Optical and Structural Properties of Composites Based on Poly and TiO[sub.2] Nanowires

This article's objective is the synthesis of new composites based on thermoplastic polyurethane (TPU) and TiO[sub.2] nanowires (NWs) as free-standing films, highlighting their structural and optical properties. The free-standing TPU-TiO[sub.2] NW films were prepared by a wet chemical method accompanied by a thermal treatment at 100 °C for 1 h, followed by air-drying for 2 h. X-ray diffraction (XRD) studies indicated that the starting commercial TiO[sub.2] NW sample contains TiO[sub.2] tetragonal anatase (A), cubic Ti[sub.0.91]O (C), and orthorhombic Ti[sub.2]O[sub.3] (OR), as well as monoclinic H[sub.2]Ti[sub.3]O[sub.7] (M). In the presence of TPU, an increase in the ratio between the intensities of the diffraction peaks at 43.4° and 48° belonging to the C and A phases of titanium dioxide, respectively, is reported. The increase in the intensity of the peak at 43.4° is explained to be a consequence of the interaction of TiO[sub.2] NWs with PTU, which occurs when the formation of suboxides takes place. The variation in the ratio of the absorbance of the IR bands peaked at 765-771 cm[sup.−1] and 3304-3315 cm[sup.−1] from 4.68 to 4.21 and 3.83 for TPU and the TPU-TiO[sub.2] NW composites, respectively, with TiO[sub.2] NW concentration equal to 2 wt.% and 17 wt.%, indicated a decrease in the higher-order aggregates of TPU with a simultaneous increase in the hydrogen bonds established between the amide groups of TPU and the oxygen atoms of TiO[sub.2] NWs. The decrease in the ratio of the intensity of the Raman lines peaked at 658 cm[sup.−1] and 635 cm[sup.−1], which were assigned to the vibrational modes E[sub.g] in TiO[sub.2] A and E[sub.g] in H[sub.2]Ti[sub.3]O[sub.7] (I[sub.TiO2-A]/I[sub.H2Ti3O7]), respectively, from 3.45 in TiO[sub.2] NWs to 0.94-0.96 in the TPU-TiO[sub.2] NW composites, which indicates that the adsorption of TPU onto TiO[sub.2] NWs involves an exchange reaction of TPU in the presence of TiO[sub.2] NWs, followed by the formation of new hydrogen bonds between the -NH- of the amide group and the oxygen atoms of Ti[sub.x]O[sub.2x-mn], Ti[sub.2]O[sub.3], and Ti[sub.0.91]O. Photoluminescence (PL) studies highlighted a gradual decrease in the intensity of the TPU emission band, which is situated in the spectral range 380-650 nm, in the presence of TiO[sub.2] NW. After increasing the TiO[sub.2] NW concentration in the TPU-TiO[sub.2] NW composite mass from 0 wt.% to 2 wt.% and 17 wt.%, respectively, a change in the binding angle of the TPU onto the