Graphene Liquid Crystals – GAELIC

The project combines the design of graphene-derived and nanoparticles suspensions, their rheological/structural/optical study in a rather linear workflow. Once designed, spectroscopy methods (Absorption, Raman) and Light,SAXS scattering techniques are used to characterized the solutions. Some rheological investigations are performed in Rheo-SAXS to determine the arrangement of the most concentrated samples under flow. Other techniques such as birefringence measurements under flows are also performed for the most diluted samples. Raman measurements are also performed to determine the response and quality of the graphene but also to assess the SERS properties of the composites.
Thin films will be proceeded from the suspensions with the most classic methods: spin-coating, dip-coating and Dr Blade. They will be studied by electronic microscopy, Raman spectroscopy. The properties of the resulting films will be related to the ones of the solutions.

After 18 months of work we can consider that the project is settled down. The basic dispersions have been produced and partly characterized. Phase diagrams have been established. Some dispersions such as graphenides can be obtained but at a too low concentration to give liquid crystals. Other such as graphene oxides and reduced graphene oxides exist in a large range of concentrations. We have shown hat some dispersions could be mixed with nanoparticles solutions without aggregation and we have characterized such composites. We have also begun to characterize the rheological behaviour of the dispersions. Most of them can be easily aligned under flow even at low concentrations. At large concentrations, specific instabilities have been studied under microdeformations approaches. We have just started to explore the formation of thin films and the typical formation of drying patterns.

The project is now well established in its materials aspects . We keep on following the initial program and especially the formation of the solid films and their properties. The part of the project with the major issues.

Concerning the scientific dissemination, several communications in international conferences (Soft Matter, ECIS, Graphene) have been already done and two papers are in preparation.

Graphene is one of the promising materials which are expected to develop industrially in the next decades. Although it has been discovered only recently (2004), many of its outstanding properties have been already considered for applications and several industrial products are expected to be mass-produced in the next years. Several effective techniques have been developed for preparing graphene and chemically derived graphene sheets: i) the costly bottom-up synthesis of large, flat, and high quality graphene single sheets suitable for electronic, micromechanical devices, sensors, ii) the design, at a lower cost but with defects and much less defined properties, of reduced graphene flakes by wet routes, starting from the oxidative exfoliation of graphene. The second class of graphene is much less defined than the first one. It is highly dispersed in size and properties with a large number of defects present into the graphene sheets due to the change in the aromatic structure and the formation of oxygen-containing groups. Moreover the graphene layers still need to be processed in materials or deposit on adequate substrates after their synthesis. The wet route has nevertheless the advantage of being easily scalable for industrial applications concerning coatings, inks, composites, energy storage, and bio applications.
Developing new processes to obtain good quality graphene materials and a controlled organization of the graphene sheets over large distances by wet routes only is still a challenge. It could not only permit to improve the performances of the future devices and products at a lower cost, but also to create new types of applications and components where the mesoscopic organization of the layers matter. The project GAELIC will explore new approaches in order to design quality coatings of graphene and metal nanoparticles-graphene hybrids, with a tunable and controlled organization, starting from graphene layers obtained by the wet route syntheses. This work will permit to develop and improve future applications where the quality and the size of the graphene layers is crucial.
The project is mainly focused on the design of liquid crystalline phases from graphene derivatives (graphenides, graphene oxide and reduced graphene oxide) and the study of their structural and rheological properties. Both pure graphene and various metal nanoparticles/graphene hybrid liquid crystals will be designed and processed in order to obtain thin films of nanostructured materials. The use of a liquid crystal has two key features which makes it more promising that a simple coating by an isotropic solution: i) it allows the use of concentrated solutions. Isotropic graphene suspensions are very diluted especially for the very large flakes. ii) it should allow a greater control of the alignment and organization of the particles and therefore an enhancement of the physical and chemical properties.
Besides the design of liquid crystal phases made of ultra-wide single-layers graphene and the development of new methods to characterize the graphene flakes, we will investigate the formation mechanisms of the thin nanostructured films and use the acquired knowledge for three targeted applications. We plan to design new SERS substrates, innovative passivation coatings and adhesion promoters for metal plating. The industrial interest of these coatings will be assessed during the project.