Study On PNIPAM Hydrogel Smart Window Material And Its Thermal Management Performance

The proportion of building energy consumption is increasing year by year,and the window is the structure with the lowest energy efficiency in the building.It is significant to develop intelligent window materials with high energy efficiency.Among them,poly(N-isopropylacrylamide)(PNIPAM)hydrogel can sense the ambient temperature and initiate phase transition.Combined with other functional materials,PNIPAM hydrogel plays an important role in light regulation in the application of smart windows.Its energysaving application prospect is great,which has attracted many researchers’ attention.However,the phase transition temperature of PNIPAM hydrogel is still higher than the room temperature,which mainly depends on the ambient heat conduction to raise the temperature to initiate the phase transition,and the near-infrared shielding effect is poor.In this thesis,PNIPAM hydrogel was prepared by chemical method.In order to optimize the performance,cesium tungsten bronze(CWO)nano powder was introduced to prepare two kinds of composite gel,and each gel was characterized and tested.The main research findings are as follows:(1)PNIPAM hydrogel was prepared by free radical polymerization,and its successful preparation was verified by SEM and FTIR.The hydrogel has ultra-high optical properties,and its average visible light transmittance(Tlum),visible light modulation capability(△Tlum)and solar light modulation capability(△Tsol)are up to 99.21%,98.95%and 86.64%respectively.The lower critical dissolution temperature(LCST)of PNIPAM hydrogel was measured to be about 31.5℃,and the good phase transition stability of PNIPAM hydrogel was verified by thermal and cold cycle phase transition tests.The outdoor sunlight experiment proved that the thermal management performance of PNIPAM hydrogel was great.(2)CWO nano-powder is modified with polyamine(PDA)to prepare CWO@PDA powder,which is combined with PNIPAM hydrogel for preparation CWO@PDA composite gel,and use SEM,EDS and XRD to characterize and test the corresponding samples.The static contrast experiment verified that the dispersion stability of the composite gel was improved,and the comprehensive evaluation showed that 0.025%wt CWO@PDA composite gel had the best optical performance,its Tlum is 65.55%,and the initial near-infrared shielding effect was 41.67%.The LCST of the composite gel was about 31.6℃,and the good phase transition stability was verified by the cold and hot cycle phase transition test.The outdoor sunlight experiment proved that the composite gel had excellent thermal management performance.(3)CWO nano powder was modified with polyvinyl alcohol(PVA)and grinding ball by high-speed stirring.CWO-PVA dispersion was prepared and combined with PNIPAM hydrogel to prepare CWO-PVA composite gel.The corresponding samples were characterized by SEM,EDS,FTIR and XRD.The effect of PVA concentration on the performance of the composite gel was investigated,and it was concluded that the optical performance and thermal management performance of the composite gel with low concentration of PVA were better.The comprehensive evaluation shows that 0.04%wt CWO-PVA composite gel has the best optical performance.While maintaining Tlum as high as 87.21%,the initial near-infrared shielding effect reaches 75.87%,and △Tlum reaches 86.98%,△Tsol,reaches 55.24%.The LCST of the composite gel was measured to be about 31.5℃.The static test proved that the composite gel had excellent dispersion stability,and the cold and hot cycle phase transition test verified that it had excellent phase transition stability.The combination of indoor infrared lamp irradiation simulation and outdoor sunlight irradiation experiment proves that the thermal management performance of the composite gel is superior.