I am currently engaged in modeling the desalination performance of Cellulose Acetate (CA)/Graphene Oxide (GO)/POSS Mixed Matrix Membranes (MMMs) for reverse osmosis (RO) applications. The primary objective of my research is to develop a comprehensive understanding of the transport phenomena and rejection mechanisms within the membrane, utilizing the Donnan-Steric Pore Model (DSPM). As part of this endeavor, I am seeking to determine the effective membrane thickness.
During the membrane preparation process, I have acquired information that the solutions of composite membranes were cast onto a non-woven Hollytex polyester substrate taped to a clean glass plate with 250 μm thicknesses using casting knife. However, I am curious if there exists any way to determine the effective thickness of the membrane without resorting to experimental methods.
Dear Reihaneh Abouei ,
As you mentioned above, fabricating a flat sheet membrane such as a flat sheet RO membrane starts by dissolving a polymer and additives in a suitable solvent by mixing and heating and then spreading or casting this solution on a non-woven polyester fabric where glued on a clean glass and then immersing it in a water coagulation bath to occur phase inversion. During phase inversion, the membrane film thickness is reduced (sometimes significantly) due to the solidification of polymer and leaching of solvent. Therefore, it is not true to consider the membrane thickness equal to the membrane casting thickness and you should use cross-sectional SEM photos or simply a thickness gauge to understand the membrane thickness. It is good to say that there is no equation to calculate the membrane thickness after the phase inversion process.
The next step is polymerization on top of the membrane surface. To do so, after drying, the membrane surface is stuck on a glass, and a rubber gasket is placed around it and MPD and TMC solutions spread on it, respectively, and finally, the membrane is cured in an oven.
Accordingly, if you want to have the exact membrane thickness you should consider the thicknesses of all of (1) non-woven fabric, (2) ultrafiltration membrane (base membrane), and (3) polyamide layer. However, the polyamide layer is so thin (lower than 10 microns) and can be ignored.
Hope it helps.
Foroogh
Foroogh Khodadadi
Dear Foroogh,
Thank you for your insightful answer. It was really helpful. I have an SEM image of the membrane. Is it possible for you to assist me in determining the thickness?
Best regards,
Reihaneh
Dear Reihaneh Abouei ,
Welcome dear Reihaneh.
Why not!
You can send me the SEM image and I will tell you the thickness. Be careful that the SEM image has to have a scale bar.
Best wishes
- Badges
- Science topic
- Similar topics
- Engineering
- Modeling