Transient Heat Transfer Study Of Flexible Devices

In recent years,with the demand for mobile and portable flexible devices,people have great interest in the development of flexible devices in various fields,including energy storage,biomedicine,bionics and so on.And the development and innovation of technologies related to flexible devices are bound to change the way we live.However,there are few reports on the transient heat transfer of flexible devices,and the problem of poor thermal conductivity of flexible devices has been hindering the further development of flexible devices towards lightness,miniaturization and high integration.In this work,two solutions are proposed to solve the above problems: one is to reduce the interface thermal resistance of flexible devices,and the other is to improve the local thermal conductivity of the devices by filling high heat conduction materials in the microchannel.According to the principle of the first method,we transfered UV-irradiated polydimethylsiloxane(PDMS)and polyimide(PI)onto a silicon substrate to create a silicon-oxygen bond(Si-O)at the interface,so as to reduc the interfacial thermal resistance of the flexible device and improve the overall thermal conductivity.According to the principle of the second method,we fabricated microchannels inside PI and PDMS and fill them with graphene and gallium-indium alloy(Ga-In),respectively,so that the local thermal conductivity of the flexible devices can be greatly improved.In this work,we first measured the thermal diffusion curves of PDMS/Si and PI/Si under different UV illumination durations and different areas of PI composite films by NanoTR system.Then we used ANSYS to establish three-layer and double-layer onedimensional thermal diffusion model,and simulated the thermal diffusion curves of PDMS/Si and PI/Si under different UV illumination durations and different areas of PI composite films.Subsequently,the corresponding thermal conductivity was obtained by comparing the simulation with the actual measured thermal diffusion curves.Then,among many PDMS-PDMS bonding methods,we chose the most efficient and simple method of partial curing and different curing rates to fabricate the microchannels inside PDMS,and used the evacuation method to fill the Ga-In alloy into the microchannels.Finally,thermocouples were used to measure the temperatures of different regions of the PDMS composite film surface under heating.The overall thermal conductivity of flexible devices can be improved by about two times by using the first method,but the first method is more widely used;the thermal conductivity of flexible devices can be improved by about ten times by using the second method,but the improvement is localized.Therefore,when using these two methods,we should use them separately or comprehensively according to the situation.