We propose a simple and original way to prepare surfactant-free SWNT/hydrosoluble polymer composites with high concentrations of individual SWNT. We first disperse single-walled carbon nanotubes (SWNT) in aqueous suspensions using bile salts (BS), and we mix them with a solution of hydrosoluble polymer, poly(vinylpyrrolidone) (PVP) or poly(vinyl alcohol) (PVA). We measure the yield using visible–NIR absorption spectroscopy, and we probe both the chemical environment of the nanotubes and the effectiveness of individualization from coupled Raman/photoluminescence studies. We evidence a direct exchange of BS molecules and PVA chains at the surface of SWNT. By contrast, no direct exchange is observed with PVP. On the other hand, we show that a simple dialysis process leads to the preparation of aqueous suspensions of SWNT covered by PVP or PVA with high yields and an effective individualization of the nanotubes.

The dynamics of colloidal particles at interfaces between two fluids plays a central role in microrheology, encapsulation, emulsification, biofilm formation, water remediation and the interface-driven assembly of materials. Common intuition corroborated by hydrodynamic theories, suggests that such dynamics is governed by a viscous force lower than that observed in the more viscous fluid. Here, we show experimentally that a particle straddling an air/water interface feels a large viscous drag that is unexpectedly larger than that measured in the bulk. We suggest that such a result arises from thermally activated fluctuations of the interface at the solid/air/liquid triple line and their coupling to the particle drag through the fluctuation–dissipation theorem. Our findings should inform approaches for improved control of the kinetically driven assembly of anisotropic particles with a large triple-line-length/particle-size ratio, and help to understand the formation and structure of such arrested materials.

The dynamics of polymer and filler in simplified industrial silica-styrene-butadiene nanocomposites (silica Zeosil 1165 MP, volume fraction 0 – 21%v) have been studied with broadband dielectric spectroscopy (BDS) and nuclear magnetic resonance (NMR). The fraction of graftable matrix chains was varied from 0 – 100%D3. The introduction of silica nanoparticles is shown to leave the segmental relaxation unaffected, an observation confirmed by the measurement of only a thin (some Angstroms thick) immobilized layer by NMR. The low-frequency measurements are resolved in two distinct dielectric Maxwell-Wagner-Sillars (MWS) processes of different behavior with respect to changes of large-scale silica structures induced by variations of filler fraction and grafting. In particular, depercolation of the silica filler at constant volume fraction with increasing grafting leaves the first MWS-process unaffected, but has direct consequences on rheological reinforcement, and decreases the strength of the second MWS by about a decade. This sensitivity to large-scale reorganizations together with a characterization of local polymer dynamics provides insight over many length- and time-scales into structure and dynamics of nanocomposites, and thus the physical origin of the reinforcement effect. 

We explore the influence of particle softness and internal structure on both the bulk andinterfacial rheological properties of colloidal suspensions. We probe bulk stresses byconventional rheology, by measuring the flow curves, shear stress versus strain rate, forsuspensions of soft, deformable microgel particles and suspensions of near hard-sphere-likesilica particles. A similar behaviour is seen for both kinds of particles in suspensions atconcentrations up to the random close packing volume fraction, in agreement with recenttheoretical predictions for sub-micron colloids. Transient interfacial stresses are measured byanalyzing the patterns formed by the interface between the suspensions and their solvent, dueto a generalized Saffman–Taylor hydrodynamic instability. At odds with the bulk behaviour,we find that microgels and hard particle suspensions exhibit vastly different interfacial stressproperties. We propose that this surprising behaviour results mainly from the difference inparticle internal structure (polymeric network for microgels versus compact solid for the silicaparticles), rather than softness alone.

Due to the existence of open channels, light could theoretically be transmitted through disorderedmedia with 100% efficiency. However, because of the large number of channels to be controlledor measured, this has been never observed experimentally. To avoid this difficulty we considerobservables easier to handle experimentally. By measuring the correlations of the field transmittedthrough a disordered medium, we were able to count the number of channels involved in transmissionand to compare this number with theory. For a sample of transmission 1=25, we get a number ofmodes about 15 times smaller than for free space propagation. This figure is in good agreementwith theoretical prediction.

It is often necessary to tailor nanoparticle (NP) interactions and their compatibility with a polymer matrix by grafting organic groups, but the commonly used silanization route offers little versatility, particularly in water. Herein, alumina-coated silica NPs in aqueous sols have been modified for the first time with low molecular-weight phosphonic acids (PAs) bearing organic groups of various hydrophobicities and charges: propyl, pentyl and octyl PAs, and two PAs bearing hydrophilic groups, either a neutraldiethylene glycol (DEPA) or a potentially charged carboxylic acid (CAPA) group. The interactions and aggregation in the sols have been investigated using zeta potential measurements, dynamic light scattering, transmission electron microscopy, and small-angle scattering methods. The surface modification has been studied using FTIR and 31P MAS NMR spectroscopies. Both high grafting density r and high hydrophobicity of the groups on the PAs induced aggregation, whereas suspensions of NPsgrafted by DEPA remained stable up to the highestr . Unexpectedly, CAPA-modified NPs showedaggregation even at low r, suggesting that the carboxylic end group was also grafted to the surface. Surface modification of aqueous sols with PAs allows thus for the grafting of a higher density and a wider variety of organic groups than organosilanes, offering an increased control of the interactions between NPs, which is of interest for designing waterborne nanocomposites.

Sickle cell anemia is a blood disorder, known to affect the microcirculation and is characterized by painful vaso-occlusive crises in deep tissues. During the last three decades, many scenarios based on the enhanced adhesive properties of the membrane of sickle red blood cells have been proposed, all related to a final decrease in vessels lumen by cells accumulation on the vascular walls. Up to now, none of these scenarios considered the possible role played by the geometry of the flow on deposition. The question of the exact locations of occlusive events at the microcirculatory scale remains open. Here, using microfluidic devices where both geometry and oxygen levels can be controlled, we show that the flow of a suspension of sickle red blood cells around an acute corner of a triangular pillar or of a bifurcation, leads to the enhanced deposition and aggregation of cells. Thanks to our devices, we follow the growth of these aggregates in time and show that their length does not depend on oxygenation levels; instead, we find that their morphology changes dramatically to filamentous structures when using autologous plasma as a suspending fluid. We finally discuss the possible role played by such aggregates in vaso-occlusive events.