Study On The Preparation And Photochromic Properties Of Inorganic-Polymeric Hybrid Films Containing Polyoxometalate

Polyoxometalates become promising candidates because of their very high electronic density and reversible mixed-valence species,which makes them suitable for photochromic and electrochromic materials.In order to realize practical application in the technological fields,the considerable attention has been focused on the study of polyoxometalates nanoparticles dispersed into polymeric networks to obtain transparent nanocomposites thin films.In this paper,Some water-soluble polymer have been used as organic matrix to construc a series of inorganic-polymeric hybrid films containing polyoxometalates.The microstructure,morphology of these hybrid films are studied by means of AFM,SEM,TEM,FTIR.With UV-vis and ESR studies the photochromic properties and mechanism of the hybrid films are investigated.Some new results are obtained from the experiments mentioned above.The main results are outlined as following;A series of photochromic hybrid films have been prepared through entrapping polyoxometalate(POM)in polyvinyl alcohol and polyvinylpyrrolidone matrix, respectively.Both kinds of the hybrid films show good photochromism.Irradiated with ultraviolet light,the electron transfer happened from organic substrates to polyanions through the charge-transfer bridge designed by hydrogen bonding,which results in the reduction of the polyanions and formation of heteropolyblue.The photoreduced process is in accordance with the charge-transfer mechanism.The interracial interactions and microstructure of the hybrid films are controlled by adjusting the concentration and sort of polyoxometalate..The studies show that the hybrid film containing phosphomclybdic acid exhibits faster photochromic efficiency and slower bleaching reaction than that containing Phosphotungstic acid,which during to the oxidation-reduction properties of process of polyoxometalate itself.A photochromic nanocomposite based on Keggin structure phosphomclybdic acid (PMoA)well dispersed in polyethyleneglycol(PEG)is fabricated.TEM image shows that PMoA nanoparticles with narrow size distribution are finely dispersed in polymer matrix.The strong coulombic interaction is built between PMoA and polymer matrix. Under UV irradiation,the film is reduced photochemically to yield a blue species, which is in according with a charge-transfer mechanism.To obtain the forming-film of the hybrid films,a no-reactive copolymer,styrene-acrylic latex(SAL)is added to the composite solution,which improves the coating and optical quality of PMoA/PEG composite,which is no reported in the previous references.The above experiment results indicate that the interactions between polyoxometalate and functional groups in polymer matrixes play definitive role in photochromism of these hybrid films.Because the bleaching process is a chemical one associated with O₂,the oxidation-reduction properties of polyoxometalate itself and the compact extent of surface morphology have great effects on the bleaching reaction...