Preparation of composite membranes

Soon after the first reports on the layer-by-layer adsorption appeared, the method was also used for surface modification of polymers [60, 61], and for the preparation of composite membranes [62-65]. Composite membranes were obtained by alternate dipping of porous supports into solutions of cationic and anionic polyelectrolytes so that an ultrathin separation layer was... 

A diamine solution in water and a diacid chloride solution in hexane are prepared. A porous substrate membrane is then dipped into the aqueous solution of diamine. The pores at the top of the porous substrate membrane are filled with the aqueous solution in this process. The membrane is then immersed in the diacid chloride solution in hexane. Because water and hexane are not miscible, an interface is formed at the boundary of the two phases. Poly condensation of diamine and diacid chloride will take place at the interface, resulting in a very thin layer of polyamide. The preparation of composite membranes by the interfacial in situ polycondensation is schematically presented in Fig. 3. 

The thickness of the membranes could be controlled in a range of 20 to 500 nm. Optical interference colors of the ultrathin membrane served as a guide for estimating thickness actual measurements were made by interferometric or gravimetric methods. Ultrathin films could be cast on a water surface from many other commercial polymers for preparation of composite membranes. However, only those formed from cellulosic or related polysaccharide esters exhibited adequate flux for use in reverse osmosis. 

M. Ulbricht published recently a comprehensive overview on the development of polymeric membranes having advanced or novel functions in the various membrane separation processes [121], The author describes novel processing technologies of polymers for membranes, the synthesis of novel polymers with well-defined structure as designed membrane materials, advanced surface functionalization of membranes, the use of templates for creating tailored barrier or surface structures for membranes, and the preparation of composite membranes for the synergistic combination of different functions by different (mainly polymeric) materials. 

Preparation of Composite Membranes Using Polymer Solutions or Dispersions as Reaction Medium for In Situ... 

Poly(vinylidene fluoride) (PVDF) porous supports coated with cellulose [92] were commercialized by Dow (ETNA membranes). PVDF is soluble only in a few organic solvents such as dimethyl acetamide. Cellulose is very stable in organic and aqueous solvents. However, because of its low solubility, preparing cellulose membranes is not a trivial task. Stengaard [72] proposed the preparation of composite membranes by coating chlorotrifluoroethylene/vinylidene fluoride (CTFE/VF) or PVDF supports with hydroxyethylcellulose and hydroxypropylcel-... 

Electron-Beam Operating Parameters Applied for the Preparation of Composite Membrane... 

Some examples of (he preparation of composite membranes by inicrt aciul polymerisation. Tlie amine is in (he aqueous phase while the acid chloride or isocyanate is in (he organic phase. 

Membranes containing macrocyclic compounds can be very efficient in the separation and identification of ions and, therefore, in the preparation of ion-selective sensors (201). The immobilization of crown ethers and cryptands by intCTcalation on 2 1 phyllosilicates (45) has been used in the preparation of composite membranes made up of sandwich-like materials encapsulated into thin polybutadiene coatings to improve their mechanical properties (202). The entrapped macrocyclic compounds modulate the transport properties of cations in aqueous solution, and this can be used for their individual discrimination and recognition. Although the mechanism controlling the ion selectivity of these composite membranes is still not clear, development of ion-selective sensors based on the coating of electrodes by this class of membranes can be envisaged. 

M.A. Balachandra, G.L. Baker, M.L. Bruening, Preparation of composite membranes by atom transfer radical polymerization initiated from a porous support, J Membr Sci, 127 (1-2), 227, 2003. 

Membranes prepared through NIPS and electrospinning can be further modified to make composite membranes. With a functional top layer and a supportive substrate, the preparation of composite membranes through different modification techniques allows wider applications. 

Ebert K., Bezak A., Nijmeizer K., Mulder M. H. V. and Strathmann H., The Preparation of Composite Membranes with a Glassy Top Layer, Euromembrane Conference, Bath, UK, 1995. 

The use of a polymer for supporting the preparation of composite membranes with thin selective palladium layers was first established by Gryaznov etal (1969). 

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