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: J/cm 3  speed: 100 Hz  output pressure: 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: 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: 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 = ee 0 E 2  electrodes squeeze elastomer in thickness V+ apply voltage

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

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 V dielectric elastomer electrode rigid constraints

Dielectric Elastomers  performance  strain: >200%  energy density: 0.75 – 3.4 J/cm 3  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

Actuator Comparison

Actuator Work

Actuator Power