Optical and Structural Properties of Composites Based on Poly(urethane) and TiO 2 Nanowires.

This article's objective is the synthesis of new composites based on thermoplastic polyurethane (TPU) and TiO ₂ nanowires (NWs) as free-standing films, highlighting their structural and optical properties. The free-standing TPU-TiO 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 ₂ NW sample contains TiO ₂ tetragonal anatase (A), cubic Ti _0.91 O (C), and orthorhombic Ti ₂ O ₃ (OR), as well as monoclinic H ₂ Ti ₃ O 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 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 ^-1 and 3304-3315 cm ^-1 from 4.68 to 4.21 and 3.83 for TPU and the TPU-TiO ₂ NW composites, respectively, with TiO 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 ₂ NWs. The decrease in the ratio of the intensity of the Raman lines peaked at 658 cm ^-1 and 635 cm ^-1 , which were assigned to the vibrational modes E _g in TiO ₂ A and E _g in H ₂ Ti ₃ O ₇ (I _TiO2-A /I _H2Ti3O7 ), respectively, from 3.45 in TiO ₂ NWs to 0.94-0.96 in the TPU-TiO ₂ NW composites, which indicates that the adsorption of TPU onto TiO ₂ NWs involves an exchange reaction of TPU in the presence of TiO ₂ NWs, followed by the formation of new hydrogen bonds between the -NH- of the amide group and the oxygen atoms of Ti _x O _2x-mn , Ti ₂ O ₃ , and Ti _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 ₂ NW. After increasing the TiO ₂ NW concentration in the TPU-TiO 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 TiO ₂ NW surface from 12.6° to 32° and 45.9°, respectively, took place.