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

摘要

To study transport phenomena and electrostatic interactions in negatively charged poly(N-isopropylacryla crylamide-co-acrylic acid) hydrogels, NIPA-AA, electroanalytical experiments with two positively charged probes, ferrocenylmethyltrimethylammonium, FcTMA(+), and hexaammineruthenium(III), Ru(NH3)6(3+), cations were performed, and the results compared with those for an uncharged electroactive probe, 1,1'-ferrocenedimethanol, Fc(MeOH)2. Steady-state voltammetry and chronoamperometry at platinum disk microelectrodes were used to determine diffusion coefficients of those probes. For temperatures below the volume phase transition of a gel, there are not significant differences in the transport behavior of cationic and uncharged probes. After the volume phase transition occurs and the gel collapses, the diffusion coefficients of all probes decrease, the change in diffusion coefficient is more pronounced for cationic probes than for a neutral probe, and depends on the charge of the cationic probe. Changes in concentration of cationic species in collapsed NIPA- AA gels were detected as a result of the volume phase transition.