Fabrication Of Functionalized Polymer Nanofibrous Membranes And Their Applications

Porous membrane-based materials have already become one of the hot research topics,due to their high separation efficiency,low cost,no secondary pollution,etc.Polymer porous membranes have been considered as a promising separation material,owing to the inherent flexibility,great processability and stability.Thus far,a variety of novel polymers have already been applied in different systems to fabricate porous membranes with specific functions and morphologies.As for the membrane technology,the barrier effect between the membranes and the selective transporting substances is crucial,which can be well affected by the raw materials of the membranes,membrane morphology,surface chemistry,and the fabrication process,etc.Thus,it is significant to develop precise optimization of these involved factors.Membrane technology is widely recognized in the past ten years,and has well been developed in the fields of environment,energy,biomedicine and so on.With the continuous expansion of its use,membrane materials with single surface chemical composition cannot fully meet the application requirements.Therefore,the selection of the substrate materials and the requirements of multi-functionalization are increasing.The research of membrane functionalization is of great scientific significance and practical application value.How to develop functionalized composite nanofibrous membranes while retaining their nanoscaled structures is always one of the core issues.The present construction of functionalized polymer porous membranes is mainly oriented by the application requirements,and the membrane-based materials with different surface morphologies and surface chemical compositions are designed.Despite the high efficiency improved in the separation and filtration systems,the stability,anti-fouling property and selectivity are still facing limitations.Thus,it is of great concern for the construction of smart surfaces,especially with the controllable surface chemistry.In order to meet the demand of polymer nanofibrous membranes in the fields of environment and energy storage,this thesis used polyacrylonitrile（PAN）,which owns great mechanical properties and is chemically modifiable,as the matrixes to focus on the design,fabrication and applications of functionalized polymer nanofibrous membranes.Based on the understanding of the surface chemistry,PAN membrane-based materials with different surface chemical compositions were fabricated,performing excellent separation and filtration capability in bi-directional oil-water separation,hybrid electrolyte Li-O₂battery and respiratory filtration,respectively.Via a thin-film coating strategy,a universal protocol has been proposed to control the surface chemistry of membrane-based materials,which provides theoretical support for the directional fabrication of novel materials with under-liquid dual lyophobic surfaces.Based on the further study of the under-liquid dual lyophobicity,the nanofibrous membrane with such wettability was introduced into the hybrid electrolyte Li-O₂battery,showing impressive long-term reversibility.This work proposes a novel strategy to design the next generation of secondary batteries.In addition,a polarity-driven path for particulates capture was achieved by precisely adjusting the surface polarity component of the membrane surface,giving rise to a respiratory nanofibrous membrane with high stability and surface polarity.It reveals remarkable improvement on the filtration efficiency,longevity and reusability,showing great potential in realizing healthy and safe reuse of public protective masks.This thesis carries out researches on the controllable fabrication and the separation performance of functionalized polymer nanofibrous membranes.It is of great significance to promote the application of chemically regulated smart surfaces in the fields of environment and energy.In recent years,studying on the functionalization of membranes exhibits great scientific significance and applied importance.Thus,how to develop functionalized nanofibrous membranes while retaining their nanoscale structural characteristics has always been one of the research hotspots.The main contents of this thesis are as follows:1.A rational protocol was proposed for controlling the under-liquid wetting behaviors of polyacrylonitrile nanofibrous membrane（PNM）.For the oil-water separation,the reasonable construction of under-liquid dual lyophobic membrane-based materials is crucial.Herein,we reported a thin-film coating strategy,which enabled eleven surfaces with modulated under-liquid wetting behaviors via a one-step polymerization process.Three different surface wetting behaviors could be obtained:1)under-water oleophobicity/under-oil hydrophilicity,2)under-liquid dual lyophobicity and 3)under-water oleophilicity/under-oil hydrophobicity.The underlying nature of the under-liquid dual lyophobicity was investigated by means of thermodynamic wetting models,revealing thermodynamic metastability.Furthermore,the introduction of the intrinsic water contact angle（θ_w）could well classify the under-liquid wetting behaviors,which allows a proper prediction of the under-liquid wettability with certain rough surfaces in a given oil-water-solid system.Meanwhile,the rational construction of a surface with specific under-liquid wettability can also be achieved based on this theoretical model.The design principle on the regulation of the under-liquid wettability effectively breaks the limitations on the fabrication of the under-liquid dual superlyophobic surfaces and opens potential applications in diverse fields in terms of such smart surfaces.2.The design of novel hybrid-electrolytes strategy promotes the fabrication of a Li-O₂battery technology.Benefitting from the under-liquid dual superlyophobic membrane（CTFPNM）as the separator component,the WiS cathoylte and aprotic anolyte could be stably segregated into each of their independent electrode reaction environments.The successful introduction of CTFPNM breaks the limitations of the solid electrolyte.The CTFPNM solved the problems of poor stability resulted from the conventional PP separator,and prevented the active water molecules from entering into the anode zone to generate Li OH intermediate products.Thus,the accelerated corrosion of the lithium metal anode caused by introducing water into the electrolytes could be avoided.Furthermore,the potential of Wi S could be fully tapped,achieving reversible high-energy-efficiency long-term Li-O₂cell cycling（Coulombic efficiency,99.50%）.The CTFPNM achieves the hybrid electrolyte strategy,which makes the Li-O2 battery technology really competitive and also provides theoretical support for the further practical applications.3.A polarity-driven protocol has been proposed for the airborne particulates capture,which was achieved through a stable N97 nanofibrous respirator.The nanoscaled fibrous structure can notably improve the physical barriers and lead to lower layer thickness,giving a great degradation of pressure drop while breathing.Through the accurate modulation of the surface polarity,the stable N97 nanofibrous respirator remarkably improved the filtration efficiency and longevity,leading to a highly efficient and stable filtration for both NaCl aerosols（0.3μm）and CV-B4（27～30 nm）viral aerosols.Meanwhile,compared with the charged nonpolar polypropylene（PP）microfibers in N95 respirators,the N97 nanofibrous respirator（TFPNM）exhibited remarkable stability in its structural morphology and surface polarity,giving rise to outstanding and stable filtration characteristics upon various disinfection treatments.Therefore,TFPNM reveals safe reusability,and shows great potential in achieving a healthy and safe reuse of the respirators for the public.