Electric Field Induced Morphological Transitions in Polyelectrolyte Multilayers

In this work, the morphological transitions in weak polyelectrolyte (PE) multilayers (PEMs) assembled from linear poly­(ethylene imine) (LPEI) and poly­(acrylic acid) (PAA) upon application of an electric field were studied. Exposure to an electric field results in the creation of a porous structure, which can be ascribed to local changes in pH from the hydrolysis of water and subsequent structural rearrangements of the weak PE constituents. Depending on the duration of application of the field, the porous transition gradually develops into a range of structures and pore sizes. It was discovered that the morphological transition of the LbL films starts at the multilayer-electrode interface and propagates through the film. First an asymmetrical structure forms, consisting of microscaled pores near the electrode and nanoscaled pores near the surface in contact with the electrolyte solution. At longer application of the field the porous structures become microscaled throughout. The results revealed in this study not only demonstrate experimental feasibility for controlling variation in pore size and porosity of multilayer films but also deepens the understanding of the mechanism of the porous transition. In addition, electrical potential is used to release small molecules from the PEMs

Two-Component Protein Hydrogels Assembled Using an Engineered Disulfide-Forming Protein–Ligand Pair

We present the development of a two-component self-assembling protein hydrogel. The building blocks of the hydrogel are two liquid-phase protein block copolymers each containing (1) a subunit of the trimeric protein CutA as a cross-linker and (2) one member of a PDZ-domain-containing protein–ligand pair whose interaction was reinforced by an engineered disulfide linkage. Mixing of the two building blocks reconstitutes a self-assembling polypeptide unit, triggering hydrogel formation. This hydrogel exhibits extremely high solution stability at neutral and acidic pHs and in a wide range of temperatures (4–50 °C). Incorporation of a “docking station peptide” binding motif into a hydrogel building block enables functionalization of the hydrogel with target proteins tagged with a “docking protein”. We demonstrated the application of an enzyme-functionalized hydrogel in a direct electron transfer enzymatic biocathode. These disulfide-reinforced protein hydrogels provide a potential new material for diverse applications including industrial biocatalysis, biosynthesis, biofuels, tissue engineering, and controlled drug delivery

Diffusion-Cooperative Model for Charge Transport by Redox-Active Nonconjugated Polymers

Charge transport processes in nonconjugated redox-active polymers with electrolytes were studied using a diffusion-cooperative model. For the first time, we quantitatively rationalized that the limited Brownian motion of the redox centers bound to the polymers resulted in the 10^3–4-fold decline of the bimolecular and heterogeneous charge transfer rate constants, which had been unexplained for half a century. As a next-generation design, a redox-active supramolecular system with high physical mobility was proposed to achieve the rate constant as high as in free solution system (>10⁷ M^–1 s^–1) and populated site density (>1 mol/L)

Diffusion-Cooperative Model for Charge Transport by Redox-Active Nonconjugated Polymers

Charge transport processes in nonconjugated redox-active polymers with electrolytes were studied using a diffusion-cooperative model. For the first time, we quantitatively rationalized that the limited Brownian motion of the redox centers bound to the polymers resulted in the 10^3–4-fold decline of the bimolecular and heterogeneous charge transfer rate constants, which had been unexplained for half a century. As a next-generation design, a redox-active supramolecular system with high physical mobility was proposed to achieve the rate constant as high as in free solution system (>10⁷ M^–1 s^–1) and populated site density (>1 mol/L)

Mixed Ionic–Electronic Conduction Increases the Rate Capability of Polynaphthalenediimide for Energy Storage

Conjugated polymers offer a number of unique and useful properties for use as battery electrodes, and recent work has reported that conjugated polymers can exhibit excellent rate performance due to electron transport along the polymer backbone. However, the rate performance depends on both ion and electron conduction, and strategies for increasing the intrinsic ionic conductivities of conjugated polymer electrodes are lacking. Here, we investigate a series of conjugated polynapthalene dicarboximide (PNDI) polymers containing oligo(ethylene glycol) (EG) side chains that enhance ion transport. We produced PNDI polymers with varying contents of alkylated and glycolated side chains and investigated the impact on rate performance, specific capacity, cycling stability, and electrochemical properties through a series of charge–discharge, electrochemical impedance spectroscopy, and cyclic voltammetry measurements. We find that the incorporation of glycolated side chains results in electrode materials with exceptional rate performance (up to 500C, 14.4 s per cycle) in thick (up to 20 μm), high-polymer-content (up to 80 wt %) electrodes. Incorporation of EG side chains enhances both ionic and electronic conductivities, and we found that PNDI polymers with at least 90% of NDI units containing EG side chains functioned as carbon-free polymer electrodes. This work demonstrates that polymers with mixed ionic and electronic conduction are excellent candidates for battery electrodes with good cycling stability and capable of ultra-fast rate performance