Mass Transport Investigated with the Electrochemical and Electrogravimetric Impedance Techniques. 2. Anion and Water Transport in PMPy and PPy Films

Characterization of conjugated polymer actuation under cerebral physiological conditions

Conjugated polymer actuators have potential use in implantable neural interface devices for modulating the position of electrode sites within brain tissue or guiding insertion of neural probes along curved trajectories. The actuation of polypyrrole (PPy) doped with dodecylbenzenesulfonate (DBS) is characterized to ascertain whether it can be employed in the cerebral environment. Microfabricated bilayer beams are electrochemically cycled at either 22 or 37 °C in aqueous NaDBS or in artificial cerebrospinal fluid (aCSF). Nearly all the ions in aCSF are exchanged into the PPy-the cations Na(+) , K(+) , Mg(2+) , Ca(2+) , as well as the anion PO4 (3-) ; Cl(-) is not present. Nevertheless, deflections in aCSF are comparable to those in NaDBS and they are monotonic with oxidation level: strain increases upon reduction, with no reversal of motion despite the mixture of ionic charges and valences being exchanged. Actuation depends on temperature. Upon warming, the cyclic voltammograms show additional peaks and an increase of 70% in the consumed charge. Bending is, however, much less affected: strain increases somewhat (6%-13%) but remains monotonic, and deflections shift (up to 20%). These results show how the actuation environment must be taken into account, and demonstrate proof of concept for actuated implantable neural interfaces.

Nanosieving of anions and cavity-size-dependent association of cyclodextrins on a 1-adamantanethiol self-assembled monolayer

In this paper, we studied charge transfer through a self-assembled monolayer (SAM) of 1-adamantanethiol on gold. Charge transfer through the 1-adamantanethiol SAM depended on the type of anion present when [Fe(CN)6]3- was used as a redox probe. The sluggish charge transfer process was monitored by cyclic voltammetry using the relatively large and hydrophobic perchlorate and hexafluorophosphate ions as the supporting electrolyte. In contrast, the charge transfer kinetics were nearly identical to those measured on bare gold with chloride, sulfate, and nitrate ions as the supporting electrolyte. We investigated the adsorption of alpha- and beta-cyclodextrin on the 1-adamantanethiol SAM via a host-guest interaction. The 1-adamantanethiol SAM could not bind beta-cyclodextrin via a host-guest interaction, probably due to the proximity of neighboring adamantine molecules on the surface. Immobilization of alpha-cyclodextrin by formation of an exterior complex with the SAM suppressed charge transfer. The adsorbed alpha-cyclodextrin was quantified using faradaic impedance experiments. The obtained adsorption isotherm was in good agreement with the Langmuir isotherm with a binding constant of 39.53 M(-1).

Kinetic Aspects of Ion Exchange in KhFek[Fe(CN)6]l·mH2O Compounds: A Combined Electrical and Mass Transfer Functions Approach

The present paper quantifies and develops the kinetic aspects involved in the mechanism of interplay between electron and ions presented elsewhere(1) for K(h)Fe(k)[Fe(CN)(6)](l)*mH(2)O (Prussian Blue) host materials. Accordingly, there are three different electrochemical processes involved in the PB host materials: H(3)O(+), K(+), and H(+) insertion/extraction mechanisms which here were fully kinetically studied by means of the use of combined electronic and mass transfer functions as a tool to separate all the processes. The use of combined electronic and mass transfer functions was very important to validate and confirm the proposed mechanism. This mechanism allows the electrochemical and chemical processes involved in the K(h)Fe(k)[Fe(CN)(6)](l)*mH(2)O host and Prussian Blue derivatives to be understood. In addition, a formalism was also developed to consider superficial oxygen reduction. From the analysis of the kinetic processes involved in the model, it was possible to demonstrate that the processes associated with K(+) and H(+) exchanges are reversible whereas the H(3)O(+) insertion process was shown not to present a reversible pattern. This irreversible pattern is very peculiar and was shown to be related to the catalytic proton reduction reaction. Furthermore, from the model, it was possible to calculate the number density of available sites for each intercalation/deintercalation processes and infer that they are very similar for K(+) and H(+). Hence, the high prominence of the K(+) exchange observed in the voltammetric responses has a kinetic origin and is not related to the amount of sites available for intercalation/deintercalation of the ions.