The Construction Of Novel Filler Networks And Thermal Performance Of Their Polymer Composites

With the development of electronic technology,people begin to require higher portability and functionality of electronics,which promotes electronic devices toward miniaturization,integration and multi-function.Meanwhile,the sharp increase of operating power in electronics has caused huge heat dissipation pressure.Unreasonable operating temperature will affect the working life and reliability of the electronics for a long time,and even causes serious thermal failures.The intrinsic thermal conductivity of the polymer matrix is very low.Although the addition of fillers can improve the thermal conductivity of polymer,it is difficult to form an effective heat-transfer network with the huge thermal resistence issues.Therefore,constructing an efficient thermally conductive filler network for high-performance thermally conductive composites has become a hotpoint.In this work,we design and construct a novel thermal conductivity network based on multi-dimensional micro/nano thermal fillers for application of high-performance thermally conductive composites.The influence of the preparation process on the morphology,structure and mechanical strength of the filler network was studied.The relationship between filler network and thermal conductivity,heat storage capacity and interface heat transfer properties of the prepared composite was analyzed.The main research contents are as follows:1.Using graphene oxide(GO)as a dispersant and reinforcing material,a novel three-dimensional boron nitride nanotube(BNNT)aerogel was prepared.With the assistance of GO nanosheet,the strongly hydrophobic but highly thermally conductive BNNTs were stably dispersed in water.The BNNTs aerogel reinforced with rGO(reduced graphene)was prepared by hydrothermal reduction and freeze-drying methods.Its honeycomb-like structure makes it have excellent mechanical properties(such as high elasticity,fatigue resistance),large specific surface area and low density(<16.3 mg/cm3).The interaction between BNNT and rGO in the aerogel was also analyzed.This three-dimensional(3D)bulk material based on two types of highly thermal conductive fillers,BNNT and rGO,can be directly used as a filler network for high-performance thermally conductive composites.2.The prepared BNNTs/rGO aerogel was used as a 3D thermal conductive network and support material for preparation of phase change thermally conductive composite with polyethylene glycol(PEG).Due to the porous structure of BNNTs/rGO aerogel and the internal hydrophobicity,the composite exhibits excellent shape stability(maintained at 100 ? for 10 min)and stable phase change temperature.The data shows that the heat storage capacity and thermal conductivity of the BNNTs/rGO/PEG composite is better than those of pure PEG and rGO/PEG composite,reaching a high value of phase change enthalpy(195.6 J/g)and thermal conductivity enhancement(32.2%)at only 1.5 wt%filler content.This high-performance phase change thermal conductivity composite has great potential in thermal management.3.In traditional composite materials,the large gap and the high interface thermal resistance between fillers make it difficult to form a efficient thermal network in the matrix.In this work,based on the interface engineering of silver nanoparticles(AgNPs),a modified alumina microsphere(AgNPs/Al2O3)filler was prepared via a simple hydrothermal reduction and freeze-drying method.In the matrix,AgNPs act as a bridge between Al2O3 microspheres,improve the interfacial thermal resistance between the fillers,and build a phonon-electron coupled dual heat transfer network.The influence of the preparation process on the morphology,size and dispersion of the filler was discussed.It's proved that the thermal conductivity of the AgNPs/A1203/silicone oil composite reaches 1.58 W/mK(higher than that of Al2O3 microsphere filler),and has suitable fluidity.This research provides new ideas and a certain preliminary basis for the future industrialization of electronic device thermal management materials,especially for thermal interface materials.