Smart Rubber Promises Self-Mending Products

An anonymous reader writes "French scientists have developed a new rubber that can heal itself after being cut or broken. If two broken ends of the material are pushed together, and left for an hour, they join to become just as stretchy as before. There is even a video of the supposed creation in action. 'Regular rubber gets its strength from the fact that long chains of polymer molecules are coupled, or "crosslinked," in three different ways: through covalent, ionic, and hydrogen bonding between molecules. Of these three bond types, only the hydrogen bonds can be remade once a material is fractured, although normally there are not enough hydrogen bonds for the rubber to re-couple in this way. The solution devised by Leibler and colleagues is to simply get rid of the ionic and covalent bonds. They developed a transparent, yellowy-brown rubber in which crosslinking is performed only by hydrogen bonds.'"

Comments

Yes necessarily

[NoData]

Carbon-carbon bonds are highly covalent and exceptionally strong. Ionic bonds are weaker and hydrogen bonds are weaker still. So, yes, necessarily this rubber is weaker. It's not the fact that it has less variety of bonding, it's the fact the sort of bonding it's left with is weak (comparatively).

Re:Yes necessarily

[blair1q]

No primordial soup for you.

In general, ionic bonds (i.e., bonds with high ionic character) are stronger than covalent bonds (i.e., bonds with low or no ionic character), simply because they are in fact the same thing, except that a difference in electron affinity causes a dipole moment to be generated, which adds electrical potential to quantum potential of the bond.

The larger the difference in electronegativity (or electron affinity, however you want to measure it), and the shorter the internuclear distance, the stronger the ionic force of the bond.

It just so happens that the quantum effect in a carbon-carbon bond is pretty strong in the first place, so there aren't many bonds, even those high in ionic character, that are stronger (although N-N is nearly twice as strong, iirc)

Putting ions in a position to have to share their ionic attraction among more atoms than they have valence electrons weakens their bonds, so there aren't many ionic substances that have nearly as strong a structure in crystal lattices.

The strength of diamong is due to the fact that (1) C-C is a fairly strong bond and (2) of the valence-4 atoms, which allow for the least disruptive crystal structure, C-C has the strongest bonds. It's that combination of no bending and strong bonds that makes diamond hard. Though there are far harder substances.

This being chemistry, someone will of course find counterexamples. It's pretty amazing how so few rules for atoms can produce so many intricate variations in behavior once you get atoms close together.

Re:Odd Then don't bed such people, OR...

[insertwackynamehere]

I know you are joking but just to be clear, using oil based lubricants and/or using multiple condoms will increase the risk of condoms breaking during sex.

nothing new here... move along.

[silicone_chemist]

Self fusing rubber compounds are nothing new. Arlon's Silicone Technologies Division http://www.arlon-std.com/ has been extruding self fusing (healing if you prefer) tapes http://www.arlon-std.com/Products/tape.htm made from silicone rubber for a long time. Other companies do as well. The tapes are primarily used for electrical insulation applications. They are fully crosslinked but when brought into contact they fuse (or heal) into a homogeneous mass. EPDM varieties are available as well. These researches have taken a different approach. Perhaps good, perhaps not. By removing the chemical crosslinks and opting for only hydrogen bonding the material is going to be inferior in many ways; tensile strength, elongation, durometer, abrasion resistance, creep resistance, etc.