Perhaps this time it may be right - taking a big chance

I wrote a while back how Shiva's measurements gave 0.29eV as the binding energies in our polymer/dye material (with an experimental uncertainty of 0.02 eV) which is responsible for forming domains that are at the heart of our theory of self-hearing .  I tried to figure out what interactions between molecules and polymer would give this energy and came up with a possibility.  But because I read the data tables incorrectly, I wrongly thought I had solved the problem.

When preparing my talk for SPIE a couple days ago, I drew the PMMA polymer chain with a molecule drawing program and added a few DO11 tautomer molecules to see where they would fit.  Miraculously, as a plopped the DO11 molecules on the page, I immediately saw that the NH from the DO11 tautomer cozies up to one oxygen in the PMMA polymer chain while the OH group naturally attaches itself to another oxygen in the chain, as shown above.  And he energy?  You got it; the sum of the two hydrogen bound energies is 0.30eV, a match.  The table below shows the energies of four types of hydrogen bonds.




There are always other possibilities that we have not yet considered, but this smells right.  Perhaps we are onto something.  Future experimentalists will allow us to test this hypothesis and zero in on what is going on when a molecule self heals.

This project has been one huge puzzle, were each new experiment presents to us a new piece.  It reminds me of how the discovers of the structure of DNA (Crick, Watson, and Wilson  ) pieced together cardboard cutouts of molecules to guess its molecular structure, and confirmed their results using x-ray scattering data from  Rosalind Franklin.  Incidentally, the story behind Franklin's contributions to the discovery of DNA and not being recognized  at the time makes for interesting reading.  I also recommend readers to check out Schrodinger's guess as the structure of DNA using simple physics principles.  The title of his very thin but fascinating book is

"What Is Life?: with 'Mind and Matter' and 'Autobiographical Sketches'"

I can imagine the thrill of discovery experienced by Crick, Wason, Wilson, and Farklin.  From little cardboard pieces and an "X" on a piece of film from an x-ray scattering experiment (shown above), they revolutionized our understanding of the workings of DNA.  Ironically, the forces that hold together the double helix reside in the hydrogen bond, the very forces that seem to be at work in our molecule/polymer system.

I am preparing my talks this morning, and plan to go on a limb proposing stating that the interaction between a DO11 molecule and a polymer chain  through hydrogen bonding underpins the phenomena of self healing.  I am not a chemist and have a naive view of the intricacies of how molecules interact.  But, I hope that my bold proposal will result in good feedback form my audience that will help us fine tune our models of the mechanisms of self healing.

I have been very excited in recent months by all of the discoveries that we are making.   Even if they end up being wrong, the process of the search for the truth is exhilarating.  Gotta run.  Too much to do.  And again, sorry for the typos!

Another paper accepted, but in record time

In a recent post, I mentioned a paper that took about 4 years to get published. In contrast, we did some work that took about 3 months to complete, and today, the manuscript was accepted for publication in JOSA B.

The topic:

Testing the diffusion hypothesis as a mechanism of self-healing in Disperse orange 11 doped in PMMA

This is an important piece of work that get's us one step closer to understanding self healing in dye-doped polymers, a phenomena that was discovered in our lab a decade ago. The first comment I always get when introducing our work at scientific meetings is that the laser is heating the material, causing the dye molecules to diffuse away from the beam. When the laser is turned off, the dye molecules diffuse back. So, rather than the molecules breaking apart and then reassembling themselves, they are just moving out then into the beam - a much less sexy phenomena.

The report of one of the reviewers summarizes our results best:

This manuscript describes a combined experimental and theoretical study on the recovery of absorption in dye-doped polymer samples exposed to high light intensities. There are several possible mechanisms for such a self-healing effect and it is of significant interest to understand which one(s) contribute. The paper presents a set of experimental data on the dynamics and spatial profile of the optical properties of the damage region. It then presents a thorough and detailed model of what is expected if diffusion of undamaged dye molecules into the damaged region is responsible for all or part of the recovery. The difference between the broadened profile of the concentration predicted by the diffusion model and the constant profile shape observed experimentally is persuasive in demonstrating that diffusion is not a significant contributor to the self-healing. The manuscript is well-presented, thorough, and sound. It warrants publication in JOSA B.

Congratulations to Shiva and Nathan for a job well done!