I am producing polymer porous membranes through non-solvent induced phase separation and I need to extend the length of finger-like structures. It seems like sponge-like structures are always formed on the side that is distant from the coagulant/polymer solution interface (the part of the nascent membrane in direct contact with the support).
What is the main parameter that affect the finger-like morphology and that can be controlled in order to promote the formation of this specific morphology only?
Additionally, which is the best analysis to reach a better understanding about the motivations and dynamics of finger-like formation process?
Parameter such as polymer concentration and selection of bath condition are playing the role in deciding the size, shape of the pores. If you want control the micro pores you to play with above two factors, but it always affects the membrane surface also.
Many thanks. I am just trying to understand the reason why the finger-like structures interrupt their formation in the middle part of the membrane thickness all of a sudden and then only sponge-like structures are formed. Should I increase the diffusion rate of the coagulant within the nascent membrane in order to reach the bottom part faster?
When the phase inversion begins, near the contact surface initial rate solvent exchange is higher results in the formation of cylindrical pore .Here polymer precipitation takes places which then act as barrier and interrupt the solvent exchange rate below this part. This is the reason for higher micro pores formation in the lower layer. In case if you want alter this pores just try with different non-solvent with different temperature to enhance the exchange rate.
· I think that you can use a series of photomicrographs taken from a videotape which indicates the steps in the coagulation process.
· In some parts, along the boundary, the progress of solid region is very slow. In the neighborhood of the solid boundary the small droplets are observed when higher magnification objective is used. These particles seemed to be solids particles floating in the surrounded liquid. The spaces left from evaporation of liquids seem to appear as macrovoids.
· read more on this paper:
Formation of Porous Filaments by immersion precipitation process
M. Karimia , M. Haghighat Kishb and H. Modarress
Hi,
finger like morphology is formed during instantaneous demixing of solvent and non-solvent. It depends on the solubility parameter of the solvent and non-solvent. Closer the solubility parameter of both, will cause instantaneous demixing. However, polymer concentration can affect this, if more polymer is present then it will take time to complete phase inversion from top to bottom and hence will get more micropores at the bottom part.
You can try this, when you immerse polymer film in non-solvent invert the film after some time (say after 5 min. need to optimize time by trial and error) so that your bottom part comes to the top and vice versa. This might help you to obtain finger like structures throughout membrane.
Parameters to be consider are polymer, solvent and non-solvent, polymer concentration, additive in casting solution and in non-solvent bath, temperature of bath etc.
I hope my answer will help you.
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