An official website of the United States government
Electron transport in complex fluids, biology, and soft matter is a valuable characteristic in processes ranging from redox reactions to electrochemical energy storage. These processes often employ conductor–insulator composites in which electron transport properties are fundamentally linked to the microstructure and dynamics of the conductive phase. While microstructure and dynamics are well recognized as key determinants of the electrical properties, a unified description of their effect has yet to be determined, especially under flowing conditions. In this work, the conductivity and shear viscosity are measured for conductive colloidal suspensions to build a unified description by exploiting both recent quantification of the effect of flow-induced dynamics on electron transport and well-established relationships between electrical properties, microstructure, and flow. These model suspensions consist of conductive carbon black (CB) particles dispersed in fluids of varying viscosities and dielectric constants. In a stable, well-characterized shear rate regime where all suspensions undergo self-similar agglomerate breakup, competing relationships between conductivity and shear rate were observed. To account for the role of variable agglomerate size, equivalent microstructural states were identified using a dimensionless fluid Mason number, , which allowed for isolation of the role of dynamics on the flow-induced electron transport rate. At equivalent microstructural states, shear-enhanced particle–particle collisions are found to dominate the electron transport rate. This work rationalizes seemingly contradictory experimental observations in literature concerning the shear-dependent electrical properties of CB suspensions and can be extended to other flowing composite systems.
more »
« less
This content will become publicly available on September 5, 2026
Visualizing energy transfer between redox-active colloids
Redox-active colloids (RACs) represent a novel class of energy carriers that exchange electrical energy upon contact. Understanding contact-mediated electron transfer dynamics in RACs offers insights into physical contact events in colloidal suspensions and enables quantification of electrical energy transport in nonconjugated polymers. Redox-based electron transport was directly observed in monolayers of micron-sized RACs containing ethyl-viologen side groups via fluorescence microscopy through an unexpected nonlinear electrofluorochromism that is quantitatively coupled to the redox state of the colloid. Via imaging studies, using this electrofluorochromism, the apparent charge transfer diffusion coefficientDCTof the RAC was easily determined. The visualization of energy transport within suspensions of redox-active colloids was also demonstrated. Our work elucidates fundamental mechanisms of energy transport in colloidal systems, informs the development of next-generation redox flow batteries, and may inspire new designs of smart active soft matter including conductive polymers for applications ranging from electrochemical sensors and organic electronics to colloidal robotics.
more »
« less
- Award ID(s):
- 2301668
- PAR ID:
- 10646916
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Publisher / Repository:
- American Association for the Advancement of Science
- Date Published:
- Journal Name:
- Science Advances
- Volume:
- 11
- Issue:
- 36
- ISSN:
- 2375-2548
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Redox provides unique opportunities for interconverting molecular/biological information into electronic signals. Here, the fabrication of a 3D‐printed multiwell device that can be interfaced into existing laboratory instruments (e.g., well‐plate readers and microscopes) to enable advanced redox‐based spectral and electrochemical capabilities is reported. In the first application, mediated probing is used as a soft sensing method for biomanufacturing: it is shown that electrochemical signal metrics can discern intact mAbs from partially reduced mAb variants (fragmentation), and that these near‐real‐time electrical measurements correlate to off‐line chemical analysis. In the second application,operandospectroelectrochemical measurements are used to characterize a redox‐active catechol‐based hydrogel film: it is shown that electron transfer into/from the film correlates to the molecular switching of the film's redox state with the film's absorbance increasing upon oxidation and the film's fluorescence increasing upon reduction. In the final example, a synthetic biofilm containing redox‐responsiveE. coliis electro‐assembled: it is shown that gene expression can be induced under reducing conditions (via reductive H2O2generation) or oxidative conditions (via oxidation of a phenolic redox‐signaling molecule). Overall, this work demonstrates that 3D printing allows the fabrication of bespoke electrochemical devices that can accelerate the understanding of redox‐based phenomena in biology and enable the detection/characterization redox activities in technology.more » « less
-
We report a procedure to obtain the search distance used to determine particle contact in dense suspensions of smooth and rough colloids. This method works by summing physically relevant length scales in an uncertainty analysis and does not require detailed quantification of the surface roughness. We suspend sterically stabilized, fluorescent poly(methyl methacrylate) colloids in a refractive index-matched solvent, squalene, in order to ensure hard sphere-like behavior. High speed centrifugation is used to pack smooth and rough colloids to their respective jamming points, ϕ J . The jammed suspensions are subsequently diluted with known volumes of solvent to ϕ < ϕ J . Structural parameters obtained from confocal laser scanning micrographs of the diluted colloidal suspensions are extrapolated to ϕ J to determine the mean contact number at jamming, 〈 z 〉 J . Contact below jamming refers to nearest neighbors at a length scale below which the effects of hydrodynamic or geometric friction come into play. Sensitivity analyses show that a deviation of the search distance by 1% of the particle diameter results in 〈 z 〉 changing by up to 10%, with the error in contact number distribution being magnified in dense suspensions ( ϕ > 0.50) due to an increased number of nearest neighbors in the first coordination shell.more » « less
-
Redox-active polymers serving as the active materials in solid-state electrodes offer a promising path toward realizing all-organic batteries. While both cathodic and anodic redox-active polymers are needed, the diversity of the available anodic materials is limited. Here, we predict solid-state structural, ionic, and electronic properties of anodic, phthalimide-containing polymers using a multiscale approach that combines atomistic molecular dynamics, electronic structure calculations, and machine learning surrogate models. Importantly, by combining information from each of these scales, we are able to bridge the gap between bottom-up molecular characteristics and macroscopic properties such as apparent diffusion coefficients of electron transport (Dapp). We investigate the impact of different polymer backbones and of two critical factors during battery operation: state of charge and polymer swelling. Our findings reveal that the state of charge significantly influences solid-state packing and the thermophysical properties of the polymers, which, in turn, affect ionic and electronic transport. A combination of molecular-level properties (such as the reorganization energy) and condensed-phase properties (such as effective electron hopping distances) determine the predicted ranking of electron transport capabilities of the polymers. We predict Dapp for the phthalimide-based polymers and for a reference nitroxide radical-based polymer, finding a 3 orders of magnitude increase in Dapp (≈10–6 cm2 s–1) with respect to the reference. This study underscores the promise of phthalimide-containing polymers as highly capable redox-active polymers for anodic materials in all-organic batteries, due to their exceptional predicted electron transport capabilities.more » « less
-
Abstract Electronic materials that allow the controlled flow of electrons in aqueous media are required for emerging applications that require biocompatibility, safety, and/or sustainability. Here, a composite hydrogel film composed of graphene and catechol is electrofabricated, and that this composite offers synergistic properties is reported. Graphene confers metal‐like conductivity and enables charge‐storage through an electrical double layer mechanism. Catechol confers redox‐activity and enables charge‐storage through a redox mechanism. Importantly, there are two functional populations of catechols: conducting‐catechols (presumably in intimate contact with graphene) allow direct electron‐transfer; and non‐conducting‐catechols (presumably physically separated from graphene) require diffusible mediators to enable electron‐transfer. Using a variety of spectroelectrochemical measurements, that the capacity of the composite for charge‐storage increases in proportion to the extent by which the catechol‐groups can undergo redox‐state switching is demonstrated. To illustrate the broad relevance of this work, how the redox‐state switching can be related to both the charge storage of energy materials and the memory of molecular electronic materials is discussed. The authors believe this work is significant because it demonstrates that: conducting and redox‐active components enable distinctly different mechanisms for charge‐storage and electron‐transfer; these components act synergistically; and mediators provide unique opportunities to extend the capabilities of electronic materials.more » « less
