Liquid Interface for Accurate Intrinsic Thermal Conductivity Measurements of Polymer Films Using the Transient Plane Source Method

Abstract Characterizing the thermal properties of micrometer-thin films is crucial for optimizing their performance in a broad range of engineering applications. The transient plane source (TPS) method is widely used for measuring bulk materials, but its direct application to thin films fails due to thermal contact resistance. By comparing TPS measurements across films of varying thicknesses, it is possible to compensate for the influence of thermal contact resistance and extract the intrinsic thermal conductivity. However, this method still suffers from significant errors, e.g., as high as 26% in case of polyolefin films, since its underlying assumption—thermal contact resistance remains identical for films of different thickness—does not always hold true for actual measurements. Here, we demonstrate that these errors can be effectively reduced to 4% by incorporating a liquid thermal interface material. Specifically, the intrinsic cross-plane thermal conductivities of high-density polyethylene, isotactic polypropylene, and regioregular poly(3-hexylthiophene) films are determined to be 0.450, 0.277, and 0.296 W/(m⋅K), respectively. Moreover, these measurements exhibit remarkable reproducibility, achieving a standard deviation below 0.02 W/(m⋅K) when the film thickness is sufficiently varied. Furthermore, potential systematic errors are investigated through a comprehensive numerical study. Overall, this study offers critical insights that considerably extend the applicability of TPS measurements for thin films.