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Mechanics of Soft Active Materials

Zhigang Suo's picture

At the invitation of David Clarke on behalf of the UCSB/Los Alamos Institute of Multiscale Materials and Structures, I gave the following three lectures:

  1. Large deformation and instability in dielectric elastomers
  2. Large deformation and instability in swelling polymeric gels
  3. Mechanics and electrochemistry of polyelectrolyte gels

The abstracts follow, and the slides are attached at the end of this post.

Lectures at UCSB and sent live to Los Alamos: 

Soft materials can be made active in that they can greatly change shape and volume in response to diverse stimuli. For example, an elastomer may strain more than 100% under an electric field. As another example, a gel may imbibe solvent molecules to swell a thousand times its initial volume. These soft active materials have broad applications in drug delivery, tissue engineering, microfluidics, and the oil industry.

My group has recently started to study the mechanics of soft active materials. We attempt to formulate theories that address commonly asked questions. How do stress, electric field, and chemical potential interplay to cause large deformation? Why do abrupt changes, or instabilities, occur?

In this series of talks I'll outline the basic theories and several specific phenomena. The sub-titles of the two talks are

  • Large deformation and instability in dielectric elastomers
  • Mechanics and electrochemistry of polyelectrolyte gels

Departmental seminar: Large deformation and instability in swelling polymeric gels

Flexible, long polymeric molecules can covalently crosslink into a three-dimensional network. The resulting material, an elastomer, is capable of large and reversible deformation. When the network is brought in contact with a solvent, the network imbibes solvent molecules and swells, resulting in an aggregate known as a gel. The swelling is also reversible: when the environment dries, the solvent molecules in the gel migrate out and evaporate. Gels are used in diverse applications, including medical devices, actuators in microfluidics, and packers in oil wells. Mixtures of macromolecular networks and mobile molecules also constitute many tissues of plants and animals.

Swelling of a network can be markedly influenced by a mechanical load. When the network, the solvent, and the mechanical load equilibrate, the deformation in the gel is usually anisotropic and inhomogeneous. This talk describes a nonlinear field theory of gels, building upon the work initiated by Gibbs, Biot, and Flory. The gel can undergo large deformation of two modes. The first mode results from the fast process of local rearrangement of molecules, allowing the gel to change shape but not volume. The second mode results from the slow process of long-range migration of the small molecules, allowing the gel to change both shape and volume. The theory is illustrated with examples of swelling induced large deformation, contact, and bifurcation.

The second edition of these slides has been posted.

PDF icon 2008.05.14 ucsb.pdf579.43 KB
PDF icon 2008 05 16 ucsb.pdf2.02 MB
PDF icon 2008 05 21 ucsb.pdf611.74 KB


Teng Li's picture


Thanks for posting your lecture slides.  Since the lecture was sent live to Los Alamos, I'm just wondering, if it's possible to make the archived video of your lecture open to public. I'm quite sure the video will make the learning process of this new field more effective and fun.


Zhigang Suo's picture

Dear Teng:  Thank you very much for your interest.  I have just asked the IT person at UCSB, and he told me that there is no permanent record of my lectures.  Sorry about it.  Best, Zhigang


Thanks  Dear Zhigang

These were very useful to me. I have download it .

In the past three years, I have research on the microcantilever base sensor and this research also will be continued in the next two years for my Ph .D degree. The mechanic was not my original specialty . I graduated from polymer science Qiqihaer University and in the following years was a teacher as polymer material of Anhui University Science and Technology.


I want to find a point between the polymer science and mechanics. In the past few years I have been interesting in the natural polymer. A article about Multi-membrane hydrogels (Se´bastien Ladet NATURE arch 2008) give more interesting in polyelectrolyte gels .


I wish I can do some work in this direction in the future.

Best Regards



Zhigang Suo's picture

Dear Chang-Guo:  Thank you very much for your interest.  My group has only started working on polymers recently.  These lectures mainly described what we have learnt so far, from reading papers, running calculations, and talking to experts in the field.  Our recent papers have been posted on iMechanica, filed with the tag Suo Group Research.  It would be great that people like you, with more background in polymers, are interested in this line of work.  We hope to hear more feedback form you.  Incidentally, we also liked the "onion paper" in Nature. 

Thanks!Your answer give me prompting.The "onion structure  of natural hydrogels was a promising work.I am very interested in it.But this time , I must do the research on microcantilever biosensor ,so I only study the hydrogels in my spare time . In the next step, I will fabricate a simple onion using Chitosan in plan.I prepare to learn more Knowledge for my research on the hydrogels.If you have any idea or good articles, Please give me in the email. I wish I can do some work in this field

zhan-sheng guo's picture

gone with the wind

Thank you for your site. I have found here much useful information...

Very cool design! I find very interesting information at this article, thanks.

Hari's picture

Dr. Suo,

 Thanks very much for your notes. I personally prefer to start with class/lecture notes before reading papers on a new topic. 


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