Diffusion-induced phase separation DIPS

The Loeb-Sourirajan process often is referred to as diffusion induced phase separation (DIPS) to reflect the role of diffusion in forming the asymmetric structure. Liquid-liquid phase separation and the resulting asymmetric structure arise from diffusion of a solvent (acetone) out of the film and diffusion of a nonsolvent (water) into the film. This physical interpretation provided the basis for the development of asymmetric membrane manufacturing processes for other polymer - solvent - non-solvent systems. 

Asymmetric membrane structures have been created from these materials using the diffusion induced phase separation process (DIPS) as well as a thermally induced phase separation process (TIPS) [23] that relies on temperature gradients to produce a gradient in phase separated domain size. Moreover, membranes formed by either process can be further modified by stretching or drawing to alter pore size and porosity. 

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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