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Tim great job AP

Fri, 2018-02-02 12:26

In reply to Hydrogel discussion response


great job


10 000 signatures! This is going very very fast...

Fri, 2018-02-02 12:11

In reply to Corriere della Sera: recruitment in Italian Academia

Thanks to all the 10 000 scientists signing out petition to change the recruitment system in Italian Academia.


10 mila firme raggiunte! Vorrei ringraziare a nome di tutti gli amministratori e moderatori del gruppo ASN, i tanti firmatari della petizione, che sta andando a una velocità che MAI ci saremmo immaginati. Continuate a seguire la vicenda, e a discutere su come meglio continuare a spingerla e indirizzarla.

Permeation barriers for hydrogels

Fri, 2018-02-02 08:53

In reply to Journal Club for February 2018: HASEL artificial muscles for high-speed, electrically powered, self-healing soft robots

Hello Christpoh,

The work of your group is very inspiring, and open up new possibilties for soft actuators. This is a breath of fresh air for the field!

I would like to come back on the recent comments of Timothy and Eric about the durability of the device in ambient atmosphere, and in water environment. Our group recently published a paper about wearable and washable hydrogels, which could be useful to design HASEL actuators with enhanced durability: Wearable and Washable Conductors for Active Textiles

We notably show that combining the effect of an hydroscopic salt and an elastomer coating can be a solution to create hydrogel devices that doesn't dry out in ambient air. Also, I would like to draw your attention to the fact that silicone elastomers have extremely high permeabilities toward water and oxygen. Ecoflex is convenient for proof-of-concept devices, but there are other rubbers, such as butyl rubber (a crosslinked polyisobutylene), which have a permeability that is about a hundred times lower than Ecoflex. This material is used to make air-tight chamber, and innerliner of tires. It is actually known to be the elastomer with the lowest permeabilities.

In our paper, we also show that the diffusion of salt (NaCl) from a hydrogel to DI water can be slowed down quantitatively with the presence of a thin butyl rubber coating. Using this material as a coating, HASEL actuators could probably work in water environment for some time.

Thank you for your amazing work! 

perhaps it is better to enlarge the debate,

Fri, 2018-02-02 08:28

In reply to I did not say review

It is not very meaningful if only you and I discuss.  Let us see opinion of others.  At present, me and you are at a dead end, not worth going on.

I did not say review

Fri, 2018-02-02 08:19

In reply to your idea is only apparently innovative

I did not say review accurately reflects the quality of papers. But review scores should somehow reflect the quality of the paper if we still have confidence in peer review. Yes, there are journals publishing reviews, see

I hate to repeat, but I have to say that your test is not related with my theory. What your test can find out is whether somebody would like to give opinions on a paper uploaded on arXiv in a public forum setting, my theory is whether the proposed ideas (localized arXiv, public but anonymous reviews/responses, and better metrics measuring paper impacts) work better for journal publication. In fact, your own comment already disclose that you have seen practical examples: you proposed epi-journals using a global arXiv (local arXiv is a refinement); you already know some journals publish reviews. Then, you have to provide other reasons for dismissing these ideas for a meaningful discourse. 

Hi Xiaoyan, 

Fri, 2018-02-02 03:40

In reply to Amazing work

Hi Xiaoyan, 

Thank you for your kind comments and thoughtful questions about our work.

Your research on electrochemical actuators is very interesting. That is a clever way to turn what is usually a problem – volume change from lithium insertion and extraction – into something beneficial! The ability to drive >10 MPa at 4 V is very impressive, especially with 1 second response time. I am curious to know how these perform after a high number of cycles.

We appreciate your questions about operation in different environments and fatigue life. Below are my answers to your questions.

1)    Whether/how environmental factors (such as temperature and humidity) affects the performance and behavior of HASEL actuators?

In our case, humidity can be an important environmental factor. We have used ionic conductors, namely PAM hydrogel swollen with LiCl, (based on reference 3 above) as our electrodes. While LiCl is hygroscopic, below a certain threshold (~10% relative humidity) water loss of the hydrogel becomes significant. Colorado is a dry climate, yet we only have issues with ionic conductors drying out during the winter months. At higher humidity levels we have not observed any change in performance of the actuators. Some HASEL actuators do not require stretchable conductors and as a result flexible electronic conductors can be used.

We have not investigated the effect of temperature on our devices, but this could be very important to consider for certain applications. We know that properties such as viscosity of the liquid dielectric will depend on temperature. The liquid dielectric we used (Envirotemp FR3) has a pour point of -20 deg C, which means below this temperature the liquid does not flow, which would be detrimental for actuation performance. Understanding the limitations of current HASEL actuator materials and determining materials for extreme conditions will be important to consider in some applications.

2)    How about the fatigue behaviors (especially reliability of actuators under high-cycle fatigue) of HASEL actuator?

We have performed some initial tests of life cycle for HASEL actuators. Donut HASEL actuators were tested for more than a million cycles under a load of 150 g. Under these conditions actuation strain was 15% and we noticed no change in performance after a million cycles. We ended the test for sake of time and not because the device failed. It would be interesting to perform longer term tests for this type of HASEL actuator to determine the maximum number for life cycle.

We also tested fatigue behavior for two other designs of HASEL actuators. A planar HASEL actuator, which is made of silicone elastomer and pre-stretched onto a rigid frame, failed after 158,000 cycles from mechanical rupture. Peano HASEL actuators, made from heat-sealed biaxially-oriented polypropylene failed after 20,000 cycles due to electrical breakdown through the heat-seal. Additional experimental testing and a better fundamental understanding of fatigue of soft and flexible materials would be useful for improving the long-term performance of HASEL actuators.

Thank you again for your comment and questions!

Eric Acome

Amazing work

Thu, 2018-02-01 23:08

In reply to Journal Club for February 2018: HASEL artificial muscles for high-speed, electrically powered, self-healing soft robots

Hi Christoph, it is an amazing work!

Two years ago, I and my collaborators (Prof. Hujian Gao at Brown and Prof. Hui Wu at Tsinghua) built an electrochemical actuator based on a rechargeable battery of LiFePO4 cathode and Si anode, by taking advantage of the giant volume expansion in Si anode microparticles after full lithiation. Our electrochemical actuator of the LiFePO4||Si battery can drive a high load greater than 10 MPa with a device response time less than 1 second. The driven voltage of the device is less than 4 V, which is two order-of-magnitude lower than that of piezoelectric materials. Such actuator might be used for the robotics by the clever design. The relevant paper is titled by Cycling of a Lithium-Ion Battery with a Silicon Anode Drives Large Mechanical Actuation.

Your HASEL actuator couples the hydraulic and electrostatic force, and exhibits the muscle-lie performance. I am curious on two aspects of your HASEL actuators: (1) whether/how the environmental factors (such as temperature and humidity) affects the performance and behavior of HEASEL actuator? (2) how about the fatigue behaviors (especially reliability of actuators under high-cycle fatigue) of HASEL actuator? Thank you very much in advance!

Hydrogel discussion response

Thu, 2018-02-01 18:55

In reply to Wonderful work!

Hello Canhui,

We are thrilled you appreciate the "simple yet effective" solutions we have presented with HASEL. We also hope our opportunities and challenges section leads to some other expert community members of iMechanica in joining us in pushing the boundaries of HASEL. 

Your questions about the hydrogel are very important to us. I answer them directly below

1. Whereas hydrogels can retain water with dissolved hygroscopic salts, the water content fluctuates with the ambient humidity. Does the fluctuation of water content (i.e. resistance) of hydrogels affect the device performance? 

The short answer, yes ambient humidity can influence the properties of the hydrogel. Ambient atmosphere is especially important in climates such as ours, in Boulder, Colorado where we have very dry air, especially in the winter months. We found that in most atmospheric conditions the hydrogel would remain hydrated for hours and there was no significant influence on the performance of the device. However, in the drier winter months, it is true our hydrogels may dry out which may increase the resistance of the electrode. However, since our HASEL devices currently use high voltage, the changes in resistance has minimal influence on actuation performance. We have not done a comprehensive study on atmospheric conditions, hydrogel resistance, and actuator performance. That may be very useful for advanced lifetime test.

Also, we are very fortunate to "stand on the shoulders of giants" and follow the hydrogel recipe developed by Y. Bai. et. al. in Professor Suo's research lab.  These PAM LiCl hydrogels have very good water retention properties. Do you know of other hydrogel compositions that we should consider for enhanced water retention? 

Lastly, in some cases, we encapsulated the hydrogel in a thin layer of ecoflex. The ecoflex was applied to the hydrogel via a spin coating process. This thin layer of ecoflex helps keep water in the hydrogel and does not significantly influence mechanical properties of the actuator. Still, ecoflex is somewhat permeable to water vapor and while improving water retention of the hydrogel electrode, it does not completely solve all hydrogel hydration issues.  The supplemental material section of the Science paper clearly discusses which systems are encapsulated and how.

2. The hydrogel electrodes may contact with other materials, and short circuit might happen if the materials are conductive. 

This is true, if the electrodes came in contact with conductive material this would cause a short circuit. In real-world application we feel this is not a common situation. Additionally, when the device is encapsulated with a thin layer of ecoflex or Kapton film, this insulating layer will make shorting the electrodes even less likely. 

Along the lines of electrodes contacting other materials, it may be possible that the HASEL device is in an environment where the electrodes are physically damaged (cut, scratched, etc.) We think it may be very interesting to incorporate self-healing conductive materials such as work we published in Advanced Materials last year (ref 20 above, 

3. Using hydrogel makes the overall device transparent. But the device cannot work in water environment.  Have you found potential solution for this issue?

Again, this is true, that this device may not work in a water environment as the hydrogels would be influenced by the surrounding water. For an application such as this we can speculate a few possible solutions. 

The first possible solution may be to look for other transparent ionically conductive electrodes such as ionogels. Again, the self-healing material we collaborated with Chao Wang on (ref 20 above) might be one possible material, plus this material has the added benefit of physical self-healing. This material used ion-dipole interaction to enable both self-healing and to keep the ionic liquid in the polymer matrix. The transparency of this material was influenced by atmospheric water vapor so this self-healing material may not be the perfect electrode for a water environment, but might point you in the right direction.

A second possible solution could again be the encapsulation route. Simply sealing the hydrogel inside a polymer that is not permeable to water might allow the device to operate in a water environment. 

Lastly, it is highly possible instead of using ionic conductors, to operate HASELs with electronic conductors. Peano-HASEL has already been demonstrated with electrical conductors. It is, of course, unlikely this device would still be transparent using metallic layers

Do you have any other ideas for this? What specific application did you have in mind, sounds interesting!

Thanks again for your comments. Please let us know what you think of our ideas to address them and reach out with any new questions.

your idea is only apparently innovative

Thu, 2018-02-01 18:10

In reply to Mike, as I said previously, I

Reviews are hardly the quality of journal papers. There is a service already to publish reviews, I forget the name, but there is.

Yes, you don't see the connection with reviewing my paper.  The point is theory to practice.  At the moment, your ideas are theories. Maybe good one, but I don't buy them, until I see them at work in practical example.  And I gave you an example, which you refuse to consider.

This is for me good enough.  You don't prove your ideas, then we are talking of commercial inventions.

Mike, as I said previously, I

Thu, 2018-02-01 18:06

In reply to Wenbin, I remain disappointed you don't want to try

Mike, as I said previously, I have difficulty to figure out the connection between reviewing your paper and my proposed journal ideas. I am not seeing that getting good reviews is easy, but my proposed ideas should help getting better reviews because these reviews will be seen by the community and benefit the community. Comparing to the epi-journal what you have proposed in another thread (epi-journals just cut down storage cost by piggybacking arXiv, which is not much and cdmHUB provided it for free anyway), I thought that these ideas offer further improvements. 

Hi, Biswajit, thanks a lot

Thu, 2018-02-01 17:45

In reply to Bioarxiv: A more recent incarnation of arxiv

Hi, Biswajit, thanks a lot for the information. I will take a look. I like your idea that we try to expand cdmHUB to include more fields of mechanics. I need to convince my stake holder first. I am glad that you like the arXiv idea. 

Re: paper on composite fatigue

Thu, 2018-02-01 17:27

In reply to Wenbin, I remain disappointed you don't want to try

Hi Mike,

Don't want to interrupt your discussion with Wenbin, but couldn't help jumping in.  

I can assure you there are many more than 10 people that work on composite fatigue.  It's just that these difficult problems are not of interest in academia.  As I have said several times, editors will need to expand their list of contacts to find these people.

Another observation is that if a paper has not garnered much interest in several years maybe the results are not of interest per se.  The publication process is supposed to weed out uninteresting results from the literature.  In that case, why burden the editorial process further?

I'm sure those who need those results have already downloaded the paper from arxiv and used the results.  It's just that you don't see them citing it.  So one has to be clear whether the goal is the dissemination of knowledge or improving one's citation count.

Enough discussion for now; need to get back to debugging :)

-- Biswajit

Bioarxiv: A more recent incarnation of arxiv

Thu, 2018-02-01 17:18

In reply to Mike, original post was to

Hi Wenbin,

If you can get hold of the funds, I'd suggest you try to expand cdmHub to include more fields of mechanics.  An example of a very successful recent model is bioarxiv  You could contact the leeaders of that effort to find out how they approached the problem and what issues they ran into.

-- Biswajit

an example from real life -- I just received

Thu, 2018-02-01 16:56

In reply to Some ideas for a possible new journal

I am trying to resuscitate a journal with a friend, and he writes me how hard it is just 5 minutes ago.  Obviously I remove all the names.

So this is just an example from real life.


Dear Professor Ciavarella, 


thank you, I am trying t do my best. You see, when the former Editor was retired the journal was in no single indexing database and looked pretty bad - issue were 1 year late and there was 1 or 2 issues per year, depending on how many papers arrived in the previous year (no paper was rejected). Nobody wanted to take over the journal. I dared to do that and it was starting with 2014. The web-page changed (but we had to use the OJS system, which I do not prefer very much, but this is what the yyyyyyyyyyyy - the publisher, could afford), the Editorial Board, the editorial policies were completely new... In 201? we got the SCOPUS and WOS indexing (starting with 201?), among a number of other, smaller indexing databases, which are simply not important. Now, all those guys who never paid attention to the journal would like to take it over, and to offer publications to their friends. But the people in charge at the KKKKKKKKK how it was and how it is now and they insist I must continue. 


The objective remains the SCIe index and the number of citations in 2018 and 2019 will be decisive (Clarivate Analytics will start finalizing the evaluation in August 2019). We look quite good so far with citations in 2016 and 2017, we just need to keep that trend. I am very happy there are some very prolific authors in this issue, particularly you. And, as I have already said 1000 times, whoever supports the journal with citations will always have the open door for publications and the Editorial Board will be reshuffled when the evaluation is finished. Those authors will also be offered to become members of the EB.


So, now you know a little bit more about the history and development of XXXXX in the next years. 


Best regards,


Wenbin, I remain disappointed you don't want to try

Thu, 2018-02-01 16:25

In reply to Some ideas for a possible new journal

my test.  You are in composites, you are working on a proposals in composites fatigue, and you haven't had any comment on my Kassapoglou paper.  I know this is a little off-topic, but not so much after all.  Your technology will not change the rule of the game:  you need to find time to read the paper in details, as Editor, to find good reviewers (and on that subject in general there are only 10 or so in the world, and most of them are not willing to do the job).

So, for me the discussion is getting boring.  You don't want to comment yourself on the Kassapoloug's arxiv paper, not even to tell me why it failed to pass the traditional system of journals, then I loose interest in your proposal, and I wish you good luck.

Re: More on Mike's questions

Thu, 2018-02-01 16:21

In reply to Biswajit, I am even more confused after your replies.

I've been out of the publishing game for many years now and don't read IJSS any longer.  So I don't know who the current editors are.  But I was mildly amused by my experience; and I didn't find it surprising given my experiences in departmental faculty meetings.

I think a starting point would be to actively expand the pool of reviewers (whether it is for a new journal or for an existing one).  A repository that specializes in mechanics would be helpful for people like me (and I hope people interested in knowledge and understanding in general).  But that will need money and resources; and some creative thinking by younger people.  Keep in mind that arxiv is now more than 20 years old.

-- Biswajit

Biswajit, I am even more confused after your replies.

Thu, 2018-02-01 16:03

In reply to Some ideas for a possible new journal

Since I am not sure which system would solve the many issues you raise.

The editor of IJSS would not be happy of your statement, it is offensive.  Since I know one of them, it must be the other, the one in US, who is the same who asked me to be out of the editorial board?

Re: On Mike's three questions about publication

Thu, 2018-02-01 15:43

In reply to better way of publication


1a) Cheaper:  Cheaper for whom?  I have to pay USD 50 to read a typical paper which may or may not have any information that's useful.  So it's definitely not cheaper for me.  Also, many academics appear to be bombared by e-mail nowadays and requests for papers have recently started to go unanswered.  So the old approach of asking for papers does not work any longer. 

1b) Editors' hard work:  The failure to find reviewers indicates that editors are not actually working that hard to find people.  They just look at the list of references and send out requests to people instead to exapnding their networks to a larger group of non-academics.  What makes you think that non-academics are not knowledgable just because they don't have the incentive to publish as frequently as academics.  In my experience, particularly in engineering, many non-academics are much more knowledgable about their fields than academics.

1c) Typesetters improving papers:  I do all the typesetting of my papers myself and design figures and tables myself too.  Elsevier's typesetters are well known for destroying equations and one has to go and recheck everything twice to make sure things are OK.  Maybe typesetters help improve Nature papers, but definitely not regular journal papers.

2) Faster:  I sent a paper to IJSS a few years ago and the editor sat on it for two years and finally sent it back saying it was unsuitable for the journal.  In the mean time, that person published a very similar paper in the same journal.  No, mechanics journals are not fast enough unless the authors and editors know each other.  Not all of us have the resources or the time to create such a network by visiting numerous conferences each year and publishing numerous papers.

3) Peer review:  I've had many peer reviews where it was clear that the reviewer didn't know what they were talking about (or had given up reading after the first few pages).  The only way to fix this problem is to broaden the pool of reviewers by creating connections with more academics and researchers outside academia.  Every review that I do takes at least a day and I don't get any reputation points for doing that, but I still review papers because I get to know about the latest thinking in the subfield.

Keep in mind that for every faculty member at a university, there are at least 50 PhDs who are working in industry.  It's your job as academics to keep in tough with these students of yours and increase the pool of reviewers.  And I'm sure academics can easily come up with more creative solutions instead of complaining about quality (after all the quality of your students reflects your quality) of reviewers available.

-- Biswajit

Re: People don't take arxiv seriously?

Thu, 2018-02-01 15:23

In reply to Mike, original post was to


I agree with you on that.  In mathematics and some subfield of physics, arxiv submissions are taken very seriously.  That's probably because results can be verified by readers and, if found inaccurate, papers have been known to be withdrawn from the repository.  The same is true of computer science, e.g., all major deep learninng papers are published on arxiv first.  That allows people to know what's being done and allows for all sorts of views to be heard, instead of just academic views.  

Personally, I've seen a huge difference in the attitude of reviewers between when I was in academia and when I was in industry.  Reviewers tend to dismiss work that's done inside industry; and I think that reflects poorly on mechanics researchers. It also removes feedback to researchers on what's considered important in industry and where there are gaps in knowledge.

-- Biswajit

Response to your questions

Thu, 2018-02-01 15:21

In reply to Nice work!

Dear Jiawei,

Thank you for your interest in our work and your stimulating questions. I have answered them below:

1. When the actuator lift weights, the part composed of elastomer membrane and soft electrode is stretchable, does that compromise the actuation?

Answer: In the case of the donut actuators, a very soft membrane can hinder actuation under heavy loads, as the liquid dielectric tends to bulge the side walls of the soft shell instead of translating the force upwards to lift the weight. For this reason, we used a stiffer elastomer, namely PDMS, instead of other softer silicone based products, such as Ecoflex.

2.The voltage applied determines how heavy the weight can lift. But for lifting heavy weight, your voltage is very high, does that hinder the practical application?

Answer: It is important to note that HASEL actuators are not strictly voltage dependent. The electrostatic stress generated within the shell is proportional to the electric field squared and dielectric constant of the solid-liquid composite dielectric. In our initial work, we used relatively thick membranes (on the order of 1mm) to construct the actuators, as these membranes were easier to handle and sufficient for proof of concept work. These thick membranes resulted in the need for rather high voltages to generate the necessary electric fields to trigger actuation. The voltages used in our initial work are indeed too high for practical applications; however, some strategies for reducing the operating voltage include increasing the dielectric constant of the composite structure or decreasing the distance between the electrodes by utilizing thinner membranes for the shell. Currently, we have designs which operate at 10 times less voltage while still generating high forces, making the electronics practical and the actuators extremely useful!

3. When the elastomer membrane contacts, does the high voltage cause electric breakdown of the elastomer?

Answer: Typical operation of HASEL actuators does not cause breakdown of the composite dielectric structure. That is, we primarily do not use electric fields which are higher than the dielectric strength of the composite dielectric (though, if we did, the actuators could self-heal from the breakdown). There is indeed a large change in the electric field after a pull-in transition; however, the maximum field is still below the dielectric strength of the composite and so breakdown does not occur. Additionally, there is always a layer of solid dielectric between the two electrodes, which prevents the electrodes from shorting during operation.

4. What is the maximum liquid you can put in the actuator? Is there any limitation? 

Answer: The content of liquid dielectric is far from optimized. We tested a few different oil contents to roughly determine what worked well for our demonstrations, but did not perform a rigorous analysis to optimize the fill amount. It’s important to note that as the amount of liquid inside the elastomer shell is increased, the distance between the electrodes in the relaxed state also increases. Therefore, the voltage required to generate the electric field necessary to trigger actuation also increases drastically. If the applied voltage is held constant throughout the pull-in transition, the electric field at the end of the transition may exceed the dielectric strength of the material and result in dielectric breakdown.




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