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

Anna W Kuziel,Mike C Payne,Noorhana Yahya,Krzysztof K Koziol,Karolina Z Milowska,Pak‐Lee Chau,Slawomir Boncel

doi:10.1002/adma.202000608

Abstract

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 thismaterial.

Highlights

The fundamental colloidal properties of pristine graphene flakes remain many applications, its interactions with adsorbates when it is placed in a liquid incompletely understood, with conflicting reports about their chemical environment
The true amphipathic nature of pristine graphene flakes is demonstrated through wet-chemistry testing, optical microscopy, electron microscopy, and density or its derivatives obtained by subsequent reduction or further functionalization[3,4]
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 matrices

Summary

Introduction

The fundamental colloidal properties of pristine graphene flakes remain many applications, its interactions with adsorbates when it is placed in a liquid incompletely understood, with conflicting reports about their chemical environment. Optical microscopy analysis revealed that the dispersibility of G3 flakes (thicker and of smaller surface area) in n-decane is significantly higher than G1 flakes (cf left panels in Figure S1A,B, Supporting Information). The presence of additional hydroxyl and epoxy groups attached to the flake edges reduces the energy differences between different orientations of the oil and water molecules (Figure S5, Supporting Information).

Results

Conclusion