iMechanica - elastomer - Comments

Re:Re: A very good topic

Chang-Guo Xue — Sat, 24 May 2008 00:48:19 -0400

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

Re: A very good topic

Zhigang Suo — Thu, 22 May 2008 12:36:59 -0400

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 a lot

zhan-sheng guo — Thu, 22 May 2008 00:20:56 -0400

gone with the wind

A very good topic

Chang-Guo Xue — Wed, 21 May 2008 22:31:26 -0400

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

Changguo

No videos available for my lectures.

Zhigang Suo — Wed, 21 May 2008 14:42:28 -0400

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

Videos of your lectures on soft active materials

Teng Li — Wed, 21 May 2008 14:02:09 -0400

Zhigang,

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.

thank you very much it is

zhan-sheng guo — Sun, 11 Nov 2007 20:02:11 -0500

thank you very much

it is interesting

Thank you for your generous

BoJing Zhu — Sat, 10 Nov 2007 09:25:49 -0500

Thank you for your generous contribution!

cynosure online

Dear Prof. Norris Thank

Xuanhe Zhao — Mon, 17 Sep 2007 11:18:18 -0400

Dear Prof. Norris

Thank you for your interests in our work.

One of the "optimal" forms of U, the strain energy function of an elastomer, has been indicated in our recent paper "Electromechanical coexistent states and hysteresis in dielectric elastomers." Physically, it means that an elastomer described by the Gaussian statistics will always have electromechanical instability. Only when the elastomer is so stiffened that its chains are near the extension limit, the instability may be avoided.

I totally agree that the effect of electrostriction is another interesting topic.

critical electric field in thin elastomers

Andrew Norris — Sun, 16 Sep 2007 22:03:14 -0400

Hi Zhigang,

Its probably pretty obvious that the same structure for the Hessian is maintained for very general forms of the free energy. The key is the decoupled vacuum electric energy. Using your APL paper, its easy to see that a free energy of the form

has critical electric field given by

where

Games could be played by asking for "optimal" forms of U.

My interest in all this is in understanding the electrostrictive effect in elastomers. This will require explicit coupling between the E and mechanical fields in the energy. That is a whole new ballgame - with lots of interesting things to be found I expect!

Re: Thin film electromechanical instability

Zhigang Suo — Sun, 16 Sep 2007 10:47:24 -0400

Dear Andy:

Quickly looked through your note. Very
interesting! To upload the note to iMechanica, you can start a new
blog entry, and upload the note. You can then link your comment to
your blog entry.

Thin film electromechanical instability

Andrew Norris — Sun, 16 Sep 2007 10:34:51 -0400

Xuanhe and Zhigang,

Your APL paper gives a really nice explanation of the loss of stability. It is the first proper description - using
finite electromechanical theory with minimal assumptions - that I am aware of.

On reading through the paper I realized that there are some algebraic
simplifications possible. The determinant of Hreduces to a quadratic in D^2. The quadratic always
has one positive and one negative root, so the nonzero critical value
of D can be found in fairly nice form as an explicit function of the
stretches. Using this, its possible to get simple expressions for the critical values under uniaxial and equal biaxial stress.

I wrote this up in a 1-page file that I sent off to APl as
a "comment". The above link is to a copy of the file on iMechanica.

Andy

An elaborated version of this paper

Xuanhe Zhao — Fri, 07 Sep 2007 21:30:56 -0400

An elaborated version of this paper has been accepted by Physical Review B. Please take a look at the second attachment.

Dear Prof

Xuanhe Zhao — Fri, 07 Sep 2007 16:47:47 -0400

Dear Prof Mockensturm:

Thanks a lot for your interests in our work. You asked a number of good questions. Let me try to answer them one by one:

1. "I was interested in what I had heard called the pull-in instability,
which I think is the same phenomena you're studying. I did not take
the analysis as far as you have. "

The instability we analyze here is actually the "pull-in instability". However, we don't feel comfortable about this name, because we found that the reason for this instability is really the non-convex natrue of the free energy function of dielectric elastomer. Therefore, we would rather call it "electromechanical instability".

2. "I was trying to see how much non-linear stiffening would be necessary to prevent this instability."

This is a really good point. I would like to refer you to our another paper "Electromechanical coexistent states and hysteresis in dielectric elastomers." We found that one may prevent the electromechanical instability by increasing the crosslink density of polymer to a very high value. For example, the crosslink density is denoted by "1/N" in Arruda-Boyce's law for rubber elasticity. We found one need a value of N<2.6 to avoid the instability.

3. "As the title implies, I think dielectric breakdown strength is an
independent material property. However, you suggest it is determined
from other material properties. Ultimately I think there is confusion
between the pull-in instability and true dielectric breakdown."

We agree that "electromechanical instability" and "true dielectric breakdown" refer to different phenomena. We beleive that, for most of the case in dielectric elastomer, the "electromechanical instability" happens first and leads to the "true dielectric breakdown". Current experiment results also seems to support our assumption.

For example, Plante, J.S. and Dubowsky, S. "Large-Scale Failure Modes of Dielectric Elastomer Actuators ." International Journal of Solids and Structures, Vol. 43, No. 25, pp. 7727-7751, December 2006.

4. Prof Mockensturm, we notice a number of very good papers from your group on dielectric elastomers. Hope you can share some of them with us on Imechanica.

dT = 0

Wei Hong — Fri, 07 Sep 2007 16:20:53 -0400

Li Han,

Sorry about the previous mistake.

Here the "free energy" is indeed the Helmholtz free energy.

For rubber, under the assumption of constant T, the change in the free energy is all from entropy (of configuration).

dW = -TdS

But the configuration entropy S is a function of the deformation.

Almost all material laws of rubber are derived from this assumption, directly or indirectly.

So in that sense, the model has already considered the entropic effect of the rubber chains.

Wei