| Modern integrated electronic devices generate a lot of heat during operation,and heat accumulation seriously affects the operational stability and reliability of electronic equipments.Polymer-based thermal interface materials(TIMs)are important means to solve the heat dissipation problem of electronic devices.However,current polymer TIMs suffer from poor heat resistance,not being able to self-healing mechanical damage or low repair efficiency,and poor adhesion properties,making them unable to meet the needs of high temperature electronics and smart electronics.The research and preparation of high-temperature-resistant epoxy resin-based TIMs can meet the requirements of high-temperature electronics for heat resistance and adhesive stability,while self-healing TIMs can solve the environmental pollution and resource waste caused by a large number of discarded electronic products.Therefore,the development of high temperature-resistant and self-healing epoxy-based TIMs is of great practical significance.In this dissertation,the preparation of two-dimensional boron nitride(BN)/epoxy TIMs and their thermal conductivity and self-healing mechanism are studied.The relationship between structure and properties is deeply and systematically studied,the thermal conductivity and self-healing mechanism of thermally conductive composites are elucidated,and their applications in the field of electronics are explored.Firstly,a BN/epoxy thermally conductive composites with high glass transition temperature(T_g),good processability and excellent bonding properties were prepared by using high heat-resistant epoxy resin as the matrix and functionalized BN as the thermally conductive filler.The results show that the functionalized BN improves the thermal stability and dimensional stability of the epoxy resin.When the content of BN is 30 wt.%,the T_g of the composite can be as high as 275°C.The coefficient of linear expansion is 15%lower than that of pure epoxy resin.The good dispersion of functionalized BN in the matrix is observed.The thermal conductivity of the composites with 30 wt.%BN is 1 34%higher than that of pure epoxy resin at 150°C,showing excellent high temperature thermal conductivity.In addition,the high-temperature thermally conductive composite exhibits excellent process performance and adhesive properties,with shear strengths of 14.2,11.78,and 11.66 MPa at room temperature,120°C,and 150°C,respectively.Importantly,the shear strength when used for silicon wafer bonding is as high as 81.34 MPa.To further improve the manufacturability of the TIMs,thermoplastic phenolic resins(PHOs)were used as tougheners and film formers for epoxy resin to prepare film TIMs with good process properties and excellent fatigue resistance.The durability and fatigue resistance of the film TIMs were investigated.The results show that the PHO can improve the film formation of the epoxy resin.When the amount of PHO is 30 phr and the amount of n BN is 30 wt.%,film TIMs with excellent process performance and mechanical properties can be obtained.Its T_greaches 215°C,and the thermal conductivity is 209.5%higher than that of without n BN.The single-lap shear strength of the film TIMs is 12.82 MPa at 150°C,demonstrating excellent high-temperature adhesive properties.When used for bonding of different materials in the electronic field,the horizontal shear strength is higher than 50 MPa,showing excellent bonding performance and bonding stability.In addition,the film TIMs exhibited excellent thermal aging resistance,hygrothermal aging resistance,and medium resistance,and the shear strength retention rate reached more than 90%after exposuring to complex environments.The shear strength retention rate is as high as 96.9%after 1 million fatigue cycles,exhibiting excellent fatigue resistance.The excellent durability and fatigue resistance are mainly due to the excellent bulk strength of TIMs and good interfacial bonding with the bonded materials.Secondly,to solve the problem of non-recyclable and irreparable of TIMs,epoxy containing flexible Si-O-Si segments are synthesized.Then cross-linked elastomers with self-healing ability are fabricated using silicone epoxy molecules,amino curing agents with dynamic chemical bonds and octaglycidyl ether-based polysilsesquioxane(POSS)as modifiers.The cross-linking characteristics and mechanical properties of elastomers are studied,the relationship between dynamic bond exchange and stress relaxation and self-healing in cross-linked elastomers is analyzed.The results show that the cross-linked elastomer can simultaneously possess good tensile strength,stretchability and excellent self-healing efficiency.The tensile strength of the elastomer can reach up to 8.43 MPa,and the self-healing efficiency can reach 97.86%.The increase of crosslink density caused by the increase of POSS content lead to the increase of the activation energy of dynamic S-S bond exchange reaction.The introduction of thermally conductive filler fBNNS improves the thermal conductivity and tensile strength of the self-healing composite.When the laoding of fBNNS is 66 wt.%,the thermal conductivity of the composite reaches 1.41 W/(m·K),the tensile strength can reach 13.74 MPa,and the healing efficiency reaches more than 91%.The healing efficiency of thermal conductivity is as high as 99.3%after 6 healing cycles.The high thermal conductivity and high healing efficiency originate from the good fBNNS thermal conduction pathway inside the composite and the dynamic S-S bond exchange in the polymer matrix,respectively.It exhibits good wettability and adhesion to different substrates and wafers,and its intrinsic shear strength can reach 5.5 MPa,and the shear impact strength is 5.66 kJ/m~2.Finally,to prepare flexible room-temperature self-healing TIMs,a room temperature self-healing flexible elastomer with excellent performance was synthesized by adjusting the molecular structure of epoxy silicone and the composition of amino curing agent.Its tensile strength is 0.455 MPa,while the elongation at break exceeds 880%.The elongation at break after self-healing for12 h at room temperature is 860%,and the self-healing efficiency of tensile strength is 86%.After the addition ofBNNS-OH,the prepared self-healing flexible thermally conductive composites still have good flexibility and room-temperature self-healing properties.When the BNNS-OH content is 60 wt.%,the thermal conductivity can reach 0.97 W/(m·K),the tensile strength healing efficiency at room temperature can reach more than 70%,and the self-healing efficiency of thermal conductivity is higher than 95%after healing at room temperature,this excellent self-healing property originates from the hydrogen bonding and molecular chain motion of the flexible polymer matrix.The shear strength when using the TIMs to bond flexible PI films is 3.1 MPa,and the adhesion to PI/Cu and PI/Au flexible/rigid components are 49.7 N/cm~2 and 41.4 N/cm~2,respectively.The good adhesive properties and flexibility adaptability to flexible substrate materials make it have good application prospects in the field of flexible electronic devices. |
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