Ion transport membranes based on conducting polymers

3D Porous Hydrogel/Conducting Polymer Heterogeneous Membranes with Electro-/pH-Modulated Ionic Rectification

Heterogeneous membranes composed of asymmetric structures or compositions have enormous potential in sensors, molecular sieves, and energy devices due to their unique ion transport properties such as ionic current rectification and ion selectivity. So far, heterogeneous membranes with 1D nanopores have been extensively studied. However, asymmetric structures with 3D micro-/nanoscale pore networks have never been investigated. Here, a simple and versatile approach to low-costly fabricate hydrogel/conducting polymer asymmetric heterogeneous membranes with electro-/pH-responsive 3D micro-/nanoscale ion channels is introduced. Due to the asymmetric heterojunctions between positively charged nanoporous polypyrrole (PPy) and negatively charged microscale porous hydrogel poly (acrylamide-co-acrylic acid) (P(AAm-co-AA)), the membrane can rectify ion transmembrane transport in response to both electro- and pH-stimuli. Numerical simulations based on coupled Poisson and Nernst-Plank equations are carried out to explain the ionic rectification mechanisms for the membranes. The membranes are not dependent on elaborately fabricated 1D ion channel substrates and hence can be facilely prepared in a low-cost and large-area way. The hybridization of hydrogel and conducting polymer offers a novel strategy for constructing low-cost, large-area and multifunctional membranes, expanding the tunable ionic rectification properties into macroscopic membranes with micro-/nanoscale pores, which would stimulate practical applications of the membranes.

Biomimetic dual sensing-actuators based on conducting polymers. Galvanostatic theoretical model for actuators sensing temperature

A theoretical model is proposed for the quantitative description of the chronopotentiometric (E-t) responses, under galvanostatic control, of either conducting polymer films or dual sensing-actuating devices. Assuming that the reaction occurs by extraction, or injection, of n consecutive electrons from, or to, a polymer chain the material moves through n consecutive oxidation or reduction states. Stair functions are obtained describing either potential or consumed electrical energy evolutions as a function of both, driving (current) and environmental (temperature, electrolyte concentration...) variables. The current quantifies the actuation of any electrochemical device (charge/discharge of batteries, movement rate, and position of muscles): the stair functions are dual actuating-sensing functions. A good agreement exists between theoretical and experimental results from either polypyrrole films or artificial muscles at different temperatures. Only two connecting wires include, at any time, sensing (potential) and working (current) information of any dual device.

Electroconductive hydrogels: synthesis, characterization and biomedical applications

Electroconductive hydrogels (ECHs) are composite biomaterials that bring together the redox switching and electrical properties of inherently conductive electroactive polymers (CEPs) with the facile small molecule transport, high hydration levels and biocompatibility of cross-linked hydrogels. General methods for the synthesis of electroconductive hydrogels as polymer blends and as polymer co-networks via chemical oxidative, electrochemical and/or a combination of chemical oxidation followed by electrochemical polymerization techniques are reviewed. Specific examples are introduced to illustrate the preparation of electroconductive hydrogels that were synthesized from poly(HEMA)-based hydrogels with polyaniline and from poly(HEMA)-based hydrogels with polypyrrole. The key applications of electroconductive hydrogels; as biorecognition membranes for implantable biosensors, as electro-stimulated drug release devices for programmed delivery, and as the low interfacial impedance layers on neuronal prostheses are highlighted. These applications provide great new horizons for these stimuli responsive, biomimetic polymeric materials.

High-impact polystyrene/polyaniline membranes for acid solution treatment by electrodialysis: preparation, evaluation, and chemical calculation

In this study different membranes were produced, aiming to evaluate their use in electrodialysis. These membranes were produced using conventional polymer (high-impact polystyrene) and polyaniline. The membrane characterization was done by FTIR spectroscopy, scanning electron microscopy (SEM), and thermogravimetry (TGA). The studies of the zinc and proton extraction ionic transport through the membranes were evaluated using a three-compartment cell. The results obtained using the produced membranes were compared to the results obtained with the commercial membrane Nafion 450. It was found that a synthesized membrane can be used to recover zinc in acid media. In addition, a preliminary computational essay about the structures of PAni and CSA is presented.

Electromodulated molecular transport in gold-nanotube membranes

We have developed a new class of synthetic membranes that contain monodisperse Au nanotubes with inside diameters of molecular dimensions (<1 nm). The Au nanotubes span the complete thickness of the membrane and can act as conduits for molecule and ion transport between solutions placed on either side of the membrane. We have recently become interested in the concept of electromodulating neutral molecule transport across these membranes. This communication describes a novel approach for accomplishing this objective. This approach makes use of an anionic surfactant which, when a positive potential is applied to the Au nanotube membrane, partitions into the nanotubes to charge the solution side of the electrical double layer at the tube walls. Because of the hydrophobic tail of the surfactant, this renders the nanotube interior hydrophobic, and the membrane now preferentially extracts and transports neutral hydrophobic molecules. Because the anionic surfactant can be expelled from the nanotubes by applying a negative potential, this provides a route for reversibly electromodulating neutral molecule transport in these membranes.