The True Amphipathic Nature of Graphene Flakes: A Versatile 2D Stabilizer

• Published in: Advanced materials (Weinheim) Vol. 32; no. 34; pp. e2000608 - n/a
• Main Authors: Kuziel, Anna W., Milowska, Karolina Z., Chau, Pak‐Lee, Boncel, Slawomir, Koziol, Krzysztof K., Yahya, Noorhana, Payne, Mike C.
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01-08-2020; Wiley-VCH Verlag
• Subjects: Basal plane; Density functional theory; Emulsions; Flakes; Graphene; graphene flakes; High temperature; interfacial self‐assembly; Materials science; Mechanical properties; Microscopy; Molecular dynamics; Optical microscopy; Physics; Pickering emulsions; Saline solutions; stabilizers; Pickering emulsions; interfacial self-assembly; graphene flakes; stabilizers
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.202000608

The fundamental colloidal properties of pristine graphene flakes remain incompletely understood, with conflicting reports about their chemical character, hindering potential applications that could exploit the extraordinary electronic, thermal, and mechanical properties of graphene. Here, the true amphipathic nature of pristine graphene flakes is demonstrated through wet‐chemistry testing, optical microscopy, electron microscopy, and density functional theory, molecular dynamics, and Monte Carlo calculations, and it is shown how this fact paves the way for the formation of ultrastable water/oil emulsions. In contrast to commonly used graphene oxide flakes, pristine graphene flakes possess well‐defined hydrophobic and hydrophilic regions: the basal plane and edges, respectively, the interplay of which allows small flakes to be utilized as stabilizers with an amphipathic strength that depends on the edge‐to‐surface ratio. The interactions between flakes can be also controlled by varying the oil‐to‐water ratio. In addition, it is predicted that graphene flakes can be efficiently used as a new‐generation stabilizer that is active under high pressure, high temperature, and in saline solutions, greatly enhancing the efficiency and functionality of applications based on this material.
Pristine graphene flakes are 2D amphiphiles with well‐defined hydrophilic edges and hydrophobic basal plane surfaces, the interplay of which allows small flakes to be utilized as stabilizers. The interactions between flakes can be controlled by varying the flake size and the oil‐to‐water ratio. Pristine graphene flakes can stabilize water/oil emulsions even under high pressure, high temperature, and in saline solutions.