Measurement of In-Plane Thermal Diffusivity of Polymer Films in Air Using Laser Periodic Heating Method

Abstract

The laser periodic heating method is widely used to measure the thermal diffusivity of various thin films. In this technique, surface temperature responses are monitored using either an infrared (IR) camera or a thermocouple (TC) detector. Under air pressure, the impact of air heat loss on these two measurement methods warrants further examination. In this study, we measured the in-plane thermal diffusivity of a polyethylene terephthalate (PET) film under air pressure using both a non-research-grade IR camera and a microscale TC. Results indicate that air heat loss significantly influenced the TC measurements, yielding an abnormally high thermal diffusivity. Comparatively, the thermal diffusivity measured by the IR camera decreased slightly as modulation frequency increased from 0.1 Hz to 1 Hz. When the thermal diffusion length was approximately three times the film thickness, the diffusivity values from the IR camera closely matched those obtained under vacuum, indicating that the non-contact IR method can effectively suppress the impact of air heat loss.