Preparation And Thermochromic Behavior Of Polydiacetylene/ZIFs Composites

Polydiacetylene(PDA)can be obtained by the polymerization of diacetylene(DA)under the irradiation of 254 nm ultraviolet light or?-rays and X-rays.PDA has unique optical properties.Under the stimulus of the external environment(heat,solvent,mechanical stress,p H,metal ions,microorganisms,etc.),the colour can change from blue to red and the UV-visible absorption peak shifts from around 640 nm to around 540nm.The PDA has optical properties that allow it to be used as a sensor,but when the stimulus is removed,the colour does not return to its original colour and cannot be reused as a sensor because of the cost.In order to get a sensor with a high usage rate,three composites with a reversible thermochromic property were designed based on polydiyne in this thesis,as follows:(1)Poly(PCDA)/ZIF-8 composites were prepared by self-assembly of zeolite imidazolate metal-organic framework(ZIF-8)and 10,12-dipentylcarbodiynoic acid(PCDA)at low temperature and then irradiated by UV light at room temperature.The poly(PCDA)/ZIF-8 composites were characterised by X-ray diffraction analysis(XRD),infrared spectroscopy(FT-IR),Raman analysis(Raman),scanning electron microscopy(SEM),dynamic light scattering(DLS)and thermogravimetry(TG)for morphology,structure and particle size.The results of the reversible thermochromic properties of the composites show that with a photopolymerization time of 3 min and an optimum mass ratio of 5:2 between PCDA and ZIF-8,multiple reversible thermochromic changes can be achieved at 30-90°C,indicating that the poly(PCDA)/ZIF-8 composites have good reversible thermochromic properties.Poly(PCDA)/ZIF-8 composite films and poly(PCDA)/ZIF-8 composite powders were also produced,both films and powders showing reversible thermochromic properties.The colour change temperature is divided into two stages,between room temperature and 120°C for blue(?)red,120-180°C for red(?)orange,and above 180°C the composite loses its thermoreversible properties.(2)The zeolite imidazole ester bimetallic organic backbone(CoZn-ZIF)was self-assembled with 10,12-dipentaeryldipropargylic acid(PCDA)at low temperature and the poly(PCDA)/CoZn-ZIF composite was obtained after UV irradiation.Improved thermochromic irreversibility of poly(PCDA)/ZIF-67 due to introduction of Zn²⁺by poly(PCDA)/CoZn-ZIF.Investigating the effects of different molar ratios of two metals in CoZn-ZIF,UV polymerization time and different mass ratios of PCDA and CoZn-ZIF in the reversible thermochromic properties of composites.Poly(PCDA)/CoZn-ZIF exhibits good reversible thermochromic properties for 3 min of illumination and a high molar ratio of Co²⁺:Zn²⁺of M5.Both the powder and the film have multi-cycle and sensitive reversible thermochromic properties and can be used as temperature sensors.(3)Poly(PCDA)/XZn-ZIF composites were prepared by replacing Co²⁺with X²⁺on the basis of poly(PCDA)/CoZn-ZIF,which reduced the temperature of discolouration from 80°C to 55°C.The low temperature reversible thermochromic properties were investigated:with increasing UV exposure time,the higher molecular weight of the polymer in the composite,reducing the tendency to return to blue after removing thermal stimuli.When the X²⁺:Zn²⁺ratio in XZn-ZIF increases,longer time is needed to return to the initial blue colour,and when the X²⁺:Zn²⁺molar ratio is M4,the composites still have good reversible thermochromic properties.