## 2 Polymer Nanocomposites for Membranes Applications
The dispersion characteristics and orientation of NTs were examined by transmission electron microscopy (TEM, Figures 19 and 20). The SNTs were well dispersed and oriented in the film plane in nanocomposites with a tube concentration of up to 4.5% (\(v/v\)), which led to a gradual increase in the gas barrier. The lowest gas permeability was 60% less than that of the original polyimide film. However, the microaggregation of nanoparticles in dispersions and their orientation were initiated at high SNT loads, and the oxygen barrier was reduced. The dependence of the permeability on the volume concentration of NT has an extreme character and is presented in Figure 4.5  
\begin{table}
\begin{tabular}{c c c c c c} \hline  & & **P (Oxygen)** & **P (Water)** & **D (Oxygen)** & **S (Oxygen)** \\ \hline
**wt \%** & **vol \%** & **lec(STP) cm m\({}^{-2}\) day\({}^{-1}\) atm\({}^{-1}\)** & **lec(STP) cm m\({}^{-2}\) day\({}^{-1}\) atm\({}^{-1}\)** & **[10\({}^{-9}\) cm\({  
At smaller SNT compositions, the NTs were nano-dispersed and in-plane orientated, thus leading to higher gas barrier. The lowest oxygen permeability found for the nanocomposites was at 4.5% (vol/vol) of NTs and it was 64% smaller than for the pristine polyimide. However, with the onset of NT micro aggregation the NT dispersion and orientation were markedly compromised and the oxygen  
Figure 4.6 Chrysotile nanotubes (ChNTS = SNT) containing polyimide nanocomposites were prepared by solution mixing-casting method [130]. Figure 4.7 TEM micrographs of microtomed nanocomposites containing various NT loadings: (**a**) 2.2% (vol/vol); (**b**) 4.5% (vol/vol); (**c**) 7.7% (vol/vol)—low magnification; (**d**) 4.5% (vol/vol) and (**e**) 7.7% (vol/vol)—high magnification [130]. barrier was noticeably reduced. The reduction of the oxygen permeability at a smaller SNT content was essentially due to diffusivity while the contribution of oxygen solubility was minor. At larger SNT content, however, the relative contributions of oxygen diffusivity and solubility were comparable. The solubility trend at larger NT compositions indicated the possibility of excluded, screened within the nano--aggregates (bundles) and micro aggregates, and thus insoluble polymeric regions. When two dependences of the relative permeability of oxygen and water (normalized to the permeability of unfilled polyimide) were presented on one graph, relative to the volumetric SNT composition, it was assumed that the observed penetration behavior is not specific for the gas (vapor) and reflects a structural change only within the nanocomposites. In accordance with [PERSON]'s formula, nanocomposites based on SNT and nanocomposites with nanodispersed and randomly oriented layers of silicate MMT showed comparable gas barriers at small concentrations of nanoparticles [130]. (VIII) It is known that the typical results of introduction of inorganic particles in the polymer which leads to a decrease in mass transfer zone [112; 130]. As was discussed above, structure of NTs, their shape, length, ratio of inner and outer diameters, and surface chemistry can influence the morphological features of the composites. Of particular interest in this context was the development of new composite materials based on aromatic polyamide-imides (PAIs), with inorganic particles of a chrysotile structure as fillers. MMMs were prepared by a solution mixing-casting method using ultrasonic agitation of poly(diphenyloxydeamide-N-phenyl phthalimide) (PAI-1) dispersions with SNT [112]. The duration of the mixing process (up to 20 h) was determined by the required degree of homogeneity of the resulting composites. The content of the inorganic components was varied from 2 to 10 wt % [112]. It should be pointed out that there is a significant difference between the composite material PAI-1-SNT and typical composites \"polymer-inorganic fillers of SNT type\" in terms of selectively increasing permeability of PAI-1 after incorporating NT [112].