I am preparing PVDF membranes for desalination purpose. After preparation and during drying in air, the membrane gradually shrinks. About1/4 size get reduced from oringinal size. I coated on a support sheet also. In that case too, shrinkage is happening. Let me know how to dry the membrane without shrinkage.
Shrinkage is due to capillary forces, so it can be minimized (although not completely avoided) by using solvents of very low surface tension (e.g., diethylether). Drying is also recommended to be slow and homogeneous: strong concentration gradients have to be avoided. The best for almost zero shrinkage is supercritical drying in CO2. Freeze-drying also produces very low shrinkage, but may modify the porosity of the membrane due to the formation of solvent ice crystals.
Alain
Shrinkage is due to capillary forces, so it can be minimized (although not completely avoided) by using solvents of very low surface tension (e.g., diethylether). Drying is also recommended to be slow and homogeneous: strong concentration gradients have to be avoided. The best for almost zero shrinkage is supercritical drying in CO2. Freeze-drying also produces very low shrinkage, but may modify the porosity of the membrane due to the formation of solvent ice crystals.
Alain
You can try sol-gel method. Add PVDF powder in DMF solvent and stir on magnetis stirrer for 4-5 hours at 70o C-75o C. Then The above sol have to be spin-casted uniformly on glass substrates at room temperature at a low spin (60 rpm) for depositing the PVDF film.Use a microwave oven heating the at 100 W(medium condition) for 3 minutes. Then you can easily peel out the PVDF membrane from the glass substrate.
Article Free-standing nanocrystalline-Cadmium sulfide/Polyvinylidene...
if the initial size is 1.35x the target size. After drying (shrinkage), you will get the good one.
- Badges
- Science topic
- Similar topics
- Engineering
- Materials Engineering
- Coating