Ref HAL: hal-01627865_v1
DOI: 10.1016/j.cis.2017.06.014
WoS: WOS:000412150100017
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11 Citations
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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.

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Ref Arxiv: 1811.06903
DOI: 10.1039/c7sm00596b
WoS: WOS:000411436600003
Ref. & Cit.: NASA ADS
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5 Citations
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Vegetable oil based hybrid films were developed thanks to a novel solvent- and heating- free method at the air-water interface using silylated castor oil cross-linked via a sol-gel reaction. To understand the mechanism of the hybrid film formation, the reaction kinetics was studied in detail by using complementary techniques: rheology, thermogravimetric analysis, and infrared spectroscopy. The mechanical properties of the final films were investigated by nano-indentation, whereas their structure was studied using a combination of wide-angle X-ray scattering, electron diffraction, and atomic force microscopy. We found that solid and transparent films form in 24 hours and, by changing the silica precursor to castor oil ratio, their mechanical properties are tunable in the MPa-range by about a factor of twenty. In addition to that, a possible optimization of the cross-linking reaction with different catalysts was explored and finally, cytotoxicity tests were performed on fibroblasts proving the absence of film toxicity. The results of this work pave the way to a straightforward synthesis of castor-oil films with tunable mechanical properties: hybrid films cross-linked at the air-water interface combine an easy and cheap spreading protocol with the features of their thermal history optimized for possible future micro/nano drug loading, thus representing excellent candidates for the replacement of non-environment friendly petroleum-based materials.

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DOI: 10.1021/acs.macromol.7b01371
WoS: WOS:000412965900033
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5 Citations
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The influence of surface-modification of TiO2-nanoparticles with phosphonic acid molecules on the structure of polymer nanocomposites has been studied by small-angle scattering and transmission electron microscopy. The grafting of phosphonic acids was done by phase transfer into chloroform, and polymer nanocomposites have been formulated by solvent casting with two polymers of slightly different hydrophobicity, PMMA and PEMA. By analyzing the shape of the scattering curves around the interparticle correlation peak, and in particular the depth of the correlation hole, information on nearest neighbor correlations between nanoparticles is obtained. While local nanoparticle arrangements are found to be independent of the global particle volume fraction, they are controlled by the degree of hydrophobicity of the alkyl phosphonic acid grafts with respect to hydrophobicity of matrix. Quantitative analysis of the correlation hole thus evidences the fine-tuning of local nanocomposite structure with phosphonic acids.

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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

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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)

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N.A.