The Construction And Personal Thermal Management Performances Of Nanocomposites Based On Solar-thermal Graphene

Personal thermal management（PTM）technology aiming for local temperature regulation at the human body level shows broad development prospects in the fields of energy,environment,and medicine due to its high energy efficiency,designability and environmental universality.However,most of the current PTM materials just have a single function that can only achieve their temperature regulation function for a specific environment.At the same time,their unique physical and chemical structure always lead to poor wearable performances as a daily fabric,which limits the large-scale practical application of PTM technology.Derived from the unique sp² hybrid carbon atom and single-layer structure,reduced graphene oxide（RGO）is one of the ideal substrates for the preparation of all-weather and multi-environment adaptive personal thermal management devices with high intrinsic thermal conductivity,high solar spectral absorption and excellent solar-thermal conversion effect,and high emittance of human thermal radiation band.Based on graphene nanosheets with efficient solar-thermal conversion,this dissertation proposes graphene-based nanocomposites with three different structural designs,namely vertical channel aerogel,porous nanocomposite metafabric and directional wicking metafabric,by introducing thermal insulation,radiative cooling and other heat transfer mechanisms for the human body in extreme environment,daily outdoor environment and under intense exercise and sweating,achieving all-weather environmental adaptive personal thermal management of a single device.The main research contents and achievements of this dissertation are as follows:（1）Nature-inspired solar-thermal gradient reduced graphene oxide aerogel-based bilayer phase change composites for self-adaptive personal thermal management:Inspired by the effect of atmospheric temperature regulation,phase change composite（GRGC）with gradient RGO skeleton and aerogel/octadecane double layer design was prepared by gradient chemical reduction,directional-freezing,vacuum-drying,bottom one-side thermal reduction and partial impregnation of octadecane phase change material.GRGC integrates RGO solar-thermal conversion,aerogel thermal insulation regulation and phase change inverse compensation at the same time.Each part of GRGC skeleton has different physical properties:the strong reduced region has stronger light absorption（95%）and thermal conductivity,which is beneficial to solar-thermal heating and heat transfer in cold environments.The weakly reduced region has a weaker light absorption（86%）and thermal conductivity,which is suitable for thermal insulation in a hot environment.Due to the double-layer structure of aerogel and phase change composite,GRGC has excellent solar-thermal performance（55℃）,energy storage performance（phase change enthalpy retention rate?Hm>90%）,and excellent leakage resistance under external stress loads.In a cold environment of-5°C,the GRGC aerogel layer can prevent internal heat loss through its thermal insulation porous structure,and use the solar-thermal conversion to in-situ heat,providing a warm microenvironment at the skin-material interface,whose interface temperature is 25.9°C higher than that of bare simulated skin,providing five times the insulation effect of cotton cloth.In a hot environment of 40°C,the phase change composite layer needs to be exposed to the environment to inhibit the solar-thermal heating of the RGO skeleton while using its phase change behavior to prevent overheating of skin.The porous aerogel layer in contact with the simulated skin can also provide stable thermal insulation for a long period protection.Compared with traditional cotton fabrics,RGO aerogel materials,and fully filled phase change composite RGC,GRGC shows excellent adaptive and comprehensive personal thermal management performance under different conditions and extreme environments.（2）Dual-functional reduced graphene oxide decorated nanoporous polytetrafluoroethylene metafabric for radiative cooling and solar-heating:In this chapter,a unique interlayer NPTFE/RGO/PDMS metafabric was prepared by assembling high infrared emission RGO layer and spectral selective NPTFE layer with transparent and robust polydimethylsiloxane（PDMS）supporting layer through a simple and convenient blade coating method for daily use in indoor/outdoor environment.The metafabric successfully integrates passive radiative cooling,solar-thermal heating,and satisfactory wearable performance.The special nanoporous structure of the NPTFE layer and the high infrared emissivity of the RGO layer endow the metafabric excellent spectral selection properties.For radiative cooling mode,the metafabric shows high solar spectral reflectance（R>90%,0.25-2.5μm）and high emissivity in the HBIR range（ε>90%,7-14μm）based on Mi scattering.Metabolic heat can be dissipated rapidly outward via the thermal radiation pathway with the high-emissive RGO layer across through the infrared transparent NPTFE,the outer NPTFE layer can reflect and scatter sunlight at the same time,inhibiting the solar radiative temperature rise by solar radiation.At a 25℃outdoor environment,metafabric show a radiative cooling effect of 3.2℃compared to the cotton cloth.The metafabric can also be switched to heating mode by simply flipping the RGO layer outward,which enables efficient solar thermal conversion through the broad spectrum absorbed RGO layer（α>90%,0.25-2.5μm）.In a cold environment of 0°C,the surface temperature of the metafabric can rise to 22°C within 2 min,which is 17.0°C higher than that of the traditional cotton cloth,providing a warm microenvironment for the skin and preventing the heat loss.In addition,the metafabric also shows good wearable properties:excellent moisture permeability(water vapor transmission rate 0.023 g cm^-2 h^-1),high elongation at break（200%）and good flexibility derived from PTFE substrate;anti-fouling performance and wash resistance derived from low surface energy and chemical inertness components,as well as good flame retardant brought by F,Si,O elements,thus presenting great potential in the field of wearable all-weather personal thermal management fabrics.（3）Directional wicking RGO/PA56 nanofiber film metafabric for personal moisture and thermal management:Based on retaining the functions of sandwiched structure metafabric in last Chapter,PA56/RGO/PDMS directional wicking metafabric with asymmetric water wettability on each side is prepared by blade coating method for collaborative management of moisture and heat,which further broadens the application of metafabric.By assembling the hydrophilic porous PA56 nanofiber film,the high-emissive RGO layer and the transparent and robust PDMS hydrophobic layer,the metafabric possesses multiple functions of solar-thermal heating in cold environment,indoor radiative cooling and rapid sweat transportation and evaporation in hot environment.PA56/RGO/PDMS metafabric is highly reflective in the solar spectrum（R>90%,0.25-2.5μm）,and highly emissive in the HBIR range（ε>80%,7-14μm）,and achieve a cooling effect of 2.5℃compared with traditional cotton fabric at 25℃indoor environment.Moreover,in a cold environment of-5℃,the metafabric can realize efficient solar thermal conversion through the broad spectrum absorbed RGO layer（α>90%,0.25-2.5μm）and increase the surface temperature to 20℃within 2min to keep warming in a cold environment.In addition,the metafabric has opposite wettability in the vertical direction,and the sweat can be spontaneously transported from the hydrophobic side of the PDMS（water contact angle 127°）to the hydrophilic side of the outer PA56（water contact angle 0°）.In the indoor environment of 28℃,the diffusion and evaporation time of 0.05 m L simulated sweat of metafabric is only 8.7 min,which is much less than 20.3 min of cotton fabric.Moreover,under the simulated sunlight,the solar-thermal effect of RGO beneath the semi-transparent wet PA56increased the local evaporation temperature from 25.6℃to 37.9℃,and then shorten the evaporation time after diffusion by 46%,and the evaporation rate of sweat reach 0.31 mg cm^-2 min^-1,accelerating the cycle of sweat absorption-evaporation-reabsorption at skin surface.Thus,the metafabric enables the rapid wicking and evaporation of sweat with cooling the skin,achieving the management of moisture and heat to keep the skin dry and cool.