Infrared Microscopy Enhanced Ångström's Method for Thermal Diffusivity of Polymer Monofilaments and Films

Ångström's method has been used to quantify thermal diffusivity of materials for over 150 years via measurement of thermal waves propagating through a long, thin sample. However, the traditional Ångström's method has some limitations. First, the traditional method is insensitive to potential variability in thermal diffusivity along the length of a sample because only two sensors are used. Second, conventional contact-based sensing techniques such as thermocouples limit the method to samples that are sufficiently large so as to be unaffected by heat loss through the sensors. Here, we develop and validate the infrared microscopy enhanced Ångström's method that overcomes these limitations and enables measurement of microscale samples. This work demonstrates the accuracy and applicability of the technique through measurement of several commercially available polymer monofilaments and films and comparison of the data to published values. This method is particularly robust to uncertainty in emissivity making it attractive for characterization of semitransparent samples.