When I pour DMSO at room temperature into a Teflon dish and immediately put it in a freezer at -20 degrees C, it freezes fine. However, when I pour DMSO at 90 degrees C and similarly pour it into a Teflon dish and immediately put it in a freezer at -20 degrees C, I end up with some of the material being a liquid even after nearly a week at -20 degrees C. All other conditions aside from the initial temperature of the DMSO is the same. I have replicated this with the same solvent and conditions of freezing, so I can preclude any problem, per se, with the DMSO. While I do have some of the liquid from the freezer saved, I do not have any instrumentation at the moment to analyze it.
Any ideas as to what might be going on?
The freezer is set at minus 20 degrees Celsius, and I let the DMSO sit at that temperature for the better part of a week.
The liquid phase was at the top.
This liquid phase only occurred when the DSMO, that was added and placed in the freezer, was at 90 degrees Celcius. With the same exact set-up and solvent but with the DMSO at about 25 degrees Celcius, it freezes solid.
The only difference, and a consistent one, is the temperature of the DMSO when I place it in the freezer.
If on top: could it be it absorbs "something" (eg. humidity - water - or something else) that reduces the freezing point for some residual volume?
As it is, the longer period of cooling migzt allow for more "something" to be absorbed. When part of the DMSO "freezes out", the absorbed "something" might increase in concentration...
But I don't get the problem with the same DMSO in the same set-up when the temperature of the DMSO is at 25 degrees Celsius.
I have similar strange phenomenon! 3 Tubes of 100% DMSO (from Molecular cloning kit) . One tube is frozen solid. The 2nd tube is half solid, half liquid. And the third tube is fully liquid. Unknown what the temperatures were when they were put in the -20, except for the frozen one, which would have been ~ +4'C
I was very confused and I'm glad someone else has observed something similar
DMSO is hygroscopic!
And mixes of water and DMSO can have freezing points as low as 40 °C (and below).
I suspect that absorbed water is responsible for the lowered freezing point.
Re the initial question: starting at 90 °C does allow for a longer period of water absorption prior "seeing" the result than when starting at 25 °C (assuming that water absorption diminishes or stops comletely once the mix is frozen solid.
To validate this, a determination of the water content would be necessary. In the cases where a frozen and a liquid phase coexist, separating both phases and determining the water content of each is expected to show differing water contents.
Important: seal the samples to prevent further absorption of water (vapor) from the ambient!
Interesting, thanks for the input. Is it likely a minute amount of water could lower the freezing temperature so much?
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