The True Amphipathic Nature of Graphene Flakes: A Versatile 2D Stabilizer.
Graphene, due to its extraordinary electronic, thermal and mechanical properties, holds great promise for applications ranging from optoelectronic, through environmental to biomedical technologies. However, for many potential large scale processing routes to efficiently manufacture and commercialize graphene based devices, composites, coatings, membranes or inks it is essential to understand the fundamental colloidal properties of pristine graphene flakes. Despite significant progress in the field in recent years, their chemical character has remained incompletely understood and there has been no consensus whether pristine graphene flakes are typical hydrophobes or could, under certain conditions, become wettable.
We have reinvestigated this question with precise experiments and rigorous quantum-mechanical, molecular dynamics and Monte Carlo studies. For the first time, calculations supported by experiments have revealed that 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 utilised as surfactants. Our findings reconcile all previous results on the chemical nature of graphene flakes. The interactions between flakes can be controlled by varying the flake size, its thickness and the oil-to-water ratio. Pristine graphene flakes can stabilize water/oil emulsions even under high pressure, high temperature and in saline solutions, conditions under which conventional surfactants fail.
The True Amphipathic Nature of Graphene Flakes: A Versatile 2D Stabilizer, AW Kuziel, KZ Milowska, PL Chau, S Boncel, KK Koziol, N Yahya, MC Payne, Adv. Mater. (2020)