Studies On Controllable Construction Of Hygroscopic Polymer Gels And Their Water-and-energy Applications

The explosive rise of the global population has created a huge demand for energy and freshwater.Although extensive efforts have been dedicated to exploring new technologies and made great progresses,there are still significant challenges for achieving energy and freshwater sustainability.Therefore,it becomes imperative for us to explore new resources and additional technologies to further replenish existing production ways of energy and freshwater.Owing to the global hydrological cycle,an about 12,900 km~3 reserve of moisture resource exists in the atmosphere that can be utilized for freshwater generation and energy management,but is often overlooked.In this regard,if this huge moisture resource can be utilized rationally,it will provide a new alternative to efficiently relieve current global challenges.Hygroscopic polymer gels(HPGs),namely,are kind of cross-linked polymeric networks capable of moisture capturing,which can spontaneously harvest moisture from the surrounding environment and store it in form of swelling.Additionally,benefited from highly tuneable physical structures and chemical properties,HPGs can be precisely controlled by corresponding material designs to achieve rapid and large-capacity hygroscopic performance.Moreover,the further integration of desirable functional additives in the HPGs allows them versatile properties to further utilize captured moisture for various freshwater-generation and energy-management applications.Therefore,HPGs have emerged as a desirable material platform used in atmospheric moisture harvesting and exploitation during the past years.However,HPGs are still evolving at an incredible rate,but remain in their early stages.For example,HPGs still have many challenges,such as low sorption amount,slow sorption rate,unstable materials structure,single function,inefficient use of captured water,hindering them in actual freshwater and energy harvesting.In order to solve above issues of HPGs,this article mainly completes the following works:First,inspired by the structure and hygroscopicity of Tillandsia leaves in nature,hygroscopic and non-volatile organic liquid(glycerin)is displaced into a hydrophilic polymeric network to obtain a composited hygroscopic organogel(POG).Compared with its single components,this POG could achieve a synergistically enhanced hygroscopicity,enabling a continuously rapid and a large-capacity moisture sorption.In addition,we in-situ observed the hygroscopic process of the resulted gel,and proposed a possible hygroscopic theoretical model in light of the relationship between its structure and properties.Furthermore,after the introduction of a hydrophilic photothermal polymeric interpenetrating network,the resulted gel could realize an excellent solar-driven interfacial moisture evaporation,realizing high-efficient photothermal atmospheric water generation.Second,building on the work of the previous chapter,we prepared an ionogel(RIG)with both strong hygroscopicity and adhesion through introducing a type of imidazole-acetate ionic liquid into the gel network,which was further applied to achieve their thermal management for the cold side of thermoelectric generators(TEGs).Compared to the commercial metal heat sinkers,the resulted RIG could dissipate more waste heat from the TEG surface through water evaporation after spontaneous moisture sorption.Meanwhile,under its strong adhesion,the RIG could overcome the issue of mechanical deformation caused by excessive water evaporation for traditional hydrogel materials.In this regard,the RIG could achieve durable and efficient heat dissipation for the cold side of TEGs in self-sustainable moisture sorption and evaporative cooling under static and dynamical operation conditions,so as to improve its thermoelectric efficiency.Third,this work has developed a general approach to optimize the hygroscopic performance of current gel materials by manipulating the cross-linking pattern of polymeric networks.Firstly,a chemical cross-linker(HPR-C)with topological pulley effect was synthesized using molecular designs.After replacing the traditional covalent cross-linkers with HPR-C in current HPGs networks,a topological hydrogel with slide cross-linking structures(T-gel)was obtained and compared with a covalent cross-linking hydrogel(E-gel)in mechanical and swelling properties to elucidate the action mechanisms of its topologically cross-linked structure.Further,a topological HPG(THG)was obtained from T-gel through a swelling-dry method.In comparison with traditional covalent cross-linking HPG(EHG),the THG could realize a more excellent hygroscopic performance at the same conditions.As a result,such a gel-network design at the molecular level is expected to synergize with the developed material-level approaches to achieve further optimization of their limit of hygroscopic performance.In summary,this thesis starts with the application requirements of HPGs.On the basis of existing research on HPGs,through the design of gel components and structures,the performance of hygroscopic gel can be promoted to meet the requirements of practical scenarios for more desirable freshwater collection and energy management.Moreover,the works in this thesis also can provide a theoretical and experimental basis for constructing hygroscopic gels to efficiently exploit moisture resources for freshwater and energy sustainability,and is expected to promote the practical usages of hygroscopic polymer gels.