The mucociliary function of the bronchial epithelium ensures the continuous clearance of the respiratory system. This function relies on two main elements: mucus and cilia beating. We perform here a rheological characterization of mucus samples extracted from ALI (Air-liquid interface) cultures of bronchial epithelium. Our approach combines macro- and micro-rheology techniques with the aim of quantifying the mucus viscoelastic properties at different length scales (from the size of bronchial cilia up to the scale on which mucus is transported). In addition, this methodology allows us to compare the rheological behavior of mucus samples corresponding to different pathologies

The mucociliary function of the bronchial epithelium ensures the continuous clearance of the respiratory system. This function relies on two main elements: mucus and cilia beating. We perform here a rheological characterization of mucus samples extracted from ALI (Air-liquid interface) cultures of bronchial epithelium. Our approach combines macro- and micro-rheology techniques with the aim of quantifying the mucus viscoelastic properties at different length scales (from the size of bronchial cilia up to the scale on which mucus is transported). In addition, this methodology allows us to compare the rheological behavior of mucus samples corresponding to different pathologies

The physical behavior of colloids suspended in a fluid close to a solid wall has been well characterized in the past[1]. Conversely the dynamical behavior of a particle close to a fluid interface is a relatively new field with strong implications in green and food processing [2]. Previous focus was limited to spherical particle’s viscous drag close to the interface [3] and wetting dynamics after interface breaching [4]. In this paper we present experimental results on the dynamics of micrometric colloids(spheres and ellipsoids)close to an interface between water based solution and air prior to the particle’s interfacebreaching. In order to study such dynamics we use a home-made pending-drop setup where particles dispersed in water based solutions (mixture with heavy water and/or with salt at different molarity) sediment towards the interface with air of the drop.The drop curvature is adjusted via the water solution pressure in order to obtain a flat interface at the particle scale. All the particle’s degreesof freedom (i.e. distance from the interface, position in a plane parallel to the interface and, for ellipsoids,orientation) are measured tracking the particle-interface interference patterns using incoherent ledswith three different wavelengths. The typical dynamics of a particle approaching the interface shows an initial sedimentation regimedriven by gravity and viscous drag. Closer to the interface a second regime arises which strongly depend on the solution molarity and density and particle morphology. For both particles morphologies the sedimentation dynamics stops at a distance from the interface of the order of hundreds nanometers. At small molarity (0.5 mM) both type of particles fluctuate around this position during the entire experimental observation time interval (10^3s). Increasing the molarity, ellipsoids more easily then spheres start to escape from this position approaching rapidly the interface till a distance of few nanometers. Such observations point out the importance of the electrostatic and morphology in the interaction with the interface. A calibration of thisinteraction will be presented by taking advantage of the buoyancy driving force changing the solution density. Building up on all these experimental observations, amodel considering the interplay between all the contributing interactions (i.e. gravity with buoyancy, electrostatics and Van der Walls) will be discussed and compared to the experimental results. [1]M. Hosoda, K. Sakai, and K. Takagi, Phys. Rev. E 58, 6275 (1998).[2] V. Sarrot, Z. Huang, D. Legendre, P. Guiraud, Chem. Eng. Sci. 62, 7359–7369 (2007).[3] G. M. Wang, R. Prabhakar and E. M. Sevick, Phys. Rev. Lett. 103, 248303 (2009).[4] A. Wang, W.B. Rogers, V.N. Manoharan, arXiv:1607.08167 [cond-mat.soft].

Biological or artificial microswimmers move performing trajectories of different kinds such as rectilinear, circular, or spiral ones. Here, we report on circular trajectories observed for active Janus colloids trapped at the air−water interface. Circular motion is due to asymmetric and nonuni form surface properties of the particles caused by fabrication. Motion persistence is enhanced by the partial wetted state of the Janus particles actively moving in two dimensions at the air−water interface. The slowing down of in plane and out of plane rotational diffusions is described and discussed.

Colloidal suspensions of anisotropic nanoparticles can spontaneously self-organize in liquid-crystalline phases beyond some concentration threshold. These phases often respond to electric and magnetic fields. At lower concentrations, usual isotropic liquids are observed but they can display very strong Kerr and Cotton-Mouton effects (i.e., field-induced particle orientation). For many examples of these colloidal suspensions, the solvent is water, which hinders most electro-optic applications. Here, for goethite (α-FeOOH) nanorod dispersions, we show that water can be replaced by polar aprotic solvents, such as N-methyl-2-pyrrolidone (NMP) and dimethylsulfoxide (DMSO), without loss of colloidal stability. By polarized-light microscopy, small-angle X-ray scattering and electro-optic measurements, we found that the nematic phase, with its field-response properties, is retained. Moreover, a strong Kerr effect was also observed with isotropic goethite suspensions in these polar aprotic solvents. Furthermore, we found no significant difference in the behavior of both the nematic and isotropic phases between the aqueous and non-aqueous dispersions. Our work shows that goethite nanorod suspensions in polar aprotic solvents, suitable for electro-optic applications, can easily be produced and that they keep all their outstanding properties. It also suggests that this solvent replacement method could be extended to the aqueous colloidal suspensions of other kinds of charged anisotropic nanoparticles.

Liquid crystal ordering is an opportunity to develop novel materials and applications with spontaneouslyaligned anisotropic particles [1,2]. In this way, the organization of graphene flakes in liquid crystals provides new methodologies for the still challenging structural characterization of such materials. In this work, we will present a review of our recent results in the preparation and characterization of lyotropic LC made from concentrated aqueous suspensions based graphene oxide (GO) and/or reduced graphene oxide (RGO), and we will show some of ours preliminary approaches to achieve large and well-ordered domains of lyotropic liquid crystals. According with literature, for graphene, it is known that GO flakes easily disperse in water and spontaneously form liquid crystals at high concentrations. However, most of their electronic functionalities are lost during the oxidation treatments. RGO is of greater interest since a large part of functionalities are recovered but chemical reduction of GO in water generally results in the aggregation of the flakes. We recently showed how to obtain water-based RGO liquid crystals stabilized by surfactant molecules [3]. Structural and thermodynamic characterizations provide statistical information on the dimensions of the graphene flakes, which are found to be comparable with those of neat graphene oxide flakes. We have started to combined these new liquid crystals with nanoparticles, these graphene-based LC/Nanoparticles composites being useful to design coatings and functional materials.
References
[1] Yuan J.; Luna A.; Neri W.; Zakri C.; Schilling T.; Colin A.; Poulin, P. Graphene liquid crystal retardedpercolation for new high-k materials. Nat. Commun. 6:8700 (2015) doi: 10.1038/ncomms9700
[2] Zakri, C.; Blanc, C.; Grelet, E.; Zamora-Ledezma, C.; Puech, N.; Anglaret, E.; and Poulin, P. Liquid crystals ofcarbon nanotubes and graphene. Phil. Trans. R. Soc. A., 371, 20120499, pp 1-15 (2013)
[3] Zamora-Ledezma, C.; Puech, N.; Zakri, C.; Grelet, E.; Moulton, S. E.; Wallace, G. G.; Gambhir, S.; Blanc, C.;Anglaret, E.; and Poulin, P. Liquid Crystallinity and Dimensions of Surfactant-Stabilized Sheets of ReducedGraphene Oxide. J. Phys. Chem. Lett., 3 (17), pp 2425–2430 (2012)

Processing routes and characterization methods commonly used in carbon nanotubes research require agood dispersion of nanotubes in liquid media. In particular, single walled carbon nanotubes (SWNT) mustbe dispersed, preferably as individuals in order to tap their full potential in optical applications [1]. Onesensitive probe of dispersion is photoluminescence (PL), since it is quenched as long as semiconductingSWNT are bundled with metallic ones. However, the detailed interpretation of the mechanismsresponsible for PL and the relation between PL intensity and dispersion state are still a matter ofcontroversy [2].
In this work, we present new insights on the near infrared photoluminescence of aqueous suspensions ofSWNT stabilized by bile salts surfactants. In one hand, the dispersion of the nanotubes is probed byabsorption spectroscopy, where the absorption coefficient shows high sensitivity to nanotube exfoliation.On the other hand, we revisit the interpretation of the NIR-PL spectra, and we discuss the differentphysical mechanisms responsible of the PL, i.e. Direct Excitonic Transitions (DET), Exciton-PhononCoupling (EPC), and Exciton Energy Transfer (EET) between nanotubes [3-7]. Finally, we discuss thekinetics of PL as a function of sonication time and debundling/exfoliation of SWNT (Figure 1).
References
[1] S. M. Bachilo, et al. Science, 298 (2002). pp 2361-2366.
[2] V.C Moore, et al. Nano letters, 3 (2003). pp 1379-1382.
[3] T. Ando, J. Phys. Soc. Jpn, 66(4) (1997). pp. 1066-1073.
[4] J. Maultzsch, et al. PRB, 72(24) (2005). pp. 241402.
[5] F. Wang, et al. Science, 308(5723) 2005. pp. 838-841.
[6] S. Chou, et al. PRL, 94(12) (2005), pp. 127402.
[7] P. Tan, et al. PRL, 99(13) (2007) pp. 137402.