## 2 Polymer Nanocomposites for Membranes Applications
Therefore, in comparison with the introduction of micron-sized particles to highly permeable membranes, leading to an adverse volume effect, the addition of nanoparticles can create a specific interface with an area of a larger order of magnitude and play a positive role. The addition of nanoparticles is a promising approach to controlling the permeability of polymer membranes. A diffusion of gaseous or liquid penetrants in a composite membrane of the filled polymer type, as mentioned earlier, is enhanced by the presence of a thin \"skin\" of the matrix material near the nanoparticle surface with a penetrant diffusion coefficient 100 times larger than the matrix. The influence of skin thickness, the fraction of the area of nanoparticles, and the method of nanoparticle distribution in the membrane on the diffusion of the penetrating substance was studied in Reference [147]. However, for the PAI nanocomposites under consideration, the water-permeability of PAI-2-SNT, other things being equal, should be lower than the permeability of PAI-1-SNT [121; 112]. We have observed in the transition from PAI-1-SNT to PAI-2-SNT an increase in the permeability of polar liquids and a decrease in permeability with cyclohexane. Apparently, the current research of the gas transport properties of the composite films under consideration with respect to CO\({}_{2}\) and CH\({}_{4}\) (selectivity of diffusion) can bring useful information. Perhaps the determining factor is the aspect number of particles introduced, which did not appear at the level of the transition in the SNT-I-III series for PAI-1 composites, but can manifest itself in the transition to nanofibers? The structural and morphological characteristics of nanoparticles, in particular, the presence of functional groups or internal channels in their structure are essential, or not? We proposed the formation and investigation of a new nanocomposite of the PAI type containing triple chain Na-Mg-hydrosilicates synthesized under the hydrothermal conditions (nanofibers with the ribbon form, SNF). The obtained fibrous Na\({}_{2}\)Mg\({}_{4}\)Si\({}_{6}\)O\({}_{16}\)(OH)\({}_{2}\) hydrosilicate have the structure built of three silicon-oxygen chains. Such nanoparticles significantly differed from the earlier studied nanotubes by other morphology and size; SNF have never been used early to form membrane nanocomposites. The introduction of these particles led to significant changes in the physical, chemical and thermo-physical properties of the material [142; 148], that probably, is in particular due to the increase in the aspect ratio and the planar orientation of SNT in composite film. The morphology (Figure 29), thermo-physical, and relaxation properties of the prepared materials have been studied and analyzed accounting for the nanoparticles structure. The introduced SNF disrupts a supramolecular structure of polymer, and the small angle peak observed in the X-ray pattern of the unfilled PAI-1 is thus absent in the X-ray diffractogram of the nanocomposite film. At the same time, the reflexes related to SNF at \(\theta\) = 9.67 and \(\theta\) = 27.7 are observed, that corresponds to the interplanar distances d/n = 9.15 and 3.20 A, respectively. It should be mentioned, that the same content of SNT in the PAI-1 does not disrupt the polymer matrix structure, and no reflexes connected with SNT were not registered. Compared to SNT, introduction of the SNF in PAI-1 film did not lead to increasing of Tg. But sub-glass transition temperature (T\(\gamma\)) connected with free volume (FFV) [148] is more sensitive to nanoparticles introduction, which is very important for gas-separation membranes. First results of the study of the pervaporation characteristics of PAI-1-SNF showed significant differences in the properties of film samples of PAI-1-SNF and PAI-1-SNT composites, as well as the initial PAI-1 [149]. Pervaporation properties of the formed membranes were studied at 40 \({}^{\circ}\)C relative to cyclohexane, ethanol, methanol and water in different sequences of experiments.