Polyphenol modification of graphene-stabilized emulsions to form electrically conductive polymer spheres

Michael J Joyce; Sean T McDermott; Khandaker Umaiya; Douglas H Adamson

doi:10.1016/j.jcis.2023.09.008

Polyphenol modification of graphene-stabilized emulsions to form electrically conductive polymer spheres

J Colloid Interface Sci. 2024 Jan;653(Pt A):327-337. doi: 10.1016/j.jcis.2023.09.008. Epub 2023 Sep 4.

Authors

Michael J Joyce¹, Sean T McDermott², Khandaker Umaiya¹, Douglas H Adamson³

Affiliations

¹ Department of Chemistry, University of Connecticut, Storrs, CT 06269, USA.
² Polymer Program, Institute of Materials Science, University of Connecticut, Storrs, CT 06269, USA.
³ Department of Chemistry, University of Connecticut, Storrs, CT 06269, USA; Polymer Program, Institute of Materials Science, University of Connecticut, Storrs, CT 06269, USA. Electronic address: douglas.adamson@uconn.edu.

PMID: 37717433
DOI: 10.1016/j.jcis.2023.09.008

Abstract

Hypothesis: Polyphenols, specifically tannic acid, should increase the hydrophilicity of graphene when added during the interfacial exfoliation through π-π stacking. Following Bancroft's rule, increasing the hydrophilicity of graphene will result in a phase inversion of water-in-oil emulsions stabilized by graphene. Polymerization of the oil phase will then lead to graphene-coated spheres rather than graphene-stabilized polyHIPEs.

Experiments: Optical particle sizing, microscopy, contact angle, and electrical conductivity measurements were performed to determine the mechanism of sphere formation in graphene-stabilized emulsions modified with tannic acid. Studies focused on the effect of graphite flake size, graphite concentration, tannic acid concentration, and oil phase composition. Particle sizing and scanning electron microscopy examined the spheres' size, shape, and surface morphology. Contact angle measurements gave insight into the change in graphene surface energy. Conductivity studies examined the graphene shell surrounding the spheres.

Findings: Adding tannic acid to graphene-stabilized emulsions induced a phase change from water-in-oil to oil-in-water. Contact angle measurements confirmed greater hydrophilicity of graphene in the presence of tannic acid. However, very high tannic acid concentrations led to a decrease in the stability of the emulsion. Varying the graphite flake size and concentration resulted in morphology and conductivity changes. Dilution of the monomer phase produced hollow microcapsules.

Keywords: Conductive spheres; Graphene; Graphene spheres; Graphite exfoliation; Oil-in-water emulsion; Polymer microspheres; Polyphenols; Pristine graphene; Tannic acid.