After reading many of the (excellent and informative) forum posts and having read the article on the 'smoking gun' in relationship to the fogging of the PDMS, I started experimenting with 'cooking/baking' the PDMS at relatively high temperatures (176C/350F). So far it seems I am on the right track, as the first vat's (I have 3 of the latest aluminum vat's for testing and production) that are backed at 175C/350F are showing remarkably resistance against fogging. So back to this thread. Here is what I have put in place for PDMS heat curing:
a) I bought an affordable small oven, with top and bottom heating elements (NO hot air). It has a remarkable accurate temperature control (not expected for this price)
b) I modified the tray by adding some aluminum bars, in order to provide two parallel rails for the vats to sit/slide on (I can place two vats at a time). Also added two aluminum side-tracks to make sure the tray is 'tight' when placed in the oven. BTW no need to remove the tray once placed in the oven. Just place / remove vats.
d) I use a cover (backing tray that came with the oven) and a bottom cover to 'insulate' the vats from direct (radiation) heat. This allows for a 'slow' and even heating.
My temperature profile after adding the PDMS (50 grams) is as follows:
1) for 30 minutes just let it sit at room temperature in the oven to make sure the PDMS gets 'level'
2) increase temperature to 75C and let it soak for two hours (PDMS will totally cured by end of 2 hours)
3) increase temperature to 125/135C and let it soak for one hour
4) increase temperature to 180C/350F and let it soak for one hour
5) Oven switched off and let it cool down till environment temperature (don't know how long this takes as I typically go to bed by then)
IMPORTANT: you CAN NOT use the standard Delron bridge as supplied by B9C when going to 180C/350C. You will need to remove it after the 2 hours at 70C. If you want to know what happens if you ever forget, see last picture below :)
Now I use an aluminum bridge, so forgetting is no longer a 'problem'.
You can follow the above process as i still do today by hand/manually, however I have just purchased on eBay a 'PID Temp controller' that will let me program the above sequence, so next time I won't have to manually adjust and wait for each step. (link to PID Temp controller http://www.ebay.com/itm/PID-TEMPERATURE-CONTROLLER-W-30-RAMP-SOAK-SSR-OUTPUT-/110627498979
) (FYI: you need to add a SSR to this device power the oven)
Pictures of oven and the tray made for the vip's + cover:
And this is what happens if you forget to remove the Delrin bridge before going to 180C/350F :
and this is the solution I had to make after my Delrin bridge 'evaporated' :
BTW: when placing the bridge, I always wrap the bridge with some paint-tape. This gives a 'perfect' sealing, preventing the PDMS from leaking under/aside the bridge.
One more picture of my vacuum pump for clearing the PDMS and the scale I use.