Liquid-phase inversion method

Compared with the liquid-phase inversion method, this phase separation process has several advantages [59] ... 

New cellulose manbranes were recently prepared by the phase inversion method using a green solvent, the ionic liquid [BMIM][C1] [32], After functionalization with a synthetic ligand 2-(3-aminophenol)-6-(4-amino-l-naphthol)-4-chloro-5-triazine, these adsorptive membranes were evaluated for human immunoglobulin G (IgG) adsorption. The authors envisage that a change in the conditions and chemistry for membrane activation with the biomimetic ligand may improve the performance of the affinity cellulose membranes. 

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). 

To date, several polymer hosts have been used in GPEs that include PEG, PPO, PAN, PMMA, poly(vinyl chloride) (PVC), PVdF, poly(vinylidene fluoride-hexafluoro propylene) (PVdF-HFP), etc. Furthermore, the Bellcore method and phase inversion method have been developed for the preparation of GPEs. The Bellcore process is critical and developed from the fabrication of PVdF-HFP copolymers. It involves the plasticization of PVdF-HFP copolymers, subsequent plasticizer removal, and the final reswelling in an electrolyte solution. Low-boiling solvents, such as diethyl ether or methanol, are successfully employed to remove dibutyl phthalate (DBF) from the polymer matrix, leaving a pore structure in the polymer layers which is then refilled with the liquid electrolyte during the cell activation process (Song et af, 1999). 

Liquid emulsions are inherently unstable to a varying degree. It is important to understand, therefore, the mechanisms that contribute to emulsion stability. Before the solidification step, instability of an emulsion can arise due to either phase separation or phase inversion (Mulder and Walstra, 1974). It is evident that the likelihood of phase inversion will increase as the fraction of dispersed phase increases. The vast majority of literature references are concerned with the stability to phase separation as coalescence or creaming in oil-in-water emulsions (Hailing, 1981 Jaynes, 1983). In addition, a method for determining the stability of water-in-oil emulsions to inversion has not been reported. It is usually assumed that certain aspects of oil-in-water emulsion theory apply in reverse to water-in-oil emulsions. 

Conventional gas liquid chromatography determines the retention of an unknown sample in the moving phase with a known stationary phase. The inverse method, however, determines the property of the stationary phase using a known volatile solute in the moving phase. The volatile molecules are referred to as probe molecules. 

Phase inversion is a process in which a polymer is transformed from a liquid to a solid state. There are a number of methods to achieve phase inversion. Among others, the dry-wet phase inversion technique and the temperature induced phase separation (TIPS) are most commonly used in the industrial membrane manufacturing. The dry-wet phase inversion technique was applied by Loeb and Sourirajan in their development... 

In this process phase inversion is introduced by lowering the temperature of the polymer solution. A polymer is mixed with a substance that acts as a solvent at a high temperature and the polymer solution is cast into a film. When the solution is cooled, it enters into an immiscible region due to the loss of solvent power. Liquid-liquid demixing occurs and the solution is separated into two phases, i.e., the polymer-lean phase is dispersed as droplets in the polymer-rich phase. Further, cooling causes gelation of polymer. Because the solvent is usually nonvolatile, it must be removed with a liquid that is miscible with the solvent but not miscible with the polymer. The membranes made by the TIPS method have pore sizes in the range of 0.1 and 1 pm and the pore structure is uniform in the depth direction. ... 

Hydrophilic MF membranes can be made by the dry-wet phase inversion technique. The latter technique is also applicable in making PVDF membranes. On the other hand, other hydrophobic MF membranes are made by the TIPS technique. In particular, semicrystalline PE, PP, and PTFE are stretched parallel to the direction of film extrusion so that the crystalline regions are aligned to the direction of stretch, while the noncrystalline region is ruptured, forming long and narrow pores. Hydrophobic membranes do not allow penetration of water into the pore until the transmembrane pressure drop reaches a threshold pressure called liquid entry pressure of water. These membranes can therefore be used for membrane distillation. Tracketching method is applied to make MF membranes from PC. 

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