## 2 Polymer Nanocomposites for Membranes Applications
New polyether imide hybrid films were prepared by a sol-gel process followed by thermal imidization using MTEOS and a poly(amic acid) containing ether linkages and isopropylate groups [70]. Experiments on the penetration of small gas molecules (He, N\({}_{2}\), O\({}_{2}\) and CO\({}_{2}\)) have shown that hybrid films with a higher silica content exhibit a higher permeability for all test gases. The hybrid films exhibited a trade-off between permeability and selectivity. An increase in the membrane permeability, depending on the concentration of silica, was accompanied by a slight reduction in selectivity (Figure 1. The highest gas permeability was found for the sample filled with 10% silica. These films have good O\({}_{2}\)/N\({}_{2}\) and CO\({}_{2}\)/N\({}_{2}\) separation properties. (IV) The most often used methods are the formation of non-porous (the dimensions of the voids correspond to the transport channels of gases or liquids by the mechanism of sorption-diffusion) and microporous mixed matrix membranes (MMM). Mixing of molecular sieving particles with polymers for the production of MMM makes it possible to combine the excellent properties of gas separation of molecular sieving materials with the processability of polymers [71]. For example, zeolite-filled microporous MMM (Zeo TIPS) were formed using the thermally induced phase separation (TIPS) process and consisted of zeolite particles in a microporous polymer matrix [72]. Zeo TIPS membranes are designed to improve upon the performance of dense polymer membranes for gas or/and liquid separations and to approach the performance of zeolite membranes avoiding their  
The correct choice of material for the matrix and sieve phases is fundamentally important for the development of the MMM [74]. The molecular sieving phase, according to the authors, should accurately distinguish the difference in size and shape of molecules. A successful example is given that a 13X zeolite with an aperture of 10 A is unlikely to act as molecular sieves for O\({}_{2}\) and N\({}_{2}\) molecules with lengths of 3.75 and 4.07 A, respectively, while zeolite 4A with an effective aperture size of 3.8 A should be able to distinguish two molecules due to entropic factors [75]. Molecular sieve membranes containing zeolite or CMS possess very attractive penetration properties because of their steric, equilibrium and kinetic effects, leading to highly selective separation of molecules of similar size [76]. Both types of particles were successfully used as fillers in the formation of MMM, and their selective transport properties can be realized to varying degrees depending on the composition and method of the membrane preparation [77]. Both components contribute to the properties of the membrane, where, in the absence of defects, the selected polymer matrix corresponds to the minimum achievable characteristics, and the introduced molecular sieves contribute to improving the selectivity of the membrane [74]. Polymers with a high glass transition temperature that now dominate in gas separation membranes have high selectivity and economically acceptable permeability, which makes them successful candidates for the polymer matrix. Although the difficulties in forming a MMM using a rigid glassy polymer as a continuous phase are evident, in particular because of poor polymer contact with the polymer sieve, some success has been reached by searching for new particle introduction techniques. Good contact between the components of the membrane is necessary. Otherwise, a lower resistance to the flow of gases is possible in the interfacial region, hence, a decrease in selectivity with increasing permeability. The great attention were attracted MMMs obtained in a result of the nanoparticles introduction in a non-porous polymer matrix. This method makes it possible to develop membranes with the improved complex of mechanical, thermo-physical properties with the maintenance of stability in the aggressive media.