## 3 Results and Discussion  
### Characterization and Properties of PEO/Clay Nanocomposites  
TGA was initially used to study thermal stability of apreptant, PEO, and Cloisite-Na\({}^{+}\) before the melt-mixing process in order to ensure that no decomposition occurs during the proper study. As can be seen in Figure 1, appointment showed thermal stability from ambient temperature until 262 \({}^{\circ}\)C, from which point onward, decomposition occurred. Aprepitant showed a two-stage thermal decomposition: a first stage from 262 till 355 \({}^{\circ}\)C and a second one from 355 till 428 \({}^{\circ}\)C, after which temperature no significant change in its mass loss was observed. PEO appeared to be more stable, with only one thermal decomposition stage, starting from 333 \({}^{\circ}\)C and ending at 455 \({}^{\circ}\)C, with a mass loss of 96%. Finally, clay showed an initial loss in its mass until 100 \({}^{\circ}\)C, corresponding to humidity loss--which was found to be present even after its heating in an oven overnight at 100 \({}^{\circ}\)C--while no significant change in its mass was observed till 700 \({}^{\circ}\)C. TGA study showed that no thermal decomposition happens at 130 \({}^{\circ}\)C, the temperature at which the melt-mixing process took place. The dispersion of sodium montmorillonite clay (Cloisite-Na\({}^{+}\)) microsized particles within PEO was quite effective as can be seen from the photographs in Figure 2, where the transparency of the 5 wt % clay/PEO composite was similar to that of the neat polymer. At the relatively high loading of 10 wt % clay, the composite films became less transparent. However, no aggregates of clay particles were observed for both loadings, proving the high efficiency of the melt mixing (by the twin-screw melt mixer) of PEO with the sodium clay. The structural characteristics of the PEO, the Cloisite-Na\({}^{+}\) clay, and the respective composites were investigated by means of FTIR and XRD measurements. Figure 3 displays the FTIR spectra of the respective samples. The characteristic peaks of pure semicrystalline PEO appear at 2868 cm\({}^{-1}\) (C-H stretching); 1465 cm\({}^{-1}\) (CH\({}_{2}\) scissoring); 1358 cm\({}^{-1}\) and 1343 cm\({}^{-1}\) (CH\({}_{2}\) wagging); 1280 cm\({}^{-1}\) and 1240 cm\({}^{-1}\) (CH\({}_{2}\) twisting); the triplet peak of C-O-C stretching at 1146 cm\({}^{-1}\), 1100 cm\({}^{-1}\), and 1061 cm\({}^{-1}\), with maximum intensity presenting at 1100 cm\({}^{-1}\)[50; 51; 52]; and the peaks at 960 cm\({}^{-1}\) (CH\({}_{2}\) rocking and C-O-C deformation); 842 cm\({}^{-1}\) (CH\({}_{2}\) rocking); and 528 cm\({}^{-1}\) (C-O-C bending) [53; 54]. The characteristics bands of Cloisite-Na\({}^{+}\) clay appear at 3630 cm\({}^{-1}\) (-OH stretching of Al-OH and Si-OH), 3443 cm\({}^{-1}\) (-OH stretching of interlayer H-O-H), 1695 cm\({}^{-1}\) (-OH bending), 1639 cm\({}^{-1}\) (interlayer H-O-H deformation), 1043 cm\({}^{-1}\) (Si-OH and Si-O-Si stretching), 916 cm\({}^{-1}\) and 798 cm\({}^{-1}\) (Al-Al-O-H and Al-O-Si bending, respectively), 622 cm\({}^{-1}\) (Al-O bending), 522 cm\({}^{-1}\) and 466 cm\({}^{-1}\) (Al-O-Si and Si-O-Si bending, respectively) [55]. The comparison of the FTIR spectra of the polymer, the clay, and the PEO/clay composite indicates that the structural features of PEO have not been deteriorated or changed, while the presence of the clay is verified by the increase of the intensity of the peak at about 1100 cm\({}^{-1}\) (from PEO) due to the superimposition of the peak at 1343 cm\({}^{-1}\) (from the clay). Figure 1: Thermogravimetric analysis curves of aprepitant, poly(ethylene oxide) (PEO), and Cloisite-Na\({}^{+}\) clay. The XRD patterns of PEO, Cloisite-Na\({}^{+}\) clay, and the respective nanocomposites are shown in Figure 4, both at low (Figure 4a) and wide-angle (Figure 4b) range. The basal spacing (d\({}_{001}\)) of the Cloisite-Na\({}^{+}\) powder, calculated from the diffraction peak at 20 = 7.55\({}^{\circ}\), was = 11.7 A (Figure 4a).