa in the transverse direction, with a relative dielectric permittivity of 79, for this polymeric based i-EAP device. These coefficients constitute the first assembly of mechanical, electrical and electroactive properties into a constitutive relation for such an active nano-structured material. More extensive data sets for completing the full constitutive model and reducing measurement uncertainty are recommended for future work.
Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2016.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 141-144).
DepartmentMassachusetts Institute of Technology. Department of Mechanical Engineering.
Massachusetts Institute of Technology