Phase-inversion process

There are also a few Cases where the phase-inversion process is accomplished by passing the belt through a liquid water bath to precipitate the polymer as is done with polyvinylidene fluoride.1 

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Of interest here is the question relating to the value for the slope coefficient, k, from equation (1), when surfactant structures incorporating both ionic (say sulphonate) and nonionic moieties are included together. The Ghanges in electric double layer effects imparted from salt addition might dominate the packing constraints and therefore the phase inversion process, or perhaps oxyethylene dehydration effects from the presence of toluene could also play a role. 

Optimal Salinities The phase inversion process may be considered to reflect the balanced nature of the adsorbed surfactant species at the oil/water interface. Simple geometric packing... 

Figure 3. Phase inversion process during the synthesis of a poly[(CO,SA,TDI)-SIN-(S,DVB)] 10/90.

Also recognized was the flexibility of such composites, the good adhesion with the carbon material and the versatility and easiness for a wide range of (bio)molecule trapping using a simple phase-inversion process for its fabrication. These CNT/PSf... 

HA and three different HA esters, supplied by Fidia Advanced Biomaterials SpA (Padua, Italy), were examined. HA esters were prepared by treating a quaternary ammonium salt of HA with an esterifying agent in a suitable aprotic solvent at a controlled temperature as described in detail elsewhere [2]. In this study we analyzed the following esters ethyl ester (HYAFF7), benzyl ester (HYAFFl 1), and dodecyl ester (HYAFF73 Figure 1). The materials used were both films and powders. Films were obtained by a phase inversion process from DMSO solutions as previously described [2,4]. 

Polymeric membranes with highly interconnected pores have been produced commercially for more than 30 years based on a phase inversion process. These... 

It has been shown (, , 2.) that a membrane casting dope is a strongly structurlzed polymer solution, and that the morphology of the membrane surface layer can be correlated to the structure of the casting solution. The latter parameter affects the nature and details of the phase inversion process occuring in the upper part of the cast solution, in an incipient skin. Thus the solution structure is one of the factors responsible for the skin properties, and consequently for the performance of the ultimately formed asymmetric membrane. 

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. 

Fig. 16 SEM image of the cross section of a theophylline-imprinted membrane asymmetric structure of imprinted membrane prepared by the wet phase inversion process. Reproduced with permission from [217]...

Composite MIP membranes can also be obtained by incorporation of MIP particles into the membrane polymer matrix by mixing the particles in an appropriate solvent with the membrane-forming polymer that is then solidified by the phase inversion process. Membranes thus prepared were used for separation, with targets such as tetracycline [257], theophylline [255], methylphosphonic acid [258], bisphenol [259], indole derivatives [260], propanolol [261], luteolin [262] and norfloxacin... 

J.G. Wijmans and C.A. Smolders, Preparation of Anisotropic Membranes by the Phase Inversion Process, in Synthetic Membranes Science, Engineering, and Applications, P.M. Bungay, H.K. Lonsdale and M.N. de Pinho (eds), D. Reidel, Dordrecht, pp. 39-56 (1986). 

Blanco, J.F., Sublet, J., Nguyen, Q.T. and Schaetzel, P. (2006) Formation and morphology studies of different polysulfones-based membranes made by wet phase inversion process. Journal of Membrane Science, 283, 27-37. 

The phase relationships of two-phase polymer systems also have been of considerable interest in recent years. In an important series of papers, Molau and co-workers (19-24) studied systems, which were denoted POO emulsions (polymeric oil-in-oil), prepared by dissolving a given polymer in monomer and then polymerizing the monomer. During polymerizations of this type the composition of the respective phases reverses, and a phase inversion process was proposed to explain this. A similar process has been suggested as the mechanism by which poly-butadiene forms the dispersed phase in the manufacture of high-impact polystyrenes (22,25). Recently, Kruse has pointed out that this phase-inversion point may correspond to that point on a ternary phase diagram at which the reaction line bisects a tie line (26), and we have advanced a similar point of view in our earlier reports (17,18, 27). 

Most of the available commercial microporous membranes such as polysulfone, polyethersulfone, polyamide, cellulose, polyethylene, polypropylene, and polyvinylidene difluoride are prepared by phase inversion processes. The concept of phase inversion in membrane formation was introduced by Resting [75] and can be defined as follows a homogeneous polymer solution is transformed into a two-phase system in which a solidified polymer-rich phase forms the continuous membrane matrix and the polymer lean phase fills the pores. A detailed description of the phase inversion process is beyond the scope of this section as it was widely discussed in Chapters 1 and 2 nevertheless a short introduction of this process will be presented. 

The difficulty in analyzing the phase inversion process is due to the interactions between the three components involved, and to the complex diffusion and convective processes that play an important role during the membrane formation. However, many researchers agree that there are two dominating factors controlling the formation of phase inversion membranes thermodynamics and kinetics, correlated to each other during the solidification of casting solutions. 

Young T-H and Chen L-W. Pore formation mechanism of membranes from phase inversion process. Desalination 1995 103(3) 233-247. Han M-J and Nam S-T. Thermodynamic and rheological variation in polysulfone solution by PVP and its effect in the preparation of phase inversion membrane. J. Membr. Sci. 2002 202(l-2) 55-61. 

Ceramics Ceramic membranes are manufactured by processes, which are completely different from polymeric membranes. Polymeric membranes are typically formed by the phase inversion process where the polymer dissolved in solvent precipitates upon exposure to nonsolvent. In contrast, ceramic membranes consist of ceramic particles that have been sintered at very high temperatures into one solid shape. It is the gaps or voids between the solid-state ceramic particles that determine... 

Strathmann, H., Production of microporous media by phase inversion processes. In Material Science of Synthetic Membranes, Lloyd, D.R., Ed., American Chemical Society, ACS Symposium Series 269, Washington, DC, 1985, p. 165. 

Most commercial UF and NF membranes and many MF membranes are made by the phase-inversion process, where a polymer is dissolved in an appropriate solvent along with appropriate pore-forming chemical agents. The polymer solution is cast into a film, either on a backing or freestanding, and then the film is immersed in a non-solvent solution that causes precipitation of the polymer. Such membranes are Polyamides, such as nylon, polyethersulfon (PESU), or... 

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