Hierarchical Structure Design,Preparation And Diversified Applications Of Phase Change Microcapsules

Fossil fuels,as the major energy resources used in the development of the community,tend to cause cost and environmental problems.Therefore,seeking green or renewable energy has become the key to sustainable social development.Solid-liquid phase variable materials（PCM）charge/discharge a lot of latent heat through phase transition,with stable physicochemical properties,high latent heat and suitable phase transition temperature,which can effectually enhance energy efficiency and has attracted more and more attention of researchers.Although solid-liquid PCM has many advantages,it shows serious problems in solid-liquid phase transition,such as large undercooling,low thermal conductivity,high fluidity and easy leakage.Using microencapsulation technology to encapsulate solid-liquid PCM in organic/inorganic shells to prepare phase change material microcapsules（MEPCM）is an effective scheme to overcome these problems,which can not only encapsulate PCM in stable solid shell package when PCM in liquid state,protect it from the influence of external environment,but also provide PCM with large specific surface area to improve its thermal response speed and heat transfer efficiency.In addition,the MEPCM with hierarchical structure can store heat energy,and its outer functional shell can provide other additional specific properties.Therefore,it has become a new trend of the development of MEPCM to design hierarchical structure with different functions to meet its diversified applications in various fields.In this paper,following the development of the latest generation of MEPCM and aiming at the application requirements of different fields,different MEPCMs with multi-component and hierarchical structure were designed and prepared.Besides,their applications in the fields of photothermal conversion,enzyme sensors and supercapacitors as an independent temperature control units were studied.The specific work are as follows:（1）Silica shell was successfully coated on the surface of polyethylene glycol（PEG）by inverse emulsion template polycondensation,then the Si O₂/PEG microcapsules with good phase change properties were synthesized.After optimizing the ratio of surfactant and cosurfactant,the microcapsule showed perfect core-shell structure,regular spherical morphology and uniform particle size distribution,and its encapsulation efficiency was over 78%,the enthalpy of phase change was about 130 J/g.High heat storage capacity,thermal stability and shape stability make it reliable and durable in phase change cycle and durability.（2）The MEPCM based on n-docosane core and carbon nanotubes（CNTs）/polydopamine（PDA）/Si O₂ hierarchical shell structure was prepared to improve solar photothermal conversion.The microcapsule has regular micro-morphology,and the enthalpy of phase change exceeds 130 J/g,which not only has good heat storage capacity,but also shows high thermal stability and recyclability.Especially,the construction of CNTs/PDA shell with excellent photon trapping ability also endows the microcapsule with good photothermal conversion ability.The microcapsule obtained the best photothermal conversion efficiency as high as 90.1%when the CNTs content was 2 wt%.（3）A self-thermoregulation glucose biosensor to detect glucose in a wider temperature range was designed by combining MEPCM and glucose oxidase（GOx）.N-docosane with phase transition temperature close to the optimal activation temperature of GOx was microencapsulated in the Si O₂ shell,and then CNTs with good bioactivity and large specific surface were modified on the surface of Si O₂ shell to prepare the microcapsules as GOx carrier.The enzyme electrode was constructed by layer-by-layer self-assembly method for glucose detection.It was found that the introduction of MEPCM made the glucose biosensor have good self-thermoregulation ability,and showed better detection performance at high temperature than the traditional biosensor without MEPCM.（4）In order to dissolve the decay of electrochemical performance at high temperature,polyaniline（PANI）/CNTs,PANI/PR microcapsules and Ni（OH）₂,Co（OH）₂/MXene microcapsules were prepared as self-thermoregulation electrode materials for supercapacitors.All the samples have perfect microcapsule structure,and the encapsulation efficiency exceeds 50%.The enthalpy of phase change above 130 J/g makes them have good thermal and thermoregulation ability.Two kinds of PANI-based self-thermoregulation electrode materials obtained higher specific capacitance at high temperature than traditional materials without MEPCM,while Ni（OH）₂ microcapsule electrode material obtained higher oxygen evolution potential,and Co（OH）₂/MXene microcapsule electrode material obtained higher specific capacitance besides oxygen evolution potential.The phase change material microcapsules with hierarchical structure of different shells developed in this paper show regular micromorphology,good heat storage and thermoregulation ability,and cyclic charge/discharge performance.In addition,according to the requirements of different application fields,the hierarchical structure MEPCM designed by this study shows great application potential in this field.The related research results of this paper have important value for promoting the design,construction and diversified application of phase change microcapsules in various fields.