| Thermal management fabric(TMF)can control the temperature of human surface to meet the thermal comfort needs.Compared with building heating,ventilation,and air conditioning systems,the energy utilization efficiency is improved and the energy consumption is reduced by TMF,addressing the problems of carbon emissions and pollution.Sunlight,as green,clean,and infinite renewable energy,can be applied to control the temperature by the reflection,absorption,conversion and storage.However,the light conversion and heat storage limit the TMF development.How to fabricate a closed-loop solar energy system is still a challenge for TMF applications,integrating solar absorption,conversion,storage and controllable release.Azobenzene is as a kind of solar energy storage molecule,possessing high cyclability,moderate energy storage capacity,efficient isomerization conversion,and bidirectional lightcontrolled energy release.The solar energy can be stored into chemical bond and released in the form of heat.The structural design of azobenzene derivatives can solve the conflict between solid isomerization and energy storage capacity,leading to obtain the highly efficient TMF.A series of azobenzene derivatives are synthesized by alkyl chain control and donor-acceptor electron effect.Compared with the norbornadiene derivatives,the molecular structure and halflife are investigated.The steric hindrance effect of the alkanyl chain efficiently weakens the π-π stacking of benzene rings,leading to the bidirectional reversible photoisomerization.Aiming at the poor photochemical stability of norbornadiene derivatives,the degradation mechanism is clarified,and the cyclability is improved by selectively cutting off wavelengths.At the photostation state of visible(Vis)and ultraviolet(UV)light,the isomerization conversion efficiency of azobenzene derivatives is explored,max.value up to 80%.The different phasechange(PC)points are exhibited under trans and cis isomer to reveal the mechanism of optically controlled PC points.Both isomerization and PC energy can be released by light stimuli,and the total energy storage density of azobenzene derivative is 205 J g-1.In order to improve the energy storage density,the solar energy and heat energy are coharvested.The effect of molar ratios of alkyl alcohol(Cn OH)and alkoxy azobenzene molecules(Cn Azo)on isomerization rates is investigated.The PC points are controlled by the molecular polarity and steric hindrance change.The crystallization point of C14 OH is 35 ℃,while it lowers to 29 ℃ at cis state,temperature difference up to 6 ℃.The binding energy of C14 OH and C14 Azo is calculated to reveal the optically controlled PC points mechanism.The total energy storage contains PC energy of Cn OH and Cn Azo,as well as isomerization energy of Cn Azo.Synchronous energy release of total energy is explained,which is high as 240 J g-1.The water is simulated as human body,and the water temperature supported by Cn OH@Cn Azo is 6 ℃ higher than that only supported by Cn OH.The dual photo-and thermo-chromic indicator is achieved by introducing azobenzene derivatives into leuco dye(LD)-based thermochromic materials.The effect of light and thermal stimulations on color properties of LD(14)is explored with various molar ratios of azobenzene derivative.At trans state(UNLOCK),LD(14)can undergo the thermochromic performance,but it is locked at cis state.The optimal ratio under the max.color control is obtained,in which the molar ratio of LD,bisphenol A,C14 OH and C14 Azo is 1:3:40:15.The mechanism of LD(14)color control is revealed by analysis of LD-based system and isomerization.Based on the photoand thermo-chromic mechanisms,the energy storage and release processes can be indicated visibly,improving the energy utilization efficiency.A Janus light absorbent/reflective air-layer fabric(Janus A/R fabric)is fabricated for improving the temperature raising performance of TMF.The front and back sides possess high solar energy absorption and human body radiation reflection,respectively,achieving thermal management.C2 Azo is melted into Si O2 aerogel to address the leakage on the fabric surface during phase transition.The isomerization and PC properties of C2 Azo in Si O2 aerogel are investigated,and the total energy storage capacity is up to 146 J g-1.The Titanium dioxide particles are loaded on the reflective layer,endowing high infrared reflectivity at 7–14 μm.Under Vis light,the surface temperature of charged-Janus A/R fabric is 6.3 ℃ higher than that of the uncharged state.In no light input case,the thermal insulation temperature of Janus A/R fabric is 1.4 ℃ higher than that of cotton fabrics.Therefore,the microenvironment temperature of human body can be regulated by solar conversion and human body radiation reflectivity.To improve solar energy spectrum utilization efficiency,both Cn OH@Cn Azo and cesium tungsten bronze powder(Cs0.32WO3)with near-infrared photothermal conversion are loaded on the fabric to prepare the visible solar storage fabric(VSSF)with full solar spectrum utilization.Cn OH@Cn Azo can be encapsulated by polystyrene with fixed molar ratio.The encapsulation efficiency and energy storage density are explored,reaching 91% and 28.5 J g-1,respectively.Compared to the pristine Cn Azo,the energy storage efficiency of VSSF is expanded to 4.8%.The colors from Cn Azo and Cs0.32WO3 are matched to improve the color contrast,resulting in high accuracy for visible energy storage indication.The surface temperature of VSSF can reached 83 ℃,which not only can manage microenvironment temperature of human body,but also can be applied in photothermal driving applications.For further increasing the energy storage density and energy storage time of the azobenzene derivatives,a pyrazole ring is substituted for one side of the benzene ring in the azobenzene molecule(PAZO).The PAZO-based energy storage fabric(MOST fabric)is prepared with high energy storage performance.The relationship among molecular structure,photoisomerization conversion rate,and energy storage half-life is explored to clarify the reason for energy storage differences between Ph–N=N–Het and Ph–N=N–Ph.The PAZO is encapsulated by benzoyl-3-hydroxyphenyl acrylate-styrene block copolymer(BHA-PS).The UV filter shell endows high isomerization conversion of PAZO even under board broad-spectrum UV light,reaching 84%.The PAZO can co-harvest the isomerization energy and PC energy,in which the total energy storage density of PAZO and its microcapsule are up to 329 and 134 J g-1,respectively.The UV filter microcapsules are loaded on the fabric surface,corresponding to the specific acupoints of the human body.Under Vis light,the surface temperature of MOST fabric is 31.6 ℃ higher than environmental temperature,achieving the thermal management with high energy storage performance and expanding its application in personal health thermal management.The design of azobenzene derivatives provides a new way for high energy storage performance systems,and also establishes a theoretical foundation for TMF with high energy storage performance. |
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