Comparison of electrochemical- and nuclear magnetic resonance spectroscopy methods for determination of diffusion coefficients in gel environment

Two advanced methods: one based on chronoamperometry in solution of any ionic strength and the second one related to nuclear magnetic resonance spectroscopy (NMR) were used to determine the difusion coefficients of the selected species in complex polymeric gels. For this purpose a series of polyacrylamide gels with different content of monomer and crosslinker were synthesized. Rod shaped samples of polymers were swelled with solutions of either 1,1'-ferrocenedimethanol, or 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt or cis-dichlorobis(2,2′-bipyridine) ruthenium(II) in D2O. These compounds were good probes for examining the transport in the gel medium due to electrochemical reaction and well-defined signals in 1H NMR spectroscopy. The values of diffusion coefficients obtained by both methods were compared and the limitations of the methods were discussed. The measurements were done at three temperatures: 25, 35 and 45 °C.