What happens to liquids such as water, alcohol, glycerol, silicone oil etc if they are placed under low temperature vacuum plasma (any type of plasma including oxygen nitrogen or air). Can they be safely placed in such a chamber in the first place?
Look at the boiling point curve for each liquid in question. They will all behave a bit differently. Water, for instance, will boil off at a relatively high pressure, but if you have the volume to surface area just right or a low starting temperature, it will self cool and freeze. Even after being frozen, the water will sublime and eventually be pumped away. If you have a large quantity of liquid with a relatively high vapor pressure, you will be unable to achieve plasma until it is mostly pumped away, it will essentially be a virtual leak in your vacuum chamber. In general, it's not a good idea to put liquids in vacuum. You'll need to consider what will happen to the pump oil in your roughing pump if you are pumping large volumes of water vapor or VOCs and consider the flammability of the VOCs as well. If you have a foreline trap, you'll need to think about the saturation point of the sorbent material. Liquids with lower vapor pressure will stay in the chamber for the most part but will outgas dissolved gasses possibly preventing plasma for a time that will be dependent on the gas solubility of the liquid. Once you are able to form plasma, the interaction with the liquid surface will cause molecular fragmentation which will likely lower the vapor pressure of those by-products thereby causing them to vaporize and be pumped away. If the reaction is fast enough it may quench the plasma. These byproducs may be flammable and/or toxic. Good luck and be careful!
Thanks a lot for the input Ron! If a low vapor pressure liquid is used, do you anticipate no plasma being formed if I were to run the plasma in a cyclic fashion? As in we apply more number of short time cycles and provide a slightly longer delay time between cycles so as to help the dissolved gases settle down?
This does not refers to .space plasma.Please refer to a chemist expert.
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Depending on the gas and vapor content and the power of the RF in the system, you should be able to strike a plasma somewhere around 1 Torr. You won't reach that pressure until the liquid has been out-gassed to some degree that will depend on the gas partial pressure and it's solubility. If your plasma cleave small molecules that have a lower vapor pressure than the bulk solution and the cleavage rate is high enough, your plasma will get quenched by the addition of the new species to the system. Once the plasma is quenched, the cleavage will stop and the new species will be pumped away returning your system to a low enough pressure to strike a plasma again. This cyclic behavior will only happen if the reaction rate is significantly greater than the pumping rate. If the reaction rate is slow or your pumping speed is fast enough, then you should be able to maintain plasma without pulsations.