## 2 Polymer Nanocomposites for Membranes Applications
For CO\({}_{2}\)/CH\({}_{4}\) separation, noticeable enhancement of CO\({}_{2}\)/CH\({}_{4}\) selectivity was observed and the \(\alpha\) (CO\({}_{2}\)/CH\({}_{4}\)) value of the hybrids increased with increasing silica content. The ODPA-TAPOB-silica hybrid membranes demonstrated \(\alpha\) values that correspond to the \(\alpha\) values of the upper boundary Robeson's curve of the CO\({}_{2}\)/CH\({}_{4}\) separation with an increase in the silica content. According to the author, the high CO\({}_{2}\)/CH\({}_{4}\) selectivity of the membrane is due to the inclusion of silicon dioxide. [PERSON] et al. studied the preparation and pretreatment effect on the structure and performance of MMM [2; 50]. MMMs made from polyethersulfone (PES) with hydrophilic zeolites 13X or 4A demonstrated the strong effect of the membrane preparation procedure on the permeability of the gases. The rapid solvent release followed by slow drying resulted in relaxation of the molecular package, increased homogeneity and less dense structure, hence the higher penetration. It was shown that a significant improvement in permeability properties occurred at high loads. PES-13X membrane was observed to show a better separation characteristic than PES-4A. It has been suggested that the transport mechanism cannot be explained solely by the molecular sieving effect, since 13X has much larger pores than 4A. The reason could be the appearance of a cavernous porous structure around the fillers, leading to partial incompatibility of polymer chains and zeolite crystals. Differences in cave structures between PES-13X and PES-4A are due to various interactions of the zeolite and polymer, which directly affects the permeability of the MMM. It should be noted that studies of MMM containing zeolites as nano-fillers of polymer matrix (rubberg or glassy polymers) did not lead to unambiguous conclusions about how the presence of micro- or nano-voids at the interface between the polymer and inorganic phases affects a selective transport in composite membranes. Completely opposite results of the introduction of zeolite nanoparticles into the polymer matrix, which affected the properties of the diffusion membrane, are known. Surprising enhancement of both membrane permeability and selectivity for molecular species as penetrants was also achieved by reinforcing the polymer membrane matrix with nano-fillers [9]. Synergetic advantage of nano-scale measurements (\"nanoeffect\") was emphasized with respect to larger scale modification. Understanding the changes in properties, when the size of the particles (or fibers) was reduced to the level of nano-scale, is important for optimizing the resulting nanocomposite. A successful example is that the addition of silicalite to silicone rubber increases both the permeability and selectivity of small gas molecules (CO\({}_{2}\), O\({}_{2}\), H\({}_{2}\), He) relative to the initial polymer, but decreases the permeability coefficients for large molecules (such as butane) [93]. As noted above, the type of nano-filler and its own features can play a decisive role in the formation of MMM properties. Discussing the properties of MMMs above, it should be taken into account that zeolite is defined as a member of a family of hydrated alumino-silicate minerals that has a framework structure with interconnected cavities occupied by large metal cations and water molecules. The nature of these void spaces and channels determine the gas transport properties of zeolites. Zeolite molecular sieve typically has a uniform pore size within the range of 3-10 A. Pores of zeolites completely exclude molecules that are larger than their diameter. In comparison with natural zeolites, synthetic zeolites are better suited for research and industrial applications because of their greater homogeneity in composition and purity, which can provide a high degree of reproducibility. More than 150 synthetic zeolites have been synthesized: Type A, Type X, Type Y, Type ZSM and so on.