PQ-PMMA modeling.

I work in holography recording gratings in PMMA. To achieve a
photosensitive material first I prepare the samples from liquid MMA +
AIBN + PQ (phenanthraquinone) in a very rustic mold that is then
slowly baked at 55C for days. The solid samples are then cut to fit
and exposed to 488 nm radiation that activated the PQ. As I
understand the PQ does a very similar job on the remaining MMA as the
AIBN did in the oven before with most of the MMA, just that instead of
heat, PQ needs 488nm radiation.
The exposure takes 32 seconds only but the grating strenght is very
low right after the exposure. After waiting for 24 hours in the dark,
a diffusion process of the unexposed PQ takes place that enhances the
contrast lets say. You can think of it as a periodic structure where
the period is given by alternating regions where the PQ is illuminated
and regions where it was NOT illuminated. The diffusion must take
place in between these regions and all over the structure. Plotting
the grating strenght versus time gives a curve that saturates after 24
hrs approx.
I am an electrical eng. working in optics and holography so my polymer
knowledge is very limited. I was wondering if there is any kind of
model for this diffusion process, like in MATLAB.
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Possibly, but it would be horribly complex as you would need to account for the diffusion of the unreacted PQ (not too difficult) as well as that of the entangled polymer chains - called reptation, which is based on the same root as "reptile", since both inch along on their bellies in the longitudinal direction.
If it is speed that you are after, increasing the temperature would certainly increase the diffusion rates. You could also add some photoinitiators/sensitizers/synergists to accelerate things along.
And since we don't get many EE's around here, I'm going to take advantage of the situation and get a friendly shot in: Emil Fischer had a 1 in 16 change of correctly identifying the sterochemistry of glucose and the other aldohexose sugars. He hit it dead on. Benjamin Franklin had a 1 in 2 chance of correctly identifying the direction of electron flow AND GOT IT WRONG. I guess that's why they say "better living throught chemisty" and not "better living through electricity".
John Aspen Research, -
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"Turning Questions into Answers"
Opinions expressed herein are my own and may not represent those of my employer.
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Sounds like a long time to make a casting. I know there are casting grades of PMMA (Elvacites) that are dissolved in MMA and contain residual BPO to complete casting. Don't know how much residual MMA you can tolerate but process would be easier. Frank
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