Ref HAL: hal-01131193_v1
DOI: 10.1021/jp511969t
WoS: 000351189100050
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4 Citations
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This work focuses on the hybrid system between C70 and a carbon nanotube (C70 peapod) where the encapsulated C70 peas and the nanotube pod are bonded through van der Waals interactions. The nonresonant Raman spectra of these nanomaterials were calculated in the framework of the bond-polarizability model combined with the spectral moment method. The optimal configurations of C70 molecules are derived using a convenient Lennard-Jones potential. We find that increasing the nanotube diameter leads to three successive configurations: lying, tilted, or standing alignments of C70 molecules along the nanotube axis. The changes of the Raman spectra as a function of the configuration of the C70 molecules inside the nanotubes are identified. The nanotube chirality and diameter effects on the Raman-active modes in peapods with different C70 filling factors are studied. This workprovides benchmark theoretical results to understand the experimental Raman spectra of C70 fullerene peapods.

Ref HAL: hal-01130620_v1
DOI: 10.1063/1.4913679
WoS: 000350546600005
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20 Citations
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We demonstrate second harmonic generation in a gallium nitride photonic crystal cavity embedded in a two-dimensional free-standing photonic crystal platform on silicon. The photonic crystal nanocavity is optically pumped with a continuous-wave laser at telecom wavelengths in the transparency window of the nitride material. The harmonic generation is evidenced by the spectral range of the emitted signal, the quadratic power dependence vs. input power, and the spectral dependence of second harmonic signal. The harmonic emission pattern is correlated to the harmonic polarizationgenerated by the second-order nonlinear susceptibilities and the electric fields of the fundamental cavity mode.

Ref HAL: hal-01123545_v1
DOI: 10.1021/acs.jpcc.5b00168
WoS: 000350840700087
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18 Citations
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New one-dimensional (1D) hybrid nanosystems are elaborated with metalated or metal free phthalocyanine molecules encapsulated into the hollow core of single-walled carbon nanotubes. The X-ray diffraction experiments coupled to simulation allow evidencing the 1D structural organization of the molecules inside the nanotubes. The angle between the molecule ring and the nanotube axis is close to 32° as determined from our density functional theory calculations. Confined molecules display Raman spectra hardly altered with respect to the bulk phase, suggesting a rather weak interaction with the tubes. For comparison, noncovalent functionalization at the outer surface of the tube is also investigated. The vibrational properties of the molecules functionalized at the outer surface of tubes display important modifications. A significant curvature of the phthalocyanine is induced by the interaction with the tube walls, leading to change of the central atom position within the molecular ring, in good agreement with our first-principles calculations.

Ref HAL: hal-01115925_v1
PMID 25679615
Ref Arxiv: 1410.5683
DOI: 10.1103/PhysRevE.91.012203
WoS: 000348681000006
Ref. & Cit.: NASA ADS
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49 Citations
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We use large scale computer simulations and finite size scaling analysis to study the shear rheology of dense three-dimensional suspensions of frictionless non-Brownian particles in the vicinity of the jamming transition. We perform simulations of soft repulsive particles at constant shear rate, constant pressure, and finite system size, and study carefully the asymptotic limits of large system sizes and infinitely hard particle repulsion. Extending earlier analysis by about two orders of magnitude, we first study the asymptotic behavior of the shear viscosity in the hard particle limit. We confirm its asymptotic power law divergence at the jamming transition, but show that a precise determination of the critical density and critical exponent is difficult due to the `multiscaling' behavior of the viscosity. Additionally, finite-size scaling analysis suggests that this divergence is accompanied by a growing correlation length scale, which also diverges algebraically. We then study the effect of soft repulsion, and propose a natural extension of the standard granular rheology to account for softness effects, which we validate from simulations. Close to the jamming transition, this `soft granular rheology' offers a detailed description of the non-linear rheology of soft particles, which differs from earlier empirical scaling forms.

Commentaires: 12 pages, 9 figs. Réf Journal: Phys. Rev. E 91, 012203 (2015)

Résumé:

The dynamics of gels formed by strongly attractive colloidal particles exhibit very peculiar behavior: correlation functions measured by scattering methods decay steeper than exponentially (as opposed to the stretched exponential typically observed in glassy systems), and particle motion is ballistic (as opposed to the more usual diffusive behavior). Quite remarkably, over the last years the same behavior has been observed in a large variety of systems, including concentrated emulsions, foams, surfactant phases, actin networks and even hard condensed matter systems such as molecular or metallic glass formers. In this seminar, I'll review these experiments and discuss current models, based on the relaxation of internal stresses.

Résumé:

Surface tension is the tendency of a liquid to minimize its interface with another substance. Surface tension literally shapes the world around us: soap bubbles and liquid drops, insects striding on a water pond, and water transport in plants are but a few phenomena where surface tension plays a key role. Does a surface tension exist between two miscible fluids? While the interface between two such fluids inevitably fades out as the liquids mix due to diffusion, physicist and mathematician D. Korteweg proposed more than a century ago that an effective, off-equilibrium surface tension rules the behavior of the interface on time scales shorter than mixing. A direct proof of Korteweg’s ideas, however, was still lacking. Here, we report on experiments probing the interface between two miscible fluids, an aqueous suspension of submicron colloidal particles and water. The suspension is confined between two plates and water is injected through a small hole in the top plate. As water is pushed through the more viscous colloidal suspension, the interface between the two fluids is destabilized, forming distinctive patterns similar to those observed for immiscible fluids. We show that the interface shape is ruled by an off-equilibrium surface tension and validate quantitatively Korteweg’s predictions. These findings open the way to a better understanding of a wealth of phenomena, from crystal nucleation and growth to shaping and forming in material science