Search results for "Kinetic"

Two-Step Crystallization Kinetics in Colloidal Hard-Sphere Systems

2005

The crystallization kinetics of colloidal hard spheres was studied using a special Bragg spectrometer with high sensitivity. In contrast with the classical scenario we observe a two-step nucleation process: the number of crystallites increases slowly at early times, followed by a dramatic reduction at intermediate times, prior to undergoing a rapid increase at late times. We explain these results in terms of a polydispersity limited growth of crystallites, where the crystallization at early times is governed by local fractionation processes, leading to a long delay prior to final crystallization.

Schmelz- und kristallisationserscheinungen bei makromolekularen substanzen. I. Kristallisationskinetische untersuchungen an isotaktischem polypropylen

1960

Die Messung der Bruttokristallisation hochpolymerer Substanzen erlaubt erst mit Hilfe der AVRAMIschen Theorie Ruckschlusse auf die Kristallisationskinetik (Keimbildung und Wachstumsgeschwindigkeit). Die Frage, ob die fur niedermolekulare Stoffe entwickelte AVRAMIsche Theorie wirklich auf Hochpolymere ubertragen werden kann, bedarf einer eingehenden Prufung. Es wurden daher mittels mikroskopischer Untersuchungen die Keimbildung und die Wachstumsgeschwindigkeit von isotaktischem Polypropylen in Abhangigkeit von der Kristallisationstemperatur getrennt gemessen und die so ermittelten Werte mit den aus der Bruttokristallisation nach AVRAMI berechneten Zahlen verglichen. Die ubereinstimmung ist v…

Thermal stability and crystallization kinetics of Al4Mn quasicrystals as studied by exoelectron emission and DTA methods

1995

2015

In many technical applications, but also in natural processes like ice nucleation in clouds, crystallization proceeds in the presence of stresses and flows, hence the importance to understand the crystallization mechanism in simple situations. We employ molecular dynamics simulations to study the crystallization kinetics of a nearly hard sphere liquid that is weakly sheared. We demonstrate that shear flow both enhances and suppresses the crystallization kinetics of hard spheres. The effect of shear depends on the quiescent mechanism: suppression in the activated regime and enhancement in the diffusion-limited regime for small strain rates. At higher strain rates crystallization again become…

1981

Controlled Synthesis of CdSe Tetrapods with High Morphological Uniformity by the Persistent Kinetic Growth and the Halide-Mediated Phase Transformati…

2012

We report scalable controlled synthesis of CdSe tetrapods with high morphological uniformity based on the continuous precursor injection (CPI) approach with halide ligands. The CPI approach involves the successive injection of precursors into the seed solution at a controlled rate so that the reaction condition remains in the kinetic growth regime. To initiate the successful development of tetrapod structure, the controlled amount of halide ligands are added during the reaction, which triggered the formation of wurtzite arms on {111}-facets of the zincblende seeds. The formation of the wurtzite phase is responsible for the halide-mediated displacement of oleate ligands, destabilizing the em…

Spontaneous cocrystal hydrate formation in the solid state: crystal structure aspects and kinetics

2013

Kinetics of anhydrous cocrystal hydration and that of cocrystal monohydrate formation from starting compounds in the solid state are studied as a function of RH and time. The propensity of the anhydrate to hydration is related to the crystal structures of anhydrous and hydrated forms.

On the Stability and Formation of Pillar[n]arenes: a DFT Study

2021

The increased use of both pillar[5]arenes and pillar[6]arenes, stimulated by increasingly efficient syntheses of both, has brought forward the question as to what drives the intermediates in this Friedel-Crafts ring formation to form a pillar[5]arene, a pillar[6]arene, or any other sized macrocycle. This study sets out to answer this question by studying both the thermodynamics and kinetics involved in the absence and presence of templating solvents using high-end wB97XD/6-311G(2p,2d) DFT calculations.

Transient absorption spectra and relaxation kinetics in Nb-doped PbWO4 scintillating crystals

2001

Abstract The spectra and relaxation kinetics of absorption induced by a pulsed electron beam were studied for undoped and Nb-doped PbWO 4 single crystals. A significant influence of Nb doping on transient absorption was found. The influence of Nb doping on the relaxation kinetics is proposed to be due to an oxygen vacancy involving electron–hole recombination. A delay was observed (35– 50 ns ) between the growth of F-centers and the irradiation pulse. A large portion of the F-centers decays within ∼16 μs due to recombination with mobile holes. The prolonged recombination processes are responsible for the decrease of the scintillation yield in PbWO 4 : Nb crystals.

Computer Simulations of I-Center Annealing in KCl and KBr Crystals. Theoretical Interpretation of Thermostimulated Experiments

1995

Results of computer simulations of the kinetics of correlated annealing of pairs of close α–I and F–I centers in KCI and KBr crystals, enhanced by I-center diffusion and Coulomb or elastic attractions, respectively, are presented. Special attention is paid to the conditions under which multi-stage annealing stages arise as it has been observed experimentally more than once. Our general conclusions are: (i) a weak elastic interaction affects the recombination kinetics and the survival probability even for relatively well-separated F–I pairs, the more so is true for the case of Coulomb attraction between charged α–I pairs; (ii) the multi-step (kink) structure arises only for close (typically,…