Time-resolved mapping of water diffusion coefficients in a working soft actuator device.

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 (D x ) and through its thickness (D z ). 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 D x and D z of about 6 x 10 -10 m 2 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 D z than in D x . 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 x 10 -10 m 2 s -1 ) at the cathode and low values (from 1 x 10 -10 m 2 s -1 ) at the anode. This was explained in terms of the effect on the Nafion nanostructure of the forced electro-migration of Li(H 2 O) x + species toward the cathode.