## 2 Polymer Nanocomposites for Membranes Applications
With the use of montmorillonite (Na\({}^{+}\)MMT) clay, belonging to the class of smectite clays (i.e., family of phyllosilicates 2:1), much effort has been made to use them as a filler for the development of new polymer-inorganic materials [105, 106]. Smectite clays are characterized by their properties as cation exchange and intercalation of molecules, and Na\({}^{+}\)MMT will tend to swell in some polar solvent [23]. (VII) Works with layered nano-materials were associated, first of all, with the search for ways of creating polymer-inorganic composites with improved barrier characteristics. Much attention was paid to processes of the exfoliation of clay nanoparticles in a polymer matrix (Figure 5). Two structural types were possible when Na\({}^{+}\)MMT was involved in the PVA matrix. The first is an intercalated structure in which one or two elongated polymer chains are inserted into the interlayer spaces of the layered clay, and the second one is the exfoliated structure in which clay layers are dispersed in the PVA matrix. In any case, the clay fillers provide a stable layer based on polymer [107]. Figure 4: Selected nanomaterials currently being evaluated as functional materials for water purification [97]. PDMS/MMT nanocomposites were obtained, in particular, by ultrasonic vibration, a mixture of silanol-terminated PDMS and a commercial organosilicate. Results of a WAXD study of nanocomposites detected the formation of exfoliated structures [13]. Figure 6a-d from Reference [108] are schematic diagrams illustrating a formation process of an exfoliated structure in the MMT-PA6 nanocomposite using the clay slurry. The clay slurry is first pumped under vigorous shear (Figure 6a). The slurry droplets tend to become finer during mixing (Figure 6a). Water of the slurry drops begin to evaporate on contact with molten PA6 (Figure 6b,c). During water evaporation, some silicate layers are fixed into molten PA6 and dispersed at the monolayer, and some dispersed as few stacking layers (Figure 6d). The tensile and flexural modulus as well as tensile strength of the nanocomposite containing 1.6 wt % MMT are higher than those of unfilled PA6 but the impact strength is 12% lower compared to PA6 [108]. [PERSON] et al. have successfully used the technique for the preparation of polyimide/MMT nanocomposites from solution dimethylacetamide (DMAC), a poly (amic acid), and a DMAC dispersion of MMT modified with dodecylammonium cations [109]. In the case of 12 CH\({}_{3}\)-MMT, the MMT appears to be homogeneously dispersed and the average diameter of the dispersed MMT particles was the smallest of all. The carbon number of the surfactant increases, the hydrophilicity of particles decreases WAXD patterns of the nanocomposite containing 12 CH\({}_{3}\)-MMT showed almost exfoliated structure, while WAXD patterns of composites prepared with 12 COOH-MMT or C10A-MMT indicated the inhomogeneic dispersion of a part of MMT in the PI matrix [109]. In another report [110], PI/MMT nanocomposites were prepared by a cast method from solutions of poly(amic acid) precursors and dodecyl-MMT in \(N\)-methyl-2-pyrrolidone as a solvent. The cured films of the rigid-rod PI/MMT were characterized by FTIR, TEM and WAXD as nanocomposites, being exfoliated at low MMT content and partially exfoliated at high MMT content. This method was discussed also as suitable for the preparation of nanocomposites of a type of covalently bonded layered silicate in PI. Figure 5: Schematic diagram showing the structure of 2:1 phyllosilicate and the polymer clay nanocomposites [13]. It was shown that the introduction of MMT into the matrix of glassy polymers could lead to a decrease in the permeability of the MMM with respect to both gases and liquids [18,111,112].