Design Realization lecture 15 John Canny Jeremy Risner

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/cm 3 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: <1 Hz output pressure: 22 MPa drive voltage: +/- 1 V

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 k. Hz 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 apply voltage V+

Dielectric Elastomers § materials available off-the-shelf § 3 M 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 electrode 1 2 3 4 V+ dielectric elastomer rigid constraints

Dielectric Elastomers § performance § § § strain: >200% energy density: 0. 75 – 3. 4 J/cm 3 speed: 10 Hz - 20 k. Hz output pressure: 3. 0 – 7. 2 MPa drive voltage: 5 k. V

Dielectric Elastomers § morphologies § planar actuators • butterfly/bowtie § unimorphs/bimorphs § rolls § bellows/speakers

Actuator Comparison

Actuator Work

Actuator Power