I mainly use polymeric nanofiltration membranes for wastewater treatment. We are told to keep membrane wet all the time. The pore sizes of membranes will change if you dry it. When we pass dye and salt water membrane pores enlarged. We sometimes refer it as membrane swollen.
One of the paper dealing with membrane swelling is "P. Denyer et al (2007) Evidence of changes in membrane pores, Desalination, 204, 296.
What is a sPEEK proton exchange membrane? Is it natural or man made? Where do you use it ? What is its application? What is NMP stand for?
Hi, first of all sPEEK is hydrophilic and swells in water. Secondly you used NMP as a solvent to prepare membrane which is soluble in water, however, NMP will not remove completely at 60 degrees. You have to use vacuum oven to remove it completely.
Try put water by dropper on the membrane rather than immersing it in water. It might work.
I hope this answers your query.
Good Luck!
First of all, @Parimal is correct, the membrane is not fully dried. NMP has a boiling point of about 202 degree C, you can us a higher temperature (e.g. 80 degree C) plus vacuum to dry the membrane.
Secondly, if the sPEEK is prepared by your self, try to reduce the reaction time between PEEK and concentrated sulphuric acid , the concentrated H2SO4 may destroy your polymer chain and make it soluble in water.
Hope this could help you a little bit.
Thank you all for your answers,
I think that the problem arises from residual NMP in the membrane. I used to heat the membrane in a vacuum oven to 120 C after detachment. Know I'm testing to detach it after heating in vacuum :) and no deformation.
@Li Shu,
The membrane I'm discussing is a dense membrane, not a porous one.
Both Dai and Karimi make good points. However you should note that even dense membranes have intermolecular porosity. Otherwise even ions would not pass. So any residual NMP will attract water, as will the Sulphonate group with which the membranes are charged. You should expect some hydration even if there is no residual NMP or sulphuric acid.
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