| The two major problems of energy shortage and environmental pollution all over the world have hindered the sustainable development of human society.Exploiting clean renewable energy and improving energy utilization efficiency are the key to achieving energy conservation and emission reduction and promoting green and low-carbon development.Phase change materials(PCMs)can absorb and release a large amount of latent heat through reversible physical phase change process,which has attracted much attention in energy integration and redistribution.Organic solid-liquid PCMs are the most widely used latent heat storage materials,but the low thermal conductivity and melting leakage problems limit their practical application.In this paper,based on different application requirements,PCMs with different melting temperature were selected.The organic solid-liquid PCMs were bound and limited by nanoencapsulation and porous adsorption of cellulose nanofiber(CNF)aerogel to construct shape-stabilized phase change composites.Different functional fillers such as cuprous oxide(Cu2O),two-dimensional transition metal carbonitride(MXene)and boron nitride nanosheets(BNNS)were introduced to endow the shape-stabilized phase change storage energy materials with additional properties,such as photothermal conversion,Joule heating,heat conduction,flame retardant and hydrophobicity.The working mechanisms of phase change composites in the fields of intelligent temperature regulating fabric,flexible wearable heater and seawater desalination were investigated.The specific work is as follows:(1)The amphiphilic block copolymer quaternized poly(2-(dimethylamino)ethyl methacrylate)-b-poly(methyl methacrylate)(QPDMAEMA-b-PMMA)was prepared by reversible addition-fragmentation chain transfer(RAFT)polymerization.Nanoencapsulated phase change materials(NanoPCMs)were fabricated by miniemulsion polymerization using QPDMAEMA-b-PMMA as emulsifier.N-octadecane and n-butyl stearate were used as binary cores,and Cu2O nanoparticles were doped into PMMA as hybrid shell.By investigating the influence of single factors on the structure and properties of nanocapsules,the optimal preparation process of nanocapsules was determined:the amount of initiator 2,2’-azobis(2-methylpropionamidine)dihydrochloride(AIBA)was 3 wt%,the amount of emulsifier QPDMAEMA140-b-PMMA50 was 3.5 wt%,the amount of crosslinking agent pentaerythritol triacrylate(PETRA)was 10 wt%,the weight ratio of core to shell was 1:1,and 8.32 g/L CuSO4 solution was added in the pre-emulsification process.Cu2O/PMMA-NanoPCMs(8.32 g/L CuSO4)exhibited a clear core-shell structure with a particle size of 100-200 nm.The sample did not leak above the melting point of PCMs.The corresponding melting and crystallization enthalpy were 102.66 J/g and 108.05 J/g respectively,the encapsulation efficiency of core materials was 86.68%,and the thermal conductivity was increased by 67.25%.After coating Cu2O/PMMA-NanoPCMs on the fabric,the finished fabric was exposed to sunlight and had remarkable heat preservation effect through light absorption,photothermal conversion and thermal storage.After the removal of sunlight,there was obvious thermal buffer due to the release of latent heat.(2)Based on pure cotton fabric,MXene/polydimethylsiloxane(PDMS)conductive network was constructed on the upper layer of fabric by vacuum filtration and drop-coating.PDMS was deposited on the surface of MXene and can improve the oxidation resistance of MXene.Carbon nanotube(CNT)/CNF/paraffin(PA)aerogel phase change composite(CCPA)was assembled on the bottom layer of fabric by freeze-drying,and thus a high-performance laminated fabric was prepared.Without sacrificing the inherent flexibility,breathability and high strength of pure cotton fabric,laminated fabric exhibited excellent dual-drive electrical/solar-thermal conversion capability due to the strong electrical/thermal conductivity and light absorption properties of MXene.The response of the laminated fabric to sunlight and electricity increased with the increase of MXene concentration.In addition,the assembly of CCPA in the bottom layer of cotton fabric endowed the laminated fabric with excellent latent heat storage and thermal insulation properties.As the volume percentage of Pickering emulsion in CNT/CNF/PA co-suspension increased,the phase change enthalpy of CCPA increased.When the concentration of MXene was 9 mg/mL,the surface temperature of the laminated fabric rose to 84.9℃ after 650 s at a driving voltage of 4.0 V due to the excellent electrical conductivity of MXene.The excellent Joule heating effect of laminated fabric can be used for deicing.The laminated fabric was irradiated at a light intensity of 1200 W/m2 and the surface temperature rose to 62℃ after 270 s,which was attributed to the light absorption of MXene.When the light was stopped,the latent heat stored in CCPA was released and the laminated fabric had obvious thermal buffer.In addition,the excellent flame retardancy and hydrophobicity of laminated fabric played an important role in reducing the fire risk and increasing the service life of wearable heaters,which was conducive to broadening its application range.(3)With CNF as the skeleton,MXene as the photo thermal material and polyethylene glycol(PEG)as the phase change storage heat component,a Janus structure PEG/CNF/MXene aerogel phase change composite(JPCMA)with hydrophobic upper layer and hydrophilic bottom layer was prepared by freeze casting one-step in situ encapsulation and subsequent silylation modification.The strong sunlight absorption and high phase change latent heat up to 165.6 J/g allowed JPCMA to store large amounts of thermal energy while evaporating water under light conditions.The stored latent heat in the absence of light was released through the crystallization of PEG,so that water evaporation can continue effectively.The amount of MXene and the solar irradiation intensity had a great influence on the water evaporation rate and efficiency of JPCMA solar interface evaporator.The water evaporation rate and efficiency of JPCMA increased with the increase of MXene amount.When the solar irradiation intensity increased,the water evaporation rate of JPCMA increased,and the evaporation efficiency decreased due to heat loss.When the mass fraction of MXene was 5%and the solar irradiation intensity was set to 1.5 kW m-2,the evaporation rate and evaporation efficiency of JPCMA-5%were measured as 1.78 kg·m-2·h-1 and 68.51%,respectively.And during the continuous water evaporation test for 10 h,the evaporation rate only fluctuated slightly.When light was removed,water evaporation depended on the release of latent heat from JPCMA.The evaporation rate and efficiency of JPCMA-5%under dark conditions were 0.74 kg·m-2·h-1 and 30.91%respectively,which was 5.3 times of the evaporation rate(0.14 kg·m-2·h-1)of the blank device.In addition,the difference of wettability between the upper and bottom layers of the latent heat JPCMA solar evaporator brought obvious salt deposition resistance effect.(4)With CNF as skeleton and hydroxylated BNNS as thermal conductivity filler,a lightweight,flexible and anisotropic Si-CNF/BNNS aerogel was prepared by silylation modification and unidirectional freeze casting technology.The as-prepared aerogel exhibited honeycomb-like porous structure in the axial direction and ordered parallel lamellar channels in the radial direction.Attributed to the hydrogen bond and silylation cross-linking of CNF with BNNS and MTMS,as well as the aligned structure of aerogel,Si-CNF/BNNS aerogel was robust axially and compressible radially.When the CNF dosage was 0.8 wt%and the mass ratio of CNF to BNNS was 3:1,the compressive strength of Si-CNF/BNNS aerogel was 56 kPa in axial direction,and the elastic recovery was 75%in radial direction.The thermal conductivity of aerogel in axial direction was almost twice that in radial direction,showing attractive radial thermal insulation performance.In addition,the aerogel had excellent flame retardant,hydrophobic,radiative cooling and environmentally friendly properties,and can be used in energy efficient buildings in large-scale production.Subsequently,phase change material PA was loaded into the porous network of Si-CNF/BNNS aerogel by vacuum assisted impregnation process,and thus the shape-stabilized PA@Si-CNF/BNNS aerogel phase change composites were prepared.The phase change enthalpy up to 177.9 J/g and latent heat retention rate of 96.9%were obtained by DSC measurement,and the composite exhibited excellent latent heat storage capacity and thermal cycle stability.The developed PA@Si-CNF/BNNS aerogel phase change composites in this work can not only isolate heat in the confined space,but also regulate the ambient temperature,which can be used for effective thermal management of buildings. |
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