American Chemical Society
jp803792c_si_001.pdf (18.03 kB)

Time-Resolved Mapping of Water Diffusion Coefficients in a Working Soft Actuator Device

Download (18.03 kB)
journal contribution
posted on 2008-08-14, 00:00 authored by Leila Naji, John A. Chudek, Richard T. Baker
Diffusion-weighted imaging was employed to spatially map the distribution of the diffusion coefficient of water, D, in bare, water-soaked, Li+-exchanged, cast Nafion and in an ionic polymer−metal composite (IPMC) soft actuator element, prepared from this bare Nafion by impregnation with Pt electrodes. D was evaluated in two orthogonal directions: along one of the long dimensions of the sample (Dx) and through its thickness (Dz). D-maps of the IPMC element were obtained both in the absence of an applied potential and in situ during the application of a 3 V dc potential across the thickness of the sample. In the bare Nafion, D-maps showed uniform values of both Dx and Dz of about 6 × 10−10 m2 s−1. In the IPMC two effects were observed: (i) D at the electroded surfaces of the IPMC was higher than at the center of the sample; (ii) this difference was much greater in Dz than in Dx. Both effects were explained by the influence of the impregnated Pt electrodes on polymer structure. The D-maps in the electrochemical measurements showed high values of D (up to 8 × 10−10 m2 s−1) at the cathode and low values (from 1 × 10−10 m2 s−1) at the anode. This was explained in terms of the effect on the Nafion nanostructure of the forced electro-migration of Li(H2O)x+ species toward the cathode.