suo group research

Choon Chiang Foo, Shengqiang Cai, Soo Jin Adrian Koh, Siegfried Bauer, Zhigang Suo.

Model of dissipative dielectric elastomers.
Journal of Applied Physics 111, 034102 (2012).

Abstract

The 26th issue of the WW-EAP Newsletter is now available at: 

http://ndeaa.jpl.nasa.gov/nasa-nde/newsltr/WW-EAP_Newsletter13-2.pdf

This newsletter on the field of electroactive polymers, edited by Dr. Yoseph Bar-Cohen, addresses the need for rapid communication of progress in the field and state-of-the-art capabilities.

For a dielectric elastomer membrane we show giant voltage-triggered expansion of area by 1692%, far beyond the largest values reported in the literature.

Abstract:A hydrostatically coupled dielectric elastomer (HCDE) actuator consists of two membranes of a dielectric elastomer, clamped with rigid circular rings.  Confined between the membranes is a fixed volume of a fluid, which couples the movements of the two membranes when a voltage or a force is applied.  This paper presents a computational model of the actuator, assuming that the membranes are neo-Hookean, capable of large and axisymmetric deformation.  The voltage-induced deformation is described by

We develop a method of poroelastic relaxation indentation (PRI) to characterize thin layers of gels.  The solution to the time-dependent boundary-value problem is obtained in a remarkably simple form, so that the force-relaxation curve obtained by indenting a gel readily determines all the poroelastic constants of the gel—the shear modulus, Poisson’s ratio, and the effective diffusivity.  The method is demonstrated with a layer of polydimethylsiloxane immersed in heptane.

I gave a seminar at Xian Jiaotong University on 27 October 2009.  I recently found the video of the seminar online.  The seminar was in Chinese, but the slides were in English.

• Video of the seminar
• Slides of the seminar  

If the subject interests you, the following papers will lead you to the literature.

Silicon can host a large amount of lithium, making it a promising electrode for high-capacity lithium-ion batteries.  Recent experiments indicate that silicon experiences large plastic deformation upon Li absorption, which can significantly decrease the stresses induced by lithiation and thus mitigate fracture failure of electrodes. These issues become especially relevant in nanostructured electrodes with confined geometries.

Silicon can host a large amount of lithium, making it a promising electrode for high-capacity lithium-ion batteries.  Upon absorbing lithium, silicon swells several times its volume; the deformation often induces large stresses and pulverizes silicon.

NONEQUILIBRIUM THERMODYNAMICS OF DIELECTRIC ELASTOMERS
Xuanhe Zhao, Soo Jin Adrian Koh, Zhigang Suo

In response to a stimulus, a soft material deforms, and the deformation provides a function. We call such a material a soft active material (SAM). This review focuses on one class of soft active materials: dielectric elastomers. Subject to a voltage, a membrane of a dielectric elastomer reduces thickness and expands area, possibly straining over 100%. The phenomenon is being developed as transducers for broad applications, including soft robots, adaptive optics, Braille displays, and electric generators.

This paper studies the poroelastic behavior of an alginate hydrogel by a combination of theory and experiment. The gel—covalently crosslinked, submerged in water and fully swollen—is suddenly compressed between two parallel plates. The gap between the plates is held constant subsequently, and the force on the plate relaxes while water in the gel migrates. This experiment is analyzed by using the theory of linear poroelasticity.

This paper uses a method based on indentation to characterize a polydimethylsiloxane (PDMS) elastomer submerged in an organic solvent (decane, heptane, pentane, or cyclohexane).  An indenter is pressed into a disk of a swollen elastomer to a fixed depth, and the force on the indenter is recorded as a function of time.  By examining how the relaxation time scales with the radius of contact, one can differentiate the poroelastic behavior from the viscoelastic behavior.  By matching the relaxation curve measured experimentally to that derived from the theory of poroelasticity, one can identify