The Study Of Thermochromic Mechanism And Film Preparation Of[?C₂H₅?₂NH₂]₂CuCL₄

Bis?diethylammonium?tetrachlorocuprate[?C₂H₅?₂NH₂]₂CuCl₄ is a organic-inorganic hybrid metal complex with a thermochromic phase change at near room temperature.This transition process,induced by the coordination geometry distortion of tetrachlorocuprate anion[CuCl4]^2-from square-planar to tetrahedral,is apparent with a switch in optical appearance.Properties like this has great potential in temperature sensors,camouflage stealth,temperature-sensitive display and information storage.However,there are still a lack of study on the preparation and practical application of[?C₂H₅?₂NH₂]₂CuCl₄,mainly because of its hygroscopicity in the atmosphere,lack of method to adjust the phase change temperature,and Poor processability.In recent years,with the rapid development of analytical characterization technology and material preparation technology,it is possible to solve the above problems.In this paper,starting from the preparation of[?C₂H₅?₂NH₂]₂CuCl₄,the molecular kinetics of the phase transition process of[?C₂H₅?₂NH₂]₂CuCl₄,the preparation of[?C₂H₅?₂NH₂]₂CuCl₄/PVA composite film and the relationship between the preparation process and properties were studied.The application prospect of the system and inkjet printing technology were discussed.?1?The[?C₂H₅?₂NH₂]₂CuCl₄ crystals were successfully prepared by four methods,including methanol solution method,ethanol solution method,melting method and grinding method.The products prepared by melting method and grinding method are bulk crystals with large size and high yield,which can reach about 90%.XRD diffraction patterns show that the two methods have impurity phase and the purity is not high.Needle-like and small size?5-50 micron?crystals can be obtained by methanol solution and ethanol solution methods.The yield is only about 15-30%.The XRD diffraction characteristic peaks of the products prepared by solution method match well with the simulated data,and the purity is higher.The product obtained by solution method has thermochromic properties.DSC curves show that the temperature of the phase change is 52?,the temperature of the phase change is 28-25?,and the TG curves show that the thermal decomposition temperature is 154?,and the decomposition product is CuCl2.?2?FTIR spectra of[?C2H5?2NH2]2CuCl4 showed that the N-H bonding was enhanced,the N-H···Cl hydrogen bonding was weakened and the alkyl thermal movement was enhanced after the heating phase transition.Two-dimensional correlation analysis showed that the change of NH2⁺precede-CH3 and-CH2-,indicating that the hydrogen bond in the molecule first responded to the temperature rise and was the main factor causing the phase transition.FTIR absorption spectra and two-dimensional correlation analysis of the cooling phase transition show that the heating and cooling phase transition are completely reversible at the molecular level.The change of NH₂⁺is fall behind-CH3 and-CH2-when cooling,which means the main factor leading to the cooling phase transition is the weakening of thermal movement of alkyl groups.?3?Polyvinyl alcohol?PVA?was used as film-forming agent to coat on PET substrate.The coating had good wettability and adhesion with[?C₂H₅?₂NH₂]₂CuCl₄solution.The contact angle was 58 degrees,and the position and shape of ink droplets could be well maintained.PVA/[?C₂H₅?₂NH₂]₂CuCl₄ composite coatings with thermochromic properties were successfully prepared by precursor solution method.The SEM image shows that[?C₂H₅?₂NH₂]₂CuCl₄ crystal is embedded in PVA with a rod-like shape of length of 1-10 m.Orthogonal test showed that the optimum mass ratio of Cu/-OH in the precursor was 0.4.when the ratio of Cu/-OH was less than 0.4,the film display a yellow color at room temperature and lost its thermochromic properties.DSC analysis showed that the lower the Cu/-OH ratio,the lower the initial phase transition temperature of the coating.The reflective and transmission spectra of variable temperature visible light show that the composite coating retains excellent thermochromic properties,and the maximum reflective peak shifts from 540 nm to 570nm after phase change at elevated temperature.?4?Using a commercial inkjet printer with[?C₂H₅?₂NH₂]₂CuCl₄ as ink,a patterned temperature sensitive label was prepared to effectively indicate whether the water temperature in the beaker is safe or not.The self-adaptive camouflage effect of thermochromic camouflage pattern in low temperature jungle environment and high temperature desert environment was simulated.