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This lecture covers the use of polymer-metal composites and conductive polymers as actuation materials. It discusses "wet" actuation methods involving ionic actuators that utilize the mobility or diffusion of ions, as well as "dry" actuation methods involving electronic actuators that utilize Coulomb forces. The performance and applications of Ionic Polymer Metal Composites (IPMC), conductive polymers like Polypyrrole (PPy), electrostricted polymers, and dielectric elastomers are explored.
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Design Realization lecture 15 John Canny / Jeremy Risner 10/9/03
Last Time • Composites: Fiberglass, carbon fiber and kevlar. • Hierarchical materials. • Cellular materials, honeycomb and foam.
This time • Polymers for actuation
“Wet” versus “Dry” actuation • “Wet” – Ionic actuators. Utilize mobility or diffusion of ions. • polymer-metal composites • conductive polymers • others . . . • “Dry” – Electronic actuators. Utilize Coulomb forces. • dielectric elastomers • electrostrictive polymers • others . . .
Polymer-Metal Composites • Ionic Polymer Metal Composites (IPMC) • ion exchange polymer membrane – selectively pass ions of a single charge - Dupont Nafion • gold plated electrodes on either side • applied voltage induces movement of ions and water – causes expansion on one side • bending movement
Polymer-Metal Composites • performance of IPMC • strain: 3% • energy density: 0.01-0.1 J/cm3 • speed: 100 Hz • output pressure: 10-30 MPa • drive voltage: 1-2 V
Polymer-Metal Composites • work best in aqueous environments • robot fish in tank EAMEX, Japan
Conductive Polymers • Polypyrrole (PPy)– conductive polymer • oxidation-reduction reaction when voltage is applied • redox induces ion flow into or out of polymer • flow in = expansion • requires electrolyte
Conductive Polymers • performance for PPy bilayer actuator • strain: 12.4% • energy density: 0.040 J/g • speed: <1Hz • output pressure: 22 MPa • drive voltage: +/- 1V
Conductive Polymers • attach polymer to a unstretchable film (gold) to create unimorph actuator
Electrostricted Polymers • Electrostricted graft elastomers • motion achieved through electrostriction • applied electric field induces a change from one polarized direction to another, or one phase to another. flexible backbone polarized chain
Electrostricted Polymers • performance • strain: 4% • energy density: 0.245 J/g • speed: 10 kHz • output pressure: 22 MPa • drive voltage: 2 – 3 KV
Dielectric Elastomers • elastomer film is sandwiched between compliant electrodes • apply electric field: E = V/m • Maxwell pressure: p = ee0E2 • electrodes squeeze elastomer in thickness apply voltage V+
Dielectric Elastomers • materials available off-the-shelf • 3M VHB acrylic tape • various silicone elastomers • desired features • high dielectric constant and breakdown strength • low elastic modulus – high % elongation • thin film
1 2 3 4 Dielectric Elastomers • increase performance through prestrain • stretch elastomer film in one planar direction • fix motion in prestrained direction • allow expansion in other planar direction during activation electrode V+ dielectric elastomer rigid constraints
Dielectric Elastomers • performance • strain: >200% • energy density: 0.75 – 3.4 J/cm3 • speed: 10Hz - 20kHz • output pressure: 3.0 – 7.2 MPa • drive voltage: 5kV
Dielectric Elastomers • morphologies • planar actuators • butterfly/bowtie • unimorphs/bimorphs • rolls • bellows/speakers
