A novel impedance sensor design for measuring the distribution and transport of fluids at the interface

Given the deleterious effects of fluids on adhesion, it is of great interest to know the transport rate and concentration of fluid at an adhesive interface. Utilizing constant frequency interfacial impedance spectroscopy (IIS) and a novel interdigitated electrode sensor design, changes in the concentration of absorbed fluid near the interface as a function of exposure time were correlated to the measured capacitance. These novel IIS sensors measure the impedance of mapped areas of the sensor defined with respect to the free edge of the coating. Consequently, these sensors can be used to measure the distribution and transport of fluids at the interface. We report results obtained for the absorption of acetone into a pressure sensitive adhesive tape with an aluminum foil backing bonded to the sensor. Because the backing is impermeable, diffusion was confined parallel to the bond plane. We demonstrate that the IIS technique is capable of detecting changes in the relative concentration of a fluid diffusing into an adhesive joint with respect to the exposed free edge of the sensor as a function of exposure time.