Zhigang Suo Room 309, Pierce Hall

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Electric Fields in Matter

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Presentation transcript:

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

Dielectric elastomer actuators Large deformation Compact Lightweight Low cost Low-temperature fabrication Kofod, Wirges, Paajanen, Bauer APL 90, 081916, 2007

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

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.

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.

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).

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

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, 134113 (2007)

Dielectric constant is insensitive to stretch Kofod, Sommer-Larsen, Kornbluh, Pelrine Journal of Intelligent Material Systems and Structures 14, 787-793 (2003).

Theory of pull-in instability polarizing thinning F Stark & Garton, Nature 176, 1225 (1955) Zhao, Suo, APL 91, 061921 (2007)

Pre-stretch increases actuation strain Experiment: Pelrine, Kornbluh, Pei, Joseph Science 287, 836 (2000). Theory: Zhao, Suo APL 91, 061921 (2007)

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, 134113 (2007)