pH-dependent structure and photochromic properties of phosphomolybdic acid/polyacrylamide composite films

A series of nanocomposite films with different pH were constructed by entrapped phosphomolybdic acid (PMoA) into polyacrylamide (PAM) networks. The structure, photochromic properties and mechanism of composite films were studied with transmission electron microscope (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), ultraviolet-visible spectra (UV-vis) and X-ray photoelectron spectroscopy (XPS). The results indicated that pH had a significant effect on the microstructure and photochromic properties of composite films. The TEM image showed that PMoA particles changed from well dispersed sphere-shape to irregular similar ball-shape with the increase of pH. XRD pattern showed that PMoA changed from crystal phase to amorphous phase with pH increased. The FT-IR results revealed that the octahedral structure of PMoA was destroyed with the increase of pH. PMoA/PAM films with pH 2 had higher photochromic efficiency than those films with other pH value. According to XPS, the different photochromic properties were caused by the microstructure change of the heteropoly compound with different pH value.