Phase inversion procedure

Several selective interactions by MIP membrane systems have been reported. For example, an L-phenylalanine imprinted membrane prepared by in-situ crosslinking polymerization showed different fluxes for various amino acids [44]. Yoshikawa et al. [51] have prepared molecular imprinted membranes from a membrane material which bears a tetrapeptide residue (DIDE resin (7)), using the dry phase inversion procedure. It was found that a membrane which contains an oligopeptide residue from an L-amino acid and is imprinted with an L-amino acid derivative, recognizes the L-isomer in preference to the corresponding D-isomer, and vice versa. Exceptional difference in sorption selectivity between theophylline and caffeine was observed for poly(acrylonitrile-co-acrylic acid) blend membranes prepared by the wet phase inversion technique [53]. 

Industrially, neutralization of the polyester and the preparation of the colloidal dispersion is carried out by a "phase inversion procedure". It consists in adding, first the given amount of amine to the preheated polyester (80 C), then dropwise the amount of water suitable to adjust the solid content of the final system. 

The reactor was assembled with a plasma treated microporous PVDF membrane containing sodium tungstate as catalytically active species. The PVDF membranes were subjected to plasma treatments in NHj fed radio frequency glow discharges in order to generate amine functions on the surface of PVDF membranes prepared by a phase-inversion procedure, which are suitable for the immobilization of Na2W04.The modes of reactor operation as forced-flow or contactor were compared, being the best results achieved with a transmembrane pressure AP = 0 (contactor mode), since this mode of operation is the one that better favours the contact between the reactants and the catalytic active sites. 

Both commercial grade and pure nonionic and anionic surfactants have been evaluated by phase inversion and optimal salinity screening procedures to establish relationships to their molecular structures. 

The described phase inversion phenomenon can be used in practice to prepare very fine and stable emulsions, so called PIT-emulsions. An example for the procedure is given in Figure 3.25. 

Figures corresponds to the system MD 60-DEA-styrene, where neutralization was achieved by the phase inversion technique (industrial procedure). It can be seen that swelling of e micelles with monomer leads to a linear relationship of ( (]) / (]) ) vs monomer...

Dispersions may also be formed by the continuous addition of one phase into another under agitated conditions. This method offers a safe procedure for handling exothermic reactions such as nitration and emulsion polymerization. The amount of phase addition will determine if phase inversion occurs. 

Three different techniques are used for the preparation of state of the art synthetic polymeric membranes by phase inversion 1. thermogelation of, a two or more component mixture, 2. evaporation of a volatile solvent from a two or more component mixture and 3. addition of a nonsolvent to a homogeneous polymer solution. All three procedures may result in symmetric microporous structures or in asymmetric structures with a more or less dense skin at one or both surfaces suitable for reverse osmosis, ultrafiltration or microfiltration. The only thermodynamic presumption for all three preparation procedures is that the free energy of mixing of the polymer system under certain conditions of temperature and composition is negative that is, the system must have a miscibility gap over a defined concentration and temperature range (4). 

Description of Relevant Preparation Parameters. In the preparation procedure of phase inversion membranes several significant parameters determining the structure and properties of the membrane can be identified ... 

All the difficulties of a fit procedure mentioned at the end of the preceding Section can be avoided if an inversion procedure is applied. Starting from the observed angular dependence of the differential cross section or the energy dependence of the total cross sections, a set of phase shifts as a function of the angular momentum or of the energy is obtained and then the potential is deduced from the phase shifts. Thus the problem is naturally divided into two steps ... 

Because of these difficulties we turn to inversion procedures which are valid in the semiclassical limit since this approximation has proved to be applicable for most of the atomic and molecular collisions. Solutions of the second step, the determination of the potential, are treated in Section IV.B.2. In general, the input information will be the phase shifts or the deflection function. Only in the high energy approximation can the potential be derived directly from the cross section. For a detailed discussion of these procedures see Buck (1974). The possibilities of determining the phase shifts or the deflection function from the cross section are treated in Section IV.B.3. The advantage of such procedures and the general requirements on the data are discussed in Section IV.B.4. The emphasis will be on procedures which have been applied to real data. Extensions to non-central or optical interaction potentials are available. Most of them, however, are still in a formal state, so that a direct application to molecular physics is not obvious. Two exceptions should be mentioned. One is a special inversion procedure for optical potentials derived by a perturbation formalism (Roberts and Ross,... 

Preparation Procedures of Asymmetric Membranes. The development of the first asymmetric phase inversion membranes was a major breakthrough in the development of ultrafiltration and reverse osmosis. These membranes were made from cellulose acetate and yielded fluxes 10 to 100 times higher than symmetric structures with comparable separation characteristics. Asymmetric phase inversion membranes can be prepared from cellulose acetate and many other polymers by the following general preparation procedure 27... 

General Observations Concerning Structures and Properties of Phase Inversion Membranes. Before going into any detailed discussion of the formation mechanism of microporous membranes, several general observations concerning the membrane structure, preparation procedures, and mass transport properties are described. 

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