Hello everyone,
Here is my problem. I'm working with Cobalt nanorods that I'm trying to align in a polymer matrix by applying an external magnetic field. In the end I would like to perform an optical measurement in transmission, so I need to work with a transparent polymer, until now we have been trying to prepare the sample inside a spectroscopic cuvette (so a volume of 1cm3) by applying vacuum to fasten solvent evaporation but it didn't work well.
Now we would like to try a polymerization technique but I have several issues:
- Ideally I must work in a glove box (no oxygen, no water) to avoid the oxydation of Cobalt, so I should not use solvents that could oxydizes the nanoparticles. So far, we know that THF and Toluene are fine.
- The initial mixture should be liquid enough so I can disperse the nanoparticles by using an ultrasonic bath
-I want to work with a slow polymerization rate (from a few minute to a few hours) so the nanoparticles have enough time to align in the field while the mixture is still viscous.
-Ideally I should not heat the mixture, at least nothing above 80 °C, so a spontaneous polymerisation or a photopolymerisation would be the best.
Would you have suggestions about the monomer (MMA or another one?) and the initiator I could use? Is is possible to add solvent to obtain a more liquid mixture?
Thanks,
Elie
Good question, indeed. For the polymers I cannot help you at all. But maybe you seek contact with Diana Ciuculescu and/or Catherine Amiens (Univ. Toulouse), who have worked with liquid phase colloidal chemistry of magnetic nanoobjects (also using THF and toluene) and might have or come up with an idea. They're both on RG, too.
Concerning the speed of polymerization I hold it likely that you will need to find some compromise. Of course, dispersion and alignment are important for what you want to do...
But keep in mind that orientation requires a homogeneous field, otherwise the guys will move and seek the position of largest field (following the field gradient, which exerces a force onto magnetic dipoles). Also, depending on concentration (mich may be dictated by what your optical instrument is able to detect) you have the enhanced risk (or chance, as you perceive it) of not only orientational alignment but chain formation due to dipolar interactions. In case you don't want this to happen, you'd like to have a relatively fast polymerization once the rods are well dispersed.
Finally, in designing the experiment you should make some estimation of the thermodynamics. You should generate an estimate of the statistical degree of orientation you can expect to obtain at a given temperature. The torque exerced on the rod to become aligned is finite (and given by the magnetic anisotropy and Zeeman energy) and temperature will counteract it. Making a serious estimate here will give you an idea of the field required. Remember it should be homogeneous and the more so the larger it has to be. in the end this might turn out to become a nontrivial combination of constraints, given the fact that very understandably you want to work in a glove box.
Good luck!
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