Research On Liquid Metal Foam-like High Thermal And Electrical Conductivity Flexible Self-healing Electronic Ski

With the continuous improvement of the manufacturing process of electronic devices,the power density and circuit frequency of electronic devices rise rapidly,which leads to the increasing demand for heat dissipation and electromagnetic shielding of electronic devices in the future.Therefore,the research of flexible electronic skin with conformal capability for thermal management and electromagnetic protection of electronic devices has become the future development trend.However,most of the existing substrate materials for flexible electronic skin are polymer materials.Due to the entanglement and agglomeration of molecules inside the materials,there are great challenges between the electrical and thermal conductivity of most malleable polymer materials and the application requirements(electrical insulation,thermal conductivity<1W m^-1K^-1).Aiming at the above problems,this paper proposes a liquid metal foam with high thermal conductivity and flexible self-healing electronic skin.The e-skin is prepared by a self-developed negative pressure injection method and contains a high proportion of interconnecting foam liquid metal.The liquid metal foam-like flexible electronic skin has extremely high isotropic thermal and electrical conductivity,as well as good softness and ductility.It can be attached to various special-shaped surfaces,so as to realize heat management and electromagnetic shielding for a variety of devices.At the same time,the flexible electronic skin has thermal self-healing ability to heal abrasion and incisions by using a thermoplastic elastomer as the base material for the liquid metal foam.Specific research work is as follows:（1）Structure design and working principle of liquid metal foam flexible and malleable electronic skin.The thermal conductivity and conduction characteristics of liquid metal foam interconnected conduction microstructure were studied,and the transfer rule of phonon electrons inside the microstructure was explored.The influence of wall thickness,connectivity configuration,minimum cross-sectional area and volume fraction of liquid metal interconnected conduction microstructure on the thermal conductivity and conduction properties was analyzed.The relationship between heat transfer and electron transfer between liquid metal and flexible polymer substrate materials was elucidated.A numerical model of thermal conductivity and conductivity of liquid metal interconnected conductive microstructure was established,and an evaluation system of thermal conductivity and conductivity of liquid metal interconnected conductive microstructure for various substrate materials was constructed based on volume fraction,thermal conductivity and conductivity.（2）Preparation method and characterization method of liquid metal foam flexible and malleable electronic skin.Study the preparation method of liquid metal foam electronic skin of thermoplastic elastomer and silicone rubber base material,explore the preparation method of foam structure thermoplastic elastomer base material based on salt template method,study the combination method of liquid metal and porous base material through negative pressure injection method,study the copper particle liquid metal composite method based on planetary stirring method.The preparation of copper particle-liquid metal composite flexible electronic skin was explored.The construction method of thermal conductivity test platform based on transient hot wire method was studied,and the thermal conductivity test of liquid metal foam-like flexible electronic skin was completed.The construction method of conductivity test platform based on four probe method was studied,and the conductivity test of liquid metal foam-like flexible electronic skin was completed.The maximum tensile limit and Young’s modulus of liquid metal foam flexible electronic skin were tested.（3）Thermal and electrical characteristics of liquid metal foam flexible electronic skin.The effect of liquid metal volume function on the thermal conductivity of flexible electronic skin was studied,and the thermal conductivity of flexible electronic skin under different liquid metal content was explored.The heat management mechanism between liquid metal electronic skin and application objects under different thermal conductivity states was studied,and the heat management ability of liquid metal flexible electronic skin to different devices was explored,so as to construct the bionic thermal conductivity regulation mechanism of liquid metal flexible electronic skin.The influence characteristics of liquid metal flexible electronic skin interconnected conduction microstructure on electromagnetic wave propagation were studied,the shielding properties of liquid metal flexible electronic skin under different tensile states were explored,the generation mechanism of the shielding properties of liquid metal flexible electronic skin was clarified,and the classification and analysis method of the shielding efficiency of liquid metal flexible electronic skin was constructed.The results show that the liquid metal foam with high thermal conductivity and conductive flexible self-healing electronic skin proposed in this paper not only has high thermal conductivity and conductive coefficient,but also has extremely high softness and stretchability,and can be closely conformed with the surface of various devices.The thermoplastic base material has good thermal self-healing performance.The specific index performance is as follows:the highest thermal conductivity can reach 8.4 W m-¹K^-1,the highest electrical conductivity can reach 1.32×106 S m^-1,the thermal conductivity can be adjusted between 0.11 and 8.4 W m^-1K^-1,the maximum tensile fracture rate is 608%,and the Young’s modulus is as low as 45 KPa.With thermoplastic elastomer as the base material,the liquid metal foam electronic skin has thermal self-healing properties.After surface incision self-healing,the thermal conductivity and maximum fracture tensile ratio can recover to 99%and 98%of the initial value,respectively.After completely cut off,the thermal conductivity and maximum fracture tensile ratio can recover to 80%and 59%of the initial value,respectively.After further doping copper particles into the liquid metal filler,the liquid metal foam-like flexible electronic skin has excellent electromagnetic shielding performance in X band（8.2-12.4 GHz）,and the electromagnetic shielding efficiency SE_T can reach 190 d B.The liquid metal foam with high thermal conductivity and conductive flexible self-healing electronic skin designed in this paper has good thermal management function and electromagnetic shielding function,which can be applied to the heat management of electronic devices and electromagnetic shielding and other application scenarios,and has a huge application prospect.At the same time,this paper provides a new idea for the application of liquid metal in the field of flexible electronic skin,which has important research significance for the development of flexible electronic skin with high thermal conductivity.