Experimental Study On Modulating The Thermal Conductivity Of The Poly(Vinylidene Fluoride) Film

With the development of highly integrated electronic devices and increasing power density,heat dissipation has become a severe challenge.Polymer materials have excellent mechanical properties,dielectric properties,and chemical properties.They are widely used in traditional electronic equipment and emerging flexible electronic devices.However,the lower thermal conductivity limits the application of polymers.Therefore,it is of great significance to study the method to modulate the thermal conductivity of polymer materials.The accuracy of thermal measurement guarantees the research on thermal materials and thermal management.In recent years,micro-nano scale thermal measurement methods that suit different materials have been developed.This work uses the 3-Omega method to measure the thermal conductivity,and in order to measure the thermal conductivity of the polymer film more accurately,the measurement platform and method were improved according to the heat transfer model.We also measured the thermal conductivity of silicon dioxide film and the thermal boundary resistance of silicon carbide/silicon dioxide,so as to verify the accuracy of the measurement platform and explore the thermal boundary resistance problem in heat transfer.In this study,PVDF composite films were prepared by filling silver nanowires.Based on the bidirectional asymmetric thermal conductivity model,the thermal conductivity of PVDF composite films filled with different content of silver nanowires was measured,and the influence of silver nanowire content on the thermal conductivity of polymer composites was analyzed.The result showed that as the content of silver nanowires increases to 10%,the thermal conductivity of PVDF composite films gradually increased to 5.2 times the original,but compared with the high thermal conductivity of the filler,the improvement is limited.The main limiting factor is the thermal boundary resistance between the filler and the polymer matrix.A new way to modulate thermal conductivity was studied,which is to increase the intrinsic thermal conductivity of polymers through electric field polarization.PVDF copolymer films with high crystallinity was prepared,and the films were completely polarized by a DC electric field exceeding its coercive electric field.Through measurement,we found that the thermal conductivity after polarization increased by 53%.By analyzing its electric hysteresis loop,the relationship between electric field strength and polarization is discussed.The mechanism of the increase in thermal conductivity caused by polarization was analyzed through morphology.The electric field polarization makes the polymer molecular chains arranged in an orderly manner,reduces the effect of phonon scattering and thus improves the thermal conductivity of the polymer.In summary,this work has studied the methods of modulating the thermal conductivity of polymer materials by filling and electric field polarization,which is valuable for the application of polymer materials in thermal management.