Properties Research Of Organic Phase Change Composites Regulated By Long-chain Azobenzene And Metal Nanoparticles

Organic phase change materials(OPCM)are considered promising solar heat storage materials due to their advantages in phase change latent heat conduction,wide melting and freezing temperature,as well as excellent chemical stability.However,the traditional OPCM has severe heat loss problem during the heat storage process,which makes normal methods difficult to meet the requirements for insulation to achieve long-term solar energy storage.Another material with large potential for solar energy storage,known as Azobenzene(AZO),can undergo a trans-cis reversible transformation on its configuration when exposed to a specific wavelength of light,while the energy level difference between the trans-cis structure can be used for the storage and release of solar energy.However,traditional azobenzene has disadvantages such as low energy density and short recovery half-life,which makes it difficult to be applied in energy storage applications efficiently.In this paper,based on the photoisomerization properties of azobenzenes and the excellent energy storage capacity of organic phase change materials,a type of light-controlled organic phase change composite materials have been developed by slightly doping with metal nanoparticles.These nanoparticles were chosen because they have unique photothermal effects and catalytic properties.The composite has a long recovery half-life,high energy storage density,and controllable energy storage and release.It provides a basis to achieve long-term high-efficiency,reversible and controllable storage of solar energy or other energy.The specific research work is as follows:(1)Hydroxyazobenzene 2,2'-dihydroxyazobenzene(AZO-1)and 4,4'-dihydroxyazobenzene(AZO-2)with reactive symmetric structure was selected,while 4,4'-dihydroxyazobenzene(AZO-2)was synthesized via Diazotization Coupling Reaction.Characterizaztions of ¹H NMR,FT-IR,XRD were performed to analyze its chemical structure by,etc.TGA analysis proves that the two AZO molecules have certain thermal stability.UV-Vis absorption spectroscopy(UV-Vis)analysis proved that the two AZOs have absorption in UV light and Vis light regions.(2)Dodecanoic acid(DA)with low price and excellent heat storage performance was selected.The long-chain azobenzene compound was synthesized by acylchloride-esterification reaction:the organic phase change material dodecanoic acid(DA)was grafted to AZO-1 and AZO-2 respectively to obtain the long-chain azobenzene compound,which is long-chain AZO-1 and Long-chain AZO-2.The trans-to-cis isomerization under the UV light was confirmed by SEM.UV-Vis absorption spectroscopy showed the well photoisomerization performance of two long-chain AZOs.TGA shows that the thermal stability of the two long-chain AZOs have well thermal stability.(3)C1 and C2 long-chain azobenzene composite OPCM were synthesized via solution blending method by respectively compounding Long-chain AZO-1 and long-chain AZO-2with DA.The structure of C1 and C2 was characterized by FT-IR,¹H NMR,XRD,etc.The crystallinity of C1 and C2 was proved by XRD,and the micro morphology of C1 and C2 was observed by SEM.The thermal stability of C1 and C2 were analyzed by TGA,while both were better than DA.The photoisomerization performance of C1 and C2 was analyzed by UV-Vis absorption spectroscopy,and the results showed that the photoisomerization performance of C1 was better than that of C2.Through the DSC test,C1 and C2 was analyzed and compared with the changes of the crystallization temperature before and after the charging.The crystallization temperature of C1 was 16.33°C lower than the crystallization temperature of pure DA.The crystallization temperature of C1 after charging was 20°C,and the photocrystallization temperature difference?T was 2°C.Meanwhile,the crystallization temperature of C2 did not change significantly before and after the charging process comparing with DA.The energy density of C1 and C2 are 212.43 J g^-1 and 198.73 J g^-1,respectively.Compared with Da,the energy density of C1 is about 18.60%higher.The results show that C1 is more reliable with better energy storage properties.(4)With good energy storage properties,C1 was chosen to dope with a small amount of metal nanomaterials Au and Ag respectively to prepare composite materials C1-Au,C1-Ag,and their component were verified by FT-IR and XRD.XRD showed that the crystallinity of C1-Au and C1-Ag was equivalent to C1,SEM revealed that the surface micromorphology of the composite material was a long sheet-like structure overlapping and interspersed with a pleated structure.The photoisomerization properties of C1-Au and C1-Ag were analyzed by UV-Vis,and compared with C1,the results show that under the same conditions,it was observed that the time of transcis isomerization of C1-Ag was shortened,the recovery half-life of C1-Au was shortend too,indicating that the isomerization performance of composite materials can be adjusted by doping different types of nano-metals to meet the needs of diversified applications.The TGA test shows that C1-Au and C1-Ag have a considerable degree of thermal stability which are able to meet the requirements of actual applications.The crystallization temperature of C1-Au and C1-Ag was analyzed by DSC,of which,The crystallization temperature of C1-Ag after charging treatment is 16.66?,the?T increases to6?,This indicates that the doping of silver nanoparticles has a greater effect on the crystallization temperature and energy density of the composites.The effect of nano-metal silver doping on the crystallization temperature and energy density of the composites.is more significant.In summary,the metal nanomaterial doped long-chain organic phase change composite material exhibits good photoisomerization characteristics and thermal stability,high energy storage density,as well as reversible and controllable energy storage release,which is expected to achieve Long-term efficient,reversible and controllable storage of solar energy and other forms of energy.