【作者】 孙明辉；

【导师】 王帅；

【作者基本信息】 华中科技大学 ， 化学， 2023， 硕士

【摘要】 随着5G通信和大功率电子设备的快速发展,电磁污染日益严重。开发高性能的电磁屏蔽材料是解决电磁污染问题的关键。银纳米线作为一维金属纳米材料,不仅具有纳米材料本身的小尺寸效应,而且具有银金属本身优异的导电性,然而基于银纳米线的透明电磁屏蔽薄膜存在透光性与电磁屏蔽效能难以兼顾的问题。此外,具有高导电性的电磁屏蔽材料的屏蔽机制主要是以反射损耗为主,产生了电磁波“二次污染”的问题。针对上述问题,本文具体研究内容及结论如下:（1）针对透明电磁屏蔽薄膜存在透光性与电磁屏蔽效能难以兼顾的问题,本文利用水热法合成了具有超高长径比的银纳米线,超高长径比的银纳米线具有兼顾光学透过性与电磁屏蔽效能的优势。具体探究了氯化钠浓度、聚乙烯吡咯烷酮与硝酸银的质量比、反应温度以及不同分子量的聚乙烯吡咯烷酮等因素对于合成银纳米线的影响,最终合成了平均直径约35 nm,平均长度约350μm的银纳米线,其长径比高达10000倍。在此基础上,探究了银纳米线用量对透明电磁屏蔽膜光、电以及电磁屏蔽效能的影响,在保持一定透光率的同时,薄膜能展现良好的电磁屏蔽效能,当透光率为68.3%时,薄膜在X波段的平均电磁屏蔽效能可以达到28.3 d B。（2）针对高导电性的电磁屏蔽材料所带来的电磁波“二次污染”的问题,本文通过水热反应、聚多巴胺包覆以及高温碳化合成了粒径均匀的Fe₃O₄@NC磁性中空纳米球,将银纳米线和Fe₃O₄@NC分层组装在柔性纺织物基底上制备成复合电磁屏蔽薄膜,并成功浸涂一层聚二甲基硅氧烷保护膜。在经过弯曲和折叠后,复合薄膜的方阻保持稳定,表现出良好的柔韧性和导电稳定性。复合薄膜在X波段的平均电磁屏蔽效能可以达到50.1 d B,而反射损耗仅为2.6 d B,反射功率系数仅为0.45。总的屏蔽效能随着吸收损耗的增加而增加,而反射损耗没有变化,证明了复合材料的电磁屏蔽机制以吸收损耗为主,这有效地降低电磁波的“二次污染”。更多还原

【Abstract】 With the rapid development of 5G technologies and high-power electronic devices,electromagnetic pollution has become an increasing problem.The development of high-performance electromagnetic shielding materials is the key to solve the electromagnetic pollution problem.As a one-dimensional metal nanomaterial,silver nanowire has not only the small size effect of the nanomaterial itself,but also the excellent electrical conductivity of the silver metal itself.However,transparent electromagnetic shielding films based on silver nanowires have the problem of balancing light transmission and electromagnetic shielding effectiveness.In addition,the shielding mechanism of electromagnetic shielding materials with high electrical conductivity is mainly based on reflection loss,resulting in the problem of"secondary pollution"of electromagnetic waves.To address the above issues,the specific research and conclusions of this paper are as follows:（1）In this paper,silver nanowires with ultra-high aspect ratio were synthesized by hydrothermal method to address the problem of the difficulty in combining optical transmission and electromagnetic shielding effectiveness of transparent electromagnetic shielding films.The effects of sodium chloride concentration,mass ratio of polyvinylpyrrolidone to silver nitrate,reaction temperature and different molecular weights of polyvinylpyrrolidone on the synthesis of silver nanowires were specifically investigated,resulting in the synthesis of silver nanowires with an average diameter of about 35 nm and an average length of about 350μm,with an aspect ratio of up to 10,000 times.On this basis,the effect of the amount of silver nanowires on the optical,electrical and electromagnetic shielding efficiency of the transparent electromagnetic shielding film was investigated,and the film could show good electromagnetic shielding efficiency while maintaining a certain light transmission rate.（2）In order to address the problem of electromagnetic wave"secondary pollution"caused by highly conductive electromagnetic shielding materials,Fe₃O₄@NC magnetic hollow nanospheres with uniform particle size were perpared by hydrothermal reaction,polydopamine coating and high-temperature carbonization,followed by assembly of silver nanowires and Fe₃O₄@NC in layers on a flexible textile substrate to produce the composite electromagnetic shielding film dip-coated with a protective layer of polydimethylsiloxane.After bending and folding,the square resistance of the composite films remained stable,showing good flexibility and conductive stability.The average electromagnetic shielding effectiveness of the composite film in X-band can reach 50.1 d B,while the reflection loss and the reflected power coefficient are only 2.6 d B and 0.45,respectively.The total shielding effectiveness increases with the increase of absorption loss,while the reflection loss remains unchanged,proving that the electromagnetic shielding mechanism of the composite film is dominated by absorption loss,which effectively reduces the electromagnetic wave"secondary pollution".更多还原