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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.

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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.

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Le confinement de microparticules dans un film mince de fluide isotrope est généralement accompagné d’une déformation des interfaces qui donne naissance à de fortes interactions capillaires entre colloïdes, de nature attractive dans la plupart des cas [1]. La situation devient différente lorsqu’il s’agit d’un film mince de fluide complexe à l’exemple d’un cristal liquide nématique. Nous avons dans un premier temps étudié et compris le comportement surprenant des particules colloïdales individuelles piégés dans un film nématique mince étalé sur un liquide isotrope [2,3].
Nous avons poursuivi l’étude du couplage capillarité/élasticité qui donne naissance à une grande richesse de phénomènes colloïdaux. A l’aide d’approches numériques (éléments finis) et d’une modélisation simplifiée de l’élasticité dans un film nématique hybride nous avons calculé les déformations et textures attendues pour des particules anisotropes, ainsi que déterminé les interactions de paires en fonction de la distance. Le calcul des positions d’équilibre mécaniques entre deux particules confinées et les observations expérimentales sont en très bon accord, ce qui valide la démarche utilisée.
[1] P. A. Kralchevsky and K. Nagayama, Adv. Colloid Interface Sci. 85, 145 (2000).
[2] H. Jeridi, M. A. Gharbi, T. Othman, and C. Blanc, Proc. Natl. Acad. Sci. 112, 14771 (2015).
[3] H. Jeridi, M. Tasinkevych, T. Othman, and C. Blanc, Langmuir 32, 9097 (2016).

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DOI: 10.1039/c7cp02970e
WoS: WOS:000408257700070
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N.A.

Ref HAL: hal-01588917_v1
DOI: 10.1039/c7py00531h
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Block copolymer assemblies are fascinating objects that have been studied for years. In this work, the PS-PNaSS-PS ABA triblock copolymer was synthesized by RAFT polymerization and self-assembled in a selective medium (THF/water). Various morphologies of aggregates were identified (spheres, cylinders, and vesicles) but we focused on large compound vesicles which gave birth to porous materials after solvent evaporation. The change in solvent composition upon drying was modeled and correlated to the change in morphology observed using microscopy techniques such as AFM, TEM and cryo-TEM. The large compound vesicles were found to partially fuse to form a bulk material before the vesicular compartments were opened to yield pores of about 30 nm.

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Ref Arxiv: 1811.08753
DOI: 10.1021/acs.langmuir.7b01199
WoS: WOS:000405536100019
Ref. & Cit.: NASA ADS
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We study the swelling and shrinking behavior of core-shell microgels adsorbed on silicon wafers. In these systems, the core is made of cross-linked poly(N isopropylmethacrylamide) and the shell consists of cross linked poly(N-n propylacrylamide). In suspension, these particles exhibit an extended linear swelling behavior in the temperature interval between the lower critical solution temperatures of the two polymers. Using ellipsometry and AFM, we show that this linear response is also observed in the adsorbed state.

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DOI: 10.1021/acs.macromol.7b00954
WoS: WOS:000405642700029
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The microstructure of polymer nanocomposites made with disordered silica filler (Zeosil(R) 1165MP) of industrial relevance and various coating agents is quantitatively analyzed using a combination of SAXS, TEM, and a recently developed structural model. The polymer matrix is formed by an end-functionalized styrene-butadiene statistical copolymer capable of covalent grafting on the silica nanoparticles. The effect of the coating agents with different alkyl chain length (C8, C12, and C18) on filler structure quantified in terms of aggregate formation, for different concentrations (up to 8%wt with respect to silica), and the effect of a commonly added catalyzer, DPG, are studied using the structural model. As a result we show that a strongly synergetic effect of both DPG and coating agent exist. Our findings open the road to a fundamental understanding and rational design of model and industrial nanocomposite formulation with optimized coating agents.