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(423) Articles dans des revues


Multiple dynamic regimes in concentrated microgel systems
Auteur(s): Sessoms David A., Bischofberger Irmgard, Cipelletti L., Trappe Véronique
(Article) Publié:
Philosophical Transactions Of The Royal Society Of London. Series A, Containing Papers Of A Mathematical Or Physical Character, vol. 367 p.50135032 (2009)
Texte intégral en Openaccess :
Ref HAL: hal00512108_v1
PMID 19933125
Ref Arxiv: 0907.2329
DOI: 10.1098/rsta.2009.0178
WoS: 000271780000003
Ref. & Cit.: NASA ADS
Exporter : BibTex  endNote
65 Citations
Résumé: We investigate dynamical heterogeneities in the collective relaxation of a concentrated microgel system, for which the packing fraction can be conveniently varied by changing the temperature. The packing fraction dependent mechanical properties are characterised by a fluidsolid transition, where the system properties switch from a viscous to an elastic lowfrequency behaviour. Approaching this transition from below, we find that the range of spatial correlations in the dynamics increases. Beyond this transition, the spatial correlation range reaches a maximum, extending over the entire observable system size of approximately 5 mm. Increasing the packing fraction even further leads to a second transition, which is characterised by the development of large zones of lower and higher dynamical activity that are well separated from each other; the range of correlation decreases at this point. This striking nonmonotonic dependence of the spatial correlation length on volume fraction is reminiscent of the behaviour recently observed at the jamming/rigidity transition in granular systems (Lechenault et al. 2008). We identify this second transition as the transition to 'squeezed' states, where the constituents of the system start to exert direct contact forces on each other, such that the dynamics becomes increasingly determined by imbalanced stresses. Evidence of this transition is also found in the frequency dependence of the storage and loss moduli, which become increasingly coupled as direct friction between the particles starts to contribute to the dissipative losses within the system. To our knowledge, our data provide the first observation of a qualitative change in dynamical heterogeneity as the dynamics switch from purely thermallydriven to stressdriven.
Commentaires: published in Phil. Trans. R. Soc. A



Dynamic light scattering measurements in the activated regime of dense colloidal hard spheres
Auteur(s): El masri Djamel, Brambilla G., Pierno Matteo, Petekidis George, Schofield Andrew, Berthier L., Cipelletti L.
(Article) Publié:
Journal Of Statistical Mechanics: Theory And Experiment, vol. p.P07015 (2009)
Texte intégral en Openaccess :
Ref HAL: hal00512107_v1
Ref Arxiv: 0903.1933
DOI: 10.1088/17425468/2009/07/P07015
WoS: 000269353300015
Ref. & Cit.: NASA ADS
Exporter : BibTex  endNote
42 Citations
Résumé: We use dynamic light scattering and numerical simulations to study the approach to equilibrium and the equilibrium dynamics of systems of colloidal hard spheres over a broad range of density, from dilute systems up to very concentrated suspensions undergoing glassy dynamics. We discuss several experimental issues (sedimentation, thermal control, nonequilibrium aging effects, dynamic heterogeneity) arising when very large relaxation times are measured. When analyzed over more than seven decades in time, we find that the equilibrium relaxation time, tau_alpha, of our system is described by the algebraic divergence predicted by modecoupling theory over a window of about three decades. At higher density, tau_alpha increases exponentially with distance to a critical volume fraction phi_0 which is much larger than the modecoupling singularity. This is reminiscent of the behavior of molecular glassformers in the activated regime. We compare these results to previous work, carefully discussing crystallization and size polydispersity effects. Our results suggest the absence of a genuine algebraic divergence of tau_alpha in colloidal hard spheres.
Commentaires: 16 pages; 12 figures



SANS study of the selforganization of gradient copolymers with ligand groups in supercritical CO2
Auteur(s): Ribaut Tiphaine, Oberdisse J., Annighofer Burkhard, Stoychev Ivan, Fournel Bruno, Sarrade Stéphane, LacroixDesmazes Patrick
(Article) Publié:
Soft Matter, vol. 5 p.49624970 (2009)
Texte intégral en Openaccess :



Dynamics of a colloidstabilized cream
Auteur(s): Herzig E. M., Robert A., Zand D. D. van 't, Cipelletti L., Pusey P. N., Clegg P. S.
(Article) Publié:
Physical Review E: Statistical, Nonlinear, And Soft Matter Physics, vol. 79 p.011405 (2009)
Texte intégral en Openaccess :
Ref HAL: hal00512105_v1
PMID 19257033
Ref Arxiv: 0812.3847
DOI: 10.1103/PhysRevE.79.011405
WoS: 000262976600046
Ref. & Cit.: NASA ADS
Exporter : BibTex  endNote
22 Citations
Résumé: We use xray photon correlation spectroscopy to investigate the dynamics of a high volume fraction emulsion creaming under gravity. The dodecaneinwater emulsion has interfaces stabilized solely by colloidal particles (silica). The samples were observed soon after mixing: as the emulsion becomes compact we discern two regimes of ageing with a crossover between them. The young emulsion has faster dynamics associated with creaming in a crowded environment accompanied by local rearrangements. The dynamics slow down for the older emulsion although our studies show that motion is associated with large intermittent events. The relaxation rate, as seen from the intensity autocorrelation function, depends linearly on the wave vector at all times; however, the exponent associated with the line shape changes from 1.5 for young samples to less than 1 as the emulsion ages. The combination of ballisticlike dynamics, an exponent that drops below 1 and large intermittent fluctuations has not been reported before.
Commentaires: 8 pages, 5 figures



Anisotropic Thin Films of SingleWall Carbon Nanotubes from Aligned Lyotropic Nematic Suspensions
Auteur(s): ZamoraLedezma C., Blanc C., Maugey M., Zakri C., Poulin P., Anglaret E.
(Article) Publié:
Nano Letters, vol. 8 p.41034107 (2008)
Ref HAL: hal00504366_v1
Exporter : BibTex  endNote
Résumé: Lyotropic nematic aqueous suspensions of singlewall carbon nanotubes can be uniformly aligned in thin cells by shearing. Homogeneous anisotropic thin films of nanotubes can be prepared by drying the nematic. Optical transmission between parallel or crossed polarizers is measured and described in order to estimate the dichroic ratio. The order parameter is measured using polarized Raman spectroscopy and found to be quite weak due to entanglement of the nanotubes and/or to an intrinsic viscoelastic behavior of the nanotube suspensions.



Tuning colloidal interactions through coordination chemistry
Auteur(s): Joubert M., In M.
(Article) Publié:
Chemphyschem, vol. 9 p.10101019 (2008)
Texte intégral en Openaccess :
Ref HAL: hal00534477_v1
PMID 18418820
DOI: 10.1002/cphc.200700593
WoS: 000255845500009
Exporter : BibTex  endNote
4 Citations
Résumé: The present work addresses the question of the range and amplitude of bridging attraction that is induced between surfactant micelles functionalized with complexing groups in the presence of coordination centers. An alkylethoxylated ester phosphate (AEP) is synthesized from a nonionic surfactant and anchored into DTAB micelles. In the absence of any coordination center, functionalized micelles repel each other. Phase behavior, dynamic light scattering and small angle neutrons scattering (SANS) experiments show that this repulsive interaction is switched to attractive by the addition of coordination centers such as aluminum cations. The extent of the composition range of coexisting phase depends on the concentration of coordination center and on the pH. Analysis of the structure factor obtained from SANS shows that the range of attraction is determined by the molecular dimension of the chelating surfactant, while the depth can be tuned with the concentration of coordination center and the pH, The strong influence of the pH is interpreted as arising from the condensation of aluminium cations that lead to high functional polynuclear complexes.



Elasticity of twodimensional crystalline monolayers of fatty acid salts at an airwater surface
Auteur(s): Daillant Jean, Pignat Jeremy, Cantin Sophie, Perrot Francoise, Mora S., Konovalov Oleg
(Article) Publié:
Soft Matter, vol. 5 p.203207 (2009)
DOI: 10.1039/b810134e
WoS: 000263272100025
10 Citations
Résumé: The elastic properties of organicinorganic twodimensional crystals floating at the water surface have been fully characterized by grazing incidence Xray diffuse scattering and highresolution diffraction. We show that the strong interaction between the organic molecules and the inorganic divalent cations is enough for these nm thick crystals to behave like true solids, with a residual tension of 1 x 10(4)10(3) N m(1). Their bending rigidity is renormalized as kappa(q) proportional to q(eta k) with eta(k) = 0.25 +/ 0.07 and a microscopic value approximate to 100 k(B)T at q = 1 x 10(9) m(1). The inplane elastic constants behave like q(eta u) with eta(u) = 1.41 +/ 0.2, obeying the scaling relation eta(u) = 2  2 eta(k). These results are consistent with a longrange phononmediated interaction between outofplane fluctuations but the values of the exponents differ from those generally obtained in numerical simulations.
