Simultaneous Rheoelectric Measurements of Strongly Conductive Complex Fluids
Name
PhysRevApplied.6.064004.pdf
Size
1.25 MB
Format
Adobe PDF
Checksum (MD5)
514fe2d8befc1d0c29cf390ac3829663
Author(s)
Helal, Ahmed H.
Divoux, Thibaut Louis Alexandre
McKinley, Gareth H
Date Issued
December 2016
Journal
Physical Review Applied
Publisher
American Physical Society
Citation
Helal, Ahmed, Thibaut Divoux, and Gareth H. McKinley. “Simultaneous Rheoelectric Measurements of Strongly Conductive Complex Fluids.” Physical Review Applied 6.6 (2016): n. pag. © 2016 American Physical Society
Version
Final published version
Abstract
We introduce an modular fixture designed for stress-controlled rheometers to perform simultaneous rheological and electrical measurements on strongly conductive complex fluids under shear. By means of a nontoxic liquid metal at room temperature, the electrical connection to the rotating shaft is completed with minimal additional mechanical friction, allowing for simultaneous stress measurements at values as low as 1 Pa. Motivated by applications such as flow batteries, we use the capabilities of this design to perform an extensive set of rheoelectric experiments on gels formulated from attractive carbon-black particles, at concentrations ranging from 4 to 15 wt %. First, experiments on gels at rest prepared with different shear histories show a robust power-law scaling between the elastic modulus G[superscript '][subscript 0] and the conductivity σ[subscript 0] of the gels—i.e., G[superscript '][subscript 0]∼σ[superscript α][subscript 0], with α=1.65±0.04, regardless of the gel concentration. Second, we report conductivity measurements performed simultaneously with creep experiments. Changes in conductivity in the early stage of the experiments, also known as the Andrade-creep regime, reveal for the first time that plastic events take place in the bulk, while the shear rate [dot over γ] decreases as a weak power law of time. The subsequent evolution of the conductivity and the shear rate allows us to propose a local yielding scenario that is in agreement with previous velocimetry measurements. Finally, to establish a set of benchmark data, we determine the constitutive rheological and electrical behavior of carbon-black gels. Corrections first introduced for mechanical measurements regarding shear inhomogeneity and wall slip are carefully extended to electrical measurements to accurately distinguish between bulk and surface contributions to the conductivity. As an illustrative example, we examine the constitutive rheoelectric properties of five different grades of carbon-black gels and we demonstrate the relevance of this rheoelectric apparatus as a versatile characterization tool for strongly conductive complex fluids and their applications.
MIT Department
Massachusetts Institute of Technology. Department of Civil and Environmental Engineering
Massachusetts Institute of Technology. Department of Mechanical Engineering
MultiScale Materials Science for Energy and Environment, Joint MIT-CNRS Laboratory
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DOI of Published Version
https://doi.org/10.1103/PhysRevApplied.6.064004
