Accueil >
Production scientifique
|
|
Structure of nanoparticles embedded in micellar polycrystals
Auteur(s): Tamborini E., Ghofraniha N., Oberdisse J., Cipelletti L., Ramos L.
(Article) Publié:
Langmuir, vol. 28 p.8562−8570 (2012)
Texte intégral en Openaccess :
Ref HAL: hal-00705673_v1
Ref Arxiv: 1205.4746
DOI: 10.1021/la301369z
WoS: 000304783300033
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
23 Citations
Résumé: We investigate by scattering techniques the structure of water-based soft composite materials comprising a crystal made of Pluronic block-copolymer micelles arranged in a face-centered cubic lattice and a small amount (at most 2% by volume) of silica nanoparticles, of size comparable to that of the micelles. The copolymer is thermosensitive: it is hydrophilic and fully dissolved in water at low temperature (T ~ 0{\deg}C), and self-assembles into micelles at room temperature, where the block-copolymer is amphiphilic. We use contrast matching small-angle neuron scattering experiments to probe independently the structure of the nanoparticles and that of the polymer. We find that the nanoparticles do not perturb the crystalline order. In addition, a structure peak is measured for the silica nanoparticles dispersed in the polycrystalline samples. This implies that the samples are spatially heterogeneous and comprise, without macroscopic phase separation, silica-poor and silica-rich regions. We show that the nanoparticle concentration in the silica-rich regions is about tenfold the average concentration. These regions are grain boundaries between crystallites, where nanoparticles concentrate, as shown by static light scattering and by light microscopy imaging of the samples. We show that the temperature rate at which the sample is prepared strongly influence the segregation of the nanoparticles in the grain-boundaries.
|
|
|
Grain refinement and partitioning of impurities in the grain boundaries of a colloidal polycrystal
Auteur(s): Ghofraniha N., Tamborini E., Oberdisse J., Cipelletti L., Ramos L.
(Article) Publié:
Soft Matter, vol. 8 p.6214-6219 (2012)
Texte intégral en Openaccess :
Ref HAL: hal-00700912_v1
Ref Arxiv: 1203.6524
DOI: 10.1039/c2sm25488c
WoS: 000304309300004
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
28 Citations
Résumé: We study the crystallization of a colloidal model system in presence of secondary nanoparticles acting as impurities. Using confocal microscopy, we show that the nanoparticles segregate in the grain boundaries of the colloidal polycrystal. We demonstrate that the texture of the polycrystal can be tuned by varying independently the nanoparticle volume fraction and the crystallization rate, and quantify our findings using standard models for the nucleation and growth of crystalline materials. Remarkably, we find that the efficiency of the segregation of the nanoparticles in the grain-boundaries is determined solely by the typical size of the crystalline grains.
|
|
|
Diffusing Wave Spectroscopy: sonder les propriétés de produits turbides par diffusion de la lumière
Auteur(s): Cipelletti L.
Conférence invité: 15 Journées de la Formulation (Bordeaux, FR, 2012-05-29)
Ref HAL: hal-00698464_v1
Exporter : BibTex | endNote
Résumé: Les techniques classiques de diffusion de la lumière sont des méthodes bien établies pour sonder la structure et les propriétés dynamiques d'un grand nombre de systèmes de la matière molle (suspensions, polymères, émulsions, phases de tensioactifs...). Une limite importante de ces méthodes est la nécessité de travailler dans le régime de diffusion simple, ce qui restreint leur emploi aux produits essentiellement transparents. Dans cet exposé, je discuterai la Diffusing Wave Spectroscopy (DWS), une extension de la diffusion de la lumière aux produits turbides. La puissance et la versatilité de cette méthode seront démontrées en s'appuyant sur des exemples d'applications, de la mesure de taille des particules, à l'étude de la stabilité des mousses, à la caractérisation des propriétés mécaniques (rhéologiques) de systèmes de la matière molle.
|
|
|
Grain refinement and partitioning of impurities in the grain boundary network of a crystal made of amphiphilic copolymers in water
Auteur(s): Ramos L., Ghofraniha N., Tamborini E., Oberdisse J., Cipelletti L.
Conference: CopAmphi 2012 (Toulouse, FR, 2012-06-05)
Résumé: Composite materials, comprising nanoparticles (NPs) dispersed in a matrix, are of great interest, since the NPs can enhance the matrix properties or impart new functionalities and because the matrix can act as a template that structures the particles at the nanometer scale. However, controlling the spatial distribution of NPs remains a challenging task, as it usually depends crucially on the particles surface chemistry. We present here a general approach to confine NPs in colloidal materials in a controlled fashion.
We design nanocomposite material obtained by dispersing small quantities of NPs (at most 2%) in a colloidal crystalline matrix composed of thermosensitive copolymer micelles. The volume fraction of the micelles increases with temperature T, until crystallization occurs due to entropic reasons. Hence our system allows crystallization to be induced at the desired rate simply by varying T. By analogy with atomic crystals, we expect the NPs, which act as impurities, to be partially expulsed from the growing lattice and to segregate in the grain boundaries.
We use scattering techniques and confocal microscopy to probe the microscopic and mesoscopic structures of the composite materials. We show that the NPs do not perturb the crystalline structure of the micelles but that different crystallization rates lead to different NPs rearrangements. We show that the NPs segregate in the grain-boundaries of the copolymer polycrystal. We demonstrate that the texture of the polycrystal can be tuned by varying independently the nanoparticle volume fraction and the crystallization rate, and quantify our findings using classical nucleation theory. Remarkably, we find that the efficiency of the segregation of the NPs in the grain-boundaries is determined solely by the typical size of the crystalline grains.
|
|
|
Aging and stress relaxation in an actin network
Auteur(s): Cipelletti L.
Conférence invité: Aging of Engineering Materials: a Computational Approach to Durability and Sustainability (Zurich, CH, 2012-02-08)
Ref HAL: hal-00662701_v1
Exporter : BibTex | endNote
Résumé: Actin networks are an essential component of living cells, to which they impart the required mechnaical properties. Here, we study in-vitro cross-linked actin networks with a combination of rheology, microscopy and a novel space-resolved dynamic light scattering method. Our measurements suggest that the aging of the network is due to the progressive release of internal stresses, made possible by unbinding - rebinding events within the network.
|
|
|
Overview of time- and space resolved dynamic light scattering methods
Auteur(s): Cipelletti L.
Conference: TRC Workshop (Noordwijk, NL, 2012-01-10)
|
|
|
Dynamical heterogeneities in glasses, colloids, and granular media
Auteur(s): Berthier L., Biroli Giulio, Boucaud Philippe, Cipelletti L., Van saarloos Wim
Ouvrage: Oxford University Press (2011) 1p.
Commentaires: , DOI = 10.1093/acprof:oso/9780199691470.001.0001
|