Search results for "Classical nucleation theory"
showing 10 items of 14 documents
Crystallization of hard-sphere colloids -- deviations from classical nucleation theory
2006
The creation of three-dimensional ordered colloidal crystals, for application in a range of nanotechnologies, has been a goal for many researchers in the past few years. The main difficulty in creating macroscopic sized crystals of densely packed colloidal particles is that colloidal particles always have a range of particle sizes - ie, they are polydisperse. This paper studied the crystallization kinetics of a hard-sphere colloid with a well defined Gaussian polydispersity. The authors find that crystallization occurs in two stages, and does not follow the simple classical nucleation picture. The paper discusses the implications of these results for research into colloidal crystals as poss…
Investigation of Finite-Size Effects in the Determination of Interfacial Tensions
2014
The interfacial tension between coexisting phases of a material is an important parameter in the description of many phenomena such as crystallization, and even today its accurate measurement remains difficult. We have studied logarithmic finite-size corrections in the determination of the interfacial tension with large scale Monte Carlo simulations, and have identified several novel contributions which not only depend on the ensemble, but also on the type of the applied boundary conditions. We present results for the Lennard-Jones system and the Ising model, as well as for hard spheres, which are particularly challenging. In the future, these findings will contribute to the understanding a…
Finite-size effects on liquid-solid phase coexistence and the estimation of crystal nucleation barriers.
2015
A fluid in equilibrium in a finite volume $V$ with particle number $N$ at a density $\rho = N/V$ exceeding the onset density $\rho_f $ of freezing may exhibit phase coexistence between a crystalline nucleus and surrounding fluid. Using a method suitable for the estimation of the chemical potential of dense fluids we obtain the excess free energy due to the surface of the crystalline nucleus. There is neither a need to precisely locate the interface nor to compute the (anisotropic) interfacial tension. As a test case, a soft version of the Asakura-Oosawa model for colloid polymer-mixtures is treated. While our analysis is appropriate for crystal nuclei of arbitrary shape, we find the nucleat…
Combined Experimental and Theoretical Investigation of Heating Rate on Growth of Iron Oxide Nanoparticles
2017
Thermal decomposition is a promising route for the synthesis of highly monodisperse magnetite nanoparticles. However, the apparent simplicity of the synthesis is counterbalanced by the complex interplay of the reagents with the reaction variables that determine the final particle size and dispersity. Here, we present a combined experimental and theoretical study on the influence of the heating rate on crystal growth, size, and monodispersity of iron oxide nanoparticles. We synthesized monodisperse nanoparticles with sizes varying from 6.3 to 27 nm simply by controlling the heating rate of the reaction. The nanoparticles show size-dependent superparamagnetic behavior. Using numerical calcula…
Monte Carlo Simulation of Crystal-Liquid Phase Coexistence
2016
When a crystal nucleus is surrounded by coexisting fluid in a finite volume in thermal equilibrium, the thermodynamic properties of the fluid (density, pressure, chemical potential) are uniquely related to the surface excess free energy of the nucleus. Using a model for weakly attractive soft colloidal particles, it is shown that this surface excess free energy can be determined accurately from Monte Carlo simulations over a wide range of nucleus volumes, and the resulting nucleation barriers are completely independent from the size of the total volume of the system. A necessary ingredient of the analysis, the pressure at phase coexistence in the thermodynamic limit, is obtained from the in…
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.
Classical nucleation theory for the crystallization kinetics in sheared liquids
2019
While statistical mechanics provides a comprehensive framework for the understanding of equilibrium phase behavior, predicting the kinetics of phase transformations remains a challenge. Classical nucleation theory (CNT) provides a thermodynamic framework to relate the nucleation rate to thermodynamic quantities such as pressure difference and interfacial tension through the nucleation work necessary to spawn critical nuclei. However, it remains unclear whether such an approach can be extended to the crystallization of driven melts that are subjected to mechanical stresses and flows. Here, we demonstrate numerically for hard spheres that the impact of simple shear on the crystallization rate…
Crystal nuclei in melts: A Monte Carlo simulation of a model for attractive colloids
2015
As a model for a suspension of hard-sphere like colloidal particles where small nonadsorbing dissolved polymers create a depletion attraction, we introduce an effective colloid-colloid potential closely related to the Asakura-Oosawa model but that does not have any discontinuities. In simulations, this model straightforwardly allows the calculation of the pressure from the Virial formula, and the phase transition in the bulk from the liquid to crystalline solid can be accurately located from a study where a stable coexistence of a crystalline slab with a surrounding liquid phase occurs. For this model, crystalline nuclei surrounded by fluid are studied both by identifying the crystal-fluid …
Nucleation kinetics in deionized charged colloidal model systems: A quantitative study by means of classical nucleation theory
2007
We have studied the nucleation kinetics of charged colloidal model systems under salt free conditions crystallizing in bcc structure covering a wide range of particle number densities $18\phantom{\rule{0.3em}{0ex}}\mathrm{\ensuremath{\mu}}{\mathrm{m}}^{\ensuremath{-}3}\ensuremath{\le}n\ensuremath{\le}66.3\phantom{\rule{0.3em}{0ex}}\mathrm{\ensuremath{\mu}}{\mathrm{m}}^{\ensuremath{-}3}$. We employed direct video-microscopic observation of individual nucleation events to obtain time resolved nucleation rate densities. Polarization microscopy and static light scattering on the resulting solids in combination with Avrami theory is used to determine the steady state nucleation rate at high unde…
Crystallization of hard spheres revisited. I. Extracting kinetics and free energy landscape from forward flux sampling
2018
We investigate the kinetics and the free energy landscape of the crystallization of hard spheres from a supersaturated metastable liquid though direct simulations and forward flux sampling. In this first paper, we describe and test two different ways to reconstruct the free energy barriers from the sampled steady state probability distribution of cluster sizes without sampling the equilibrium distribution. The first method is based on mean first passage times, and the second method is based on splitting probabilities. We verify both methods for a single particle moving in a double-well potential. For the nucleation of hard spheres, these methods allow us to probe a wide range of supersatura…