I need to understand movement of water in lyophilized product. After lyophilization, when the product is exposed to moisture, whether the water molecules travel into all the pores available or it settles at the top layer itself or it goes down into the product and establishes an equilibrium with the entire product mass.
I have got some experience preparing hydrated protein powders. The protein (or your substance) in solution is first freeze dried, then I put it into a desiccator over some drying agent until no further weight loss occurs. Now, to hydrate the dried powder it is put into a saturated water atmosphere in a different desiccator. The water from the atmosphere than hydrates the powder homogeneously and establishes an equilibrium with the entire product. You can check the amount of absorbed water by weighing the product. Different hydrated water environments can be prepared by choosing saturated salt solutions instead of pure water, which will result in different hydration levels at full equilibrium.
If you just pipette water on top of the hydrated product, then only the first layer on top will absorb the water leaving the bottom dry. You can mix it with a spatula, but this is quite messy.
Regards, Andreas
All the mechanisms that you mention may occur. It all depends on the time given and the kinetics of the system. For any system, an equilibrium is established if enough time is given. The path to the equilibrium state may differ based on the system specifics such as the constituents of the lyophilized product and their concentrations, mechanism of water addition,i.e., is it vapor or liquid water etc..
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