I measured proton conductivity of polymer electrolyte membrane in dry state and found that negative activation energy before glass transtion temperature (Tg) and a positive activation energy above TG. I would like to know What is the physical meaning of the negative activation energy?
How "dry" was your sample ? Wouldn't it be due to dehydration of remaining water molecules from some hydrated protons ?
Dear Dr. Yamaguchi, Thanks for your comment. I dry my sample by evacuated it at room temperature only.
If I understand the dialog above, your problem could be clarified by annealing your sample about 50 degrees above Tg for an hour or so. Then cool and run your thermal analysis from low to high temperature.
Polymeric electrolytes behave in complex ways, because of the strongly polar components in a predominantly non-polar matrix. Not only is drying a complex process, but also the association process of the polar components is strongly influenced by sample history.
What you're looking for is whether anomalies disappear after annealing. In particular, "drying" will be ineffective unless done at the higher annealing temperature before the run. In addition, imperfections in your sample should also disappear by such annealing. Once you've done that, let us know if you still have a negative activation energy.
To: F. L Floyd
Thanks for your comment. I agree with you but I would like to explain my measured data. It is common for five samples of porotonated polymer membranes measured under vacuum (relatively dry) , The conductivity decrease by increasing temperature before glass transition temperature and after that it increases with temperature.
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