Search results for "Nucleation"
showing 10 items of 364 documents
Kinetic model for surface reconstruction
2002
Institut fu ¨r Physikalische und Theoretische Chemie, Technische Universitat Braunschweig, Hans-Sommer-Strase 10,38106 Braunschweig, Germany~Received 7 December 2001; published 25 July 2002!A microscopic kinetic model for the ab @e.g., hex131 for Pt~100! and 132131 for Pt~110!#surface reconstruction is investigated by means of the mean field approximation and Monte Carlo simulations.It considers homogeneous phase nucleation that induces small surface phase defects. These defects can grow ordecline via phase border propagation in dependence on the chemical coverage by an adsorbate A ~CO!.Anasymmetry in the adsorbate surface diffusion from one surface phase to the other gives rise to two criti…
Free-energy barriers for crystal nucleation from fluid phases.
2017
Monte Carlo simulations of crystal nuclei coexisting with the fluid phase in thermal equilibrium in finite volumes are presented and analyzed, for fluid densities from dense melts to the vapor. Generalizing the lever-rule for two-phase coexistence in the canonical ensemble to finite volume, "measurements" of the nucleus volume together with the pressure and chemical potential of the surrounding fluid allows to extract the surface free energy of the nucleus. Neither the knowledge of the (in general non-spherical) nucleus shape nor of the angle-dependent interface tension is required for this task. The feasibility of the approach is demonstrated for a variant of the Asakura-Oosawa model for c…
Metastability of Traffic Flow in Zero-Range Model
2007
The development of traffic jams in vehicular flow is an everyday example of the occurence of phase separation in low-dimensional driven systems, a topic which has attracted much recent interest [1–4]. In [5] the existence of phase separation is related to the size-dependence of domain currents and a quantitative criterion is obtained by considering the zero-range process (ZRP) as a generic model for domain dynamics. We use zero-range picture to study the phase separation in traffic flow in the spirit of the probabilistic (master equation) description of transportation [6]. Significantly, we find [7] that prior to condensation studied in previous works [8, 9] the system can exist in a homoge…
Coupled Multi-Field Continuum Methods for Porous Media Fracture
2015
The focus of the present contribution is on the numerical modelling of hydraulic fracture in fluid-saturated heterogeneous materials, which can be carried out on a macroscopic scale using extended continuum porous media theories. This accounts for the crack nucleation and propagation, deformation of the solid matrix and change in the flow of the interstitial fluid. In particular, fluid-saturated porous materials basically represent volumetrically interacting solid-fluid aggregates, which are modelled using the Theory of Porous Media. The hydraulic- or tension-induced fracture occurs in the solid matrix and is simulated using a diffusive phase-field modelling approach. This way of fracture t…
Simulation of vapor-liquid coexistence in finite volumes: a method to compute the surface free energy of droplets.
2009
When a fluid at a constant density $\ensuremath{\rho}$ in between the densities of coexisting vapor $({\ensuremath{\rho}}_{\text{v}})$ and liquid $({\ensuremath{\rho}}_{\ensuremath{\ell}})$ at temperatures below criticality is studied in a (cubic) box of finite linear dimension $L$, phase separation occurs in this finite volume, provided $L$ is large enough. For a range of densities, one can observe a liquid droplet (at density ${\ensuremath{\rho}}_{\ensuremath{\ell}}^{\ensuremath{'}}$ slightly exceeding ${\ensuremath{\rho}}_{\ensuremath{\ell}}$) coexisting in stable thermal equilibrium with surrounding vapor (with density ${\ensuremath{\rho}}_{\text{v}}^{\ensuremath{'}}g{\ensuremath{\rho}}…
A Theoretical Study of the Wet Removal of Atmospheric Pollutants. Part II: The Uptake and Redistribution Of (NH4)2SO4Particles and SO2Gas Simultaneou…
1987
Abstract A theoretical model has been formulated which allows the processes which control the wet deposition of atmospheric aerosol particles and pollutant gases to be included in cloud dynamic models. The cloud considered in the model was allowed to grow by condensation and collision–coalescence, to remove aerosol particles by nucleation and impaction scavenging, and to remove pollutant gases by convective diffusion. The model was tested by using a simple air-parcel model as the dynamic framework. In this form the model was used to determine the fate of ammonium sulfate [(NH4)2SO4] particles and sulfur dioxide (SO2) gas as they became scavenged by cloud and precipitation drops. Special emp…
Colloidal crystallization dynamics
1997
At sufficiently strong interparticle interaction, colloidal particles may form ordered crystalline arrays much in analogy to atomic systems. Well characterized model colloidal suspensions have therefore become valuable model systems for the study of the kinetics of crystal nucleation, growth and ripening. Significant progress has been made in this area throughout the past few years. Precise control of interaction parameters and new instrumental developments have allowed for quantitative determination of nucleation rate densities and growth velocities in monodisperse ‘hard’ and ‘soft sphere’ systems. Results confirm classical theories of nucleation and growth adapted to colloidal systems. Th…
Efficient size control of copper nanoparticles generated in irradiated aqueous solutions of star-shaped polyelectrolyte containers
2015
Physical chemistry, chemical physics 17(17), 11490-11498(2015). doi:10.1039/C5CP00269A
Thermoanalytical study of nucleating effects in polypropylene composites
1996
Interfacial structure plays an important role in the performance of polypropylene composites. Transcrystalline interfacial layer were determined in talc filled polypropylene. The crystallization and melting behaviour of talc and CaCC3 filled polypropylene could be modified with smaller amount of additives like elastomer and surfactants. Through the effect of these additives the structure of interface and the degree of crystallinity could be controlled in filled polypropylene.
Thermal stability of PP with acetylated sisal fiber: Romero Garc�a kinetic method
2003
This work deals the effect of acetylated and non-acetylated sisal fiber 011 thermal degradation of polypropylene. Applying the R-G method at constant conversion levels of 0.1, 0.3, 0.5, 0.7 and 0.9 to thermograms of the ”PP/untreated sisal fiber” blend, E, values of 99, 213, 224, 187, and 145 kJ/mol were obtained, whereas they were 99, 299, 255, 205, 154 kJ/mol for the “PP/treated sisal fiber” blend. On the other hand, with the R-G method at constant temperature, activation energies within the range of 156-417 kJ/mol were obtained for the “PP/treated sisal fiber” blend and within the range of 126-344 kJ/mol for the “PP/untreated sisal fiber” blend. Additionally, the method establishes as do…