Search results for "Crystallization"
showing 10 items of 774 documents
'Cold' crystallization in nanostructurized 80GeSe2-20Ga2Se3 glass
2015
International audience; 'Cold' crystallization in 80GeSe 2-20Ga 2 Se 3 chalcogenide glass nanostructurized due to thermal annealing at 380°C for 10, 25, 50, 80, and 100 h are probed with X-ray diffraction, atomic force, and scanning electron microscopy, as well as positron annihilation spectroscopy performed in positron annihilation lifetime and Doppler broadening of annihilation line modes. It is shown that changes in defect-related component in the fit of experimental positron lifetime spectra for nanocrystallized glasses testify in favor of structural fragmentation of larger free-volume entities into smaller ones. Nanocrystallites of Ga 2 Se 3 and/or GeGa 4 Se 8 phases and prevalent GeSe…
Compatibilized Polyamide 6/Polyethylene Blends Clay Nanocomposites: Effect of the Degradation and Stabilization of the Clay Modifier
2008
Abstract Blends of polyamide 6 (PA6) and high-density polyethylene (HDPE) were compatibilized using an already investigated method and a sample of Cloisite 15A, a montmorillonite modified with ammonium quaternary salts was added. The blends were prepared in a twin screw extruder and characterized from a morphological, rheological and mechanical point of view. The results indicated that, despite a good morphology achieved in the filled blends and a moderate intercalation of the clay, the mechanical properties are far from being good, especially the ultimate properties. In order to investigate the possible influence of the inhibition of the crystallization and of the degradation of the organi…
In Situ Heating TEM Study of Onion-like WS2 and MoS2 Nanostructures Obtained via MOCVD
2007
We report on the in situ heating transmission electron microscopy (TEM) study of WS2 and MoS2 nanoparticles obtained from metal–organic chemical vapor deposition (MOCVD). The general behavior of MoS2 and WS2 is similar: Round, amorphous particles in the pristine sample transform to hollow, onion-like particles upon annealing. A second type of particle with straight layers exhibits only minor changes. A significant difference between both compounds could be demonstrated in their crystallization behavior. The results of the in situ heating experiments are compared to those obtained from an ex situ annealing process under Ar.
Morphosynthesis of Strontianite Nanowires Using Polyacrylate Templates Tethered onto Self-Assembled Monolayers
2005
Strontianite nanowires have been synthesized on self-assembled monolayers (SAM) in the presence of polyacrylate templates. The morphology of this product exhibits characteristic differences from that of products obtained in the absence of polyacrylate. It is demonstrated that the template-induced crystallization process involves the interaction between the SAM surface, polyacrylate (a dissolved polyelectrolyte), and the cations/anions in solution. By the combination of these components, hierarchically ordered mineral hybrid structures are formed.
Octave-spanning ultraflat supercontinuum with soft-glass photonic crystal fibers
2009
We theoretically identify some photonic-crystal-fiber structures, made up of soft glass, that generate ultrawide (over an octave) and very smooth supercontinuum spectra when illuminated with femtosecond pulsed light. The design of the fiber geometry in order to reach a nearly ultraflattened normal dispersion behavior is crucial to accomplish the above goal. Our numerical simulations reveal that these supercontinuum sources show high stability and no significant changes are detected even for fairly large variations of the incident pulse. Ministerio de Ciencia e Innovación (TEC2008-05490) and Generalitat Valenciana (GV/2007/043).
Merging models of biomineralisation with concepts of nonclassical crystallisation: is a liquid amorphous precursor involved in the formation of the p…
2012
16 pages; International audience; The calcitic prisms of Pinna nobilis (Pinnidae, Linnaeus 1758) are shown to be perfect examples of a mesocrystalline material. Based on their ultrastructure and on the occurrence of an amorphous transient precursor during the early stages of prism formation, we provide evidence for the pathway of mesocrystallisation proposed by Seto et al. (2012), which proceeds not by self-organized oriented attachment of crystalline nano-bricks but by aggregation of initially amorphous nanogranules which later transform by epitaxial nucleation to a threedimensional array of well aligned nanocrystals. We further fathom the role of a liquid amorphous calcium carbonate in bi…
Crystallization kinetics of colloidal model suspensions: recent achievements and new perspectives
2014
Colloidal model systems allow studying crystallization kinetics under fairly ideal conditions with rather well characterized pair interactions and minimized external influences. In complementary approaches therefore experiment, analytic theory and simulation have been employed to study colloidal solidification in great detail. These studies were based on advanced optical methods, careful system characterization and sophisticated numerical methods. Both the effects of the type, strength and range of the pair-interaction between the colloidal particles and those of the colloid-specific polydispersity were addressed in a quantitative way. Key parameters of crystallization were derived and comp…
Drastic Variation of the Microstructure Formation in a Charged Sphere Colloidal Model System by Adding Merely Tiny Amounts of Larger Particles
2010
We have investigated the changes of the crystallization scenario in charged sphere colloidal suspensions upon adding tiny amounts of a second, larger and higher charged particle species (size ratio 4.3, charge ratio 1.6). For even minute amounts of added particles, less than 1%, the whole crystallization behavior changes dramatically and for this reason the resulting microstructure of the solidified material. Both nucleation and growth of crystals slow down drastically and considerably coarsen the resulting microstructure. We show that this is related to a considerable decrease of the kinetic prefactors of both nucleation and growth, while at the same time the nucleation barrier height show…
Crystal nucleation versus vitrification in charged colloidal suspensions
2007
We investigated the solidification behaviour of thoroughly deionised aqueous suspensions of polystyrene latex spheres by various optical scattering methods. We found a dramatic increase in the nucleation rate densities with increasing particle number density. Crystalline and nanocrystalline samples showed two relaxation processes on widely separated time scales. For an index-matched suspension of perfluorinated particles an amorphous state was accessible with the glass-typical signature of frozen long-time relaxation. From our results we propose a route into the amorphous state different to that observed in hard-sphere suspensions. It seems that in charged-sphere systems the increased nucle…
Heterogeneous and homogeneous crystal nucleation in colloidal hard-sphere like microgels at low metastabilities
2011
We studied the crystallization kinetics of the homogeneous bulk as well as of the heterogeneous wall crystallization in a colloidal hard sphere model system within the fluid crystal coexistence region. Using time resolved static light scattering and Bragg microscopy we determined several parameters characterizing the crystallization process (induction times, growth coefficients, nucleation rate densities,…). By performing further analysis according to classical nucleation theory we can show that wall crystallization is favored by a vanishing nucleation barrier height leading to the conclusion that a hard sphere crystal completely wets a structureless hard wall.