| Polyimide?PI?is a polymer material with excellent comprehensive properties,which has high research value in microelectronic packaging materials.However,the thermal conductivity of the conventional PI film is only about 0.16 W/?m·K?,which cannot be dissipated in time during work,which has a serious negative impact on the service life of the material and the safety of the equipment.Therefore,improving the thermal conductivity of PI has attracted widespread attention while maintaining the excellent performance of PI itself.Silver nanowires?AgNWs?have excellent thermal conductivity and can effectively improve the thermal conductivity of PI as a thermally conductive filler.The problem is that AgNWs acts as a conductor,which greatly reduces the insulation performance of PI,and AgNWs tend to agglomerate and has poor dispersion in the PI matrix.In this paper,a new type of PI composite film with good thermal conductivity was prepared by surface coating of AgNWs and using electrospinning technology to solve the above problems.In this paper,AgNWs were prepared by polyol method,and the surface coating of AgNWs was carried out by sol-gel method to prepare AgNWs@SiO2with core-shell structure.AgNWs/PAA and AgNWs@SiO2/PAA composite glues werepreparedbyin-situpolymerization,andAgNWs/PAAand AgNWs@SiO2/PAA electrospun fiber membranes were obtained by electrospinning,respectively.After the film is glued,the electrospun silver nanowire/polyimide?E-AgNWs/PI?and electrospun silica coated silver nanowire/polyimide?E-AgNWs@SiO2/PI?are prepared by thermal imidization.A part of AgNWs/PAA composite glue was used to prepare AgNWs/PI composite film by thermal imidization after laminating.The characteristics of AgNWs,AgNWs@SiO2 and AgNWs@SiO2/PAA were characterized by X-ray diffraction?XRD?,scanning electron microscopy?SEM?and transmission electron microscopy?TEM?.The thermal conductivity,thermal weight loss and thermal conductivity of the composite films were investigated.The electrical constant,dielectric loss,and volume resistivity were tested and analyzed.The results show that AgNWs with a purity of about 20?m,a diameter of about 80 nm,and an average aspect ratio of about 250 are successfully prepared.On the surface of AgNWs,a layer of SiO2 with a thickness of about 20 nm was successfully coated,and the coating effect was obvious.AgNWs@SiO2/PAA electrospun fiber filaments have a diameter of about 400 nm.AgNWs@SiO2 was successfully incorporated into the fiber filaments and aligned along the fiber filaments.In this way,the thermal conductivity network of the PI composite film was formed.With the increase of filler content,the thermal conductivity of AgNWs/PI,E-AgNWs/PI and E-AgNWs@SiO2/PI composite films showed a trend of increasing gradually.When the filler mass fraction was 25%,the thermal conductivity of AgNWs/PI,E-AgNWs/PI and E-AgNWs@SiO2/PI are 2.75W/?m·K?,2.92 W/?m·K?,and 2.8 W/?m·K?,respectively 17.2,18.2,and 17.5 times the PI.The thermal decomposition temperatures of AgNWs/PI,E-AgNWs/PI,and E-AgNWs@SiO2/PI were 573.1?,596.2?,and 583.9?,respectively.The thermal decomposition temperature of E-AgNWs@SiO2/PI was 16.1?higher than that of unmodified PI.When the filler content is the same,the dielectric constant and dielectric loss of E-AgNWs@SiO2/PI are lower than the dielectric constant and dielectric loss of AgNWs/PI,E-AgNWs/PI.When the test frequency is 100 Hz and the mass fraction of AgNWs@SiO2 is 25%,the dielectric constant and dielectric loss of E-AgNWs@SiO2/PI are 4.96 and 0.0116,respectively.Among the three composite films prepared,the volume resistivity of E-AgNWs@SiO2/PI was optimal and was 1.79×1013?·m. |
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