Investigations Of Thermal Transportation And Ionic Thermoelectric Effect Of Hydrogels

Hydrogel is an important part of human body with good biocompatibility and customizable physicochemical properties.Therefore,hydrogel has been widely used in emerging fields of flexible electronics,soft robots and etc.The heat dissipation properties in hydrogel-based systems worth to be taken seriously,therefore the study of heat transport properties of hydrogels is important.Meanwhile,hydrogel has the potential to become the soft ionic thermoelectronic matrials.For hydrogels,the the impact of the polymer network in their thermal transportation and ionic thermoelectronic effect is not clear.In this thesis,several hydrogels with similar chemical structures were studied,and the regulation of the thermal transportation and the ion thermoelectric effect of hydrogels were investigation by controlling the network structure of hydrogel polymers.The main content and innovatins in the research are as follows:Chemically crosslinked Polyacrylamide（PAAm）hydrogel is one of the most commonly used hydrogels in the field of flexible electronics,and its simple structure is beneficial to simplify the understanding of the thermal transport characteristics of hydrogels.We firstly choose PAAm hydrogel as the research object.The thermal conductivity tested by the 3 Omega method varied from 0.33 Wm^-1K^-1 to 0.51 Wm^-1K^-1.The thermal conductivity of hydrogels can be controlled by 50%without adding any additives.The change amplitude of thermal conductivity of PAAm hydrogels is similar to the change amplitude in polymers composites with inorganic nanofillers.Combining with the theory analysis and material characterization,this work reaveals the crosslinking effect in the PAAm hydrogels:while the crosslinking density of the hydrogel increased continuously,the increased transmission path competes with the enhanced phonon scattering.Meanwhile,three kinds of hydrogels with similar chemical structure to PAAm hydrogel were also studied.It is believed that the water content and the hydrophilic property can improve the thermal conductivity to some extent.The regulation of polymer network structure can also affect the thermoelectric effect of hydrogel.Polyvinyl alcohol（PVA）hydrogel with different network structures and crystallinity can be achieved by different freezing thawing preparation schemes.The directional structure of PVA hydrogel is beneficial to further expand the ionic thermoelectric effect of the materials,and the crystallinity of PVA hydrogel also has an effect on the ion thermoelectric effect of the materials.The experimental results,materials characterization and theory analysis proved that the manipulation of polymer network is efficient to regulate the ionic thermoelectric effect of the PVA hydrogels.In the research,the preparation of anisotropic flexible ion thermoelectric materials is realized,and the conclusion is:the two key factors that control the ionic thermoelectric effect of hydrogel are the influence of polymer network structure on steric hindrance and the difference of ionic diffusion rate caused by the difference of crystallinity.Finally,the thesis used the low thermal conductivity and the ionic thermoelectric effect of above hydrogels to realize the application of PVA hydrogels in three kinds of low-grade heat collection,namely,fingertip power generation,hot water power generation and wast heat collection.At the same time,using the photothermal effect in graphene oxide and ionic thermoelectronic effect in PAAm hydrogels,the thesis realized the photothermal power generation through biological tissue,which proved the potential of hydrogels in the passive power generation in vivo.