The Measurement Study Of The Thermal Conductivity Of Polyacrylamide And Polyvinyl Alcohol Hydrogels And Polyvinyl Alcohol Electrospun Films

Due to Hydrogels' extraordinary mechanical properties and biocompatibility,research on them as flexible electrons has emerged in recent years.However,research on hydrogels' thermal conductivity is still scarce.As the functions of flexible electronics continue to be complex and power consumption increases,heat dissipation in hydrogels may become a key factor limiting their further application.In order to address these problems,the thermal conductivity of hydrogels was measured by 3 Omega method.Firstly,the effect of crosslinking density,water content,and temperature on the thermal conductivity of hydrogel was explored by using polyacrylamide(PAAm)hydrogel as an example.It was found that the thermal conductivity of PAAm hydrogel increases first and then decreases with the increase of the crosslinking density.The crosslinking effect was attributed to the competition between the increased conduction pathways and the enhanced phonon scattering effect.Moreover,water content can act as filler in polymers which leads to nearly 40 % enhancement in thermal conductivity in PAAm hydrogels with water content vary from 23 to 88 wt%.Furthermore,the thermal conductivity of PAAm hydrogel is insensitive to temperature in the range of 25~40 ?.To improve the thermal conductivity of hydrogel,the effect of stretching and doping highthermal-conductivity filler on its thermal conductivity was investigated by using polyvinyl alcohol(PVA)hydrogel as an example.It was found that the thermal conductivity of PVA hydrogel is insensitive to stretching when the strain in the range of 0~200 %.And the thermal conductivity of PVA hydrogel is also unchanged when the content of boron nitride nanosheets in the range of 0~5 wt%.This suggests that whether those methods used to increase the thermal conductivity of polymeric materials is effective in hydrogel materials requires more research.Further,this thesis proposes a possible strategy to enhance the thermal conductivity of hydrogels by first increasing the thermal conductivity of the polymer network and then filling the water into the network.In order to preliminarily verify this strategy,the effectiveness of electrospinning and doped silver nanowires on the thermal conductivity of PVA were studied.In addition,the thesis systematically analyzes the uncertainty in these experiments.The uncertainty analyses provide good guidance for the design and analysis of experiments.