I have a photochromic organic compound not dissolving in anything except for hot toluene or DMF. I want to make a PMMA bulk material with my compound dispersed in a cube/sheet of PMMA as micro-nano crystals.
PMMA at 160 deg C (melting point) always lead to some coloration of PMMA itself. Alternatively, is it reasonable that I disperse the microcrystals in MMA monomer fluid, with some AIBN, then heat it up in a mold To get a photochromic cube?
Further, if the crystals are small enough, how small it should be to have transparent window?
Hi,
in what form come your nanocrystals? If it is a solid powder, it's most likely aggregated, and you need to disperse it. I recommend ultrasonication with a high-energy probe. If it is already dispersed (check by DLS or other relevant technique), you may add it directly to the PMMA solution, but you won't make a mistake if you ultrasonicate it either. The final dispersion is controlled by a complex interaction between PMMA, your nanocrystals, and the solvent. To get a good dispersion, PMMA must adsorb on the nanocrystals in extended confirmation. The adsorption can be tuned by the solvent, concentration, and some other factors. You may use mixture solvents if you need to change the solvent parameters while keeping your nanocrystals soluble. The drying must be quick to prevent aggregation; then, it could be molded into sheets or cubes by standard thermoplastic means. We have a series of papers on this topic:
Article Phase diagram of bare particles in polymer nanocomposites: U...
Article Thermodynamic Parameters Controlling Nanoparticle Spatial Pa...
Article Bulk Polymer Nanocomposites with Preparation Protocol Govern...
The coloration doesn't come from PMMA but from toluene. I would say use a different solvent, but that's tricky. However, you don't need to dissolve your nanocrystals beforehand; you may add it as powder and stabilize it sterically with the adsorbed PMMA if you manage to find the proper conditions.
The thermosetting approach could also be used if you don't mind that MMA is a volatile hazardous chemical and that a considerable amount of unreacted monomer is left behind unless you use frontal polymerization. The dispersion step with ultrasonication is pretty much the same as with the polymer solution.