Design And Preparation Of Elastomer With Pre-linked Nickel Chains For Smart Electromagnetic Interference Shielding

With the widespread use of smart electronic devices,the operating environment of traditional electromagnetic interference(EMI)shielding materials is becoming increasingly complex.This poses a significant challenge to their EMI shielding performance,as they can not be dynamically adjusted in real-time to meet the needs of signal transceiver devices.Therefore,the development of intelligent electromagnetic materials and structures with dynamically adjustable EMI shielding performances is of great significance.Nickel-based composite materials have attracted widespread attention in the fields of resistive sensors and EMI shielding due to their excellent negative piezoresistivity and simple fabrication process.Taking advantages of the negative piezoresistivity and low manufacturing cost of nickel-based composite materials,smart EMI shielding materials with adjustable strain sensitivity were designed and prepared.A systematic study was conducted on their microstructures,electrical properties,mechanical properties,and EMI shielding performances.The main progresses of this thesis as follows:1.Addressing the low strain sensitivity,large strain for off/on function switching,and complicated preparation of smart electromagnetic materials,the elastomer of pre-linked nickel chains with off/on switchable EMI shielding performances was successfully prepared using a simply shear mixing method.By controlling the particle size and content of nickel carbonyl particles,stirring intensity,and curing agent content,the distribution of nickel particles in Polydimethylsiloxane(PDMS)was optimized.During the tensile-release loading process,the pre-linked nickel chains are in contact with each other to form three-dimensional conductive networks,the elastomer of pre-linked nickel chains gradually transforms from an insulator to a conductor.By utilizing the abrupt change in electrical properties,the elastomer of pre-linked nickel chains achieves off/on switchable EMI shielding performance(2.8 ～ 37.6 d B).In addition,by controlling the distribution morphology of nickel chains in PDMS,the elastomer of pre-linked nickel chains with different strain sensitivities for mechanically responsive EMI shielding were obtained.2.Addressing the issues of low switchable range of EMI shielding performance,excessive electromagnetic wave reflection,and single regulation model in single-layer elastomer of pre-linked nickel chains,off/on switchable EMI shielding performances of the elastomer with pre-linked nickel chains was optimized using a sandwich structure.A sandwich structure of the elastomer with prelinked nickel chains was prepared by utilizing the adhesion between Sylgard 184 PDMS and Ecoflex00-30 PDMS.Multiple reflections of electromagnetic waves occur between the layers,and at 20%strain,the EMI shielding effectiveness of the sandwich structure of the elastomer with pre-linked nickel chains reaches 60.0 d B with switchable range of 54.4 d B.The absorption loss of the electromagnetic waves reaches 46.2 d B.Additionally,the elastomer of pre-linked nickel chains with surface microstructures were prepared by combining sandpaper with a polymethyl methacrylate template.The influence of single/double surface microstructures and the size of surface microstructures on the EMI shielding performance of the elastomer of pre-linked nickel chains was investigated.The surface microstructures enhance the response to compression stress,and the elastomer of pre-linked nickel chains with double-sided microstructures exhibited the largest switchable range of EMI shielding effectiveness.Among them,the elastomer of pre-linked nickel chains with microstructures prepared by 36-grit sandpaper was more sensitive to compression stress,and its EMI shielding performance was improved by 3.6 d B under a pressure of 100 k Pa.