1. Zhigang Suo suo@seas.harvard.edu Room 309, Pierce Hall
Elastic dielectrics
Zhigang Suo
Room 309, Pierce Hall
Battery
Dielectric Elastomer
Compliant Electrode
Reference State
Current State

2. Dielectric elastomer actuators
Large deformation
Compact
Lightweight
Low cost
Low-temperature fabrication
Kofod, Wirges, Paajanen, Bauer
APL 90, , 2007

3. Parallel-plate capacitor
battery
electrode
vacuum
electrode P
force
Electric field
e0, permittivity of vacuum
Electric displacement field
stress field
Maxwell stress

4. An atom in an electric field
battery
Hydrogen atom
External electric field displaces positive and negative charges somewhat.
Polarization: Induce more change on the electrodes.
Deformation: Distort the shape of the atom.

5. A dipole in an electric field
battery
Polar molecules
External electric field reorients dipoles.
Polarization: Induce more change on the electrodes.
Deformation: Distort the shape of the sample.

6. thinning or thickening? + -
Maxwell stress
Electrostriction
Subject to an electric field, many polymers thin, but many ceramics thicken.
Cheng, Zhang, MRS Bulletin 33, 183 (2008).

7. Thermodynamics of elastic dielectrics
Suo, Zhao, Greene, J. Mech. Phys. Solids 56, 467 (2008)
Reference State
Current State
For elastic dielectrics, work fully converts to free energy:
Free-energy density
Equations of state

8. Ideal dielectric elastomers
Dielectric behavior is liquid-like, unaffected by deformation.
Ideal electromechanical coupling is purely a geometric effect:
Choose a free energy of stretching. For example, neo-Hookean law:
incompressibility
Zhao, Hong, Suo, Physical Review B 76, (2007)

9. Dielectric constant is insensitive to stretch
Kofod, Sommer-Larsen, Kornbluh, Pelrine
Journal of Intelligent Material Systems and Structures 14, (2003).

10. Theory of pull-in instability
polarizing
thinning F
Stark & Garton, Nature 176, 1225 (1955)
Zhao, Suo, APL 91, (2007)

11. Pre-stretch increases actuation strain
Experiment: Pelrine, Kornbluh, Pei, Joseph
Science 287, 836 (2000).
Theory: Zhao, Suo
APL 91, (2007)

12. Coexistent states stiffening thinning polarizing thick thin
Cross section
Top view
Coexistent states: flat and wrinkled
Experiment: Plante, Dubowsky,
Int. J. Solids and Structures 43, 7727 (2006)
Theory: Zhao, Hong, Suo
Physical Review B 76, (2007)