Polymer-assisted phase Inversion

Sol 2 is present either when one phase separates into two phases or when two phases are prevented from recombining into a single phase. It is expedient to entitle this factor inoompatibilityt and to discuss the various phase inversion processes in terms of the reasons for incompatibility. In the sections to follow four phase inversion processes are discussed a dry process, a wet process, a thermal process and a polymer assisted phase inversion process. 

The Polymer Assisted Phase Inversion (PAPI) Process... 

The polymer assisted phase inversion (PAPI) variation of the phase Inversion process utilizes a solution consisting of a solvent and two physically compatible polymers to cast a dense film with a morphology known as an interpenetrating polymer network (IPN). 

When using supercritical fluids in place of liquids (non-solvent),an advanced, and greener, manufacturing approach to induce precipitation of the polymer can be achieved. This approach is commonly named the supercritical assisted phase inversion method (SAPIM) (Cardea et al, 2010). 

The majority of polymeric membranes can be formed via a phase separation/inversion process by which a polymer solution (in which the solvent is the continuous phase) inverts into a swollen three-dimensional macromolecular network or gel (where the polymer is the continuous phase). Phase separation can be induced by solvent evaporation (the dry-cast process), nonsolvent/solvent exchange (the wet-cast process), cooling (the thermal-cast process), and polymer leaching (the polymer-assisted process). 

As described earlier in the section on bead or suspension polymers (Section 3.3.1.2), a solution of monomer(s) is prepared in water and then mixed into a low to medium viscosity non-volatile oil phase. In this process, which is often referred to as an inverse emulsion polymerisation technique, surfactants which promote the formation of water-in-oil emulsions are commonly used. These would usually be materials with an HLB (hydrophihc-lipophilic balance) value in the range 4—7, an example of which is sorbitan mono-oleate. In order to achieve the desired droplet particle size of a maximum around 1 pim prior to polymerisation, high shear homogenisers are used to assist the formation of such very small... 

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