| With the progress of science and technology and the rapid development of the 5G era,the operation and updating speed of intelligent wireless communication equipment is also accelerating.However,the resulting electromagnetic interference and electromagnetic pollution will not only pollute the environment and endanger human health,but also interfere with the normal operation of electronic communication equipment and even cause major safety accidents.In order to prevent electromagnetic wave from harming human body and environment,the suppression or mitigation of electromagnetic interference(EMI)has become an important research field in materials science.Conductive polymer fiber composite(CFC)has been widely used in electromagnetic shielding materials because of its lightweight,breathable,flexible and adjustable conductive network But there are two problems to be solved:(1)the contradiction between high conductivity(high EMI SE)and good mechanical properties;(2)Control of surface wettability to meet wearable electronic comfort requirements.To solve these problems,in this paper,the core-shell structure is constructed amd the interaction between fiber and silver nanoparticles is regulated,so as to realize the high conductivity and electromagnetic shielding efficiency of CFC without sacrificing the flexibility and mechanical strength of the material.In addition,by adjusting the surface chemical composition and designing the double-layer fiber structure with good interface compatibility,the CFC with asymmetric infiltration and unidirectional water transport function was prepared.The relationship among microstructure,macroscopic properties and application of the materials was studied.The thesis consists of the following three parts:1.A conductive network containing Ag NPs was constructed on the surface of PU fiber by impregnation-reduction method.PVP can improve the adsorption capacity of silver precursor(silver trifluoroacetic acid)on PU fiber membrane,so as to improve the conductivity of fiber composite membrane.In addition,PVP as an interface binder can also enhance the interaction between conductive particles and the matrix PU,thus improving the mechanical properties and durability of the composite film.Through a series of characterization and testing,the influence of PVP concentration and molecular weight on the composite membrane structure was studied detail,and the relationship between surface structure and properties was explored.The results show that the maximum conductivity of the nano-composite membrane can reach up to 245.7±30.6 S/cm,and the electromagnetic shielding efficiency(EMI SE),SE/d and specific efficiency SSE(SE divided by density)of X-band are 96.9 dB,959.7 dB/mm and 169.7 dB cm3/g,respectively.And it can maintain good electromagnetic shielding performance after ultrasonic,tensile and other cyclic wear tests.At the same time,the membrane also has excellent electric heating properties,antibacterial properties and breathable properties.2.Fe3O4/PVP/Ag@PU composite membrane was prepared by adding PVP into silver mirror reaction precursor(silver nitrate)and using ultrasonic assisted interfacial sintering.The introduction of Fe3O4 nanoparticles not only endows the fiber film with excellent magnetic properties,but also further enhances the interfacial interaction between the fiber and the silver shell,thus improving the stability and durability of the material.The silver content in the composite can be increased by using silver nitrate precursor,and then Fe3O4 nanoparticles can be used to construct a more perfect electrical and thermal conductivity network on the matrix surface.The characterization results show that the composite membrane has an obvious core-shell structure,and the surface conductive shell is very complete and dense.The test results show that the highest conductivity of the composite nanofiber membrane is 5000 S/cm,the horizontal thermal conductivity is 4.41 W/(m*k),and the highest electromagnetic shielding efficiency can be 102.13 dB.The composite membrane also has excellent biocompatibility,sensing and electrothermal properties.3.The superhydrophilic CS/Ag@PU composite membrane was prepared by introducing chitosan into the silver nitrate precursor solution,and then the hydrophobic PU was introduced into one side of CS/Ag@PU by electrospinning technology to construct Janus membrane with the asymmetric wettability.Due to the similarity of components and fiber geometry on both sides of the Janus film,and the ability of chitosan to enhance interface interaction,the two sides of the Janus film are well bonded,and have good mechanical properties and excellent durability.Through a series of performance tests,the effects of different chitosan concentrations on the conductivity and electromagnetic shielding efficiency,and the effects of electrospinning time on the directional transport time of liquid were studied.The results showed that CS/Ag@PU composite membrane had the highest electrical conductivity(1409±140.4 S/cm),horizontal thermal conductivity(12.24 W/(m*k))and EMI SE(93.08 dB)when chitosan concentration was 0.25 mg/ml.In addition,by adjusting the thickness of the hydrophobic layer,the one-way transport time of the liquid can be shortened to 7 s.Due to the inconsistent optical and thermal properties of the composite film,the human body can be insulated and cooled down by turning over the material(the temperature can rise nearly 7℃ in insulation mode,and decrease 2.5℃ in cooling mode). |
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