pH sensors based on polyelectrolytic hydrogels

The purpose of chemical sensors consists in converting chemical input data into output signals suitable for electronic measuring processes. The sensors are characterized by a material-recognizing element and a transducer. The transducer converts the non-electric measuring value into an electrical signal. Hydrogels are cross-linked polymers which swell in solvents to appreciable extent. The amount of solvent uptake depends on the polymer structure and can be made responsive to environmental factors, such as solvent composition, pH value, temperature, electrical voltage etc. Hydrogels are capable to convert reversibly chemical energy into mechanical energy making them interesting as sensitive material for appropriate sensors. In the present work, in order to realize pH sensors, poly(vinyl alcohol)/poly(acrylic acid) (PVA/PAA) blend hydrogels with a pH value dependent swelling behavior were used as chemo-mechanical transducers. The influence of the kinetics of the induced charge (in the swollen polyelectrolyte gel) on the response time, the signal value and the sensitivity of the proposed pH sensors were investigated and the measurement conditions necessary for high signal reproducibility were determined.