The Properties of Water in Capillary Systems.
HYDRONAUTICS INC LAUREL MD
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The relative amounts of freezing and non-freezing water in various cellulose acetate CA membranes have been determined by differential scanning calorimetry. It has been found that A significant fraction 17-40 percent of the water 1.0-3.1 g H2O per g dry CA in any membrane does not freeze at temperatures as low as -40C. The amount of non-freezing bound water 0.4-0.7g non-freezing water per g dry CA depends upon the nature of the membrane, and is significantly higher than the total amount of water all of which is non-freezing absorbed from liquid water by a dense film of the same polymer about 0.18g water per g dry CA. The structures of the membranes have been studied by scanning-electron-microscopy. The results suggest that the amounts of non-freezing water in cellulose acetate membranes decrease with the increase in the packing density compactness of polymer within the membrane. NMR techniques proved to be a powerful tool for studying freezing processes of water in membranes. The amounts of water contained in a wet membrane equilibrated with water vapors at 90 percent R.H. was approximately, twice that adsorbed on a freeze-dried membrane under identical equilibration conditions. The amount of non-freezing water in a wet membrane representing equilibration at 100 percent R.H. is approximately equal to the amount of water present in an identical membrane. Author
- Physical Chemistry