Hydrogel Sensors for Process Monitoring

Abstract

For the direct measurement of chemical concentrations of substances in process liquids, sensors need to be fast and reliable. We investigated the usability of hydrogels as sensitive coating materials for piezo-electric thickness shear mode resonators. Hydrogels are cross-linked polymer networks that show well-defined shifts of their degree of swelling upon changes of environmental parameters such as ionic concentrations, concentrations of organic solvents or temperature. These changes of gel properties are then transferred into an electrical signal. The novel sensor solution exhibits response times of only few seconds and matches the reliability of innovative process measuring technology. A method for its application specific adaption is presented. It is based on optimizing the interrelation of the sensor structure, the manufacturing technology for the hydrogel layer, and the processing of the measured data. The performance of the method is illustrated with the example of a PVA/PAAhydrogel coated sensor which monitors the concentration of a cleaner used in surface technology. The developed measurement device for this application was approved with a measurement error of less than 5 %.