Phase inversion method

The phase inversion method is developed to prepare hollow fiber inorganic membranes. Since the porous substrate and the separation layer are formed in a single step for this method, the preparation process can be 

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P. Izquierdo, J. Esquena, T.F. Tadros, J.C. Dederen, M.J. Garcia, N. Azemar, and C. Solans Formation and Stability of Nano-Emulsions Prepared Using the Phase Inversion Method. Langmuir 18, 26 (2002). 

In order to obtain thin skinned, high flux membranes from PVA, several approaches were tried. The method presented in this article is reminiscent of the classical phase inversion method, which is widely applied in casting of asymmetric RO membranes. However, instead of using a gelling bath composed of a nonsolvent... 

In an alternative approach, MIP membranes can be obtained by generating molec-ularly imprinted sites in a non-specific matrix of a synthetic or natural polymer material during polymer solidification. The recognition cavities are formed by the fixation of a polymer conformation adopted upon interaction with the template molecule. Phase inversion methods have used either the evaporation of polymer solvent (dry phase separation) or the precipitation of the pre-synthesised polymer (wet phase inversion process). The major difficulties of this method lay both in the appropriate process conditions allowing the formation of porous materials and recognition sites and in the stability of these sites after template removal due to the lack of chemical cross-linking. 

Today the majority of polymeric porous flat membranes used in microfiltration, ultrafiltration, and dialysis are prepared from a homogenous polymer solution by the wet-phase inversion method [59-66]. This method involves casting of a polymer solution onto an inert support followed by immersion of the support with the cast film into a bath filled with a non-solvent for the polymer. The contact between the solvent and the non-solvent causes the solution to be phase separated. This process involves the use of organic solvents that must be expensively removed from the membrane with posttreatments, since residual solvents can cause potential problems for use in biomedical apphcations (i.e., dialysis). Moreover, long formation times and a limited versatihty (reduced possibUity to modulate cell size and membrane stmcture) characterize this process. 

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

The spiral wound membranes tested for extraction of impurity-free NaSCN from aqueous process solution were polyamide (PA-300), CTA-700, PERMA-400, and PERMA-250. PA-300 was prepared by interfacial polymerization technique, while the PERMA membranes were prepared by coating a novel proprietary copolymer onto a microporous polysulfone substrate followed by cross-linking of the top layer. Thus, the morphology of these membranes was TFC. CTA-700 was asymmetric in nature and was prepared by solution casting and phase inversion method. 

An integrally skinned asymmetric membrane with a porous skin layer (hereafter called substrate membrane) is prepared from a polymer solution by applying the dry-wet phase inversion method and dried according to the method described later, before being dipped into a bath containing a dilute solution of another polymer. When the membrane is taken out of the bath, a thin layer of coating solution is deposited on top of the substrate membrane. The solvent is then removed by evaporation, leaving a thin layer of the latter polymer on top of the substrate membrane. 

Membranes for vapor removal from air have a structure similar to the prism membrane, but they are prepared on a different principle.Aromatic PEI is used to produce a porous substrate membrane by the dry-wet phase inversion method. This polymer was chosen over PS/PES because of the higher durability of PEI to organic vapors. Unlike an asymmetric PS substrate for the prism membrane, the top layer of asymmetric PEI membrane has a large number of pores, the size of which is equivalent to those of UF membranes. When a layer of silicone rubber is coated on the top layer of the porous substrate membrane, the silicone rubber layer will govern the selectivity and the porous support will provide only mechanical strength to the composite membrane. Because the permeabilities of water and organic vapors through the silicone... 

The literature describes numerous manufacturing methods for synthetic membranes. A recent review by Pusch and Walch (1) considers membranes from a number of techniques for manufacturing membranes and discusses applications ranging from microfiltration to desalination to gas separation. In this paper, a thermal phase-separation technique of preparing membranes Is presented. The method Is a development of an Invention described In US Patent 4,247,498 by Anthony J. Castro (,2). This technique Is similar In many respects to the classical phase-inversion methods however, the additional consideration of thermal solubility characteristics of the poly-mer/solvent pair offers new possibilities to membrane production. 

Pore structures of typical polymeric ultrafiltration membranes, produced by so called "phase inversion methods," consist of interconnected, irregular, three-dimensional networks of pores, interstices and voids in their skin layers. 

Selectively permeable membranes can be produced using a molecular imprinting approach. Using a phase inversion method, a poly(acrylonitrile-co-acrylic acid) ultrafiltration membrane was imprinted with theophylline [52], When solutions of theophylline and caffeine were filtered, a significantly greater amount of theophylline was retained within the membrane (Figure 6.33). 

Curcumin-loaded CS/cellulose microcrystal composite films can be prepared by the vapour induced phase inversion method and show good antimicrobial action against bacteria and fungi. Cellulose fibres made of CS/lignosulfonate (LS) multilayers exhibit... 

In addition, PEEK-WC membranes have been prepared by using a phase inversion process with supercritical fluids. The supercritical fluid acts as a non-solvent. In comparison to the dry/wet phase inversion method, the supercritical fluid allows the cell size and the membrane morphology to modulate by changing the experimental conditions, such as polymer concentration, temperature, and pressure. A dry membrane can be obtained rapidly and without additional post-treatments. ... 

Microemulsions can be prepared by controlled addition of lower alkanols (butanol, pentanol, and hexanol) to milky emulsions to produce transparent solutions comprising dispersions of either water-in-oil (w/o) or oil-in-water (o/w) in nanometer or colloidal dispersions (-100 nm). The alkanols (called cosurfactants) lower the interfacial tension between oil and water sufficiently for almost spontaneous formation. The miscibility of oU, water, and amphiphile (surfactant plus cosurfactant) depends on the overall composition, which is systan specific. Phase inversion method is further divided into two types ... 

Phase inversion methods are based on spontaneous O/W nanoemulsion formation induced by controlling the interfacial behavior, from predominantly lipophilic to predominantly hydrophilic, of the surfactants at the O/W interface, in response to changes in system compositions or environmental conditions. ... 

Owing to the formulation requirements of phase inversion methods, the nanoemulsions are highly unstable to coalescence when conditions closer to the phase inversion are attained, such as upon incorporation in real foods, or during high temperatures treatments. " ... 

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. 

CS is, on the other hand, soluble in acidic solutions and has an excellent film-forming ability. Microporous CS membranes were prepared through phase inversion method and subsequently coupled with various types of ligands to generate... 

The molecular recognition capabilities of polyelectrolyte multilayers have also been investigated by Laschewesky [55], while imprinted films have been grown on membrane surfaces in approaches similar to the phase inversion method for preparing a membrane imprinted with theophylline. Wang et al. [56] adopted an acrylonitri-le/dithiocarbamoyl-methylstyrene copolymer (Fig. 16) to effect separation of caffeine from the theophylline-imprinted membrane. 

Figure 3 Schematic illustration of imprint process of THO in copolymer membrane P(AN-co-AA) by phase inversion method [63,64]. From Ref 46.

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