Online monitoring of the curing of adhesives with a miniaturised interdigital sensor using impedance spectroscopy

Monitoring adhesives during manufacturing and their lifetime has become increasingly important due to the variety of materials and applications. Impedance spectroscopy is a suitable method for online monitoring of the curing process. We present a miniaturised interdigital structure to monitor the curing process of the adhesives using impedance spectroscopy. Compared to other sensors, our sensor is ultrathin, so that it disappears in the adhesive joint. Therefore, it can remain in the joint and be used for lifetime monitoring. In addition it is suitable for thin adhesive layers due to its fine grid. We demonstrate that the impedance of the sensor embedded in the adhesive gives insight into the curing mechanisms. Therefore monitoring of a dispersion and an epoxy is shown. In addition, the curing cycles can be reliably controlled using this monitoring method. The permittivity of the adhesives is extracted from the impedance measurements, applying analytical models of the electrical field of the interdigital structure.