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4 April 2007 Modeling of nonlinear effects in pH sensors based on polyelectrolytic hydrogels
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pH-sensitive hydrogels are capable of reversibly converting chemical energy into mechanical energy and therefore they are widely used as sensitive materials for pH sensors. However nonlinear effects such as hysteresis and drift are observed in the swelling behaviour of the polyelectrolytic hydrogels complicating the calibration procedure for the pH sensor and affecting the signal reproducibility. In the present work, in order to realize a pH sensor with a high signal reproducibility and high long-term stable sensor sensitivity, the complicated kinetics of gel swelling/deswelling processes is analysed and the origin of the hysteresis nonlinearities is elucidated. It is found that the long-time drift in the sensor characteristic is caused by the drift of hydrated ions and water into the gel or out of the gel in dependence on the pH range of the solution and on the chemical reactions which occur in the gel during the swelling or shrinking processes. The rate of the water drift is determined by the change rate of the concentration of ionized groups which increase the gel hydrophilicity and consequently the gel swelling.
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Margarita Guenther, Gerald Gerlach, and Thomas Wallmersperger "Modeling of nonlinear effects in pH sensors based on polyelectrolytic hydrogels", Proc. SPIE 6524, Electroactive Polymer Actuators and Devices (EAPAD) 2007, 652417 (4 April 2007);

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