(373e) Characterizing Graphene Oxide Suspensions with Rheological Testing and Modeling, Neutron Scattering, and Electrochemical Performance

Electron transfer in carbon based colloidal particle systems make them a good candidate for a variety of electronics applications from flowable batteries to conductive coatings. In order to develop a toolbox to design application driven conductive suspensions, it is important to be able to understand primary particle morphology, surface chemistry, aggregate morphology and network structure. To this end, our group has synthesized graphene oxide using the modified Hummer’s method¹ to use as the basis for our study in colloidal particles in homogenous suspension after ultracentrifugation. The surface chemistry of the graphene oxide in aqueous solution determines the degree of aggregation and the formation of hierarchical structures. The inherent graphene properties and concentration (loading) affect the electronic conductivity, mass transport, and stability of the microstructure in flowable electrochemical applications. Therefore, we have characterized the graphene oxide using electrochemical techniques such as cyclic voltammetry and impedance spectroscopy to evaluate its electronic and ionic conductivity.

Moreover, to understand the evolving microstructure, and its contribution to conductivity we incorporated rheological testing. The evolving microstructure of the graphene contributes to particle (sheet to sheet) interaction. Rheological data shows shear thinning with the graphene suspensions In addition, we show both the linear Small Amplitude Oscillatory Shear and nonlinear Large Amplitude Oscillatory Shear flow experiments as well as results of fitting and predicting the rheological flows with contemporary thixo-elasto-visco-plastic (TEVP) models. We will present our ultra-Small Angle Neutron Scattering results with USANS. From this we hypothesize that our material structure is linked to a breakdown of a hierarchical fractal structure in these suspensions. Preliminary Small Angle Neutron Scattering (SANS) and USANS measurements seem to validate this hypothesis. We show the graphene oxide suspension has a mid q feature that can be associated with the primary particle structure and a large upturn at low-q (inverse aggregate length scale) due to the formation of larger structures in the sample. In order to fully characterize the graphene-oxide we show a combination of SANS and USANS. We plan extract primary particle size, aggregate size and fractal dimension from the SANS/USANS data and correlate these properties directly to the conductivity and linear rheological properties.

Lastly, we will demonstrate a correlation between our rheological model’s prediction of thixotropy, or microstructure with elastic and viscous features of our transient rheological data using Sequence of Physical Processes (SPP). We will use SPP and the TEVP modeling to show mechanical differences in the preparation (500g vs. 1000g formulations). We will show how the evolving microstructure contributes to the mechanical properties of the material with Cole-Cole plots. In addition, we will construct the full graphene oxide characterization with the USANS/SANS, rheological modeling, SPP framework analysis, and conductivity of the microstructure itself.

References

[1] Yu et al. Sci Rep (2016)

[2] Horner et al. JOR (2019).

[3] Rogers Rheo. Acta (2017).

[4] Richards et al. JOR (2017).

[5] Hipp et al. JOR (2019).