Application of sensitive hydrogels in chemical and pH sensors

Abstract

In the present work, pH‐sensitive poly(vinyl alcohol)/poly(acrylic acid) (PVA/PAA) blends as well as hydrogels based on poly(N‐isopropylacrylamide) (PNIPAAm), which are sensitive to organic solvent concentration in aqueous solutions, were used in silicon micromachined sensors. A sensitivity of approximately 15 mV/pH was obtained for a pH sensor with a 50 μm thick PVA/PAA hydrogel layer in a pH range above the acid exponent of acrylic acid (pKa=4.7). The output voltage versus pH‐value characteristics and the long‐term signal stability of hydrogel‐based sensors were investigated and the measurement conditions necessary for high signal reproducibility were determined. The influence of the preparation conditions of the hydrogel films on the sensitivity and response time of the chemical and pH sensors is discussed.

Ultra-fine polyelectrolyte fibers from electrospinning of poly(acrylic acid)

“…Due to the dissociation of carboxylic acid groups of PAA the osmotic pressure inside the fibers is higher than that in the surrounding solution, which causes the influx of surrounding solution into the fibers, and thus makes the fibers swell. The repulsion among the partially ionized PAA molecules may also give more room for water molecules to diffuse into the fibers [21].…”

Kinetics of pH Response for Copolymer Films with Dilute Carboxylate Functionality

“…The time constant at lower frequencies is from the polymer/metal interface, and the one at higher frequencies is from the polymer film and corresponds to the combined capacitance and resistance of the polymer film. At |Z| 2 ) (Z R ) 2 + (Z I ) 2 (2) pH 11, the film resistance is still evident from 1 to 40 kHz, representing a small but measurable barrier to ion transfer. While EIS can be used to evaluate the film performance and extract useful properties such as the film resistance and capacitance, each spectrum requires about 10 min to accumulate, precluding a detailed analysis of kinetics on the time scale of several seconds to a few minutes.…”

Binary Zero-Power Sensors: an alternative solution for power-free energy-autonomous sensor systems

“…Hydrogel swelling or shrinking leads to a conversion from chemical into mechanical energy and vice versa generating enormous forces. This behavior enables the usage of hydrogels for sensors and actuators (Gerlach et al 2004Guenther et al 2005;Arndt et al 2000). It can be used favorably for BIZEPS sensors considered here.…”