Studies of Transport Phenomena and Electrostatic Interactions in Polyacrylate Gels

Wojciech Hyk and Malgorzata Ciszkowska*

Department of Chemistry, Brooklyn College, The City University of New York, Brooklyn, New York 11210-2889

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.