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Updated: 22 hours 58 min ago

dynamic covalent bond vs. noncovalent bonds

Sat, 2018-12-08 23:26

In reply to Dynamic covalent bonds vs. noncovalent bonds

Hi Zhigang, there are some subtle differences between dynamic covalent bond and noncovalent bond. For a polymer composed of dynamic covalent bond, its viscosity decreases relatively slowly with the increase of temperature, following Arrhenius equation. For a polymer composed of noncovalent bonds (e.g. van der waals interaction for most thermoplastic), its viscosity decreases rapidly with the increase of temperature. In general, the binding dynamics/strength of noncovalent bonds are more temperature-sensitive than dynamic covalent binds.  I learned those from Zhijian when he first joined our group. 

Another possible advantage for dynamic covalent bonds may be that it can also work equally well in dry elastomer. For the ionic interaction, water is essential for enabling the ion migration. For hydrogen-bond enabled self-healing, dry enviroment may be fine as well. 

Recently, people try to use polymer with dynamic convalent bond to replace theromplastic for making fiber reinforced polymer composites. The performance the new composite decays less severely with the increase of temperature.

It will be interesting to compare the differences of the self-healing performance of the gel composed of (different) noncovalent bonds or dynamic covalent bond.  I don't think it is clear. 

Hi Jiawei

Sat, 2018-12-08 22:54

In reply to Pig skin protein as stitching polymer

Hi Jiawei, I cannot answer either of the quesiton with confidence. For your first question, I suspect the effective component contains geltain, elastin and other proteins. For the second question, I guess the protein may diffuse into the cellulose of wood to form strong bond, considering the porous structure of wood. I don't have evidence though. It may be fun to take a look under microscope, which should be fairly easy.  

Dynamic covalent bonds in hydrogels

Sat, 2018-12-08 22:00

In reply to I am very interested on

It depends on what kind of dynamic covalent bonds you want to use. The synthesis of some dynamica covalent bonds can be very simple. While the non-covalent bonds like multiple hydrogen bonding interaction can be a little difficult.

In fact, the newly reported dynamic covalent bonds are those traditionally recognized as stable and themoset covalent bonds. Recently, it is found that, with the addition of catalysts, the covalent bonds can be dynamic at certain conditions.  However, in many dynamic covalent bonds (ester, carbamate, Diels-Alder reaction) (Adv. Mater. 2017,29, 1606100), the triggering condition needs high temperature, which limits their applications in hydrogels. Among them, two kinds of dynamic covalent bonds, disulfide bonds and Schiff base may be useful in the tough adhesions. Both of them are summaried in the review mentioned by Zhigang. The disulfide bonds can be triggered by UV light and the Schiff base bonds are sensitive to pH conditions.

The bulk dissipation depends on the time scale of the reaction of dynamic covalent bonds. If the strain rate in the measurement is slow enough, I think the bulk disspation in dynamic bonds and noncovalent bonds may be similar. However, in the measurment, the time scale is much shorter than the time scale of dynamic covalent bonds. So the dynamic covalent bonds act as the conventional covalent bonds. We can not expect huge bulk dissipation in them.

In our lab, we are also interested in the dissipation of the materials with dynamic covalent bonds. We may have some results in the near future.

I was working on a deadline,

Sat, 2018-12-08 21:56

In reply to Pig skin protein as stitching polymer

I was working on a deadline, but I just couldn't help but join this exciting conversation when a group of mechanicians began to discuss dynamic bonds, topology, self-healing, proteins, furnitures and cocking with significant contents and implications. Soft materials is arguably one of a few topics in mechanics that can cause such excitement, diversity, depth, profoundness, fun and eventually benefits to the society.

A specific reply to Jiawei's post. To our knowledge, the phase seperation and aggregation of proteins can give tough, strong and reversible adhesion. One example is elastin-like polypeptides, whose phase seperation and adhesion can be triggered by ionic strength of the solution. There are other previous examples including gelatin and fibrin that we cited in the paper.

 

That is really interesting!

Sat, 2018-12-08 21:35

In reply to For the last comment, my

That is really interesting! Where does the fracture happen? At the interface or in the bulk hydrogel?

Pig skin protein as stitching polymer

Sat, 2018-12-08 21:14

In reply to Topological adhesion for wood

Dear Shengqiang,

Thank you for raising up such interesting glue! I have two small question. 1, Is the pig skin glue you mentioned a gelatin? Because I remember when I cook pig feet, the soup becomes jelly when it is cold, but when I put it on hot rice, it quickly melt. 2, You say it is topological adhesion for wood, does it mean the pig skin proten can interpenetrate with the cellulose of the wood?

Pig skin protein as stitching polymer

Sat, 2018-12-08 21:09

In reply to Topological adhesion for wood

Dear Shengqiao,

Thank you for raising up such interesting glue! I have two small question. 1, Is the pig skin glue you mentioned a gelatin? Because I remember when I cook pig feet, the soup becomes jelly when it is cold, but when I put it on hot rice, it quickly melt. 2, You say it is topological adhesion for wood, does it mean the pig skin proten can interpenetrate with the cellulose of the wood?

I am very interested on

Sat, 2018-12-08 21:03

In reply to Dynamic covalent bonds vs. noncovalent bonds

I am very interested on dynamic covalent bond, and I realize that more and more such dynamic bonds are used in hydrogel. In your opinion, is design and synthesis of dynamic bonds in hydrogel more challenging in practice compared to noncovalent bonds? 

If we want huge bulk dissipation, is dynamic bonds better than noncovalent bonds?

For the last comment, my

Sat, 2018-12-08 20:51

In reply to Hi Zhijian,

For the last comment, my topological adhesion paper has one data shows that the measured adhesion energy is even higher than the fracture energy of the hydrogel.

Very nice and deep work! I am

Sat, 2018-12-08 20:47

In reply to Mechanics in designing soft and tough adhesion

Very nice and deep work! I am wondering how two figures interact with each other if you stretch the material really large.

This is interesting thought.

Sat, 2018-12-08 20:40

In reply to Hi Hyunwoo,

This is interesting thought. But the equation itself does not tell you how strong the weak bonds are that can elicit the bulk hysteresis. It is intriguing to study how the strength of interfacial bonds influence the bulk dissiaption.

Hi Qihan,

Sat, 2018-12-08 20:30

In reply to Hi Jiawei,

Hi Qihan,

Yes. The topological adhesion can be applicable for any polymer network, so long as the chain can go into both networks and make stitch.

Molecular stitching is one version, we also have another version, called molecular staple. Can you think anything macroscopic version of fastening two objects that can be created in the molecular level?

The last comment is quite interesting, currently I am also exploring some properties.

Dynamic covalent bonds vs. noncovalent bonds

Sat, 2018-12-08 17:14

In reply to Dynamic covalent bonds vs. noncovalent bonds

Thanks, Zhigang. Yes. The roles of dynamic covalent bonds and noncovalent bonds are very similar, breaking and reforming. In my opinion, the difference may be bond strength. The covalent bonds are stronger than the non-covalent bonds, which seems important for the tough adhesion in bulk and surface treatment approach. For the topological design, I am not sure whether strong bond strength is critically important or not. Some understanding in these approaches can help the design of tough adhesives.

The disadvantage of dynamic covalent bond may be the side reaction. Sometimes they can not be totally reversible. 

Dynamic covalent bonds vs. noncovalent bonds

Sat, 2018-12-08 16:23

In reply to Dear Zhigang,

Thank you Zhijian.  So far as the mechanical behavior of hydrogels is concerned, dynamic covalent bonds and noncovalent bonds serve the same attributes:  they can break and reform. These attributes lead to, respectively, toughness and heal.

The similarity between dynamic covalent bonds and noncovalent bonds is clearly articulated in a review of self-healing hydrogels.  The devil is in details.  Table 1 of the review lists the condition of heal.  In our Ca-alginate-polyacrylamide hydrogel, heal happens at elevated temperatures (e.g., 80C).  People are cooked by then. Many other gels now can heal at room temperature, in minutes or faster.

From your perspective, do dynamic covalent bonds bring any advantage over noncovalent bonds?  Perhaps they are just different chemistries, and have different attributes unrelated to mechanical behavior.  I’d love to hear your view.

Thermoreversible adhesion, thermodetachable topological adhesion

Sat, 2018-12-08 16:00

In reply to Topological adhesion for wood

Excellent point.  We've playing with animal glues.  

Topological adhesion for wood

Sat, 2018-12-08 15:51

In reply to Topological adhesion

In ancient China (in particular Ming and Qing Dynasty), people made wood furniture by using glue. The glue is a bio-protein (from for example skin of pigs), which is a liquid at high temperature and gelled at low temperature. The wood furniture can be very study at room temperature. Nowadays, when an experienced craftsman tries to repair those anique, they simply spray boiled water onto the furniture and then can easily dissemble them (the bio-gel turns to liquid state)- (on-demand detachment). 

 

Topological adhesion

Sat, 2018-12-08 15:02

In reply to Stimuli-responsive adhesion

Hi Jiawei and Zhigang,

I am very interested in the topological ahesion done by you. In the lab, we actually often use the mechaism implicitly. When we try to glue two elastomer, one way we often adopt is to partially cure both elastomers, put them in contact with each other and let the curring process finish to enable the bonding. For this case, reversible bonding and detachment cannot be achieved, as demonstrated in your work.   

 

An exciting field

Sat, 2018-12-08 14:55

In reply to Journal Club for December 2018: Bonding hydrophilic and hydrophobic soft materials for functional soft devices

Dear Qihan, 

Thanks for the timely review and insightful elaborations. Most of us have witnessed the rapid advancement in the field of chemo-mechanics of adhesion in recent years. Though I have noticed most of work cited here, your summary and the incurred discussions indeed make the development of the field much clearer to me. 

In chemistry field, recently, there have also been some signficant progress in the adhesion field. For example, the work done by Messersmith group on Mussel inpired adhesion, which must be known to many of you.  

I imagine deeper interactions between mechanics and chemistry may lead to new opportunities in the field. 

 

 

Dear Zhigang,

Sat, 2018-12-08 13:15

In reply to Stimuli-responsive adhesion

Dear Zhigang,

Thanks for your comments. The topological adhesion is really a nice design without the need for treatment of raw materials. This strategy can also be easily combined with reversible polymer networks. 

The dynamic covalent bond is a newly emerging field. Up to now, most of the dynamic covalent bonds are triggered by high temperature in the presence of catalysts, which limits their applications in certain fields. Only those which can be triggered by light, including the disulfide bonds and reversible addition fragmentation transfer reagents, have been reported in designing self-healing hydrogels. 

More and more dynamic covalent bonds, which can be triggered in mild conditions, may be developed in the future and applied in tough adhesion.

Stimuli-responsive adhesion

Sat, 2018-12-08 08:03

In reply to Dear Qihan,

Dear Zhijian,

Thank you very much to bringing your enormous expertise in chemistry to this discussion.  This discussion reminds me of a previous iMechanica discussion hosted by you and Shengqiang, where you discussed extensively on dynamic covalent bonds.  These reversible covalent bonds, along with so many noncovalent bonds, have transformed the development of polymers and polymer gels.  A particularly lively field is self-healing materials.  

It is conceivable that the same dynamic bonds will transform the development of adhesion.  Here we can use dynamic bonds to add functions to adhesion. An example is topological adhesion.  Here a trigger (a change in pH) can cause both strong adhesion and on-demand detachment.  The strong adhesion requires no functional groups in the two adherends. A third species of polymers stitches the preexisting networks of the two adherends.  That is, the stitching polymers act like a molecular suture. As noted in the paper, one can imagine other triggers (ions, molecules, temperature, light). The possibilities are wide open.    

May the new development of adhesion adhere mechanics and chemistry in new ways.

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