Thermal Effusivity as a Non-Destructive Method to Characterize Thin Films

摘要

Mathis Instruments Thermal Conductivity Probe (TC Probe) offers a potential non-destructive method for looking at changes in a 3- to 5-mil polymer coating. The TC Probe is based on a modified hot wire technique, operating under constant current conditions. The temperature of the heating element is monitored during sample testing, and changes in the temperature at the interface between the probe and sample surface, over the testing time, are continually measured. Because the coatings are thin, the potential for heat transfer into the substrate is a potential problem. Care must be taken to assure that the analysis time is set to eliminate or at least minimize thermal penetration. The effusivity is a function of the density, heat capacity, and thermal conductivity. As a polymer coating degrades as a result of environmental exposure, the structure of the polymer changes. Chain scission reduces molecular weight and shorter polymer chains become more mobile. Resulting changes in the polymer density and thermal conductivity can be observed using the TC Probe.