I used a freeze dryer for the first time today, with a 40 mL aqueous sample of dialyzed graphene quantum dots in a 100 mL flat bottom glass container. We have a commercial system with automated pressure and temperature control. I kept the sample frozen and it didn't melt before the freeze dry cycle started. The temperature decreased to -45 C and the pressure decreased shortly after. After a few hours, I could see what looked like an aerogel.
After 9 hours, I took it out of the freeze dryer. However, within 2 minutes my sample melted down into a dark puddle as condensation formed on my glass. Do you know what the problem may be? I don't believe that graphene quantum dots are hygroscopic. A fluffy piece of aerogel I salvaged from the container remained dry (with the consistency of cotton candy) indefinitely. How do I prevent condensation on my glass container?
Kyle - I cannot be sure, however 40ml dry in 9 hours sounds quite short. I suspect that the middle was still frozen / ice. Depending on the system and the settings, I would expect that you would need more like 24 hours for this.
Kind regards,
Rob
Dear Kyle,
usually the freeze drying process is not finished when sublimation has ended. At this point your frozen "free" water has been eliminated. You still have to eliminate the bound water to the water content at which your sample ist stable under storage conditions. For this you have to increase temperature. This has an advantage, too. Ehen opening your freeze dryerthere will be no condensation!
I added a file for you that describes the process in p,T and T, concentration diagrams (in german) but you will easily figure out the meaning,
best regards,
Harald
I have a similar problem as Kyle Michelson , in my case, I'm trying to freeze-dry milkfat using sodium caseinate, lactose, and maltodextrin. After 24 hours of drying the 25 ml sample, it started melting few minutes after taking it out. I freeze-dried for another 24 hours and the cell material dried to powder but the butter was still liquid at the bottom of the petri dish. Please can anybody help me resolve this? thank you
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