I am studying polysulfone-based composite membranes using various additives.
Dear Nur -E- Alam ,
I studied all PEG molecular weights from 200 to 35000 Da and many articles about this hydrophilic additive.
To brief:
"The formation of the membrane's top layer goes through two stages: 1- precipitation and 2- soaking.
To explain, an increament in PEG molecular weight enhances the viscosity of the casting solution. On the other hand, the higher the PEG molecular weight, the longer the PEG molecule chain length, and then the poorer the mobility of PEG molecules. Consequently, these two factors would hamper component exchanges during the precipitation process, and then lead to precipitation rate reduction. A viscosity enhancement of casting solutions and a decrease in the PEG mobility also make it more difficult for PEG molecules to diffuse out from the casting solution into the coagulation bath. Hence, some PEG molecules can remain in the renascent membrane after a precipitation process. Moreover, the higher the PEG molecular weight, the more the amount of residual PEG. Therefore, these aggregated PEG molecules disperse uniformly on the membrane surface. That is to say, during the precipitation process the formed top surface should not be porous, but be relatively dense with a great deal of aggregated residual PEG. Polymer molecules can be considered as immobile because of their very high molecular weight, whereas PEG additives with a low molecular weight may have better mobility. Thus PEG molecules can leach out along with solvent. Accordingly, lower MWs of PEG would form smaller pore size during leaching out in precipitation process while bigger MWs of PEG that formed aggregated networks on the membrane surface would form bigger pore size after leaching during soaking process.
Reference:
Zuo, D. Y., Xu, Y. Y., Xu, W. L., & Zou, H. T. (2008). The influence of PEG molecular weight on morphologies and properties of PVDF asymmetric membranes. Chinese Journal of Polymer Science, 26(04), 405-414.
Hope you the best
- Badges
- Science topic
- Similar topics
- Engineering
- Chemical Engineering
- Membranes