Preparation And Photochromic Property Of Inorganic-Organic Composites Based On LDHs

In this work, the photochromism of series of layered double hydroxides under UV-light irradiation has been observed. Series of LDHs/polymer, which have photochromism or photosensitivity have been successfully synthesized. Powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), ultraviolet-visible absorption spectroscopy (UV-vis) and elemental analysis were used to investigate the crystalline structure, chemical composition and photosensitive behavior of these composites.Series of layered double hydroxides powder or film have been synthesized by coprecipitation method, and its structure, composition as well as photochromic mechanism have been thoroughly studied by XRD, FT-IR, UV-vis and elemental analysis. It was found that the transition metal element with d electron which can be excitated in the host layer play an important role on the photochromic property. The specific octahedral crystal field of Ni²⁺ ions coordinated by nitrate anion or carbonate anion or chloride anion were metastable state, which leads to the photochromism of NiAl-NO₃/CO₃/Cl-LDHs.Series of LDHs/polymer composites were prepared by blending LDHs and polymer in a heated double-roller mixer. FT-IR and UV-vis were used to investigate the photosensitive behavior of these composites. It was found that the LDHs lead to the photochromism of LDHs/polymer composites and did not affect the stability of polymer. The different photosensitive behavior of LDHs/polymer composites was caused by the difference of polymeric matrix. The photosensitive behavior of some LDHs/polymer composites were reduced because of polymeric matrix. Compared with the photosensitive behavior of LDHs/polymer composites prepared by LDPE, EVA and PS, it can be seen that LDPE was the best polymeric matrix.The photosensitive behavior of NiAl-NO₃-LDHs/LDPE composite was studied in depth. The effect of varying the amount of added NiAl-NO₃-LDHs and UV exposure time on the photochromic properties of the composite has been investigated. The results showed that the photochromic phenomenon become more apparent with increasing amount of NiAl-NO₃-LDHs. When the amount reaches 5 phr (parts per hundred resin), the composite exhibits good photochromic properties and reproducibility. The color change rate of the composite reaches a maximum when the irradiation time exceeds 20 min. The addition of LDPE improves the photochromic cyclability of NiAl-NO₃-LDHs significantly. The addition of nanoscale NiAl-NO₃-LDHs also improves the mechanical properties of LDPE to some extent.NiAl-NO₃-LDHs/LDPE, NiAl-NO₃-LDHs/EVA, NiAl-NO₃-LDHs/PS and NiAl-NO₃-LDHs/PVA composites were prepared by solution co-mixing method. FT-IR and UV-vis were used to investigate the photosensitive behavior of these composites. It has been found that the composites prepared by solution co-mixing method have higher dispersion ratio and lower photosensitive behavior than that prepared by blending LDHs and polymer in a heated double-roller mixer. The reason for their difference might be the high dispersion ratio caused lower LDHs particle amount in unit area. The ethanol used to prepare the composites may reduce the photochromic property. Compared with the photosensitive behavior of NiAl-NO₃-LDHs/polymer composites prepared by solution co-mixing method using LDPE, EVA, PS and PVA, it can be seen that PVA was the best polymeric matrix.Twoα-Ni(OH₂) /LDPE composites were prepared: one by blending LDHs and polymer in a heated double-roller mixer and the other by solution co-mixing method. UV-vis was used to investigate the photosensitive behavior of these composites. The results showed thatα-Ni(OH)₂/LDPE composite has higher photosensitive behavior than that of NiAl-NO₃-LDHs/LDPE composite. Compared with the photosensitive behavior of the twoα-Ni(OH)₂/LDPE composites, it can be seen that the ethanol used in solution co-mixing method caused lower photosensitive behavior.