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)

In this work, we explore the preparation and deposition of graphene oxide (GO)-metal (gold and palladium) nanoparticles (NPs) composites as thin films via wet routes. The properties of such films are examined, in view of Surface Enhanced Raman Spectroscopy (SERS) applications and as adhesion promoter thin films. It has been indeed shown that the encapsulation of metal NP within a few layers of graphene greatly improves the stability, reproducibility and sensitivity of SERS effect [1]. On the other hand, graphene oxide films decorated with metal nanoparticles are good non-etching adhesion promotors candidates for electroless deposition of metal thin films on non-metal substrates like glass or polymers [2, 3]. We discuss the preparation of the suspensions and the parameters (GO dispersion concentration, withdrawal speed and immersion time, functionalization of the substrates) which permit a good control of the deposition by dip-coating. The structure of the resulting thin films is characterized by Atomic Force Microscopy (AFM), Phase Shifting Interferometry (PSI) and Raman spectroscopy to determine the topography, thickness and homogeneity of the deposited layers. Their SERS and adhesion properties are then discussed.References[1] Y. Liu, Y. Hu, and J. Zhang, J. Phys. Chem. C, 2014, 1187, p. 8993‑ 8998.[2] S. P. Koenig, N. G. Boddeti, M. L. Dunn, and J. S. Bunch,2011, Nat. Nanotechnol.,6, p. 543‑ 546.[3] Q. Ma, X. Zhu, D. Zhang, and S. Liu, 2014, J. Mater. Chem. C,22, p. 8956‑ 8961.

We explore the preparation and use of graphene dispersions and graphene-nanoparticles composites viawet routes in order to create organized thin films (for passivation, adhesion and design of SERS substrates, seeFig.) At large concentrations, the liquid crystal ordering is an opportunity to spontaneously organize the materials.At lower concentrations, a special care has to be taken during the deposition of the thinnest films.In this work, we have focused on the design and the characterization of thin layers made of graphene oxide andgold nanoparticles (GO/AuNps) for their Surface Enhanced Raman Spectroscopy (SERS) properties. The objectivehere is to establish the main rules that control (during the deposition) the structure of the films and their resultingSERS properties. We have used various techniques such as dip-coating, spin coating with varying parameters, aswell as surface functionalization before deposition. The thin films have been characterized by AFM and theirperformance have been tested with Raman spectroscopy.

Graphene oxide dispersions are easily obtained in water. Due to the high aspect ratio of the flakes, liquid crystalsthen forms a nematic phase at moderate concentrations [1,2], which allows to design various composites withnanoparticles. Preparing organized materials and thin films from these dispersions however requires a good controlof the liquid crystal ordering during the deposition and the drying of the films.Here we have focused on mechanical instabilities that are frequently observed in thin graphene liquid crystallayers, when they are submitted to weak constraints. We have shown how to create and stabilize large-sizedperiodic textures (millimeter scale, see fig.1). The patterns have been characterized under optical and electronicmicroscopies. They result 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 concentrationsare present in the literature.

The aim of the present work is to study by means of thermodynamic measurements, i.e. isotherms of adsorption and desorption of water and Infrared (IR) spectroscopy, the effect of the interlayer cations on the mechanism of adsorption-desorption of water in the case of a montmorillonite exchanged with alkaline-earth metals. For the first time, the net isosteric heat of water adsorption and desorption is determined from isotherms recorded at three temperatures. The net isosteric heat is a very useful parameter for getting more insights into the sorption mechanism since it provides information about the sorption energy evolution which can be complementary to that obtained from structural or gravimetric measurements. The homoionic montmorillonite samples are prepared from purification and cationic exchanged in aqueous solution of the raw material, i.e the reference SWy-2 Wyoming material. XRD at the dry state and elemental chemical analysis confirm that the treatment does not deteriorate the clay structure and yield the expected homoionic composition. The adsorption and desorption isotherms measured at various temperatures show that the nature of the interlayer, i.e. exchangeable, cation changes the adsorbed/desorbed amount of water molecules for a given water relative pressure. The total amount of water adsorbed at = 0.5 follows the cation sequence Ca>Mg>Ba. Although the adsorption isosteric heat also follows the cation sequence Ca>Mg>Ba, that of desorption obeys a slightly different sequence Ca~Mg>Ba. This discrepancy between the adsorption and desorption heat is due to the higher irreversibility of water sorption process in the Ca exchanged montmorillonite. Finally, analysis of the IR spectra recorded at room temperature and under a primary vacuum reveals that the amount of adsorbed water follows the same sequence as that of the isosteric heat of adsorption and shows the coexistence of liquid-like and solid-like water confined in the interlayer space.

The degree of curing of epoxy composites and coatings is one key parameter to control the reliability of manufacturing processes, particularly in printed circuit board (PCB) manufacturing where epoxy buildup composites are partially cured before processing. We show that the reaction of curing of an industrially relevant buildup composite (epoxy-phenol reinforced with silica fillers) can be monitored by diffuse reflectance infrared Fourier transform (DRIFT) in the near-infrared range. The accuracy of DRIFT measurements is confirmed by comparison with measurements in transmission mode on reference composite samples. DRIFT is demonstrated to offer an easy and reliable measurement of the epoxy degree of curing on PCB coupons.