5 research outputs found
Electric Field Induced Morphological Transitions in Polyelectrolyte Multilayers
In
this work, the morphological transitions in weak polyelectrolyte
(PE) multilayers (PEMs) assembled from linear polyÂ(ethylene imine)
(LPEI) and polyÂ(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<sup>3–4</sup>-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 (>10<sup>7</sup> M<sup>–1</sup> s<sup>–1</sup>) 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<sup>3–4</sup>-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 (>10<sup>7</sup> M<sup>–1</sup> s<sup>–1</sup>) 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 ÎĽm), 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