Lignin is one of the most abundant bio-polymers present in nature and its valorization is still a challenge to an economically feasible biorefinery concept. The heterogeneity and scarce reactivity of lignin are significant hurdles to the development of new valorization processes. We propose an in situ extraction electrochemical depolymerization system. Kraft lignin dissolved in a deep eutectic solvent together with an extractant phase is able to form a stable emulsion. Electro-oxidation of the emulsion using a nickel or graphite electrode results in successful depolymerization and simultaneous fractionation of the products. Over-oxidation of the depolymerization products is anticipated to be suppressed upon swift extraction from the lignin phase into the extraction phase.

In this critical review we compare two geometries in partial wetting: a liquid drop on a planar substrate and a spherical particle at a planar liquid interface. We show that this comparison is far from being trivial even if the same physical interactions are at play in both geometries. Similarities and differences in terms of free energies and frictions will be discussed. Contact angle hysteresis, the impact of surface roughness and line pinning on wetting will be described and compared to selected experimental findings.

Nous discutons les signatures Raman de nanotubes de carbone monofeuillets (single-wall carbon nanotubes,SWNT) et de feuillets de graphène monofeuillets (single layer graphene, SLG) dispersés dans l’eau (fig. 1) et leurorigine physique. Les encres de SWNT sont stabilisées avec des tensio-actifs. Les études optiques dans le procheinfrarouge permettent de mesurer simultanément le signal Raman et le signal de photoluminescence caractéristiquedes nanotubes dispersés à l’échelle individuelle (fig. 2, gauche). Le signal de PL est sensible à l’environnementdiélectrique des nanotubes et permet d’étudier les interactions avec le tensio-actif [1]. A fortes concentrations, lesSWNT forment des phases cristal liquide et l’étude de la polarisation des signaux Raman/PL conduit à la mesure du paramètre d’ordre orientationnel [2]. Les encres de SWNT peuvent être déposées par jet d’encre, les textures des dépôts et leur conductivité électrique dépendent de la concentration des encres [3].
Des encres de graphène SLG, baptisées ‘‘eau de graphène’’ peuvent être préparées sans tensioactif en dispersant despolyélectrolytes de SLG dans de l’eau dégazée [4]. Les signatures Raman des SLG dispersées dans l’eau sontvoisines de celles des SLG suspendues dans l’air (fig. 2), avec des décalages modérés des bandes principales quisont discutées en terme de dopage et de contraintes mécaniques [5]. Les défauts ponctuels observés sur les SLG dispersées dans l’eau peuvent être facilement éliminés par un recuit des dépôts à 800°C.
References
[1] F. Torres-Cañas et al, J. Phys. Chem. C 119 (2015), pp. 703-709
[2] C. Zamora-Ledezma et al, J. Phys. Chem. C 115 (2011), pp. 3272-3278
[3] F. Torres-Cañas et al, Mat. Res. Exp. 4 (2016)
[4] G. Bepete et al, Nature Chem. 9 (2016), pp. 347-352
[5] G. Bepete et al, J. Phys. Chem. C 120 (2016), pp. 28204-28214

Most of the potential applications in carbon nanotubes and graphene-based composites require suitable methods for making aligned assemblies on a large scale. Liquid crystal ordering is an opportunity to develop such materials and applications [1]. In this talk, we will present a review of our recent results in the preparation and characterization of lyotropic liquid crystals based on concentrated aqueous suspensions, stabilized by surfactants, of single-walled carbon nanotubes (SWNT) or reduced graphene oxide (RGO). In the first part we will focus on anisotropic conductive films, which are prepared by shearing and drying the LC. In particular, we will show how the electrical conductivity anisotropy increases with the orientational order parameter of the nematic liquid crystal. The order parameter can be tuned by controlling the length and entanglement of the nanotubes [1-2]. In the second part we present recent results on the morphology and anisotropy of thin conductive lines of SWCNT, inkjet-printed. Its Their morphology can be tuned from rail track to quasi-continuous lines by increasing nanotube concentration and drop density. The average order parameter is in the range 0.2–0.4 for all samples. The electrical resistivity is larger for rail tracks with respect to continuous layers, due to large amounts of electrical dead-ends in and between the inner edges of rail tracks [4]. Finally we will present how to prepare water-based Graphene Oxide (GO), and Reduced Graphene Oxide (RGO) liquid crystals stabilized by surfactant molecules. We will discuss their structural and thermodynamic characterizations, which provide indirect but statistical information on the organizations and dimensions of the graphene flakes [1-3].
1. C. Zakri et al, Phil. Trans. R. Soc. A. 371 (2013) 201204995(15)
2. Zamora-Ledezma, C. et al. J. Phys. Chem. Lett., 3 (17), pp 2425–2430 (2012)
3. Yuan J. et al. Nat. Commun. 6:8700 doi: 10.1038/ncomms9700 (2015).
4. F. Torres-Canas et al, Mater. Res. Express. DOI: 10.1088/2053-1591/aa5687 (2017)

N.A.

Nematic Liquid Crystals (CL) dominate the market for high-resolution display devices.Unfortunately, their relatively slow response times (> 1 ms) greatly limit their use in thedevelopment of more efficient screens (3D screens) and components (switches, couplers,filters). In this context, newly discovered Twist-Bend Nematic (TBN) similar to the usualnematic phases, but spontaneously deformed at the level of a few nanometers, due to thecurved shape of the molecules, are very promising [1]. In fact, the more rigid structure ofTBN makes it possible to achieve ultra-short electrical field response times (<1 μs). Thestudy of TBN and their potential in new applications requires to master their anchoring, i.e.their orientation on the solid confinement walls.
In this paper we present an experimental study of a newly synthesized TBN the: N,N0 -Bis(4,40-cyanobiphenymethylidene)-nonane-1,9-diamine (CBI-9-ICB), under well controlledanchoring and confinement conditions.
In the experiment, the compound is inserted by capillarity in a cell made by two parallel glassplates with few microns gap. Different anchoring conditions have been examined. We showthat rubbed polyvinyl alcohol (PVA) and Dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride (DMOAP) treated substrates give different anchoring and texture fromthat given by usual nematic as 4-Cyano-4'-pentylbiphenyl (5CB). In Figure 1 is represented atypical TBN texture observed under Polarizing Optical Microscope in a cell withhomogeneous planar anchoring obtained with rubbed PVA. Stripes parallel to the anchoringorientation having a wavelength proportional to the cell thickness are measured. The sametexture is also found in rubbed Polyimide substrates. Currently, two models are proposed toexplain this texture. The first is related to the Helfrich-Hurault instability due to the presenceof TBN pseudo-layers [2]. The second is based on the peculiar elasticity of the TBN directorfield [3]. Although it is not clear how these models could reproduce the observed lineardependence of pattern periodicity as a function of the cell gap. In Figure 2 is reported theTBN texture for silane treated glass plates that gives, for ordinary nematic, homeotropic (i.e.perpendicular to the plate) anchoring. The resulting anchoring for TBN is surprisingly planardegenerated as one can infer from the presence of half-strength disclinations. A mosaictexture with homogeneously oriented domains reminiscent of SmC mosaic also appears.Such textures will be discussed in the framework of the elastic theory of TBN.
References:
[1] C. Meyer, G. R. Luckhurst and I. Dozov, Phys. Rev. Lett., 2013,111 (6), 0031-9007.
[2 P. K. Challa,V. Borshch,O. Parri, Phys. Rev. Lett., 2014, 89 (6), 1539-3755.
[3] V. P. Panov, M. Nagaraj, J. K. Vij, Phys. Rev. Lett., 2010, 105 (16), 0031-9007.

Des solutions colloïdales sont assez facilement obtenues à partir de nanoparticules de carbone (nanotubes ou dérivés du graphène) dispersées dans l’eau [1]. L’obtention de mésophases nécessite cependant un soin expérimental dans le tri des nanoparticules et dans la qualité des dispersions. La persistance de fortes interactions attractives et d’agrégats dans une solution peuvent en effet déstabiliser lentement ces phases ou au mieux modifier fortement leurs propriétés visco-élastiques. Depuis plusieurs années, nous étudions comment obtenir à partir de ces solutions, des films et couches minces de propriétés variables en contrôlant les conditions de préparation et de dépôts (orientation des particules, texturation).
Dans ce travail, nous décrirons comment créer et stabiliser des textures périodiques de grande échelle dans des phases nématiques d’oxyde de graphène (voir fig.1). Ces textures ont été caractérisées en microscopie optique et électronique et nous discuterons de leur origine et de leur stabilité.
Références:
[1] C. Zakri, et al. Phil. Trans. R. Soc. A., , 2013, 371, 20120499.