## 2 Polymer Nanocomposites for Membranes Applications
The introduction of SNT into polyamide-imide films (PAI-1 or PAI-2) changes the properties of these polymers, that was showed in Reference [29] and this effect was studied in References [140; 141]. Figure 26: Permeability by water and cyclohexane (at 40 \({}^{\circ}\)C) of non-porous membranes PAI-1, PAI-1-NT, PAI-2, and PAI-2-NT [121]. Figure 25: Photomicrographs of ultra—thin cross—cuts for (**a,b**) PAI-1-SNT-II and (**c,d**) PAI-2-SNT-II. Magnifications: (**a,b,d**) 2000; (**c**) 3000 [121]. It is important that the properties of PAI-1 change completely differently from the properties of PAI-2 when introducing the same nano-filler-SNT in the same quantities under the same conditions. The data presented in the publications [29; 112] show and clearly illustrate the differences in properties given by the nano-filling. At the same time, there is no single-valued correlation between these changes and transport properties. Thermal stability and Tg of composites based on PAI-1 with 2 wt % SNT were investigated by TGA and DSC [142]. It was shown that composites had a higher glass transition temperature as compared with that of PAI-1 (275 and 291 \({}^{\circ}\)C). Equally bright changes in the state of the polymer matrix were observed earlier in polymernano-filler systems and are well described [1; 143]. With inorganic particle and nanoparticle inclusions, nucleation of crystallization can occur. Nanoparticles can replace the absence of primary nuclei, thus promoting crystallization. At higher nanoparticle content, the increased viscosity (decreased chain diffusion rate) can lead to decreased crystallization kinetics. In this case, the crystallization process is influenced by several competing factors. For crystallization nanocomposites based on layered clay silicate it was noted that the nucleation occurs in many systems to reduce the overall crystallization rate, especially at higher amounts of nanoclay content [1; 143]. The influence of different types of carbon nanoparticles on the recrystallization process of polyimide R-BAPB was studied [144]. It was proved that the nucleating effect of carbon nanoparticles depends strongly on their inherent crystallinity. Graphitic nanoparticles already at a low concentration of \(\sim\)1 vol % induce the nucleation of polyimide R-BAPB. The polymer structure and dynamics are known to have a great influence on small penetrant diffusion. The important question of the \"nano-effect\" of nanoparticles or fibers after their inclusion in a polymer-based composite film is addressed relative to crystallization and glass transition behavior [1]. It was shown, in many the cases nanocomposites studied could be approximated using a model of a continuous medium, thus \"nano-effect\" was not observed. This should not be surprising, since the size of the gas molecules penetrating were still significantly lower than the modification of nanoscale. Nanoscale is considered where the dimensions of the modifying particles, plates or fibers are in the range of 1-100 nm. The differences would be expected in those cases where glass transition temperature (Tg) of the matrix polymer changed. In other words, \"nano-effect\" noted in the literature has been the change in the Tg of the polymer matrix with the addition of nano-sized particles. Both increasing and decreasing in the Tg have been reported dependent upon the interaction between the matrix and the particle [1]. The difference in the state of the PAI-1 and PAI-2 matrices after introducing the same (including in size and morphology) SNT into the same conditions is also accompanied by a difference in the sizes of the formed agglomerates (an average of 10 nanoparticles In the agglomerate From SNT is formed in the case of PAI-1, and on average 2 NTs in the agglomerate--in the case of PAI-2) [112; 142]. Of course, the interaction between the SNT and the polymer of the matrix, perhaps connected with the formation of hydrogen bonds, for example, -OH... HOOC- in the case of PAI-2, plays a role.