Electrolyte diodes and hydrogels: Determination of concentration andpKvalue of fixed acidic groups in a weakly charged hydrogel

Abstract

Current-voltage (CV) characteristics of polyvinyl alcohol (PVA)-glutardialdehyde hydrogel cylinders were measured in aqueous KCl solutions. To this end a new special apparatus was constructed where the gel cylinder connects two electrolyte reservoirs. The measured quantities are the electric current flowing through the gel and the potential difference between the two reservoirs. Concentration polarization near the gel-liquid interfaces is decreased considerably by applying an intense mechanical stirring in both reservoirs. Under these conditions below 1 V concentration polarization is negligible, and the CV curves are nearly straight lines. It was found that the gel applied here is a weakly charged anionic hydrogel. Concentration of fixed anions was determined from the slope of these lines measured in 0.001 and 0.01 molar KCl solutions. Fixed anion concentration of the same piece of gel was measured also with a different method, when the gel was used in an acid-base diode. In this case one reservoir contained 0.1 molar HCl, and the other 0.1 molar KOH. From the results of the two measurements, the concentration (4.45 x 10(-3) M) and the pK value (4.03) of the fixed acid groups responsible for the anionic character of the gel was calculated. The pK value is compatible with fixed carboxylic acid groups contaminating the PVA gel. Furthermore, concentration polarization phenomena in the boundary layers nearby the gel were studied in 0.001 M KCl solutions, measuring the diodelike CV characteristic of a gel cylinder, when stirring was applied only at one side of the gel. Boundary layers facing the cathode or the anode responded in a different way to stirring. The difference cannot be explained completely with the hypothesis of electroconvection suggested previously.

Integration of Hydrogels with Hard and Soft Microstructures

“…[60][61][62] The hydrogel was synthesized as a cylinder that was inserted into a narrow, 0.7 mm diameter bore through a polyvinylchloride (PVC) disk of thickness 3.2 mm. This disk separated the two electrolyte chambers.…”

Adaptive moving mesh algorithm based on local reaction rate

“…Unfortunately we were not able to reach convergence, if the above discussed full system of differential equations is applied (mass balance equations are set up for each species). For stationary investigations the concentration of the fixed anions can be calculated from the equilibrium, where denotes the estimated total concentration of the fixed groups ( Iván et al, 2004 ), therefore the mass-balance equation is used for the mobile ions ( , , , ) only.…”

Capacitive Ionic Current Measurement in a Polymer-Electrolyte Transistor

“…This creates a dielectric layer over the electrode that is nonuniform over the length of the electrode. The polymer to be used is polyvinyl alcohol (PVA) with a glutaraldehyde crosslinker [2].…”