Nonsolvent-induced phase separation

Guillen G, Pan Y, Li M. Preparation and characterization of membranes formed by nonsolvent induced phase separation A review. Ind Eng Ghent Res. 2011 50(7) 3798-3817. 

By far the most used technique for membrane preparation is the immersion precipitation method (nonsolvent-induced phase separation). A homogenous polymer solution is cast as thin him and subsequently immersed into a nonsolvent bath, typically water or mixtures of water and solvent. The dif-fusional exchange of solvent and nonsolvent brings the him solution into an instable state resulting in phase separation, either by liquid-liquid (l-l) and/or solid-liquid (s-l) demixing, depending on the type of polymer and the precipitation conditions employed [92,93]. 

SNIPS Self-assembly and nonsolvent-induced phase separation... 

In the nonsolvent induced-phase separation process, a nonsolvent penetrates into a polymer solution by difrusion. Since phase separation occurs quickly in the surface where the penetration starts, and slowly in the inner part where the penetration proceeds comparatively slowly, the membrane has an asymmetrical stmeture, which has a smaller pore size in the smface and a larger pore size in the inner part. An example of UF having the asymmetrical stmeture is shown in Figure 5.3. 

Figure 5.2 Illustration of a preparation system of hoUow-fiber membranes by nonsolvent induced-phase separation process.

Figure 3 (a) Temperature-induced phase separation (b) Nonsolvent-induced phase separation. 

G.R. GuiUen, G.Z. Ramon, H.P. Kavehpour, R.B. Kaner, and E.M.V. Hock, Direct microscopic observation of membrane formation by nonsolvent induced phase separation, Journal of Membrane Science 431 (2013) 212-220. 

Bulk addition of nanoparticles refers to the use of nanoparticles as additives during the membrane synthesis process by phase inversion (Kim and Van der Braggen 2010). Nanoparticles are dispersed in the polymer solution, which is then cast on a support layer and contacted with a nonsolvent, in the case of diffusion- or nonsolvent-induced phase separation (DIPS or NIPS). In the eventual membrane, the nanoparticles are present in the inner structure of the membrane, and not exclusively on the membrane surface. Therefore, the functionalities of the nanoparticles that were used can only be partly exploited. For example, catalytic activities would not be efficient, as the nanoparticles that should act as catalyst are shielded by the polymer material. This is a concern particularly for photocatalytic materials such as Ti02, which are often employed for mixed matrix membranes. 

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