(516a) High Speed Production of Graphene Oxide Membranes and Their Potential Usage in Harsh Environments

The shape anisotropy and enhanced solubility of graphene oxide (GO) in a wide variety of solvents provides the perfect environment to showcase isotropic-to-nematic colloidal phase transitions. As a result, the fluid phase of GO starts to demonstrate properties such as higher viscosity and elasticity compared to the isotropic phase. Membranes of graphene oxide have primarily been fabricated from isotropic phase of GO by processes such as vacuum filtration; which does not attend to manufacturing speeds required by industries. Our research program endeavours to address this issue given the large possibilities in applications ranging from permeable filtration membranes, strategically constructed battery separators, strain sensors, lab-on-chip devices, and supercapacitors.

We have over the years developed quantitative polarized light imaging techniques to quantify fine structure, alignment, texture of the liquid crystalline phases and thin films of GO ¹,²; which have helped us develop processing-property correlations³. We have also shown that large-area GO (13 x 14 cm²) filtration membranes can be produced in < 5 seconds using a high speed gravure printer which have demonstrated molecular sieving properties and suitability in membrane separation processes.⁴ The GO membranes enable permeation, maintaining structural stability in a wide variety of polar protic, polar aprotic, and non-polar solvents, such a wide palette of solvent usage is difficult to achieve with other membranes. Flux in the GO membranes scales inversely with the dielectric constant of the solvent (i.e. an interaction parameter), and also inversely with the viscosity as per continuum predictions, enabling us to develop predictive flux correlations⁵. The GO membranes can also be cleaned with bleach for continuous re-use in separation of tannic acid from water, and means to improve the chemical oxidation resistance are being investigated. The scalability and adaptability of our membrane fabrication technique is leading to commercial adaptation and laboratory-to-market translation of products such as nanofiltration membranes.

1 Tkacz, R. et al. pH dependent isotropic to nematic phase transitions in graphene oxide dispersions reveal droplet liquid crystalline phases. Chemical Communications 50, 6668-6671, doi:10.1039/C4CC00970C (2014).

2 Tkacz, R., Oldenbourg, R., Fulcher, A., Miansari, M. & Majumder, M. Capillary-Force-Assisted Self-Assembly (CAS) of Highly Ordered and Anisotropic Graphene-Based Thin Films. The Journal of Physical Chemistry C 118, 259-267, doi:10.1021/jp4080114 (2014).

3 Sheath, P. & Majumder, M. Flux accentuation and improved rejection in graphene-based filtration membranes produced by capillary-force-assisted self-assembly. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 374, doi:10.1098/rsta.2015.0028 (2016).

4 Akbari, A. et al. Large-area graphene-based nanofiltration membranes by shear alignment of discotic nematic liquid crystals of graphene oxide. Nature Communications 7, 10891, doi:10.1038/ncomms10891 https://www.nature.com/articles/ncomms10891#supplementary-information (2016).

5 Akbari, A. et al. Solvent Transport Behavior of Shear Aligned Graphene Oxide Membranes and Implications in Organic Solvent Nanofiltration. ACS Applied Materials & Interfaces 10, 2067-2074, doi:10.1021/acsami.7b11777 (2018).