Résumé
Aqueous dispersions of graphene-derived monolayers form liquid crystal at rather low concentrations due to the high aspect ratio of these flakes [1,2]. If graphene oxide dispersions are easily obtained in water, reduced graphene oxide necessitates the use of surfactants [3]. Preparing organized materials and thin films from these dispersions then requires a good control of the liquid crystal ordering during the deposition and the drying of the films.The flakes easily align at high shear [4,5], which has allowed us to complete previous optical characterizations of the various graphene layers (birefringence and linear dichroism). However at low shear or under small dispalcements, thin films often show peculiar patterns (such as the periodic textures shown in Fig.1). We have shown how to create and stabilize large-sized periodic textures. The patterns have been characterized under optical and electronic microscopies. Their stability can be explained by the competition between the anchoring field of the substrate and the presence of a yield stress resulting from the peculiar elastic and rheological properties of the graphene oxide liquid crystals. Our results also clarify why long-standing hypotheses on the presence of exotic phases [1] at large concentrations are present in the literature.References[1] Z. Xu, C. Gao Nat Commun., 2, 571 (2011).[2] C. Zakri et al., Phil. Trans. A, 371, 20120499 (2013).[3] C. Zamora et al, J. Phys. Chem. Lett. 3, 2425 (2012).[4] P. Poulin et al, Proc Natl Acad Sci USA, 113, 11088 (2016).[5] S-H Honga, T.Z. Shena and J. K. Songa, Liquid Crystals, 42, 261 (2015)