Measuring in-plane thermal conductivity of polymers using a membrane-based modified Angstrom method

It is essential to characterize the in-plane thermal conductivity of polymer materials accurately in many applications. Although there exist a few appropriate steady and transient characterizing techniques to accomplish the task, the methods often require complicated micro-fabrication, calibration or additional property determination procedures (e.g., some transient approaches only yield in-plane thermal diffusivity. Thus the volumetric heat capacity C-V needs to be measured independently in order to calculate the thermal conductivity.). In this work, we have employed a membrane-based modified Angstrom (MMA) method to directly measure the in-plane thermal conductivity of several micrometer thick polymer materials. The suspended polymer membranes are patterned with double metal strips made by simple shadow mask deposition. The metal strips are used to create periodical Joule heating and to perform temperature sensing. The measurement of the in-plane thermal conductivity is carried out without requiring the knowledge of the C-V value. The accuracy of the approach has been verified by numerical calculations. The measured thermal conductivities for poly(tetrafluoroethylene) (PTFE) and polyimide (PI) samples were found to be comparable with available literature values. Since the in-plane thermal diffusivity of the membrane can be obtained simultaneously, its reliability was also evaluated. Moreover, the possibilities of applying the MMA method to other materials (e.g., high thermal conductivity membrane) have been discussed. This study suggests that the MMA method coupled with shadow-masking technique may offer a straightforward and reliable way of measuring the in-plane thermal conductivity of several micrometer thick free-standing membranes.