Studies of Transport Phenomena and Electrostatic Interactions in Polyacrylate Gels

Abstract

The transport of uncharged electroactive probes, 1,1‘-ferrocenedimethanol and 4-hydroxy-TEMPO, and electroactive cations, Tl+, was studied in polyacrylate hydrogels using steady-state voltammetry at platinum and mercury film microelectrodes. It was found that, for concentrations of polymer less than 1.5%, the diffusion coefficient of uncharged probes does not differ significantly from that observed in aqueous solutions without a polymeric network. For the probe cation, strong electrostatic interactions were observed between Tl+ and anionic polymeric networks; those interactions resulted in a significant decrease in the diffusivity of Tl+ cations. Experimental data for Tl+ transport in sodium polyacrylate gels were compared with predictions of Manning's theory for polyelectrolyte solutions. Electrostatic interactions between Tl+ and anionic polyacrylate three-dimensional gel network were found stronger than those predicted for solutions of an equivalent polyelectrolyte. Electrostatic effects for gels were found even stronger when Tl+ cations served as counterions in thallium polyacrylate gels; the transport of Tl+ counterion was more suppressed in those gels than for a Tl+ probe in sodium polyacrylate, especially for small values of charge separation distance in polymeric units. The mobility of a counterion forming a gel, Na+, was also studied using conductance measurements, and appropriate expressions for conductivity as a function of poly(acrylic acid) neutralization degree were developed based on Manning's line charge model. Experimental conductivity data for Na+ agreed with predictions of the model.

Measurement of Donnan potentials in gels by in situ microelectrode voltammetry

“…In cases where the diffusion coefficient (D Cd-gel /D Cd-sol ) ratio deviates significantly from 1, it can be estimated by the methods previously outlined in the literature [41] by independently determining the diffusion coefficient of Cd in the gel phase. The current work, however, assumes that this ratio is close to unity.…”

“…Tercier and Buffle [39] developed an antifouling agarose gel layer covered, Hg-plated, Ir-based microelectrode that minimized fouling associated with in situ measurements in natural waters. Application of Ag-amalgam electrodes for the study of polymeric gels has also been exploited by Ciszkowska and co-workers [40][41][42][43][44][45]. Together with Pt-microelectrodes, transport of the uncharged electroactive probes, 1,1 0 -ferrocenedimethanol and 4-hydroxy-TEMPO (2,2,6,6-tetramethyl-1-pipperidinyloxy), and the electroactive cation, Tl + , were examined in polyacrylate hydrogels using a steady-state voltammetric approach.…”

Diffusiophoretic mobility of charged porous spheres in electrolyte gradients

“…We assume that the values of η, f, ε, D ± , and ω are constant. For counterions in polyelectrolyte networks, a theory for the ionic self-diffusion [24] and some experimental data [25] predict that the parameter ω (which is the normalized diffusion coefficient of the small ions in the porous structure) can have a value as low as 0.25-0.31. Here, ω is taken to be the same for both ionic species.…”

Transport of Ions and Electrostatic Interactions in Thermoresponsive Poly(N-Isopropylacrylamide-co-acrylic acid) Hydrogels: Electroanalytical Studies

“…Many experimental techniques have been used to study transport in polymeric gels, including light scattering spectroscopy [17][18][19], NMR spectroscopy [20][21][22], radioactive tracer methods [23], as well as electroanalytical techniques, steady-state voltammetry [24] and chronoamperometry [25]. We have shown the effectiveness of steady-state voltammetry in transport studies in NIPA-AA thermoresponsive gels [8,15,16].…”