what causes difference in pore radius in membranes when observed in SEM cross section images? is it the typical structure or may there be another morphologies ?
The membrane you have is asymmetric membrane. the controlling parameters are kinetic and thermodynamic parameters. in other words, the mixing and viscosity of the dope solution affects strongly the formed membranes after soldification. also, Follow this review http://pubs.acs.org/doi/abs/10.1021/ie101928r
HI,
The pore morphology you are describing is called ink bottle type pores. These pores results by mixing-demixing phenomenon while phase inversion process. Other pore morphology such as macro void, sponge-like structure and finger like morphology also exists depending on the membrane formation process such as delayed demixing or instantaneous demixing.
I hope this is helpful to you.
I want to know what happens while solution and water transport that the openings are tighter on one side and wider at the other side? they are tighter adjacent to air, right? I mean the side adhered to the glass slide should have wider pore opening .... is that true?
Would your question be related to microfiltration membranes with an evaporative cast or a UF membrane with an immersion cast?
Hi,
Ink bottle pore morphology is helpful in MF wherein during transport of solution or water or feed particles get trapped in the neck part or upper part of the membrane while bottom part which is wider allows faster passage of the permeating component. But these pores can get easily blocked or if the membrane is dry pores get collapsed. Thus membrane should not be dry. Hope this is helpful.
Yes I am questioning about UF membranes fabricated via phase inversion .
Thank you so much. surely that was helpful. so you say MF filters should be wet before filtration operation begins? is it also right for the UF ones?
Hi,
Yes, it is better to use the wet membranes in both cases. As MF and UF carried out under pressure.
Thank you very much. is that condition provided through for example a 1 hour filtration with pure water befor the main operation starts or we should keep them wet the whole time between fabrication step till filtration? I mean should we eliminate the drying step completely or we can rinse it after drying and immediately before the filtration?
It is advisable to keep them in water after fabrication till filtration. You can just soak membranes on tissue paper before filtration. Add 10% glycerin to storage tank and keep water changing frequently to avoid any bacterial growth.
Thank you so much for your valuable information.
is it possible for you please to introduce a book or a text which contains some explanations about the way the pores form while immersion in coagulation bath and what occurs that the get wider or tighter....
thank u in advance
http://pubs.acs.org/doi/abs/10.1021/ie101928r, refer this article. Also, you can also refer to "Basic principals of membrane technology" by Marcel Mulder.
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