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Sample records for homogeneous crystal nucleation

  1. Homogeneous crystal nucleation in polymers.

    PubMed

    Schick, Christoph; Androsch, R; Schmelzer, Juern W P

    2017-07-14

    The pathway of crystal nucleation significantly influences the structure and properties of semi-crystalline polymers. Crystal nucleation is normally heterogeneous at low supercooling, and homogeneous at high supercooling, of the polymer melt. Homogeneous nucleation in bulk polymers has been, so far, hardly accessible experimentally, and was even doubted to occur at all. This topical review summarizes experimental findings on homogeneous crystal nucleation in polymers. Recently developed fast scanning calorimetry, with cooling and heating rates up to 106 K s-1, allows for detailed investigations of nucleation near and even below the glass transition temperature, including analysis of nuclei stability. As for other materials, the maximum homogeneous nucleation rate for polymers is located close to the glass transition temperature. In the experiments discussed here, it is shown that polymer nucleation is homogeneous at such temperatures. Homogeneous nucleation in polymers is discussed in the framework of classical nucleation theory. The majority of our observations are consistent with the theory. The discrepancies may guide further research, particularly experiments to progress theoretical development. Progress in the understanding of homogeneous nucleation is much needed, since most of the modelling approaches dealing with polymer crystallization exclusively consider homogeneous nucleation. This is also the basis for advancing theoretical approaches to the much more complex phenomena governing heterogeneous nucleation. © 2017 IOP Publishing Ltd.

  2. Homogeneous crystal nucleation in binary metallic melts

    NASA Technical Reports Server (NTRS)

    Thompson, C. V.; Spaepen, F.

    1983-01-01

    A method for calculating the homogeneous crystal nucleation frequency in binary metallic melts is developed. The free energy of crystallization is derived from regular solution models for the liquid and solid and is used, together with model-based estimates of the interfacial tension, to calculate the nucleation frequency from the classical theory. The method can account for the composition dependence of the maximum undercooling observed in a number of experiments on small droplet dispersions. It can also be used to calculate the driving force for crystal growth and to obtain more precise estimates of the homogeneous crystal nucleation frequency in glass-forming alloys. This method, although approximate, is simple to apply, and requires only knowledge of the phase diagram and a few readily available thermodynamic quantities as input data.

  3. Homogeneous crystal nucleation in Ni droplets

    NASA Astrophysics Data System (ADS)

    Kožíšek, Zdeněk; Demo, Pavel

    2017-10-01

    Crystal nucleation kinetics is often represented by induction times or metastable zone widths (Kulkarni et al., 2013; Bokeloh et al., 2011). Repeating measurements of supercooling or time delay, at which phase transition is detected, are statistically processed to determine the so-called survivorship function, from which nucleation rate is computed. The size distribution of nuclei is difficult to measure near the critical size directly, and it is not clear which amount of nuclei is formed at the moment when the phase transition is detected. In the present paper, kinetic nucleation equations are solved for the crystal nucleation in Ni liquid droplet to determine the number of nuclei formed within a considered system. Analysis of supercooling experimental data, based on the classical nucleation theory CNT), computes appropriate values of the nucleation rate. However, CNT underestimates the number of nuclei F (F ≪ 1 for supercritical sizes). Taking into account the dependence of the surface energy on nucleus size to data analysis overcomes this discrepancy and leads to reasonable values of the size distribution of nuclei.

  4. Cirrus crystal nucleation by homogeneous freezing of solution droplets

    NASA Technical Reports Server (NTRS)

    Heymsfield, Andrew J.; Sabin, Robert M.

    1989-01-01

    A numerical model consisting of a system of differential equations is used to study cirrus crystal nucleation in a rising parcel containing a distribution of cloud condensation nuclei. The evolution of the particle population and the thermodynamic variables in the parcel are examined. The results suggest that, if homogeneous freezing is not considered, liquid water should be detected below -40 C. If homogeneous freezing is considered, the rapid growth of ice crystals and vapor depletion prevent water saturation from being reached. It is shown that the likelihood of a droplet being frozen is increased by lower temperatures, larger droplet diameter, or lower solution density.

  5. Crystallization in supercooled liquid Cu: Homogeneous nucleation and growth

    SciTech Connect

    E, J. C.; Wang, L.; Luo, S. N.; Cai, Y.; Wu, H. A.

    2015-02-14

    Homogeneous nucleation and growth during crystallization of supercooled liquid Cu are investigated with molecular dynamics simulations, and the microstructure is characterized with one- and two-dimensional x-ray diffraction. The resulting solids are single-crystal or nanocrystalline, containing various defects such as stacking faults, twins, fivefold twins, and grain boundaries; the microstructure is subject to thermal fluctuations and extent of supercooling. Fivefold twins form via sequential twinning from the solid-liquid interfaces. Critical nucleus size and nucleation rate at 31% supercooling are obtained from statistical runs with the mean first-passage time and survival probability methods, and are about 14 atoms and 10{sup 32} m{sup −3}s{sup −1}, respectively. The bulk growth dynamics are analyzed with the Johnson-Mehl-Avrami law and manifest three stages; the Avrami exponent varies in the range of 1–19, which also depends on thermal fluctuations and supercooling.

  6. Crystallization in supercooled liquid Cu: Homogeneous nucleation and growth

    NASA Astrophysics Data System (ADS)

    E, J. C.; Wang, L.; Cai, Y.; Wu, H. A.; Luo, S. N.

    2015-02-01

    Homogeneous nucleation and growth during crystallization of supercooled liquid Cu are investigated with molecular dynamics simulations, and the microstructure is characterized with one- and two-dimensional x-ray diffraction. The resulting solids are single-crystal or nanocrystalline, containing various defects such as stacking faults, twins, fivefold twins, and grain boundaries; the microstructure is subject to thermal fluctuations and extent of supercooling. Fivefold twins form via sequential twinning from the solid-liquid interfaces. Critical nucleus size and nucleation rate at 31% supercooling are obtained from statistical runs with the mean first-passage time and survival probability methods, and are about 14 atoms and 1032 m-3s-1, respectively. The bulk growth dynamics are analyzed with the Johnson-Mehl-Avrami law and manifest three stages; the Avrami exponent varies in the range of 1-19, which also depends on thermal fluctuations and supercooling.

  7. Homogeneous versus heterogeneous crystal nucleation in Li2O-2SiO2 glass

    NASA Technical Reports Server (NTRS)

    Weinberg, M. C.; Neilson, G. F.; Uhlmann, D. R.

    1984-01-01

    When analyzing crystal nucleation in glasses, it is difficult to distinguish between homogeneous and heterogeneous nucleation. A method is proposed to investigate the nature of crystal nucleation in Li2O-2SiO2, and calculations are performed to determine under which conditions saturation effects help ascertain the nature of the nucleation. The capability of detecting impurity particles in unheated glass via standard micrographic techniques (SEM or REM) and small angle X-ray scattering (SAXS) is explored. Results indicate that if the maximum impurity particle densities do not exceed 2 x 10 to the 7th per cu cm then heterogeneous nucleation may be excluded and most impurity particles with densities in excess of 10 to the 10th per cu cm are detectable by SAXS. It is concluded that crystal nucleation in this system most probably occurs homogeneously.

  8. Temperature-dependent mechanisms of homogeneous crystal nucleation in quenced Lennard-Jones liquids

    SciTech Connect

    Peng, L.; Morris, James R; Lo, Y. C.

    2008-01-01

    We have observed homogeneous crystal nucleation in Lennard-Jones liquid by molecular dynamics simulations. A clear nucleation time delay has been observed at T=0.677T{sub m} and T=0.629T{sub m} indicating the presence of a barrier, in contrast to recent reports [Trudu et al., Phys. Rev. Lett. 97, 105701 (2006)]. The structure of nuclei observed in the previous results and in the present work is evidence of transient-time dominated nucleation, not of a spinodal. Very rapid nucleation is observed at T=0.484T{sub m}, indicating either a low (but finite) barrier or possibly a spinodal transformation. No spinodal effect has been observed in similar simulations of crystal nucleation in aluminum at any temperature [Aga et al., Phys. Rev. Lett. 96, 245701 (2006)], suggesting that different qualitative behaviors may be possible in what would seem to be similar potentials.

  9. Interfacial free energy adjustable phase field crystal model for homogeneous nucleation.

    PubMed

    Guo, Can; Wang, Jincheng; Wang, Zhijun; Li, Junjie; Guo, Yaolin; Huang, Yunhao

    2016-05-18

    To describe the homogeneous nucleation process, an interfacial free energy adjustable phase-field crystal model (IPFC) was proposed by reconstructing the energy functional of the original phase field crystal (PFC) methodology. Compared with the original PFC model, the additional interface term in the IPFC model effectively can adjust the magnitude of the interfacial free energy, but does not affect the equilibrium phase diagram and the interfacial energy anisotropy. The IPFC model overcame the limitation that the interfacial free energy of the original PFC model is much less than the theoretical results. Using the IPFC model, we investigated some basic issues in homogeneous nucleation. From the viewpoint of simulation, we proceeded with an in situ observation of the process of cluster fluctuation and obtained quite similar snapshots to colloidal crystallization experiments. We also counted the size distribution of crystal-like clusters and the nucleation rate. Our simulations show that the size distribution is independent of the evolution time, and the nucleation rate remains constant after a period of relaxation, which are consistent with experimental observations. The linear relation between logarithmic nucleation rate and reciprocal driving force also conforms to the steady state nucleation theory.

  10. Molecular simulation of homogeneous nucleation of crystals of an ionic liquid from the melt

    SciTech Connect

    He, Xiaoxia; Shen, Yan; Hung, Francisco R.; Santiso, Erik E.

    2015-09-28

    The homogeneous nucleation of crystals of the ionic liquid [dmim{sup +}][Cl{sup −}] from its supercooled liquid phase in the bulk (P = 1 bar, T = 340 K, representing a supercooling of 58 K) was studied using molecular simulations. The string method in collective variables [Maragliano et al., J. Chem. Phys. 125, 024106 (2006)] was used in combination with Markovian milestoning with Voronoi tessellations [Maragliano et al., J. Chem. Theory Comput. 5, 2589–2594 (2009)] and order parameters for molecular crystals [E. E. Santiso and B. L. Trout, J. Chem. Phys. 134, 064109 (2011)] to sketch a minimum free energy path connecting the supercooled liquid and the monoclinic crystal phases, and to determine the free energy and the rates involved in the homogeneous nucleation process. The physical significance of the configurations found along this minimum free energy path is discussed with the help of calculations based on classical nucleation theory and with additional simulation results obtained for a larger system. Our results indicate that, at a supercooling of 58 K, the liquid has to overcome a free energy barrier of the order of 60 kcal/mol and to form a critical nucleus with an average size of about 3.6 nm, before it reaches the thermodynamically stable crystal phase. A simulated homogeneous nucleation rate of 5.0 × 10{sup 10} cm{sup −3} s{sup −1} was obtained for our system, which is in reasonable agreement with experimental and simulation rates for homogeneous nucleation of ice at similar degrees of supercooling. This study represents our first step in a series of studies aimed at understanding the nucleation and growth of crystals of organic salts near surfaces and inside nanopores.

  11. Molecular simulation of homogeneous nucleation of crystals of an ionic liquid from the melt

    NASA Astrophysics Data System (ADS)

    He, Xiaoxia; Shen, Yan; Hung, Francisco R.; Santiso, Erik E.

    2015-09-01

    The homogeneous nucleation of crystals of the ionic liquid [dmim+][Cl-] from its supercooled liquid phase in the bulk (P = 1 bar, T = 340 K, representing a supercooling of 58 K) was studied using molecular simulations. The string method in collective variables [Maragliano et al., J. Chem. Phys. 125, 024106 (2006)] was used in combination with Markovian milestoning with Voronoi tessellations [Maragliano et al., J. Chem. Theory Comput. 5, 2589-2594 (2009)] and order parameters for molecular crystals [E. E. Santiso and B. L. Trout, J. Chem. Phys. 134, 064109 (2011)] to sketch a minimum free energy path connecting the supercooled liquid and the monoclinic crystal phases, and to determine the free energy and the rates involved in the homogeneous nucleation process. The physical significance of the configurations found along this minimum free energy path is discussed with the help of calculations based on classical nucleation theory and with additional simulation results obtained for a larger system. Our results indicate that, at a supercooling of 58 K, the liquid has to overcome a free energy barrier of the order of 60 kcal/mol and to form a critical nucleus with an average size of about 3.6 nm, before it reaches the thermodynamically stable crystal phase. A simulated homogeneous nucleation rate of 5.0 × 1010 cm-3 s-1 was obtained for our system, which is in reasonable agreement with experimental and simulation rates for homogeneous nucleation of ice at similar degrees of supercooling. This study represents our first step in a series of studies aimed at understanding the nucleation and growth of crystals of organic salts near surfaces and inside nanopores.

  12. Molecular simulation of homogeneous nucleation of crystals of an ionic liquid from the melt.

    PubMed

    He, Xiaoxia; Shen, Yan; Hung, Francisco R; Santiso, Erik E

    2015-09-28

    The homogeneous nucleation of crystals of the ionic liquid [dmim(+)][Cl(-)] from its supercooled liquid phase in the bulk (P = 1 bar, T = 340 K, representing a supercooling of 58 K) was studied using molecular simulations. The string method in collective variables [Maragliano et al., J. Chem. Phys. 125, 024106 (2006)] was used in combination with Markovian milestoning with Voronoi tessellations [Maragliano et al., J. Chem. Theory Comput. 5, 2589-2594 (2009)] and order parameters for molecular crystals [E. E. Santiso and B. L. Trout, J. Chem. Phys. 134, 064109 (2011)] to sketch a minimum free energy path connecting the supercooled liquid and the monoclinic crystal phases, and to determine the free energy and the rates involved in the homogeneous nucleation process. The physical significance of the configurations found along this minimum free energy path is discussed with the help of calculations based on classical nucleation theory and with additional simulation results obtained for a larger system. Our results indicate that, at a supercooling of 58 K, the liquid has to overcome a free energy barrier of the order of 60 kcal/mol and to form a critical nucleus with an average size of about 3.6 nm, before it reaches the thermodynamically stable crystal phase. A simulated homogeneous nucleation rate of 5.0 × 10(10) cm(-3) s(-1) was obtained for our system, which is in reasonable agreement with experimental and simulation rates for homogeneous nucleation of ice at similar degrees of supercooling. This study represents our first step in a series of studies aimed at understanding the nucleation and growth of crystals of organic salts near surfaces and inside nanopores.

  13. Studies on elasticity of single crystals: Homogeneous dislocation nucleation and disordered colloidal crystals

    NASA Astrophysics Data System (ADS)

    Hasan, Asad

    In this 2-part thesis we study first study incipient plastic behavior in deformation of single crystals. We perform atomistic computer simulations to study the mechanism of homogeneous dislocation nucleation in a 2D hexagonal crystalline film during indentation with a circular nanoindenter. The nucleation process is governed by vanishing of energy associated with a single normal mode which is largely confined to a plane of adjacent atoms. For fixed film thickness, L, the spatial extent, ξ, of the critical mode grows with indenter radius, R. For fixed R/L, ξ grows with systems roughly as ξ ˜ L0.4. We, furthermore, perform a mesoscale analysis to determine the lowest energy normal mode for mesoscale regions of varying radius, rmeso, centered on the core of the critical mode. The energy of the lowest normal mode, λmeso, decays very rapidly with rmeso and λmeso ≈ 0 for rmeso ≳ ξ. The lowest normal mode shows a spatial extent, ξmeso , which has a sublinear power-law increase with r meso for rmeso ≲ ξ and saturates at rmeso ≈ 1.5 ξ. We demonstrate that the ξmeso/ξ versus r meso/ξ curve is universal and is independent of film thickness or indenter radius. Thus we have a scenario where the analysis of small regions, rmeso ≲ ξ, in the material can reveal the presence of incipient instability but gives excellent estimates for the energy and spatial extent of the critical mode only for r meso ≳ 1.5 ξ. In this sense homogeneous dislocation nucleation is a quasi-local phenomenon. In the second part we consider the issues encountered in extracting the elasticity of colloidal crystal from displacement correlation data as measured via optical microscopy techniques. We compute the effective dispersion and density of states of two-dimensional sub-regions of fully three dimensional f.c.c. crystals. As our model is fully atomistic, it allows realistic treatment of wavevectors up to the Brillouin zone boundary. We study sub-regions of both a [111] and [100

  14. Free energy barriers for homogeneous crystal nucleation in a eutectic system of binary hard spheres.

    PubMed

    Ganagalla, Srinivasa Rao; Punnathanam, Sudeep N

    2013-05-07

    In this study, the free energy barriers for homogeneous crystal nucleation in a system that exhibits a eutectic point are computed using Monte Carlo simulations. The system studied is a binary hard sphere mixture with a diameter ratio of 0.85 between the smaller and larger hard spheres. The simulations of crystal nucleation are performed for the entire range of fluid compositions. The free energy barrier is found to be the highest near the eutectic point and is nearly five times that for the pure fluid, which slows down the nucleation rate by a factor of 10(-31). These free energy barriers are some of highest ever computed using simulations. For most of the conditions studied, the composition of the critical nucleus corresponds to either one of the two thermodynamically stable solid phases. However, near the eutectic point, the nucleation barrier is lowest for the formation of the metastable random hexagonal closed packed (rhcp) solid phase with composition lying in the two-phase region of the phase diagram. The fluid to solid phase transition is hypothesized to proceed via formation of a metastable rhcp phase followed by a phase separation into respective stable fcc solid phases.

  15. Nanosecond homogeneous nucleation and crystal growth in shock-compressed SiO2

    NASA Astrophysics Data System (ADS)

    Shen, Yuan; Jester, Shai; Qi, Tingting; Reed, Evan

    Understanding the kinetics of shock-compressed SiO2 is of great importance for mitigating optical damage for high-intensity lasers and for understanding meteoroid impacts. Experimental work has placed some thermodynamic bounds on the formation of high-pressure phases of this material, but the formation kinetics and underlying microscopic mechanisms are yet to be elucidated. Here, by employing multiscale molecular dynamics studies of shock-compressed fused silica and quartz, we find that silica transforms into a poor glass former that subsequently exhibits ultrafast crystallization within a few nanoseconds. We also find that, as a result of the formation of such an intermediate disordered phase, the transition between silica polymorphs obeys a homogeneous reconstructive nucleation and grain growth model. Moreover, we construct a quantitative model of nucleation and grain growth, and compare its predictions with stishovite grain sizes observed in laser-induced damage and meteoroid impact events.

  16. Nanosecond homogeneous nucleation and crystal growth in shock-compressed SiO2.

    PubMed

    Shen, Yuan; Jester, Shai B; Qi, Tingting; Reed, Evan J

    2016-01-01

    Understanding the kinetics of shock-compressed SiO2 is of great importance for mitigating optical damage for high-intensity lasers and for understanding meteoroid impacts. Experimental work has placed some thermodynamic bounds on the formation of high-pressure phases of this material, but the formation kinetics and underlying microscopic mechanisms are yet to be elucidated. Here, by employing multiscale molecular dynamics studies of shock-compressed fused silica and quartz, we find that silica transforms into a poor glass former that subsequently exhibits ultrafast crystallization within a few nanoseconds. We also find that, as a result of the formation of such an intermediate disordered phase, the transition between silica polymorphs obeys a homogeneous reconstructive nucleation and grain growth model. Moreover, we construct a quantitative model of nucleation and grain growth, and compare its predictions with stishovite grain sizes observed in laser-induced damage and meteoroid impact events.

  17. Nanosecond homogeneous nucleation and crystal growth in shock-compressed SiO2

    NASA Astrophysics Data System (ADS)

    Shen, Yuan; Jester, Shai B.; Qi, Tingting; Reed, Evan J.

    2016-01-01

    Understanding the kinetics of shock-compressed SiO2 is of great importance for mitigating optical damage for high-intensity lasers and for understanding meteoroid impacts. Experimental work has placed some thermodynamic bounds on the formation of high-pressure phases of this material, but the formation kinetics and underlying microscopic mechanisms are yet to be elucidated. Here, by employing multiscale molecular dynamics studies of shock-compressed fused silica and quartz, we find that silica transforms into a poor glass former that subsequently exhibits ultrafast crystallization within a few nanoseconds. We also find that, as a result of the formation of such an intermediate disordered phase, the transition between silica polymorphs obeys a homogeneous reconstructive nucleation and grain growth model. Moreover, we construct a quantitative model of nucleation and grain growth, and compare its predictions with stishovite grain sizes observed in laser-induced damage and meteoroid impact events.

  18. Nanosecond Timescale Homogeneous Nucleation and Crystal Growth in Shock-Compressed SiO2

    NASA Astrophysics Data System (ADS)

    Shen, Yuan; Barak, Shai; Qi, Tingting; Reed, Evan

    2015-06-01

    Understanding the kinetics of shock compressed SiO2 is of great importance for mitigating optical damage for high intensity lasers and understanding meteoroid impacts. Experimental work has placed some thermodynamic bounds on the formation of high pressure crystal phases, but the kinetics and microscopic mechanisms are yet to be elucidated. The latter are particularly relevant for this material which has long-lived metastable states. Enabled by million atom multiscale shock technique (MSST) molecular dynamics studies of shock compressed fused silica and quartz using variations on the BKS analytical potential, we discover here that crystallization occurs within as little as a few nanoseconds. In surprising contrast to shock induced solid-solid phase transformations in metals, we find that the transition from quartz obeys a diffusion mediated homogeneous nucleation and growth model due to formation of an intermediate disordered phase. We construct a quantitative model of diffusion mediated nucleation and growth kinetics and compare to stishovite grain sizes observed in laser damage events and near the Barringer Crater. We also study the effect of quantum nuclear effects using the quantum bath MSST and find that shock temperatures are shifted up to 500 K from classical values.

  19. Homogeneous nucleation kinetics

    NASA Technical Reports Server (NTRS)

    Rasmussen, D. H.; Appleby, M. R.; Leedom, G. L.; Babu, S. V.; Naumann, R. J.

    1983-01-01

    Homogeneous nucleation kinetics are rederived in a manner fundamentally similar to the approach of classical nucleation theory with the following modifications and improvements. First, the cluster is a parent phase cluster and does not require energization to the parent state. Second, the thermodynamic potential used to describe phase stability is a continuous function along the pathway of phase decomposition. Third, the kinetics of clustering corresponds directly to the diffusional flux of monomers through the cluster distribution and are formally similar to classical theory with the resulting kinetic equation modified by two terms in the preexponential factor. These terms correct for the influence of a supersaturation dependent clustering within the parent phase and for the influence of an asymmetrical cluster concentration as a function of cluster size at the critical cluster size. Fourth, the supersaturation dependence of the nucleation rate is of the same form as that given by classical nucleation theory. This supersaturation dependence must however be interpreted in terms of a size dependent surface tension. Finally, there are two scaling laws which describe supersaturation to either constant nucleation rate or to the thermodynamically determined physical spinodal.

  20. Homogenous Nucleation and Crystal Growth in a Model Liquid from Direct Energy Landscape Sampling Simulation

    NASA Astrophysics Data System (ADS)

    Walter, Nathan; Zhang, Yang

    Nucleation and crystal growth are understood to be activated processes involving the crossing of free-energy barriers. Attempts to capture the entire crystallization process over long timescales with molecular dynamic simulations have met major obstacles because of molecular dynamics' temporal constraints. Herein, we circumvent this temporal limitation by using a brutal-force, metadynamics-like, adaptive basin-climbing algorithm and directly sample the free-energy landscape of a model liquid Argon. The algorithm biases the system to evolve from an amorphous liquid like structure towards an FCC crystal through inherent structure, and then traces back the energy barriers. Consequently, the sampled timescale is macroscopically long. We observe that the formation of a crystal involves two processes, each with a unique temperature-dependent energy barrier. One barrier corresponds to the crystal nucleus formation; the other barrier corresponds to the crystal growth. We find the two processes dominate in different temperature regimes. Compared to other computation techniques, our method requires no assumptions about the shape or chemical potential of the critical crystal nucleus. The success of this method is encouraging for studying the crystallization of more complex

  1. Seeding approach to crystal nucleation.

    PubMed

    Espinosa, Jorge R; Vega, Carlos; Valeriani, Chantal; Sanz, Eduardo

    2016-01-21

    We present a study of homogeneous crystal nucleation from metastable fluids via the seeding technique for four different systems: mW water, Tosi-Fumi NaCl, Lennard-Jones, and Hard Spheres. Combining simulations of spherical crystal seeds embedded in the metastable fluid with classical nucleation theory, we are able to successfully describe the nucleation rate for all systems in a wide range of metastability. The crystal-fluid interfacial free energy extrapolated to coexistence conditions is also in good agreement with direct calculations of such parameter. Our results show that seeding is a powerful technique to investigate crystal nucleation.

  2. Molecular dynamics simulations of steady-state crystal growth and homogeneous nucleation in polyethylene-like polymer.

    PubMed

    Yamamoto, Takashi

    2008-11-14

    Molecular mechanisms of crystal growth and homogeneous nucleation from the melt of polyethylene-like linear polymer are investigated by molecular dynamics simulations. The present paper is aimed at extending our previous work with respect to the system size and the boundary condition, thereby enabling detailed studies on the structures of sufficiently large lamellae and fully equilibrated melt. Lamellae of uniform thickness but with marked tapered edges are found to grow at constant velocity from the substrate. Three-dimensional shape of the growing lamellae exhibits peculiar undulation at the growth front, the origin of which is suggested to be the inhomogeneous thickness distribution within the lamellae. Trajectories of chains crystallizing onto the growth front reveal an unexpected pathway for chain folding, where a partially attached chain stem forms a new fold by plunging its head back into a neighboring stem position through slithering snake motions of the chain. Detailed statistics of folds and cilia show that the folds are rather neat and mostly make re-entries into the nearest or the second or third nearest neighboring stem positions, whereas the cilia are generally short but with a small number of longer cilia forming thick amorphous layers. Structure of supercooled melt investigated versus temperature reveals that, at moderate degree of supercooling, the overall chain conformation remains Gaussian random coil but the persistent length of chains increases monotonically with increasing supercooling. Exceptions are at the largest supercooling where homogeneous nucleation takes place; usual melt structure becomes rapidly unstable and emerges many crystallites of random orientations. During early 10-20 ns after the quench, density of melt, radius of gyration of chains, and fraction of kinked bonds show marked alterations. These structural changes are highly cooperative and are considered simply due to the emergence of many embryonic crystals in the melt

  3. Molecular simulation of homogeneous crystal nucleation of AB2 solid phase from a binary hard sphere mixture

    NASA Astrophysics Data System (ADS)

    Bommineni, Praveen Kumar; Punnathanam, Sudeep N.

    2017-08-01

    Co-crystal formation from fluid-mixtures is quite common in a large number of systems. The simplest systems that show co-crystal (also called substitutionally ordered solids) formation are binary hard sphere mixtures. In this work, we study the nucleation of AB2 type solid compounds using Monte Carlo molecular simulations in binary hard sphere mixtures with the size ratio of 0.55. The conditions chosen for the study lie in the region where nucleation of an AB2 type solid competes with that of a pure A solid with a face-centered-cubic structure. The fluid phase composition is kept equal to that of the AB2 type solid. The nucleation free-energy barriers are computed using the seeding technique of Sanz et al. [J. Am. Chem. Soc. 135, 15008 (2013)]. Our simulation results show that the nucleation of the AB2 type solid is favored even under conditions where the pure A solid is more stable. This is primarily due to the similarity in the composition of the fluid phase and the AB2 type solid which in turn leads to much lower interfacial tension between the crystal nucleus and the fluid phase. This system is an example of how the fluid phase composition affects the structure of the nucleating solid phase during crystallization and has relevance to crystal polymorphism during crystallization processes.

  4. Homogeneous ice nucleation from supercooled water.

    PubMed

    Li, Tianshu; Donadio, Davide; Russo, Giovanna; Galli, Giulia

    2011-11-28

    Homogeneous ice nucleation from supercooled water was studied in the temperature range of 220-240 K through combining the forward flux sampling method (Allen et al., J. Chem. Phys., 2006, 124, 024102) with molecular dynamics simulations (FFS/MD), based on a recently developed coarse-grained water model (mW) (Molinero et al., J. Phys. Chem. B, 2009, 113, 4008). The calculated ice nucleation rates display a strong temperature dependence, ranging from 2.148 ± 0.635 × 10(25) m(-3) s(-1) at 220 K to 1.672 ± 0.970 × 10(-7) m(-3) s(-1) at 240 K. These rates can be fitted according to the classical nucleation theory, yielding an estimate of the effective ice-water interface energy γ(ls) of 31.01 ± 0.21 mJ m(-2) for the mW water model. Compared to experiments, our calculation underestimates the homogeneous ice nucleation rate by a few orders of magnitude. Possible reasons for the discrepancy are discussed. The nucleating ice embryo contains both cubic ice Ic and hexagonal ice Ih, with the fraction of each structure being roughly 50% when the critical size is reached. In particular, a novel defect structure containing nearly five-fold twin boundaries is identified in the ice clusters formed during nucleation. The way such defect structure is formed is found to be different from mechanisms proposed for the formation of the same defect in metallic nanoparticles and thin film. The quasi five-fold twin boundary structure found here is expected to occur in the crystallization of a wide range of materials with the diamond cubic structure, including ice.

  5. Suppression of homogeneous crystal nucleation of the NiAl intermetallic by a composition gradient: A molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Yi, Peng; Falk, Michael L.; Weihs, Timothy P.

    2017-05-01

    Molecular dynamics simulations of homogeneous nucleation of the NiAl intermetallic phase from a liquid solution on cooling indicate that this phase transformation is suppressed in the presence of a composition gradient. A simulation method is designed to generate a sustaining composition gradient at the interface between two materials. As the composition gradient increases, the nucleation energy barrier rises, the critical nucleus size increases, and the nucleus shape develops an increasing asymmetry. A polymorphic nucleation model for a disk-shaped nucleus that incorporates the composition dependence of interfacial free energies was observed to describe the atomic-scale details of the simulation well. Critical nuclei shapes and volumes predicted by the model match with those appearing in the molecular dynamics simulations.

  6. Heterogeneous and homogeneous nucleation compared: rapid nucleation on microscopic impurities.

    PubMed

    Sear, Richard P

    2006-03-16

    We use computer simulation to calculate the rates of both homogeneous nucleation and heterogeneous nucleation on microscopic impurities. We do so in perhaps the simplest model of fluids and magnets: the two-dimensional Ising model. We expect our results to be qualitatively applicable to many simple and complex fluids. We find that heterogeneous nucleation on an impurity that is not only microscopic but also as small as possible, that is, a single fixed spin, is more than four orders of magnitude faster than homogeneous nucleation. The rate of heterogeneous nucleation then increases by a factor of approximately five for each additional fixed spin in the impurity. These results suggest that impurities as small as single molecules can result in homogeneous nucleation being irrelevant due to heterogeneous nucleation on these microscopic impurities being much faster.

  7. Interplay between the Relaxation of the Glass of Random l/d-Lactide Copolymers and Homogeneous Crystal Nucleation: Evidence for Segregation of Chain Defects.

    PubMed

    Androsch, René; Schick, Christoph

    2016-05-19

    Random l-isomer rich copolymers of poly(lactic acid) containing up to 4% d-isomer co-units have been cooled from the molten state to obtain glasses free of crystals and homogeneous crystal nuclei. The kinetics of enthalpy relaxation and the formation of homogeneous crystal nuclei have then been analyzed using fast scanning chip calorimetry. It has been found that the relaxation of the glass toward the structure/enthalpy of the supercooled liquid state is independent of the presence of d-isomer co-units in the chain. Formation of homogeneous crystal nuclei in the glassy state requires the completion of the relaxation of the glass. However, nucleation is increasingly delayed in the random copolymers with increasing d-isomer chain defect concentration. The data show that the slower formation of homogeneous crystal nuclei in random l/d-lactide copolymers, compared to the homopolymer, is not caused by different chain-segment mobility in the glassy state but by the segregation of chain defects in this early stage of the crystallization process.

  8. Crystal nucleation in lithium borate glass

    NASA Technical Reports Server (NTRS)

    Smith, Gary L.; Neilson, George F.; Weinberg, Michael C.

    1988-01-01

    Crystal nucleation measurements were made on three lithium borate compositions in the vicinity of Li2O-2Br2O3. All nucleation measurements were performed at 500 C. Certain aspects of the nucleation behavior indicated (tentatively) that it proceeded by a homogeneous mechanism. The steady state nucleation rate was observed to have the largest value when the Li2O concentration was slightly in excess of the diborate composition. The change in nucleation rate with composition is controlled by the variation of viscosity as well as the change in free energy with composition. The variation of nucleation rate is explained qualitatively in these terms.

  9. Crystal nucleation of colloidal hard dumbbells.

    PubMed

    Ni, Ran; Dijkstra, Marjolein

    2011-01-21

    Using computer simulations, we investigate the homogeneous crystal nucleation in suspensions of colloidal hard dumbbells. The free energy barriers are determined by Monte Carlo simulations using the umbrella sampling technique. We calculate the nucleation rates for the plastic crystal and the aperiodic crystal phase using the kinetic prefactor as determined from event driven molecular dynamics simulations. We find good agreement with the nucleation rates determined from spontaneous nucleation events observed in event driven molecular dynamics simulations within error bars of one order of magnitude. We study the effect of aspect ratio of the dumbbells on the nucleation of plastic and aperiodic crystal phases, and we also determine the structure of the critical nuclei. Moreover, we find that the nucleation of the aligned close-packed crystal structure is strongly suppressed by a high free energy barrier at low supersaturations and slow dynamics at high supersaturations.

  10. Study on nucleation kinetics of lysozyme crystallization

    NASA Astrophysics Data System (ADS)

    Lin, Chen; Zhang, Yang; Liu, Jing J.; Wang, Xue Z.

    2017-07-01

    The nucleation kinetics of hen egg-white lysozyme crystallization was investigated using a hot stage cooling crystallizer and a microscope to monitor the solution crystallization process in real time. Images of crystals were continuously recorded under varied precipitant and protein concentrations. The nucleation rate was found to be higher at higher precipitant concentration, and increase monotonically with protein concentration if the precipitant concentration was held constant. Attempt was made to interpret the experimental data using classical nucleation theory. It was found that the model predictions are lower than the experimental values at low supersaturations but agree well with experimental data at high supersaturations. The trends in the experimental data suggest that two nucleation mechanisms might co-exist: heterogeneous nucleation seems to be the dominant at low supersaturation while at higher supersaturation homogeneous nucleation seems to play the major role.

  11. Nucleation precursors in protein crystallization

    PubMed Central

    Vekilov, Peter G.; Vorontsova, Maria A.

    2014-01-01

    Protein crystal nucleation is a central problem in biological crystallography and other areas of science, technology and medicine. Recent studies have demonstrated that protein crystal nuclei form within crucial precursors. Here, methods of detection and characterization of the precursors are reviewed: dynamic light scattering, atomic force microscopy and Brownian microscopy. Data for several proteins provided by these methods have demonstrated that the nucleation precursors are clusters consisting of protein-dense liquid, which are metastable with respect to the host protein solution. The clusters are several hundred nanometres in size, the cluster population occupies from 10−7 to 10−3 of the solution volume, and their properties in solutions supersaturated with respect to crystals are similar to those in homogeneous, i.e. undersaturated, solutions. The clusters exist owing to the conformation flexibility of the protein molecules, leading to exposure of hydrophobic surfaces and enhanced intermolecular binding. These results indicate that protein conformational flexibility might be the mechanism behind the metastable mesoscopic clusters and crystal nucleation. Investigations of the cluster properties are still in their infancy. Results on direct imaging of cluster behaviors and characterization of cluster mechanisms with a variety of proteins will soon lead to major breakthroughs in protein biophysics. PMID:24598910

  12. Nucleation and Crystallization in nucleated Polymers

    NASA Astrophysics Data System (ADS)

    Schick, Christoph; Zhuravlev, Evgeny; Wurm, Andreas

    2012-02-01

    Crystallization is commonly considered as nucleation followed by a growth process. Here we apply the recently developed technique, differential fast scanning calorimetry (DFSC), for a unique, new look at the crystal growth of poly(epsilon-caprolactone) (PCL) and PCL carbon nanotube composites from 185 K, below the glass transition temperature, to 330 K, close to the equilibrium melting temperature. The DFSC allows temperature control of the sample and determination of its heat capacity during temperature treatments by employing cooling and heating rates from 50 to 50,000 K/s. First, the crystal nucleation and overall crystallization half times were determined simultaneously in the range of temperatures where crystallization of PCL occurs. After attempting to analyze the experiments with the classical nucleation and growth model a new methodology is described, which addresses the specific problems of crystallization of flexible linear macromolecules. The structures seem to range from having practically unmeasurable latent heats of ordering (nuclei) to being clearly-recognizable, ordered species with rather sharp disordering endotherms at temperatures from the glass transition to equilibrium melting (increasingly perfect and larger crystals). The mechanisms and kinetics of growth (if any) involve a detailed understanding of the interaction with the surrounding rigid amorphous fraction (RAF) in dependence of crystal size and perfection. E. Zhuravlev, J.W.P. Schmelzer, B. Wunderlich and C. Schick, Kinetics of nucleation and crystallization in poly(epsilon-caprolactone) (PCL), Polymer 52 (2011) 1983-1997.

  13. Parameterization of homogeneous ice nucleation for cloud and climate models based on classical nucleation theory

    NASA Astrophysics Data System (ADS)

    Khvorostyanov, V. I.; Curry, J. A.

    2012-10-01

    A new analytical parameterization of homogeneous ice nucleation is developed based on extended classical nucleation theory including new equations for the critical radii of the ice germs, free energies and nucleation rates as simultaneous functions of temperature and water saturation ratio. By representing these quantities as separable products of the analytical functions of temperature and supersaturation, analytical solutions are found for the integral-differential supersaturation equation and concentration of nucleated crystals. Parcel model simulations are used to illustrate the general behavior of various nucleation properties under various conditions, for justifications of the further key analytical simplifications, and for verification of the resulting parameterization. The final parameterization is based upon the values of the supersaturation that determines the current or maximum concentrations of the nucleated ice crystals. The crystal concentration is analytically expressed as a function of time and can be used for parameterization of homogeneous ice nucleation both in the models with small time steps and for substep parameterization in the models with large time steps. The crystal concentration is expressed analytically via the error functions or elementary functions and depends only on the fundamental atmospheric parameters and parameters of classical nucleation theory. The diffusion and kinetic limits of the new parameterization agree with previous semi-empirical parameterizations.

  14. Parameterization of homogeneous ice nucleation for cloud and climate models based on classical nucleation theory

    NASA Astrophysics Data System (ADS)

    Khvorostyanov, V. I.; Curry, J. A.

    2012-03-01

    A new analytical parameterization of homogeneous ice nucleation is developed based on extended classical nucleation theory including new equations for the critical radii of the ice germs, free energies and nucleation rates as the functions of the temperature and water saturation ratio simultaneously. By representing these quantities as separable products of the analytical functions of the temperature and supersaturation, analytical solutions are found for the integral-differential supersaturation equation and concentration of nucleated crystals. Parcel model simulations are used to illustrate the general behavior of various nucleation properties under various conditions, for justifications of the further key analytical simplifications, and for verification of the resulting parameterization. The final parameterization is based upon the values of the supersaturation that determines the current or maximum concentrations of the nucleated ice crystals. The crystal concentration is analytically expressed as a function of time and can be used for parameterization of homogeneous ice nucleation both in the models with small time steps and for substep parameterization in the models with large time steps. The crystal concentration is expressed analytically via the error functions or elementary functions and depends only on the fundamental atmospheric parameters and parameters of classical nucleation theory. The diffusion and kinetic limits of the new parameterization agree with previous semi-empirical parameterizations.

  15. Homogeneous freezing nucleation of stratospheric solution droplets

    NASA Technical Reports Server (NTRS)

    Jensen, Eric J.; Toon, Owen B.; Hamill, Patrick

    1991-01-01

    The classical theory of homogeneous nucleation was used to calculate the freezing rate of sulfuric acid solution aerosols under stratospheric conditions. The freezing of stratospheric aerosols would be important for the nucleation of nitric acid trihydrate particles in the Arctic and Antarctic stratospheres. In addition, the rate of heterogeneous chemical reactions on stratospheric aerosols may be very sensitive to their state. The calculations indicate that homogeneous freezing nucleation of pure water ice in the stratospheric solution droplets would occur at temperatures below about 192 K. However, the physical properties of H2SO4 solution at such low temperatures are not well known, and it is possible that sulfuric acid aerosols will freeze out at temperatures ranging from about 180 to 195 K. It is also shown that the temperature at which the aerosols freeze is nearly independent of their size.

  16. Homogeneous freezing nucleation of stratospheric solution droplets

    NASA Astrophysics Data System (ADS)

    Jensen, Eric J.; Toon, Owen B.; Hamill, Patrick

    1991-10-01

    The classical theory of homogeneous nucleation was used to calculate the freezing rate of sulfuric acid solution aerosols under stratospheric conditions. The freezing of stratospheric aerosols would be important for the nucleation of nitric acid trihydrate particles in the Arctic and Antarctic stratospheres. In addition, the rate of heterogeneous chemical reactions on stratospheric aerosols may be very sensitive to their state. The calculations indicate that homogeneous freezing nucleation of pure water ice in the stratospheric solution droplets would occur at temperatures below about 192 K. However, the physical properties of H2SO4 solution at such low temperatures are not well known, and it is possible that sulfuric acid aerosols will freeze out at temperatures ranging from about 180 to 195 K. It is also shown that the temperature at which the aerosols freeze is nearly independent of their size.

  17. Effect of gravity wave temperature variations on homogeneous ice nucleation

    NASA Astrophysics Data System (ADS)

    Dinh, Tra; Podglajen, Aurélien; Hertzog, Albert; Legras, Bernard; Plougonven, Riwal

    2015-04-01

    Observations of cirrus clouds in the tropical tropopause layer (TTL) have shown various ice number concentrations (INC) (e.g., Jensen et al. 2013), which has lead to a puzzle regarding their formation. In particular, the frequently observed low numbers of ice crystals seemed hard to reconcile with homogeneous nucleation knowing the ubuquity of gravity waves with vertical velocity of the order of 0.1 m/s. Using artificial time series, Spichtinger and Krämer (2013) have illustrated that the variation of vertical velocity during a nucleation event could terminate it and limit the INC. However, their study was limited to constructed temperature time series. Here, we carry out numerical simulations of homogeneous ice nucleation forced by temperature time series data collected by isopycnic balloon flights near the tropical tropopause. The balloons collected data at high frequency (30 s), so gravity wave signals are well resolved in the temperature time series. With the observed temperature time series, the numerical simulations with homogeneous freezing show a full range of ice number concentrations (INC) as previously observed in the tropical upper troposphere. The simulations confirm that the dynamical time scale of temperature variations (as seen from observations) can be shorter than the nucleation time scale. They show the existence of two regimes for homogeneous ice nucleation : one limited by the depletion of water vapor by the nucleated ice crystals (those we name vapor events) and one limited by the reincrease of temperature after its initial decrease (temperature events). Low INC may thus be obtained for temperature events when the gravity wave perturbations produce a non-persistent cooling rate (even with large magnitude) such that the absolute change in temperature remains small during nucleation. This result for temperature events is explained analytically by a dependence of the INC on the absolute drop in temperature (and not on the cooling rate). This

  18. Computer simulations of homogeneous nucleation of benzene from the melt.

    PubMed

    Shah, Manas; Santiso, Erik E; Trout, Bernhardt L

    2011-09-08

    Nucleation is the key step in crystallization by which the molecules (or atoms or ions) aggregate together, find the right relative orientations, and start to grow to form the final crystal structure. Since nucleation is an activated step involving a large gap in time scales between molecular motions and the nucleation event itself, nucleation must be studied using rare events methods. We employ a technique developed previously in our group known as aimless shooting [Peters, B.; Trout, B. L. J. Chem. Phys., 2006, 125, 054108], which is based on transition path sampling, to generate reactive trajectories between the disordered and ordered phases of benzene. Using the likelihood maximization algorithm, we analyze the aimless shooting trajectories to identify the key order parameters or collective variables to describe the reaction coordinate for the nucleation of benzene from the melt. We find that the local bond orientation and local relative orientation order parameters are the most important collective variables in describing the reaction coordinate for homogeneous nucleation from the melt, as compared to cluster size and space-averaged order parameters. This study also demonstrates the utility of recently developed order parameters for molecular crystals [Santiso, E. E.; Trout, B. L. J. Chem. Phys., 2011, 134, 064109].

  19. Nucleation of Crystals in Solution

    NASA Astrophysics Data System (ADS)

    Vekilov, Peter G.

    2010-07-01

    Solution crystallization is an essential part of processes in the chemical and pharmaceutical industries and a major step in physiological and pathological phenomena. Crystallization starts with nucleation and control of nucleation is crucial for the control of the number, size, perfection, polymorphism and other characteristics of the crystalline materials. Recently, there have been significant advances in the understanding of the mechanism of nucleation of crystals in solution. The most significant of these is the two-step mechanism of nucleation, according to which the crystalline nucleus appears inside pre-existing metastable clusters of size several hundred nanometers, which consist of dense liquid and are suspended in the solution. While initially proposed for protein crystals, the applicability of this mechanism has been demonstrated for small molecule organic materials, colloids, and biominerals. This mechanism helps to explain several long-standing puzzles of crystal nucleation in solution: nucleation rates which are many orders of magnitude lower than theoretical predictions, nucleation kinetic dependencies with steady or receding parts at increasing supersaturation, the role of heterogeneous substrates for polymorph selection, the significance of the dense protein liquid, and others. More importantly, this mechanism provides powerful tools for control of the nucleation process by varying the solution thermodynamic parameters so that the volume occupied by the dense liquid shrinks or expands.

  20. Protein crystal nucleation in pores

    PubMed Central

    Nanev, Christo N.; Saridakis, Emmanuel; Chayen, Naomi E.

    2017-01-01

    The most powerful method for protein structure determination is X-ray crystallography which relies on the availability of high quality crystals. Obtaining protein crystals is a major bottleneck, and inducing their nucleation is of crucial importance in this field. An effective method to form crystals is to introduce nucleation-inducing heterologous materials into the crystallization solution. Porous materials are exceptionally effective at inducing nucleation. It is shown here that a combined diffusion-adsorption effect can increase protein concentration inside pores, which enables crystal nucleation even under conditions where heterogeneous nucleation on flat surfaces is absent. Provided the pore is sufficiently narrow, protein molecules approach its walls and adsorb more frequently than they can escape. The decrease in the nucleation energy barrier is calculated, exhibiting its quantitative dependence on the confinement space and the energy of interaction with the pore walls. These results provide a detailed explanation of the effectiveness of porous materials for nucleation of protein crystals, and will be useful for optimal design of such materials. PMID:28091515

  1. Overview: Experimental studies of crystal nucleation: Metals and colloids

    NASA Astrophysics Data System (ADS)

    Herlach, Dieter M.; Palberg, Thomas; Klassen, Ina; Klein, Stefan; Kobold, Raphael

    2016-12-01

    Crystallization is one of the most important phase transformations of first order. In the case of metals and alloys, the liquid phase is the parent phase of materials production. The conditions of the crystallization process control the as-solidified material in its chemical and physical properties. Nucleation initiates the crystallization of a liquid. It selects the crystallographic phase, stable or meta-stable. Its detailed knowledge is therefore mandatory for the design of materials. We present techniques of containerless processing for nucleation studies of metals and alloys. Experimental results demonstrate the power of these methods not only for crystal nucleation of stable solids but in particular also for investigations of crystal nucleation of metastable solids at extreme undercooling. This concerns the physical nature of heterogeneous versus homogeneous nucleation and nucleation of phases nucleated under non-equilibrium conditions. The results are analyzed within classical nucleation theory that defines the activation energy of homogeneous nucleation in terms of the interfacial energy and the difference of Gibbs free energies of solid and liquid. The interfacial energy acts as barrier for the nucleation process. Its experimental determination is difficult in the case of metals. In the second part of this work we therefore explore the potential of colloidal suspensions as model systems for the crystallization process. The nucleation process of colloids is observed in situ by optical observation and ultra-small angle X-ray diffraction using high intensity synchrotron radiation. It allows an unambiguous discrimination of homogeneous and heterogeneous nucleation as well as the determination of the interfacial free energy of the solid-liquid interface. Our results are used to construct Turnbull plots of colloids, which are discussed in relation to Turnbull plots of metals and support the hypothesis that colloids are useful model systems to investigate crystal

  2. Effect of cloud-scale vertical velocity on the contribution of homogeneous nucleation to cirrus formation and radiative forcing

    NASA Astrophysics Data System (ADS)

    Shi, X.; Liu, X.

    2016-06-01

    Ice nucleation is a critical process for the ice crystal formation in cirrus clouds. The relative contribution of homogeneous nucleation versus heterogeneous nucleation to cirrus formation differs between measurements and predictions from general circulation models. Here we perform large-ensemble simulations of the ice nucleation process using a cloud parcel model driven by observed vertical motions and find that homogeneous nucleation occurs rather infrequently, in agreement with recent measurement findings. When the effect of observed vertical velocity fluctuations on ice nucleation is considered in the Community Atmosphere Model version 5, the relative contribution of homogeneous nucleation to cirrus cloud occurrences decreases to only a few percent. However, homogeneous nucleation still has strong impacts on the cloud radiative forcing. Hence, the importance of homogeneous nucleation for cirrus cloud formation should not be dismissed on the global scale.

  3. Crystallization of Nucleator Nanofibrils in Polypropylene Melt

    NASA Astrophysics Data System (ADS)

    Lipp, J.; Cohen, Y.; Khalfin, R. L.; Shuster, M.; Terry, A. E.

    2007-03-01

    Self-associating molecules act as nucleating agents in polypropylene (PP) in order to increase the crystallization rate and decrease the crystallite size, by forming a fine network of nanofibrils within the polymer melt. The thermodynamic and kinetic basis for formation of this structure is not clear. Current models usually invoke a spinodal decomposition mechanism, as temperature is lowered into an immiscibility gap. This presentation deals with 1,3:2,4-Di(3,4-dimethylbenzylidene)sorbitol [dMdBS] in PP. The kinetics of structure formation was evaluated using small angle x-ray scattering, including synchrotron measurements. The results indicate a crystallization process by means of a nucleation and growth mechanism, which is controlled by the rate of homogeneous nucleation. The thermodynamic temperature of this process, determined for two different dMdBS concentrations from the temperature dependence of the crystallization half-time, agrees with that obtained by group-contribution calculation of the solubility parameters. dMdBS nanofibril formation has a remarkable effect on PP crystallization in melt-spun fibers. Just 0.4% additive at a moderate spin-draw ratio yields a crystalline morphology comprised of parallel chain-folded lamellae, with the lamellar normal highly aligned along the fiber axis.

  4. Homogeneous vs. heterogeneous nucleation in water-dicarboxylic acid systems

    NASA Astrophysics Data System (ADS)

    Hienola, A. I.; Vehkamäki, H.; Riipinen, I.; Kulmala, M.

    2009-03-01

    Binary heterogeneous nucleation of water-succinic/glutaric/malonic/adipic acid on nanometer-sized particles is investigated within the frame of classical heterogeneous nucleation theory. Homogeneous nucleation is also included for comparison. It is found that the nucleation probabilities depend on the contact angle and on the size of the seed particles. New thermodynamical properties, such as saturation vapor pressure, density and surface tension for all the dicarboxylic acid aqueous solutions are included in the calculations. While the new surface tension and density formulations do not bring any significant difference in the computed nucleation rate for homogeneous nucleation for succinic and glutaric acids, the use of the newly derived equations for the vapor pressure decrease the acid concentrations in gas phase by 3 orders of magnitude. According to our calculations, the binary heterogeneous nucleation of succinic acid-water and glutaric acid-water - although it requires a 3-4 orders of magnitude lower vapor concentrations than the homogeneous nucleation - cannot take place under atmospheric conditions. On the other hand binary homogeneous nucleation of adipic acid-water systems might be possible under conditions occuring in upper boundary layer. However, a more detailed characterization of the interaction between the surface and the molecules of the nucleating vapor should be considered in the future.

  5. Rate of Homogenous Nucleation of Ice in Supercooled Water.

    PubMed

    Atkinson, James D; Murray, Benjamin J; O'Sullivan, Daniel

    2016-08-25

    The homogeneous freezing of water is of fundamental importance to a number of fields, including that of cloud formation. However, there is considerable scatter in homogeneous nucleation rate coefficients reported in the literature. Using a cold stage droplet system designed to minimize uncertainties in temperature measurements, we examined the freezing of over 1500 pure water droplets with diameters between 4 and 24 μm. Under the assumption that nucleation occurs within the bulk of the droplet, nucleation rate coefficients fall within the spread of literature data and are in good agreement with a subset of more recent measurements. To quantify the relative importance of surface and volume nucleation in our experiments, where droplets are supported by a hydrophobic surface and surrounded by oil, comparison of droplets with different surface area to volume ratios was performed. From our experiments it is shown that in droplets larger than 6 μm diameter (between 234.6 and 236.5 K), nucleation in the interior is more important than nucleation at the surface. At smaller sizes we cannot rule out a significant contribution of surface nucleation, and in order to further constrain surface nucleation, experiments with smaller droplets are necessary. Nevertheless, in our experiments, it is dominantly volume nucleation controlling the observed nucleation rate.

  6. Role of the Prestructured Surface Cloud in Crystal Nucleation

    NASA Astrophysics Data System (ADS)

    Lechner, Wolfgang; Dellago, Christoph; Bolhuis, Peter G.

    2011-02-01

    For the homogeneous crystal nucleation process in a soft-core colloid model, we identify optimal reaction coordinates from a set of novel order parameters based on the local structure within the nucleus, by employing transition path sampling techniques combined with a likelihood maximization of the committor function. We find that nucleation is governed by solid clusters that consist of an hcp core embedded within a cloud of surface particles that are highly correlated with their nearest neighbors but not ordered in a high-symmetry crystal structure. The results shed new light on the interpretation of the surface and volume terms in classical nucleation theory.

  7. Sigmoid kinetics of protein crystal nucleation

    NASA Astrophysics Data System (ADS)

    Nanev, Christo N.; Tonchev, Vesselin D.

    2015-10-01

    A non-linear differential equation expressing the new phase nucleation rate in the different steps of the process (non-stationary and stationary nucleation and in the plateau region) is derived from basic principles of the nucleation theory. It is shown that one and the same sigmoid (logistic) function describes both nucleation scenarios: the one according to the classical theory, and the other according to the modern two-stage mechanism of protein crystal formation. Comparison to experimental data on both insulin crystal nucleation kinetics and on bovine β-lactoglobulin crystallization indicates a good agreement with the sigmoidal prediction. Experimental data for electrochemical nucleation and glass crystallization obey the same sigmoid time dependence, and suggest universality of this nucleation kinetics law.

  8. Homogeneous nucleation of methane hydrates: unrealistic under realistic conditions.

    PubMed

    Knott, Brandon C; Molinero, Valeria; Doherty, Michael F; Peters, Baron

    2012-12-05

    Methane hydrates are ice-like inclusion compounds with importance to the oil and natural gas industry, global climate change, and gas transportation and storage. The molecular mechanism by which these compounds form under conditions relevant to industry and nature remains mysterious. To understand the mechanism of methane hydrate nucleation from supersaturated aqueous solutions, we performed simulations at controlled and realistic supersaturation. We found that critical nuclei are extremely large and that homogeneous nucleation rates are extremely low. Our findings suggest that nucleation of methane hydrates under these realistic conditions cannot occur by a homogeneous mechanism.

  9. Interpretation of DTA experiments used for crystal nucleation rate determinations

    NASA Technical Reports Server (NTRS)

    Weinberg, Michael C.

    1991-01-01

    An analysis is presented of two schemes which have been proposed for the determination of the temperature dependence of homogeneous crystal nucleation rates in glasses via DTA measurements. The first method is based upon the postulate that the inverse of the temperature at which the DTA crystallization rate is maximum, will increase monotonically as the number density of nucleated particles increases. The secone method is based on the observation that the intensity at T(p) (peak height) increases as T(p) grows. The validity of both of these methods is assessed for inorganic glasses for two specific crystal growth models.

  10. The dependence of homogeneous nucleation rate on supersaturation.

    PubMed

    Girshick, Steven L

    2014-07-14

    The claim that classical nucleation theory (CNT) correctly predicts the dependence on supersaturation of the steady-state rate of homogeneous nucleation is reexamined in light of recent experimental studies of nucleation of a range of substances, including water, argon, nitrogen, and several 1-alcohols. Based on these studies (which include, for water, a compilation of nine different studies), it is concluded that the dependence of nucleation rate on supersaturation is not correctly predicted by CNT. It is shown that CNT's incorrect prediction of the supersaturation dependence of nucleation rate is due to its incorrect prediction of the Gibbs free energy change associated with formation of small clusters from the monomer vapor, evaluated at the substance's equilibrium vapor pressure, even though that free energy change is itself a function only of temperature.

  11. Homogeneous nucleation of non-metals and metals

    NASA Astrophysics Data System (ADS)

    Rudek, Markus Martin

    1998-11-01

    Homogeneous nucleation rates as functions of both supersaturation and temperature were measured in an upward thermal diffusion cloud chamber for four n- alkanes, i.e., n-heptane, n-octane, n-nonane, and n- decane, for two n-alcohols, i.e., n-pentanol and n- hexanol, and for m-xylene. Nucleation rates from about 10-4 to 5×100 drops cm-3 s- 1 were obtained in the temperature range, 241 K to 340 K. Their dependences on supersaturation and temperature were compared to predictions of several nucleation theories: Classical Theory, the Internally Consistent Classical Theory, two versions of the Kalikmanov-van Dongen Theory, and the Delale-Meier Theory. Each theory predicted the dependence of the nucleation rate on supersaturation reasonably well, but large temperature dependent correlation factors were needed for quantitative agreement between measured and predicted nucleation rates. However, all substances had a very similar temperature dependence to their multiplicative correction factor. The homogeneous nucleation of supersaturated cesium vapor was investigated in a thermal diffusion cloud chamber operating in both the upward and the downward mode. In the upward operating mode, critical supersaturations were measured in the temperature range, 421K to 554K. In the downward operating mode, it was possible to circumvent experimental difficulties due to phoretic effects which arise at low pressures in measurements in the upward mode. This enabled measurements of critical supersaturations over the temperature range, 289K to 452K. The use of the downward mode enabled the extension of the temperature range of the measurements by 70K towards lower temperatures. This makes cesium the substance whose homogeneous nucleation has been measured, in a thermal diffusion cloud chamber, over the largest range of temperatures, 289K to 554K. These measured critical supersaturations were compared to the predictions of the Internally Consistent version of Classical nucleation Theory and to

  12. Kinetics of homogeneous nucleation in many component systems

    NASA Technical Reports Server (NTRS)

    Hirschfelder, J. O.

    1974-01-01

    Reiss's classical treatment of the kinetics of homogeneous nucleation in a system containing two chemical components is extended to many-component systems. The formulation is analogous to the pseudo-stationary state theory of chemical reaction rates with the free energy as a function of the composition of the embryo taking the place of the potential energy as a function of interatomic distances.

  13. Kinetics of homogeneous nucleation on many-component systems

    NASA Technical Reports Server (NTRS)

    Hirschfelder, J. O.

    1974-01-01

    Reiss's (1950) classical treatment of the kinetics of homogeneous nucleation in a system containing two chemical components is extended to many-component systems. The formulation is analogous to the pseudostationary-state theory of chemical reaction rates, with the free energy as a function of the composition of the embryo taking the place of the potential energy as a function of interatomic distances.

  14. Comparison of parameterizations for homogeneous and heterogeneous ice nucleation

    NASA Astrophysics Data System (ADS)

    Koop, T.; Zobrist, B.

    2009-04-01

    The formation of ice particles from liquid aqueous aerosols is of central importance for the physics and chemistry of high altitude clouds. In this paper, we present new laboratory data on ice nucleation and compare them with two different parameterizations for homogeneous as well as heterogeneous ice nucleation. In particular, we discuss and evaluate the effect of solutes and ice nuclei. One parameterization is the λ-approach which correlates the depression of the freezing temperature of aqueous droplets in comparison to pure water droplets, Tf, with the corresponding depression, Tm, of the equilibrium ice melting point: Tf = λ × Tm. Here, λ is independent of concentration and a constant that is specific for a particular solute or solute/ice nucleus combination. The other approach is water-activity-based ice nucleation theory which describes the effects of solutes on the freezing temperature Tf via their effect on water activity: aw(Tf) = awi(Tf) + aw. Here, awi is the water activity of ice and aw is a constant that depends on the ice nucleus but is independent of the type of solute. We present new data on both homogeneous and heterogeneous ice nucleation with varying types of solutes and ice nuclei. We evaluate and discuss the advantages and limitations of the two approaches for the prediction of ice nucleation in laboratory experiments and atmospheric cloud models.

  15. Homogenous Surface Nucleation of Solid Polar Stratospheric Cloud Particles

    NASA Technical Reports Server (NTRS)

    Tabazadeh, A.; Hamill, P.; Salcedo, D.; Gore, Warren J. (Technical Monitor)

    2002-01-01

    A general surface nucleation rate theory is presented for the homogeneous freezing of crystalline germs on the surfaces of aqueous particles. While nucleation rates in a standard classical homogeneous freezing rate theory scale with volume, the rates in a surface-based theory scale with surface area. The theory is used to convert volume-based information on laboratory freezing rates (in units of cu cm, seconds) of nitric acid trihydrate (NAT) and nitric acid dihydrate (NAD) aerosols into surface-based values (in units of sq cm, seconds). We show that a surface-based model is capable of reproducing measured nucleation rates of NAT and NAD aerosols from concentrated aqueous HNO3 solutions in the temperature range of 165 to 205 K. Laboratory measured nucleation rates are used to derive free energies for NAT and NAD germ formation in the stratosphere. NAD germ free energies range from about 23 to 26 kcal mole, allowing for fast and efficient homogeneous NAD particle production in the stratosphere. However, NAT germ formation energies are large (greater than 26 kcal mole) enough to prevent efficient NAT particle production in the stratosphere. We show that the atmospheric NAD particle production rates based on the surface rate theory are roughly 2 orders of magnitude larger than those obtained from a standard volume-based rate theory. Atmospheric volume and surface production of NAD particles will nearly cease in the stratosphere when denitrification in the air exceeds 40 and 78%, respectively. We show that a surface-based (volume-based) homogeneous freezing rate theory gives particle production rates, which are (not) consistent with both laboratory and atmospheric data on the nucleation of solid polar stratospheric cloud particles.

  16. Homogenous Surface Nucleation of Solid Polar Stratospheric Cloud Particles

    NASA Technical Reports Server (NTRS)

    Tabazadeh, A.; Hamill, P.; Salcedo, D.; Gore, Warren J. (Technical Monitor)

    2002-01-01

    A general surface nucleation rate theory is presented for the homogeneous freezing of crystalline germs on the surfaces of aqueous particles. While nucleation rates in a standard classical homogeneous freezing rate theory scale with volume, the rates in a surface-based theory scale with surface area. The theory is used to convert volume-based information on laboratory freezing rates (in units of cu cm, seconds) of nitric acid trihydrate (NAT) and nitric acid dihydrate (NAD) aerosols into surface-based values (in units of sq cm, seconds). We show that a surface-based model is capable of reproducing measured nucleation rates of NAT and NAD aerosols from concentrated aqueous HNO3 solutions in the temperature range of 165 to 205 K. Laboratory measured nucleation rates are used to derive free energies for NAT and NAD germ formation in the stratosphere. NAD germ free energies range from about 23 to 26 kcal mole, allowing for fast and efficient homogeneous NAD particle production in the stratosphere. However, NAT germ formation energies are large (greater than 26 kcal mole) enough to prevent efficient NAT particle production in the stratosphere. We show that the atmospheric NAD particle production rates based on the surface rate theory are roughly 2 orders of magnitude larger than those obtained from a standard volume-based rate theory. Atmospheric volume and surface production of NAD particles will nearly cease in the stratosphere when denitrification in the air exceeds 40 and 78%, respectively. We show that a surface-based (volume-based) homogeneous freezing rate theory gives particle production rates, which are (not) consistent with both laboratory and atmospheric data on the nucleation of solid polar stratospheric cloud particles.

  17. Critical humidities of homogeneous and heterogeneous ice nucleation: Inferences from extended classical nucleation theory

    NASA Astrophysics Data System (ADS)

    Khvorostyanov, Vitaly I.; Curry, Judith A.

    2009-02-01

    A generalization of classical ice nucleation theory is used to derive analytical expressions for the critical (threshold) humidities of homogeneous and heterogeneous freezing. The critical radius and energy of an ice embryo and nucleation rates were derived previously by the authors as functions of temperature, pressure, water saturation ratio, and radii of freezing particles. Here we invert the analytical expressions for the nucleation rates and solve them relative to the critical water and ice saturation ratios (or critical relative humidities). The critical humidities are expressed as analytical functions of temperature, pressure, nucleation or cooling rates, radius of freezing particles and their physico-chemical properties, misfit strain, and activation energy. Calculations of critical ice relative humidities are made using these equations over an extended temperature range down to -75°C and are compared with previous empirical parameterizations and experimental data, and differences are interpreted in the context of variation of the other parameters. It is shown that the critical humidities for heterogeneous ice nucleation are lower than those for homogeneous nucleation; however, this difference is not constant but depends substantially on the temperature and properties of freezing aerosol. Some simple parameterizations for cloud and climate models are suggested.

  18. Homogeneous nucleation of a noncritical phase near a continuous phase transition

    SciTech Connect

    Sear, Richard P.

    2001-06-01

    Homogeneous nucleation of a new phase near a second, continuous, transition, is considered. The continuous transition is in the metastable region associated with the first-order phase transition, one of whose coexisting phases is nucleating. Mean-field calculations show that as the continuous transition is approached, the size of the nucleus varies as the response function of the order parameter of the continuous transition. This response function diverges at the continuous transition, as does the temperature derivative of the free-energy barrier to nucleation. This rapid drop of the barrier as the continuous transition is approached means that the continuous transition acts to reduce the barrier to nucleation at the first-order transition. This may be useful in the crystallization of globular proteins.

  19. Precision expansion cloud chamber for homogeneous nucleation studies

    NASA Astrophysics Data System (ADS)

    Schmitt, John L.

    1981-11-01

    The author describes an expansion cloud chamber for the study of the nucleation of a single component vapor (homogeneous nucleation). The design draws on the many years of experience in this Center in construction of chambers for homogeneous nucleation of water. Design features of the chamber are: exact control of temperature (±0.03 ° C), pressure (±0.5 mm Hg), and automatic control of cycling. Construction features are: all construction materials are stainless steel, glass, or fluorocarbon plastics; the piston seal is a very flexible welded stainless steel bellows; the chamber can be made very clean by heating under vacuum and it is compatible with many substances, e.g., ethanol, nonane, and toluene. Performance features are: excellent repeatability of the expansion cycle over a temperature range of 45° to —15 °C and in day to day operation. Safety features are: automatic detection and warning and inerting against fire and explosion from combustible vapor in the chamber enclosure. The determination of the gas temperature at the maximum expansion is discussed as well as the importance of the ''fast'' pulse technique for the measurement of high nucleation rates.

  20. Crystallization and nucleation kinetics in volcanic systems

    NASA Astrophysics Data System (ADS)

    Agostini, C.; Fortunati, A.; Carroll, M. R.; Scaillet, B.; Landi, P.

    2011-12-01

    The main objective of this experimental study is to constrain and quantitatively model the complex solidification process that transforms a magma in a solid material. Of major interest are crystal nucleation and growth driven by isothermal decompression of hydrous magmas, and comparison with results from more abundant crystal growth/nucleation data obtained in isobaric cooling experiments. This research concerns two different volcanic systems, Pantelleria (peralkaline rhyolite) and Stromboli (basalt), to better understand how crystallization kinetics can affect different magma compositions. For Stromboli volcanic system TZM apparatus has been used to perform decompression runs at Bayerisches Geoinstitut in Bayreuth (DE). As for Pantelleria composition, cooling experiments has been done using IHPV devices at ISTO of Orléans (FR), on the basis of previous phase equilibrium work (Di Carlo et al., 2010). First obtained results for Stromboli case show high rates of nucleation and crystal growth during the initial stages of crystallization which were followed by crystal growth at approximately constant number densities as equilibrium was approached. Shapes of crystals growing in melts are controlled by the kinetics of crystallization and may provide information about the degree of undercooling experienced by batches of magma en route to the surface (Lofgren, 1980). The study of crystallization kinetics through phases growth rates (Couch et al., 2003), together with the calculation of nucleation density and nucleation rates (Hammer et al., 1999) represent a step toward the estimation of the time scales of magmatic processes in volcanic systems and the interpretation of shallow magmatic processes. The results for Stromboli suggest average crystal growth timescales on the order of weeks, but this is complicated by clear evidence that some crystals have experienced repeated periods of both dissolution and growth (Landi et al., 2004).

  1. Heterodimer formation and crystal nucleation of gramicidin D.

    PubMed Central

    Burkhart, B M; Gassman, R M; Langs, D A; Pangborn, W A; Duax, W L

    1998-01-01

    The linear pentadecapeptide antibiotic gramicidin D is a heterogeneous mixture of six components. Precise refinements of three-dimensional structures of naturally occurring gramicidin D in crystals obtained from methanol, ethanol, and n-propanol demonstrate the unexpected presence of stable left-handed antiparallel double-helical heterodimers that vary with the crystallization solvent. The side chains of Trp residues in the three structures exhibit sequence-specific patterns of conformational preference. Tyr substitution for Trp at position 11 appears to favor beta ribbon formation and stabilization of the antiparallel double helix that acts as a template for gramicidin folding and nucleation of different crystal forms. The fact that a minor component in a heterogeneous mixture influences aggregation and crystal nucleation has potential applications to other systems in which anomalous behavior is exhibited by aggregation of apparently homogeneous materials, such as the enigmatic behavior of prion proteins. PMID:9788907

  2. Nucleation of protein crystals: critical nuclei, phase behavior, and control pathways

    NASA Astrophysics Data System (ADS)

    Galkin, Oleg; Vekilov, Peter G.

    2001-11-01

    We have studied the nucleation of crystals of the model protein lysozyme using a novel technique that allows direct determinations of homogeneous nucleation rates. At constant temperature of 12.6°C we varied the thermodynamic supersaturation by changing the concentrations of protein and precipitant. We found a broken dependence of the homogeneous nucleation rate on supersaturation that is beyond the predictions of the classical nucleation theory. The nucleation theorem allows us to relate this to discrete changes of the size of the crystal nuclei with increasing supersaturation as (10 or 11)→(4 or 5)→(1 or 2). Furthermore, we observe that the existence of a second liquid phase at high protein concentrations strongly affects crystal nucleation kinetics. We show that the rate of homogeneous nucleation of lysozyme crystals passes through a maximum in the vicinity of the liquid-liquid phase boundary hidden below the liquidus (solubility) line in the phase diagram of the protein solution. We found that glycerol and polyethylene glycol (PEG), which do not specifically bind to proteins, shift this phase boundary and significantly suppress or enhance the crystal nucleation rates, although no simple correlation exists between the action of PEG on the phase diagram and the nucleation kinetics. This provides for a control mechanism which does not require changes in the protein concentration, or the acidity and ionicity of the solution. The effects of the two additives on the phase diagram strongly depend on their concentration and this provides opportunities for further tuning of nucleation rates.

  3. The Nucleation and Growth of Protein Crystals

    NASA Technical Reports Server (NTRS)

    Pusey, Marc

    2004-01-01

    Obtaining crystals of suitable size and high quality continues to be a major bottleneck in macromolecular crystallography. Currently, structural genomics efforts are achieving on average about a 10% success rate in going from purified protein to a deposited crystal structure. Growth of crystals in microgravity was proposed as a means of overcoming size and quality problems, which subsequently led to a major NASA effort in microgravity crystal growth, with the agency also funding research into understanding the process. Studies of the macromolecule crystal nucleation and growth process were carried out in a number of labs in an effort to understand what affected the resultant crystal quality on Earth, and how microgravity improved the process. Based upon experimental evidence, as well as simple starting assumptions, we have proposed that crystal nucleation occurs by a series of discrete self assembly steps, which 'set' the underlying crystal symmetry. This talk will review the model developed, and its origins, in our laboratory for how crystals nucleate and grow, and will then present, along with preliminary data, how we propose to use this model to improve the success rate for obtaining crystals from a given protein.

  4. The Nucleation and Growth of Protein Crystals

    NASA Technical Reports Server (NTRS)

    Pusey, Marc

    2004-01-01

    Obtaining crystals of suitable size and high quality continues to be a major bottleneck in macromolecular crystallography. Currently, structural genomics efforts are achieving on average about a 10% success rate in going from purified protein to a deposited crystal structure. Growth of crystals in microgravity was proposed as a means of overcoming size and quality problems, which subsequently led to a major NASA effort in microgravity crystal growth, with the agency also funding research into understanding the process. Studies of the macromolecule crystal nucleation and growth process were carried out in a number of labs in an effort to understand what affected the resultant crystal quality on Earth, and how microgravity improved the process. Based upon experimental evidence, as well as simple starting assumptions, we have proposed that crystal nucleation occurs by a series of discrete self assembly steps, which 'set' the underlying crystal symmetry. This talk will review the model developed, and its origins, in our laboratory for how crystals nucleate and grow, and will then present, along with preliminary data, how we propose to use this model to improve the success rate for obtaining crystals from a given protein.

  5. A compact setup to study homogeneous nucleation and condensation

    NASA Astrophysics Data System (ADS)

    Karlsson, Mattias; Alxneit, Ivo; Rütten, Frederik; Wuillemin, Daniel; Tschudi, Hans Rudolf

    2007-03-01

    An experiment is presented to study homogeneous nucleation and the subsequent droplet growth at high temperatures and high pressures in a compact setup that does not use moving parts. Nucleation and condensation are induced in an adiabatic, stationary expansion of the vapor and an inert carrier gas through a Laval nozzle. The adiabatic expansion is driven against atmospheric pressure by pressurized inert gas its mass flow carefully controlled. This allows us to avoid large pumps or vacuum storage tanks. Because we eventually want to study the homogeneous nucleation and condensation of zinc, the use of carefully chosen materials is required that can withstand pressures of up to 106 Pa resulting from mass flow rates of up to 600 lN min-1 and temperatures up to 1200 K in the presence of highly corrosive zinc vapor. To observe the formation of droplets a laser beam propagates along the axis of the nozzle and the light scattered by the droplets is detected perpendicularly to the nozzle axis. An ICCD camera allows to record the scattered light through fused silica windows in the diverging part of the nozzle spatially resolved and to detect nucleation and condensation coherently in a single exposure. For the data analysis, a model is needed to describe the isentropic core part of the flow along the nozzle axis. The model must incorporate the laws of fluid dynamics, the nucleation and condensation process, and has to predict the size distribution of the particles created (PSD) at every position along the nozzle axis. Assuming Rayleigh scattering, the intensity of the scattered light can then be calculated from the second moment of the PSD.

  6. A compact setup to study homogeneous nucleation and condensation.

    PubMed

    Karlsson, Mattias; Alxneit, Ivo; Rütten, Frederik; Wuillemin, Daniel; Tschudi, Hans Rudolf

    2007-03-01

    An experiment is presented to study homogeneous nucleation and the subsequent droplet growth at high temperatures and high pressures in a compact setup that does not use moving parts. Nucleation and condensation are induced in an adiabatic, stationary expansion of the vapor and an inert carrier gas through a Laval nozzle. The adiabatic expansion is driven against atmospheric pressure by pressurized inert gas its mass flow carefully controlled. This allows us to avoid large pumps or vacuum storage tanks. Because we eventually want to study the homogeneous nucleation and condensation of zinc, the use of carefully chosen materials is required that can withstand pressures of up to 10(6) Pa resulting from mass flow rates of up to 600 l(N) min(-1) and temperatures up to 1200 K in the presence of highly corrosive zinc vapor. To observe the formation of droplets a laser beam propagates along the axis of the nozzle and the light scattered by the droplets is detected perpendicularly to the nozzle axis. An ICCD camera allows to record the scattered light through fused silica windows in the diverging part of the nozzle spatially resolved and to detect nucleation and condensation coherently in a single exposure. For the data analysis, a model is needed to describe the isentropic core part of the flow along the nozzle axis. The model must incorporate the laws of fluid dynamics, the nucleation and condensation process, and has to predict the size distribution of the particles created (PSD) at every position along the nozzle axis. Assuming Rayleigh scattering, the intensity of the scattered light can then be calculated from the second moment of the PSD.

  7. Homogeneous ice nucleation at moderate supercooling from molecular simulation.

    PubMed

    Sanz, E; Vega, C; Espinosa, J R; Caballero-Bernal, R; Abascal, J L F; Valeriani, C

    2013-10-09

    Among all of the freezing transitions, that of water into ice is probably the most relevant to biology, physics, geology, or atmospheric science. In this work, we investigate homogeneous ice nucleation by means of computer simulations. We evaluate the size of the critical cluster and the nucleation rate for temperatures ranging between 15 and 35 K below melting. We use the TIP4P/2005 and the TIP4P/ice water models. Both give similar results when compared at the same temperature difference with the model's melting temperature. The size of the critical cluster varies from ∼8000 molecules (radius = 4 nm) at 15 K below melting to ∼600 molecules (radius = 1.7 nm) at 35 K below melting. We use Classical Nucleation Theory (CNT) to estimate the ice-water interfacial free energy and the nucleation free-energy barrier. We obtain an interfacial free energy of 29(3) mN/m from an extrapolation of our results to the melting temperature. This value is in good agreement both with experimental measurements and with previous estimates from computer simulations of TIP4P-like models. Moreover, we obtain estimates of the nucleation rate from simulations of the critical cluster at the barrier top. The values we get for both models agree within statistical error with experimental measurements. At temperatures higher than 20 K below melting, we get nucleation rates slower than the appearance of a critical cluster in all water of the hydrosphere during the age of the universe. Therefore, our simulations predict that water freezing above this temperature must necessarily be heterogeneous.

  8. Condensation of water vapor in rarefaction waves. I - Homogeneous nucleation

    NASA Technical Reports Server (NTRS)

    Sislian, J. P.; Glass, I. I.

    1976-01-01

    A detailed theoretical investigation has been made of the condensation of water vapor/carrier gas mixtures in the nonstationary rarefaction wave generated in a shock tube. It is assumed that condensation takes place by homogeneous nucleation. The equations of motion together with the nucleation rate and the droplet growth equations were solved numerically by the method of characteristics and Lax's method of implicit artificial viscosity. It is found that, for the case considered, the condensation wave formed by the collapse of the metastable nonequilibrium state is followed by a shock wave generated by the intersection of characteristics of the same family. The expansion is practically isentropic up to the onset of condensation. The condensation front accelerates in the x,t plane. The results of the computations for a chosen case of water vapor/nitrogen mixture are presented by plotting variations of pressure, nucleation rate, number density of critical clusters, and condensate mass-fraction along three particle paths. Some consideration is given to homogeneous condensation experiments conducted in a shock tube. Although a direct comparison of the present theoretical work and these experiments is not possible, several worthwhile interpretative features have resulted nevertheless.

  9. Interfacial supersaturation, secondary nucleation, and crystal growth

    NASA Astrophysics Data System (ADS)

    Tai, Clifford Y.; Wu, Jenn-Fang; Rousseau, Ronald W.

    1992-02-01

    A theory describing the source of nuclei in secondary nucleation is presented and used to rationalize experimental data from the literature, some of which had appeared to be conflicting. The theory rests on a model in which an adsorption layer consisting of clusters of growth units of varying size is formed on the surface of growing crystals. The existence of the layer is related to the two-resistance model of crystal growth; by varying system conditions, the relative importance of the two resistances is altered and thereby changes the interfacial supersaturation even though overall supersaturation remains constant. Interracial supersaturation and contact energy determine kinetics in a system dominated by contact nucleation.

  10. Cluster Mechanism of Homogeneous Crystallization (Computer Study)

    NASA Astrophysics Data System (ADS)

    Belashchenko, D. K.

    2008-12-01

    A molecular dynamics (MD) study of homogeneous crystallization of liquid rubidium is conducted with an inter-particle pair potential. The equilibrium crystallization temperature of the models was 313 K. Models consisted of 500, 998, and 1968 particles in a basic cube. The main investigation method was as follows: to detect (along the MD run) the atoms with Voronoi polyhedrons (VP) of 0608 type (“0608-atoms,” as in a bcc crystal) and to detect the bound groups of 0608-atoms (“0608-clusters”) that could play the role of the seeds in crystallization. Full crystallization was observed only at temperatures lower than 185 K with the creation of a predominant bcc crystal. The crystallization mechanism of Rb models differs drastically from the mechanism adopted in classical nucleation theory. It consists of the growth of the total number of 0608-atoms on cooling and the formation of 0608-clusters, analogous to the case of coagulation of solute for a supersaturated two-component solution. At the first stage of the process the clusters have a very loose structure (something like medusa or octopus with many tentacles) and include inside atoms with other Voronoi polyhedron types. The dimensions of clusters quickly increase and approach those of the basic cube. 0608-atoms play the leading role in the crystallization process and activate the transition of the atoms involved in the 0608-coordination. The fast growth of the maximum cluster begins after it attains a critical size (about 150 0608-atoms). The fluctuations of cluster sizes are very important in the creation of a 0608-cluster of critical (threshold) size. These fluctuations are especially large in the interval from 180 K to 185 K.

  11. Homogeneous Nucleation of Methane Hydrate in Microsecond Molecular Dynamics Simulations.

    PubMed

    Sarupria, Sapna; Debenedetti, Pablo G

    2012-10-18

    We report atomistically detailed molecular dynamics simulations of homogeneous nucleation of methane hydrate in bulk aqueous phase in the absence of any interface. Subcritical clusters of water and methane molecules are formed in the initial segment of the simulations, which then aggregate to give the critical hydrate nucleus. This occurs over time scales of several hundred nanoseconds, indicating that the formation and aggregation of subcritical clusters can contribute significantly to the overall rate of hydrate nucleation. The clusters have elements of sI hydrate structure, such as 5(12) and 5(12)6(2) cages as well as other uncommon 5(12)6(3) and 5(12)6(4) cages, but do not possess long-range order. Clusters are dynamic in nature and undergo continuous structural rearrangements.

  12. Polymorphic crystals selected in the nucleation stage

    NASA Astrophysics Data System (ADS)

    Zhang, Hui-Jun; Peng, Shu-Ming; Zhou, Xiao-Song; Ju, Xin

    2014-08-01

    Molecular dynamics simulations are used to explore the atomic mechanism of formation of polymorphic crystals. Cooling the Lennard-Jones systems, we observe that the system almost always evolves into a polymorphic crystal with either fivefold-symmetric stacking faults or single-direction stacking faults. The detailed analysis reveals that such an evolution depends on the configuration of fcc/hcp concomitance in the nucleation stage. A defect-induced model is then introduced to illustrate these two evolution routes. Through calculating the formation energies of the defective critical nuclei, we find that the polymorphic crystals seem to be determined by their critical nuclei, in which the relatively lower formation energy ensures the preponderance of the fivefold-symmetric cluster. Before the nucleation, we observe that thermal fluctuations prefer hcp-like particles over fcc-like ones while in the nucleation and growth stage this preference reverses. Notably, an extended step rule of Ostwald is seemingly suitable to characterise the growth process because of the temporary hcp layers appearing among fcc layers in the growth stage. Although the crystalline cluster with single-direction stacking faults has higher growth rate and structural order than its competitor, the component (fcc and hcp) proportion of the final crystals is almost always constant regardless of the polymorphic type. Our finding renews the understanding of the polymorphism of crystals, and possibly draws more attention of people intending to control the polymorphic structures through nucleation.

  13. Nucleation and structural growth of cluster crystals.

    PubMed

    Leitold, Christian; Dellago, Christoph

    2016-08-21

    We study the nucleation of crystalline cluster phases in the generalized exponential model with exponent n = 4. Due to the finite value of this pair potential for zero separation, at high densities the system forms cluster crystals with multiply occupied lattice sites. Here, we investigate the microscopic mechanisms that lead to the formation of cluster crystals from a supercooled liquid in the low-temperature region of the phase diagram. Using molecular dynamics and umbrella sampling, we calculate the free energy as a function of the size of the largest crystalline nucleus in the system, and compare our results with predictions from classical nucleation theory. Employing bond-order parameters based on a Voronoi tessellation to distinguish different crystal structures, we analyze the average composition of crystalline nuclei. We find that even for conditions where a multiply occupied fcc crystal is the thermodynamically stable phase, the nucleation into bcc cluster crystals is strongly preferred. Furthermore, we study the particle mobility in the supercooled liquid and in the cluster crystal. In the cluster crystal, the motion of individual particles is captured by a simple reaction-diffusion model introduced previously to model the kinetics of hydrogen bonds.

  14. Anomalous Behavior of the Homogeneous Ice Nucleation Rate in "No-Man's Land".

    PubMed

    Laksmono, Hartawan; McQueen, Trevor A; Sellberg, Jonas A; Loh, N Duane; Huang, Congcong; Schlesinger, Daniel; Sierra, Raymond G; Hampton, Christina Y; Nordlund, Dennis; Beye, Martin; Martin, Andrew V; Barty, Anton; Seibert, M Marvin; Messerschmidt, Marc; Williams, Garth J; Boutet, Sébastien; Amann-Winkel, Katrin; Loerting, Thomas; Pettersson, Lars G M; Bogan, Michael J; Nilsson, Anders

    2015-07-16

    We present an analysis of ice nucleation kinetics from near-ambient pressure water as temperature decreases below the homogeneous limit TH by cooling micrometer-sized droplets (microdroplets) evaporatively at 10(3)-10(4) K/s and probing the structure ultrafast using femtosecond pulses from the Linac Coherent Light Source (LCLS) free-electron X-ray laser. Below 232 K, we observed a slower nucleation rate increase with decreasing temperature than anticipated from previous measurements, which we suggest is due to the rapid decrease in water's diffusivity. This is consistent with earlier findings that microdroplets do not crystallize at <227 K, but vitrify at cooling rates of 10(6)-10(7) K/s. We also hypothesize that the slower increase in the nucleation rate is connected with the proposed "fragile-to-strong" transition anomaly in water.

  15. Anomalous behavior of the homogeneous ice nucleation rate in “No-Man’s Land”

    DOE PAGES

    Laksmono, Hartawan; McQueen, Trevor A.; Sellberg, Jonas A.; ...

    2015-07-02

    We present an analysis of ice nucleation kinetics from near-ambient pressure water as temperature decreases below the homogeneous limit T H by cooling micrometer-sized droplets (microdroplets) evaporatively at 10³-10⁴ K/s and probing the structure ultrafast using femtosecond pulses from the Linac Coherent Light Source (LCLS) free-electron X-ray laser. Below 232 K, we observed a slower nucleation rate increase with decreasing temperature than anticipated from previous measurements, which we suggest is due to the rapid decrease in water's diffusivity. This is consistent with earlier findings that microdroplets do not crystallize at <227 K, but vitrify at cooling rates of 10⁶–10⁷ K/s.more » We also hypothesize that the slower increase in the nucleation rate is connected with the proposed "fragile-to-strong" transition anomaly in water.« less

  16. Anomalous Behavior of the Homogeneous Ice Nucleation Rate in “No-Man’s Land”

    PubMed Central

    2015-01-01

    We present an analysis of ice nucleation kinetics from near-ambient pressure water as temperature decreases below the homogeneous limit TH by cooling micrometer-sized droplets (microdroplets) evaporatively at 103–104 K/s and probing the structure ultrafast using femtosecond pulses from the Linac Coherent Light Source (LCLS) free-electron X-ray laser. Below 232 K, we observed a slower nucleation rate increase with decreasing temperature than anticipated from previous measurements, which we suggest is due to the rapid decrease in water’s diffusivity. This is consistent with earlier findings that microdroplets do not crystallize at <227 K, but vitrify at cooling rates of 106–107 K/s. We also hypothesize that the slower increase in the nucleation rate is connected with the proposed “fragile-to-strong” transition anomaly in water. PMID:26207172

  17. Homogeneous nucleation in liquid nitrogen at negative pressures

    SciTech Connect

    Baidakov, V. G. Vinogradov, V. E.; Pavlov, P. A.

    2016-10-15

    The kinetics of spontaneous cavitation in liquid nitrogen at positive and negative pressures has been studied in a tension wave formed by a compression pulse reflected from the liquid–vapor interface on a thin platinum wire heated by a current pulse. The limiting tensile stresses (Δp = p{sub s}–p, where p{sub s} is the saturation pressure), the corresponding bubble nucleation frequencies J (10{sup 20}–10{sup 22} s{sup –1} m{sup –3}), and temperature induced nucleation frequency growth rate G{sub T} = dlnJ/dT have been experimentally determined. At T = 90 K, the limiting tensile stress was Δp = 8.3 MPa, which was 4.9 MPa lower than the value corresponding to the boundary of thermodynamic stability of the liquid phase (spinodal). The measurement results were compared to classical (homogeneous) nucleation theory (CNT) with and without neglect of the dependence of the surface tension of critical bubbles on their dimensions. In the latter case, the properties of new phase nuclei were described in terms of the Van der Waals theory of capillarity. The experimental data agree well with the CNT theory when it takes into account the “size effect.”.

  18. Homogeneous nucleation in liquid nitrogen at negative pressures

    NASA Astrophysics Data System (ADS)

    Baidakov, V. G.; Vinogradov, V. E.; Pavlov, P. A.

    2016-10-01

    The kinetics of spontaneous cavitation in liquid nitrogen at positive and negative pressures has been studied in a tension wave formed by a compression pulse reflected from the liquid-vapor interface on a thin platinum wire heated by a current pulse. The limiting tensile stresses (Δ p = p s - p, where p s is the saturation pressure), the corresponding bubble nucleation frequencies J (1020-1022 s-1 m-3), and temperature induced nucleation frequency growth rate G T = dln J/dT have been experimentally determined. At T = 90 K, the limiting tensile stress was Δ p = 8.3 MPa, which was 4.9 MPa lower than the value corresponding to the boundary of thermodynamic stability of the liquid phase (spinodal). The measurement results were compared to classical (homogeneous) nucleation theory (CNT) with and without neglect of the dependence of the surface tension of critical bubbles on their dimensions. In the latter case, the properties of new phase nuclei were described in terms of the Van der Waals theory of capillarity. The experimental data agree well with the CNT theory when it takes into account the "size effect."

  19. Molecular Dynamics Simulations of Homogeneous Crystallization in Polymer Melt

    NASA Astrophysics Data System (ADS)

    Kong, Bin

    2015-03-01

    Molecular mechanisms of homogeneous nucleation and crystal growth from the melt of polyethylene-like polymer were investigated by molecular dynamics simulations. The crystallinity was determined by using the site order parameter method (SOP), which described local order degree around an atom. Snapshots of the simulations showed evolution of the nucleation and the crystal growth through SOP images clearly. The isothermal crystallization kinetics was determined at different temperatures. The rate of crystallization, Kc, and the Avrami exponents, n, were determined as a function of temperature. The forming of nucleis was traced to reveal that the nucleis were formed with more ordered cores and less ordered shells. A detailed statistical analysis of the MD snapshots and trajectories suggested conformations of the polymer chains changed smoothly from random coil to chain folded lamella in the crystallization processes.

  20. Homogeneous nucleation of crystalline order in superdense liquid 4He

    NASA Astrophysics Data System (ADS)

    Pederiva, F.; Ferrante, A.; Fantoni, S.; Reatto, L.

    1995-09-01

    We present the results of a numerical crystallization experiment in 4He performed with the shadow wave function and the variational Monte Carlo method. The experiment consists in Monte Carlo simulations starting from liquidlike configurations of the atoms at a density well above the melting point. The system presents spontaneous nucleation of crystalline seeds, proving the spontaneous symmetry-breaking property of the shadow wave function. The final configurations display a face-centered-cubic structure grown preferentially by \\{111\\} planes, accompanied by stacking disorder.

  1. Improved Success of Sparse Matrix Protein Crystallization Screening with Heterogeneous Nucleating Agents

    PubMed Central

    Thakur, Anil S.; Robin, Gautier; Guncar, Gregor; Saunders, Neil F. W.; Newman, Janet; Martin, Jennifer L.; Kobe, Bostjan

    2007-01-01

    Background Crystallization is a major bottleneck in the process of macromolecular structure determination by X-ray crystallography. Successful crystallization requires the formation of nuclei and their subsequent growth to crystals of suitable size. Crystal growth generally occurs spontaneously in a supersaturated solution as a result of homogenous nucleation. However, in a typical sparse matrix screening experiment, precipitant and protein concentration are not sampled extensively, and supersaturation conditions suitable for nucleation are often missed. Methodology/Principal Findings We tested the effect of nine potential heterogenous nucleating agents on crystallization of ten test proteins in a sparse matrix screen. Several nucleating agents induced crystal formation under conditions where no crystallization occurred in the absence of the nucleating agent. Four nucleating agents: dried seaweed; horse hair; cellulose and hydroxyapatite, had a considerable overall positive effect on crystallization success. This effect was further enhanced when these nucleating agents were used in combination with each other. Conclusions/Significance Our results suggest that the addition of heterogeneous nucleating agents increases the chances of crystal formation when using sparse matrix screens. PMID:17971854

  2. Estimation of homogeneous nucleation flux via a kinetic model

    NASA Technical Reports Server (NTRS)

    Wilcox, C. F.; Bauer, S. H.

    1991-01-01

    The proposed kinetic model for condensation under homogeneous conditions, and the onset of unidirectional cluster growth in supersaturated gases, does not suffer from the conceptual flaws that characterize classical nucleation theory. When a full set of simultaneous rate equation is solved, a characteristic time emerges, for each cluster size, at which the production rate, and its rate of conversion to the next size (n + 1) are equal. Procedures for estimating the essential parameters are proposed; condensation fluxes J(kin) exp ss are evaluated. Since there are practical limits to the cluster size that can be incorporated in the set of simultaneous first-order differential equations, a code was developed for computing an approximate J(th) exp ss based on estimates of a 'constrained equilibrium' distribution, and identification of its minimum.

  3. Nozzle-Free Liquid Microjetting via Homogeneous Bubble Nucleation

    NASA Astrophysics Data System (ADS)

    Lee, Taehwa; Baac, Hyoung Won; Ok, Jong G.; Youn, Hong Seok; Guo, L. Jay

    2015-04-01

    We propose and demonstrate a physical mechanism for producing liquid microjets by taking an optoacoustic approach that can convert light to sound through a carbon-nanotube-coated lens, where light from a pulsed laser is converted to high momentum sound wave. The carbon-nanotube lens can focus high-amplitude sound waves to a microspot of <1 00 μ m near the air-water interface from the water side, leading to microbubbles in water and subsequent microjets into the air. Laser-flash shadowgraphy visualizes two consecutive jets closely correlated with bubble dynamics. Because of the acoustic scattering from the interface, negative pressure amplitudes are significantly increased up to 80 MPa, even allowing homogeneous bubble nucleation. As a demonstration, this nozzle-free approach is applied to inject colored liquid into a tissue-mimicking gel as well as print a material on a glass substrate.

  4. Thermodynamics of homogeneous nucleation of mesospheric ice particles

    NASA Astrophysics Data System (ADS)

    Zasetsky, A. Y.; Petelina, S. V.

    2009-05-01

    Although our knowledge of the upper mesospheric region is continuously improving, many aspects of mesospheric dynamics and thermodynamics are still unclear. We address some of these open questions related to the thermodynamics of water at the conditions intrinsic for the polar summer mesosphere. For this we use recently published theoretical and laboratory results on the properties of water at very low temperatures. We present the hypothesis of homogeneous nucleation of ice nano-particles in the polar summer mesosphere. The nucleation of condensed phase is traced back to the first step on the formation pathway, which is assumed to be the transition of water vapor to amorphous cluster. Amorphous clusters then freeze into water ice, likely metastable cubic ice, when they reach the critical size. The estimates based on the equilibrium thermodynamics give the critical size (radius) of amorphous water clusters as about 1.0 nm. The same estimates for the final transition step, that is the transformation of cubic to hexagonal ice, give the critical size of about 15 nm at typical upper mesospheric conditions during the polar summer (about 150K temperature and about 109cm-3 water vapor density).

  5. Homogeneous ice nucleation from aqueous inorganic/organic particles representative of biomass burning: water activity, freezing temperatures, nucleation rates.

    PubMed

    Knopf, Daniel A; Rigg, Yannick J

    2011-02-10

    Homogeneous ice nucleation plays an important role in the formation of cirrus clouds with subsequent effects on the global radiative budget. Here we report on homogeneous ice nucleation temperatures and corresponding nucleation rate coefficients of aqueous droplets serving as surrogates of biomass burning aerosol. Micrometer-sized (NH(4))(2)SO(4)/levoglucosan droplets with mass ratios of 10:1, 1:1, 1:5, and 1:10 and aqueous multicomponent organic droplets with and without (NH(4))(2)SO(4) under typical tropospheric temperatures and relative humidities are investigated experimentally using a droplet conditioning and ice nucleation apparatus coupled to an optical microscope with image analysis. Homogeneous freezing was determined as a function of temperature and water activity, a(w), which was set at droplet preparation conditions. The ice nucleation data indicate that minor addition of (NH(4))(2)SO(4) to the aqueous organic droplets renders the temperature dependency of water activity negligible in contrast to the case of aqueous organic solution droplets. The mean homogeneous ice nucleation rate coefficient derived from 8 different aqueous droplet compositions with average diameters of ∼60 μm for temperatures as low as 195 K and a(w) of 0.82-1 is 2.18 × 10(6) cm(-3) s(-1). The experimentally derived freezing temperatures and homogeneous ice nucleation rate coefficients are in agreement with predictions of the water activity-based homogeneous ice nucleation theory when taking predictive uncertainties into account. However, the presented ice nucleation data indicate that the water activity-based homogeneous ice nucleation theory overpredicts the freezing temperatures by up to 3 K and corresponding ice nucleation rate coefficients by up to ∼2 orders of magnitude. A shift of 0.01 in a(w), which is well within the uncertainty of typical field and laboratory relative humidity measurements, brings experimental and predicted freezing temperatures and homogeneous ice

  6. In situ FT-IR study on the homogeneous nucleation of nanoparticles of titanium oxides from highly supersaturated vapor

    NASA Astrophysics Data System (ADS)

    Ishizuka, Shinnosuke; Kimura, Yuki; Yamazaki, Tomoya

    2016-09-01

    The formation of nanoparticles of titanium oxides by homogeneous nucleation from highly supersaturated vapors was investigated by in situ Fourier transform IR spectroscopy and by observation of the resulting nanoparticles by transmission electron microscopy (TEM). Titanium metal was thermally evaporated in a specially designed chamber under a gaseous atmosphere of oxygen and argon. Nanoparticles nucleated and subsequently grew as they flew freely through the oxidizing gas atmosphere. Nascent nanoparticles of titanium oxides showed a broad IR absorption band at 10-20 μm. Subsequently, the cooled nanoparticles showed a sharp crystalline anatase feature at 12.8 μm. TEM observations showed the formation of spherical anatase nanoparticles. The IR spectral evolution showed that the titanium oxides nucleated as metastable liquid droplets, and that crystallization proceeded through secondary nucleation from the supercooled liquid droplets. This suggests that history of the titanium oxide nanoparticles, such as the temperature and oxidation that they experience after nucleation, determines their polymorphic form.

  7. Deposition nucleation viewed as homogeneous or immersion freezing in pores and cavities

    NASA Astrophysics Data System (ADS)

    Marcolli, C.

    2013-06-01

    Heterogeneous ice nucleation is an important mechanism for the glaciation of mixed phase clouds and may also be relevant for cloud formation and dehydration at the cirrus cloud level. It is thought to proceed through different mechanisms, namely contact, condensation, immersion and deposition nucleation. Supposedly, deposition nucleation is the only pathway which does not involve liquid water but occurs by direct water vapor deposition on a surface. This study challenges this classical view by putting forward the hypothesis that what is called deposition nucleation is in fact homogeneous or immersion nucleation occurring in pores and cavities that may form between aggregated primary particles and fill with water at relative humidity RHw < 100% because of the inverse Kelvin effect. Evidence for this hypothesis of pore condensation and freezing (PCF) originates from a number of only loosely connected scientific areas. The prime example for PCF is ice nucleation in clay minerals and mineral dusts, for which the data base is best. Studies on freezing in confinement carried out on mesoporous silica materials such as SBA-15, SBA-16, MCM-41, zeolites and KIT have shown that homogeneous ice nucleation occurs abruptly at T=230-235 K in pores with diameters (D) of 3.5-4 nm or larger but only gradually at T=210-230 K in pores with D=2.5-3.5 nm. Melting temperatures in pores are depressed by an amount that can be described by the Gibbs-Thomson equation. Water adsorption isotherms of MCM-41 show that pores with D=3.5-4 nm fill with water at RHw = 56-60% in accordance with an inverse Kelvin effect. Water in such pores should freeze homogeneously for T < 235 K even before relative humidity with respect to ice (RHi) reaches ice saturation. Ice crystal growth by water vapor deposition from the gas phase is therefore expected to set in as soon as RHw > 100%. Pores with D > 7.5 nm fill with water at RHi > 100% for T < 235 K and are likely to freeze homogeneously as soon as they are

  8. The Homogeneous Nucleation of Amorphous Water Particles in the Upper Mesosphere

    NASA Astrophysics Data System (ADS)

    Murray, B. J.

    2008-12-01

    Particles dominantly composed of water are known to exist in the high latitude upper mesosphere during the summer months. However, the mechanism through which they nucleate remains unknown. In the past the homogeneous nucleation of ice directly from the vapour phase has been ruled out on the basis of homogeneous nucleation theory. It is postulated here that particles of amorphous water, ultra-viscous condensed water with a liquid like structure, may nucleate directly from the vapour phase in the summer mesosphere. It is demonstrated here that the energy barrier to nucleation of an amorphous water particle may be much smaller than that to nucleate a crystalline ice particle. These amorphous water particles may later crystallise to form cubic crystalline ice particles. It is concluded that homogeneous nucleation of amorphous water particles can not be ruled out as a potential mechanism of condensed water cloud formation in the upper mesosphere.

  9. Communication: Bubbles, crystals, and laser-induced nucleation.

    PubMed

    Knott, Brandon C; LaRue, Jerry L; Wodtke, Alec M; Doherty, Michael F; Peters, Baron

    2011-05-07

    Short intense laser pulses of visible and infrared light can dramatically accelerate crystal nucleation from transparent solutions; previous studies invoke mechanisms that are only applicable for nucleation of ordered phases or high dielectric phases. However, we show that similar laser pulses induce CO(2) bubble nucleation in carbonated water. Additionally, in water that is cosupersaturated with argon and glycine, argon bubbles escaping from the water can induce crystal nucleation without a laser. Our findings suggest a possible link between laser-induced nucleation of bubbles and crystals.

  10. Communication: Bubbles, crystals, and laser-induced nucleation

    NASA Astrophysics Data System (ADS)

    Knott, Brandon C.; LaRue, Jerry L.; Wodtke, Alec M.; Doherty, Michael F.; Peters, Baron

    2011-05-01

    Short intense laser pulses of visible and infrared light can dramatically accelerate crystal nucleation from transparent solutions; previous studies invoke mechanisms that are only applicable for nucleation of ordered phases or high dielectric phases. However, we show that similar laser pulses induce CO2 bubble nucleation in carbonated water. Additionally, in water that is cosupersaturated with argon and glycine, argon bubbles escaping from the water can induce crystal nucleation without a laser. Our findings suggest a possible link between laser-induced nucleation of bubbles and crystals.

  11. Fluorescence Studies of Protein Crystal Nucleation

    NASA Technical Reports Server (NTRS)

    Pusey, Marc L.; Sumida, John

    2000-01-01

    One of the most powerful and versatile methods for studying molecules in solution is fluorescence. Crystallization typically takes place in a concentrated solution environment, whereas fluorescence typically has an upper concentration limit of approximately 1 x 10(exp -5)M, thus intrinsic fluorescence cannot be employed, but a fluorescent probe must be added to a sub population of the molecules. However the fluorescent species cannot interfere with the self-assembly process. This can be achieved with macromolecules, where fluorescent probes can be covalently attached to a sub population of molecules that are subsequently used to track the system as a whole. We are using fluorescence resonance energy transfer (FRET) to study the initial solution phase self-assembly process of tetragonal lysozyme crystal nucleation, using covalent fluorescent derivatives which crystallize in the characteristic P432121 space group. FRET studies are being carried out between cascade blue (CB-lys, donor, Ex 376 nm, Em 420 nm) and lucifer yellow (LY-lys, acceptor, Ex 425 nm, Em 520 nm) asp101 derivatives. The estimated R0 for this probe pair, the distance where 50% of the donor energy is transferred to the acceptor, is approximately 1.2 nm, compared to 2.2 nm between the side chain carboxyls of adjacent asp101's in the crystalline 43 helix. The short CB-lys lifetime (approximately 5 ns), coupled with the large average distances between the molecules ((sup 3) 50 nm) in solution, ensure that any energy transfer observed is not due to random diffusive interactions. Addition of LY-lys to CB-lys results in the appearance of a second, shorter lifetime (approximately 0.2 ns). Results from these and other ongoing studies will be discussed in conjunction with a model for how tetragonal lysozyme crystals nucleate and grow, and the relevance of that model to microgravity protein crystal growth

  12. Homogeneous nucleation rate measurements and the properties of critical clusters

    SciTech Connect

    Wyslouzil, Barbara E.; Strey, Reinhard; Wölk, Judith; Wilemski, Gerald; Kim, Yoojeong

    2009-10-06

    By combining a range of experimental techniques, quantitative nucleation rate measurements can now be made over {approx} 20 orders of magnitude. These rates can be used to directly test the predictions of nucleation theories or scaling laws. They can also provide direct information regarding the properties of the critical clusters - the first fragments of the new phase that are in unstable equilibrium with the supersaturated mother phase. This paper reviews recent progress in the field of vapor phase nucleation with a special focus on integrating the results from supersonic nozzle and nucleation pulse chamber studies.

  13. Do protein crystals nucleate within dense liquid clusters?

    SciTech Connect

    Maes, Dominique; Vorontsova, Maria A.; Potenza, Marco A. C.; Sanvito, Tiziano; Sleutel, Mike; Giglio, Marzio; Vekilov, Peter G.

    2015-06-27

    The evolution of protein-rich clusters and nucleating crystals were characterized by dynamic light scattering (DLS), confocal depolarized dynamic light scattering (cDDLS) and depolarized oblique illumination dark-field microscopy. Newly nucleated crystals within protein-rich clusters were detected directly. These observations indicate that the protein-rich clusters are locations for crystal nucleation. Protein-dense liquid clusters are regions of high protein concentration that have been observed in solutions of several proteins. The typical cluster size varies from several tens to several hundreds of nanometres and their volume fraction remains below 10{sup −3} of the solution. According to the two-step mechanism of nucleation, the protein-rich clusters serve as locations for and precursors to the nucleation of protein crystals. While the two-step mechanism explained several unusual features of protein crystal nucleation kinetics, a direct observation of its validity for protein crystals has been lacking. Here, two independent observations of crystal nucleation with the proteins lysozyme and glucose isomerase are discussed. Firstly, the evolutions of the protein-rich clusters and nucleating crystals were characterized simultaneously by dynamic light scattering (DLS) and confocal depolarized dynamic light scattering (cDDLS), respectively. It is demonstrated that protein crystals appear following a significant delay after cluster formation. The cDDLS correlation functions follow a Gaussian decay, indicative of nondiffusive motion. A possible explanation is that the crystals are contained inside large clusters and are driven by the elasticity of the cluster surface. Secondly, depolarized oblique illumination dark-field microscopy reveals the evolution from liquid clusters without crystals to newly nucleated crystals contained in the clusters to grown crystals freely diffusing in the solution. Collectively, the observations indicate that the protein-rich clusters in

  14. Flow-Induced Crystallization and Nucleation in Isotactic Polypropylenes

    NASA Astrophysics Data System (ADS)

    Milner, Scott

    2015-03-01

    Flow-induced crystallization (FIC) occurs when a brief interval of strong flow precedes a temperature quench; many more nuclei form, resulting in a much more fine-grained solid morphology and better material properties. Common industrial polymer processing (injection molding) depends on FIC, which has been the subject of many experimental studies, most commonly on isotactic polypropylene (iPP). The prevailing hypothesis is that FIC results from flow aligning chains in the melt, increasing the melt free energy with respect to the crystal, hence acting like undercooling. Here, I combine experimental results for FIC and homogeneous nucleation with theoretical estimates for critical nuclei, to assess the prevailing hypothesis. Current best information supports the view that chain stretching (not just alignment) is necessary and sufficient to explain the observed increase in nucleation rate. Important puzzles remain: 1) shear applied at temperatures well above the equilibrium melting temperature Tm = 187 C is effective for FIC, and 2) a sheared sample may be held for hours above Tm, and still crystallize faster when quenched.

  15. Ice nucleation in solutions and freeze-avoiding insects-homogeneous or heterogeneous?

    PubMed

    Zachariassen, Karl Erik; Kristiansen, Erlend; Pedersen, Sindre Andre; Hammel, Harold T

    2004-06-01

    This article challenges the common view that solutions and cold-hardy freeze-avoiding insects always freeze by heterogeneous nucleation. Data are presented to show that the nucleation temperatures of a variety of solutions and freeze-avoiding insects are a function of the water volume as described by the data previously published by Bigg in 1953. The article also points out that the relationships between melting point depression and depression of nucleation temperature are different for samples undergoing homogeneous nucleation and those undergoing heterogeneous nucleation. Aqueous solutions and freeze-avoiding insects display a relationship like that of homogeneously nucleated samples. It is also argued that the identity of the "impurities" assumed to cause heterogeneous nucleation in aqueous solutions and insects is obscure and that the "impurities" have features which make their existence rather unlikely.

  16. Nacre biomineralisation: A review on the mechanisms of crystal nucleation.

    PubMed

    Nudelman, Fabio

    2015-10-01

    The wide diversity of biogenic minerals that is found in nature, each with its own morphology, mechanical properties and composition, is remarkable. In order to produce minerals that are optimally adapted for their function, biomineralisation usually occurs under strict cellular control. This control is exerted by specialised proteins and polysaccharides that assemble into a 3-dimensional organic matrix framework, forming a microenvironment where mineral deposition takes place. Molluscs are unique in that they use a striking variety of structural motifs to build their shells, each made of crystals with different morphologies and different calcium carbonate polymorphs. Much of want is known about mollusc shell formation comes from studies on the nacreous layer, or mother-of-pearl. In this review, we discuss two existing models on the nucleation of aragonite crystals during nacre formation: heteroepitaxial nucleation and mineral bridges. The heteroepitaxial nucleation model is based on the identification of chemical functional groups and aragonite-nucleating proteins at the centre of crystal imprints. It proposes that during nacre formation, each aragonite tablet nucleates independently on a nucleation site that is formed by acidic proteins and/or glycoproteins adsorbed on the chitin scaffold. The mineral bridges model is based on the identification of physical connections between the crystals in a stack, which results in a large number of crystals across several layers sharing the same crystallographic orientation. These observations suggest that there is one nucleation event per stack of tablets. Once the first crystal nucleates and reaches the top interlamellar matrix, it continues growing through pores, giving rise to the next layer of nacre, subsequently propagating into a stack. We compare both models and propose that they work in concert to control crystal nucleation in nacre. De novo crystal nucleation has to occur at least once per stack of aligned crystals

  17. Do protein crystals nucleate within dense liquid clusters?

    PubMed

    Maes, Dominique; Vorontsova, Maria A; Potenza, Marco A C; Sanvito, Tiziano; Sleutel, Mike; Giglio, Marzio; Vekilov, Peter G

    2015-07-01

    Protein-dense liquid clusters are regions of high protein concentration that have been observed in solutions of several proteins. The typical cluster size varies from several tens to several hundreds of nanometres and their volume fraction remains below 10(-3) of the solution. According to the two-step mechanism of nucleation, the protein-rich clusters serve as locations for and precursors to the nucleation of protein crystals. While the two-step mechanism explained several unusual features of protein crystal nucleation kinetics, a direct observation of its validity for protein crystals has been lacking. Here, two independent observations of crystal nucleation with the proteins lysozyme and glucose isomerase are discussed. Firstly, the evolutions of the protein-rich clusters and nucleating crystals were characterized simultaneously by dynamic light scattering (DLS) and confocal depolarized dynamic light scattering (cDDLS), respectively. It is demonstrated that protein crystals appear following a significant delay after cluster formation. The cDDLS correlation functions follow a Gaussian decay, indicative of nondiffusive motion. A possible explanation is that the crystals are contained inside large clusters and are driven by the elasticity of the cluster surface. Secondly, depolarized oblique illumination dark-field microscopy reveals the evolution from liquid clusters without crystals to newly nucleated crystals contained in the clusters to grown crystals freely diffusing in the solution. Collectively, the observations indicate that the protein-rich clusters in lysozyme and glucose isomerase solutions are locations for crystal nucleation.

  18. Structure of supersaturated solution and crystal nucleation induced by diffusion

    NASA Astrophysics Data System (ADS)

    Ooshima, Hiroshi; Igarashi, Koichi; Iwasa, Hideo; Yamamoto, Ren

    2013-06-01

    The effect of a seed crystal on nucleation of L-alanine from a quiescent supersaturated solution was investigated. When a seed crystal was not used, nucleation did not occur at least for 5 h. When a seed crystal was introduced into the supersaturated solution with careful attention to avoid convection of the solution, fine crystals appeared at the place far from the seed crystal. At that time, there was no convection at the place that fine crystals appeared. Namely, there was no possibility that those fine crystals came from the surface of seed crystal. We supposed that nucleation was induced by directional diffusion of solute molecules caused by growth of the seed crystal. In order to prove this hypothesis, we designed an experiment using an apparatus composed of two compartments divided by a dialysis membrane that L-alanine molecules could freely permeate. Two supersaturated solutions having a supersaturation ratio of 1.2 and a smaller ratio were placed in the two compartments in the absence of seed crystals. This apparatus allowed the directional diffusion of solute molecules between two solutions. Nucleation occurred within 30 min. The frequency of nucleation among 7-times repeated experiments was in proportion to the difference of supersaturation ratio between the two solutions. This result poses a new mechanism of the secondary nucleation that the directional diffusion caused by growth of existing crystals induces nucleation.

  19. High-frequency gravity waves and homogeneous ice nucleation in tropical tropopause layer cirrus

    NASA Astrophysics Data System (ADS)

    Jensen, Eric J.; Ueyama, Rei; Pfister, Leonhard; Bui, Theopaul V.; Alexander, M. Joan; Podglajen, Aurélien; Hertzog, Albert; Woods, Sarah; Lawson, R. Paul; Kim, Ji-Eun; Schoeberl, Mark R.

    2016-06-01

    The impact of high-frequency gravity waves on homogeneous-freezing ice nucleation in cold cirrus clouds is examined using parcel model simulations driven by superpressure balloon measurements of temperature variability experienced by air parcels in the tropical tropopause region. We find that the primary influence of high-frequency waves is to generate rapid cooling events that drive production of numerous ice crystals. Quenching of ice nucleation events by temperature tendency reversal in the highest-frequency waves does occasionally produce low ice concentrations, but the overall impact of high-frequency waves is to increase the occurrence of high ice concentrations. The simulated ice concentrations are considerably higher than indicated by in situ measurements of cirrus in the tropical tropopause region. One-dimensional simulations suggest that although sedimentation reduces mean ice concentrations, a discrepancy of about a factor of 3 with observed ice concentrations remains. Reconciliation of numerical simulations with the observed ice concentrations will require inclusion of physical processes such as heterogeneous nucleation and entrainment.

  20. Droplet crystallisation in large scale direct molecular dynamics simulations of homogeneous vapor-to-liquid nucleation

    NASA Astrophysics Data System (ADS)

    Diemand, J.; Tanaka, K. K.; Tanaka, H.; Angelil, R.

    2014-12-01

    We use large scale direct (NVE and NVT) molecular dynamics simulations to study phase transitions. Typical runs contain one billion atoms and run for up to 100 million time-steps. This corresponds to scales of micrometers and microseconds and allows us to resolve similar nucleation rates as probed in some laboratory experiments. In homogeneous vapor-to-liquid nucleation simulations using Lennard-Jones atoms (Diemand et al. JCP 2013) and various water models (ongoing work) we observe a second phase transition form liquid-to-solid in some of the lower temperature runs (see Tanaka et al. JCP 2011 for one such case). Here we will describe the crystallisation of these supercooled liquid-like nano-clusters in detail. We will present crystal structure, nucleation and growth rates for a range of temperatures, droplet sizes and interaction potentials and compare with model predictions. Since our liquid nano-droplets are condensing naturally out of the vapour phase, as in clouds and some experiments and industrial processes, we can address some specific questions relevant in these contexts: How does the droplet size, structure and especially its surface affect the freezing process? To what extend does the latent heat from the ongoing condensation onto the droplets surface delay and alter crystallisation? Can frozen nano-clusters grow by direct de-sublimation from the vapour, or is there always a liquid-like surface? And can they form directly without going through a liquid-like proto-cluster stage?

  1. New metastable form of ice and its role in the homogeneous crystallization of water.

    PubMed

    Russo, John; Romano, Flavio; Tanaka, Hajime

    2014-07-01

    The homogeneous crystallization of water at low temperature is believed to occur through the direct nucleation of cubic (Ic) and hexagonal (Ih) ices. Here, we provide evidence from molecular simulations that the nucleation of ice proceeds through the formation of a new metastable phase, which we name Ice 0. We find that Ice 0 is structurally similar to the supercooled liquid, and that on growth it gradually converts into a stacking of Ice Ic and Ih. We suggest that this mechanism provides a thermodynamic explanation for the location and pressure dependence of the homogeneous nucleation temperature, and that Ice 0 controls the homogeneous nucleation of low-pressure ices, acting as a precursor to crystallization in accordance with Ostwald's step rule of phases. Our findings show that metastable crystalline phases of water may play roles that have been largely overlooked.

  2. Efficient nucleation of stardust silicates via heteromolecular homogeneous condensation

    NASA Astrophysics Data System (ADS)

    Goumans, T. P. M.; Bromley, Stefan T.

    2012-03-01

    Dust particles, ubiquitous throughout the Universe, continuously evolve in processes closely entangled with the stellar life cycle. Dust nucleates in outflows of dying stars and is heavily processed in the journey through the interstellar medium, until it is finally subsumed in a next-generation star or its surrounding planetary system. Although the formation of silicates has been studied experimentally and theoretically for decades, the stardust nucleation process in the condensation zone of oxygen-rich stellar outflows still remains mysterious. These silicates are mostly ternary oxides consisting of O, Mg and Si, which cannot nucleate directly from gaseous monomers. Previous work has suggested that silicates form on nucleation seeds consisting of low-abundant elements or from addition of metals to SiO-nuclei. However, our extensive computational study of the thermodynamic properties of a large number of clusters shows that pure SiO nucleation is unfeasible, while heteromolecular nucleation of Mg, SiO and H2O is a plausible mechanism to form magnesium silicates under stellar outflow conditions.

  3. Note: Homogeneous TIP4P/2005 ice nucleation at low supercooling.

    PubMed

    Reinhardt, Aleks; Doye, Jonathan P K

    2013-09-07

    We present a partial free energy profile for the homogeneous nucleation of ice using an all-atom model of water at low supercooling, at which ice growth dynamics are reasonably accessible to simulation. We demonstrate that the free energy profile is well described by classical nucleation theory, and that the nucleation barrier is entropic in origin. We also estimate to first order the temperature dependence of the interfacial free energy.

  4. Note: Homogeneous TIP4P/2005 ice nucleation at low supercooling

    NASA Astrophysics Data System (ADS)

    Reinhardt, Aleks; Doye, Jonathan P. K.

    2013-09-01

    We present a partial free energy profile for the homogeneous nucleation of ice using an all-atom model of water at low supercooling, at which ice growth dynamics are reasonably accessible to simulation. We demonstrate that the free energy profile is well described by classical nucleation theory, and that the nucleation barrier is entropic in origin. We also estimate to first order the temperature dependence of the interfacial free energy.

  5. Homogeneous bubble nucleation in rhyolitic magmas: An experimental study of the effect of H2O and CO2

    NASA Astrophysics Data System (ADS)

    Mourtada-Bonnefoi, C. C.; Laporte, D.

    2002-04-01

    Rapid decompression experiments were performed to study homogeneous bubble nucleation in a crystal-free rhyolitic liquid at 800°C. Bubble nucleation was produced by lowering the pressure at 1-10 MPa s-1 from an initial value between 200 and 295 MPa to a final value below the volatile saturation pressure PSat. Six volatile compositions with 4.1-7.7 wt % H2O and 10-1200 ppm CO2 were investigated. For each composition we determined the critical pressure PHoN below which homogeneous nucleation can proceed. The samples quenched below PHoN showed a nucleated core with a large number of uniformly spaced bubbles. With decreasing pressure, bubble number densities increased from <1011 m-3 (for samples quenched just below PHoN) to >1015 m-3. The degree of supersaturation required for homogeneous nucleation, ΔPHoN (= PSat - PHoN), increased with decreasing H2O content or increasing CO2 content. Huge values of ΔPHoN, >=135 to 310 MPa, were measured in the H2O-poor compositions (4.1-4.6 wt % H2O; 50-1100 ppm CO2); much lower values from ~60 to 160 MPa were obtained in the H2O-rich compositions (7.0-7.7 wt % H2O; 10-630 ppm CO2). The high ΔPHoN in liquids with 4-5 wt % H2O should result in the buildup of large degrees of supersaturation during magma ascent, a very late nucleation event, and a rapid (explosive) vesiculation. By contrast, rhyolitic liquids with much larger water contents have higher saturation pressures and much lower ΔPHoN: bubble nucleation may therefore occur at depth in the volcanic conduit favoring a subsequent near-equilibrium degassing.

  6. Control of Protein Crystal Nucleation and Growth Using Stirring Solution

    NASA Astrophysics Data System (ADS)

    Niino, Ai; Adachi, Hiroaki; Takano, Kazufumi; Matsumura, Hiroyoshi; Kinoshita, Takayoshi; Warizaya, Masaichi; Inoue, Tsuyoshi; Mori, Yusuke; Sasaki, Takatomo

    2004-11-01

    We have previously developed a protein crystallization technique using a stirring protein solution and revealed that (i) continuous stirring prevents excess spontaneous nucleation and accelerates the growth of protein crystals and (ii) prestirring (solution stirring in advance) promotes the crystal nucleation of hen egg-white lysozyme. In bovine adenosine deaminase (ADA) crystallization, continuous stirring improves the crystal quality but elongates the nucleation time. In this paper, in order to control both the crystal nucleation and growth of ADA using a Micro-Stirring technique, we carried out five different stirring patterns such as (i) no stirring, (ii) continuous stirring, (iii) prestirring, (iv) poststirring (stirring late in the growth period) and (v) restirring (combined pre- and poststirring). The results showed that high-quality well-shaped crystals were obtained under the continuous stirring and restirring conditions and the nucleation time under the prestirring and restirring conditions was shorter than that under the continuous stirring and poststirring conditions. Consequently, high-quality crystals were promptly obtained under the restirring condition. These results suggest that we are able to control both the nucleation and growth of protein crystals with the stirring techniques.

  7. Nucleation of crystals that are mixed composites of all three polymorphs in the Gaussian core model

    NASA Astrophysics Data System (ADS)

    Mithen, J. P.; Callison, A. J.; Sear, R. P.

    2015-06-01

    We present results of computer simulations of homogeneous crystal nucleation in the Gaussian core model. In our simulations, we study the competition between the body-centered-cubic (bcc), face-centered-cubic (fcc), and hexagonal-close-packed crystal phases. We find that the crystal nuclei that form from the metastable fluid phase are typically "mixed"; they do not consist of a single crystal polymorph. Furthermore, when the fcc phase is stable or fcc and bcc phases are equally stable, this mixed nature is found to persist far beyond the size at the top of the nucleation barrier, that is, far into what would be considered the growth (rather than nucleation) regime. In this region, the polymorph that forms is therefore selected long after nucleation. This has implications. When nucleation is slow, it will be the rate-limiting step for crystallization. Then, the step that determines the time scale for crystallisation is different from the step that controls which polymorph forms. This means that they can be independently controlled. Also between nucleation and polymorph selection, there is a growing phase that is clearly crystalline not fluid, but this phase cannot be assigned to any one polymorph.

  8. Nucleation of crystals that are mixed composites of all three polymorphs in the Gaussian core model.

    PubMed

    Mithen, J P; Callison, A J; Sear, R P

    2015-06-14

    We present results of computer simulations of homogeneous crystal nucleation in the Gaussian core model. In our simulations, we study the competition between the body-centered-cubic (bcc), face-centered-cubic (fcc), and hexagonal-close-packed crystal phases. We find that the crystal nuclei that form from the metastable fluid phase are typically "mixed"; they do not consist of a single crystal polymorph. Furthermore, when the fcc phase is stable or fcc and bcc phases are equally stable, this mixed nature is found to persist far beyond the size at the top of the nucleation barrier, that is, far into what would be considered the growth (rather than nucleation) regime. In this region, the polymorph that forms is therefore selected long after nucleation. This has implications. When nucleation is slow, it will be the rate-limiting step for crystallization. Then, the step that determines the time scale for crystallisation is different from the step that controls which polymorph forms. This means that they can be independently controlled. Also between nucleation and polymorph selection, there is a growing phase that is clearly crystalline not fluid, but this phase cannot be assigned to any one polymorph.

  9. Determining whether metals nucleate homogeneously on graphite: A case study with copper

    DOE PAGES

    Appy, David; Lei, Huaping; Han, Yong; ...

    2014-11-05

    In this study, we observe that Cu clusters grow on surface terraces of graphite as a result of physical vapor deposition in ultrahigh vacuum. We show that the observation is incompatible with a variety of models incorporating homogeneous nucleation and calculations of atomic-scale energetics. An alternative explanation, ion-mediated heterogeneous nucleation, is proposed and validated, both with theory and experiment. This serves as a case study in identifying when and whether the simple, common observation of metal clusters on carbon-rich surfaces can be interpreted in terms of homogeneous nucleation. We describe a general approach for making system-specific and laboratory-specific predictions.

  10. Determining whether metals nucleate homogeneously on graphite: A case study with copper

    SciTech Connect

    Appy, David; Lei, Huaping; Han, Yong; Wang, Cai -Zhuang; Tringides, Michael C.; Shao, Dahai; Kwolek, Emma J.; Evans, J. W.; Thiel, P. A.

    2014-11-05

    In this study, we observe that Cu clusters grow on surface terraces of graphite as a result of physical vapor deposition in ultrahigh vacuum. We show that the observation is incompatible with a variety of models incorporating homogeneous nucleation and calculations of atomic-scale energetics. An alternative explanation, ion-mediated heterogeneous nucleation, is proposed and validated, both with theory and experiment. This serves as a case study in identifying when and whether the simple, common observation of metal clusters on carbon-rich surfaces can be interpreted in terms of homogeneous nucleation. We describe a general approach for making system-specific and laboratory-specific predictions.

  11. Determining whether metals nucleate homogeneously on graphite: A case study with copper

    SciTech Connect

    Appy, David; Lei, Huaping; Han, Yong; Wang, Cai-Zhuang; Tringides, Michael C; Shao, Dahai; Kwolek, Emma J; Evans, J W; Thiel, P A

    2014-11-01

    We observe that Cu clusters grow on surface terraces of graphite as a result of physical vapor deposition in ultrahigh vacuum. We show that the observation is incompatible with a variety of models incorporating homogeneous nucleation and calculations of atomic-scale energetics. An alternative explanation, ion-mediated heterogeneous nucleation, is proposed and validated, both with theory and experiment. This serves as a case study in identifying when and whether the simple, common observation of metal clusters on carbon-rich surfaces can be interpreted in terms of homogeneous nucleation. We describe a general approach for making system-specific and laboratory-specific predictions.

  12. Superheating and Homogeneous Single Bubble Nucleation in a Solid-State Nanopore

    PubMed Central

    Nagashima, Gaku; Levine, Edlyn V.; Hoogerheide, David P.; Burns, Michael M.; Golovchenko, Jene A.

    2014-01-01

    We demonstrate extreme superheating and single bubble nucleation in an electrolyte solution within a nanopore in a thin silicon nitride membrane. The high temperatures are achieved by Joule heating from a highly focused ionic current induced to flow through the pore by modest voltage biases. Conductance, nucleation, and bubble evolution are monitored electronically and optically. Temperatures near the thermodynamic limit of superheat are achieved just before bubble nucleation with the system at atmospheric pressure. Bubble nucleation is homogeneous and highly reproducible. This nanopore approach more generally suggests broad application to the excitation, detection, and characterization of highly metastable states of matter. PMID:25062192

  13. Homogeneous ice nucleation and supercooled liquid water in orographic wave clouds

    NASA Technical Reports Server (NTRS)

    Heymsfield, Andrew J.; Miloshevich, Larry M.

    1993-01-01

    This study investigates ice nucleation mechanisms in cold lenticular wave clouds, a cloud type characterized by quasi-steady-state air motions and microphysical properties. It is concluded that homogeneous ice nucleation is responsible for the ice production in these clouds at temperatures below about -33 C. The lack of ice nucleation observed above -33 C indicates a dearth of ice-forming nuclei, and hence heterogeneous ice nucleation, in these clouds. Aircraft measurements in the temperature range -31 to -41 C show the following complement of simultaneous and abrupt changes in cloud properties that indicate a transition from the liquid phase to ice: disappearance of liquid water; decrease in relative humidity from near water saturation to ice saturation; increase in mean particle size; change in particle concentration; and change in temperature due to the release of latent heat. A numerical model of cloud particle growth and homogeneous ice nucleation is used to aid in interpretation of our in situ measurements. The abrupt changes in observed cloud properties compare favorably, both qualitatively and quantitatively, with results from the homogeneous ice nucleation model. It is shown that the homogeneous ice nucleation rates from the measurements are consistent with the temperature-dependent rates employed by the model (within a factor of 100, corresponding to about 1 C in temperature) in the temperature range -35 deg to -38 C. Given the theoretical basis of the modeled rates, it may be reasonable to apply them throughout the -30 to -50 C temperature range considered by the theory.

  14. Homogeneous condensation - Freezing nucleation rate measurements for small water droplets in an expansion cloud chamber

    NASA Technical Reports Server (NTRS)

    Hagen, D. E.; Anderson, R. J.; Kassner, J. L., Jr.

    1981-01-01

    Experimental data on ice nucleation, presented in an earlier paper, are analyzed to yield information about the homogeneous nucleation rate of ice from supercooled liquid and the heights of energy barriers to that nucleation. The experiment consisted of using an expansion cloud chamber to nucleate from the vapor a cloud of supercooled pure water drops and the observation of the fraction of drops which subsequently froze. The analysis employed standard classical homogeneous nucleation theory. The data are used to extract the first experimental measurement (albeit indirect) of the activation energy for the transfer of a water molecule across the liquid-ice interface at temperatures near -40 C. The results provide further evidence that the local liquid structure becomes more icelike as the temperature is lowered.

  15. Fluorescence Studies of Protein Crystal Nucleation

    NASA Technical Reports Server (NTRS)

    Pusey, Marc L.

    1999-01-01

    Fluorescence can be used to study protein crystal nucleation through methods such as anisotropy, quenching, and resonance energy transfer (FRET), to follow pH and ionic strength changes, and follow events occurring at the growth interface. We have postulated, based upon a range of experimental evidence that the growth unit of tetragonal hen egg white lysozyme is an octamer. Several fluorescent derivatives of chicken egg white lysozyme have been prepared. The fluorescent probes lucifer yellow (LY), cascade blue, and 5-((2-aminoethyl)aminonapthalene-1-sulfonic acid (EDANS), have been covalently attached to ASP 101. All crystallize in the characteristic tetragonal form, indicating that the bound probes are likely laying within the active site cleft. Crystals of the LY and EDANS derivatives have been found to diffract to at least 1.7 A. A second group of derivatives is to the N-terminal amine group, and these do not crystallize as this site is part of the contact region between the adjacent 43 helix chains. However derivatives at these sites would not interfere with formation of the 43 helices in solution. Preliminary FRET studies have been carried out using N-terminal bound pyrene acetic acid (Ex 340 nm, Em 376 nm) lysozyme as a donor and LY (Ex -425 nm, Em 525 nm) labeled lysozyme as an acceptor. FRET data have been obtained at pH 4.6, 0.1 M NaAc buffer, at 5 and 7% NaCl, 4 C. The corresponding Csat values are 0.471 and 0.362 mg/ml (approximately 3.3 and approximately 2.5 x 10(exp -5) M respectively). The data at both salt concentrations show a consistent trend of decreasing fluorescence intensity of the donor species (PAA) with increasing total protein concentration. This decrease is more pronounced at 7% NaCl, consistent with the expected increased intermolecular interactions at higher salt concentrations reflected in the lower solubility. The calculated average distance between any two protein molecules at 5 x 10(exp -6) M is approximately 70nm, well beyond the

  16. Fluorescence Studies of Protein Crystal Nucleation

    NASA Technical Reports Server (NTRS)

    Pusey, Marc L.

    1999-01-01

    Fluorescence can be used to study protein crystal nucleation through methods such as anisotropy, quenching, and resonance energy transfer (FRET), to follow pH and ionic strength changes, and follow events occurring at the growth interface. We have postulated, based upon a range of experimental evidence that the growth unit of tetragonal hen egg white lysozyme is an octamer. Several fluorescent derivatives of chicken egg white lysozyme have been prepared. The fluorescent probes lucifer yellow (LY), cascade blue, and 5-((2-aminoethyl)aminonapthalene-1-sulfonic acid (EDANS), have been covalently attached to ASP 101. All crystallize in the characteristic tetragonal form, indicating that the bound probes are likely laying within the active site cleft. Crystals of the LY and EDANS derivatives have been found to diffract to at least 1.7 A. A second group of derivatives is to the N-terminal amine group, and these do not crystallize as this site is part of the contact region between the adjacent 43 helix chains. However derivatives at these sites would not interfere with formation of the 43 helices in solution. Preliminary FRET studies have been carried out using N-terminal bound pyrene acetic acid (Ex 340 nm, Em 376 nm) lysozyme as a donor and LY (Ex -425 nm, Em 525 nm) labeled lysozyme as an acceptor. FRET data have been obtained at pH 4.6, 0.1 M NaAc buffer, at 5 and 7% NaCl, 4 C. The corresponding Csat values are 0.471 and 0.362 mg/ml (approximately 3.3 and approximately 2.5 x 10(exp -5) M respectively). The data at both salt concentrations show a consistent trend of decreasing fluorescence intensity of the donor species (PAA) with increasing total protein concentration. This decrease is more pronounced at 7% NaCl, consistent with the expected increased intermolecular interactions at higher salt concentrations reflected in the lower solubility. The calculated average distance between any two protein molecules at 5 x 10(exp -6) M is approximately 70nm, well beyond the

  17. Effect of an electric field on nucleation and growth of crystals

    NASA Astrophysics Data System (ADS)

    Yurov, V. M.; Guchenko, S. A.; Gyngazova, M. S.

    2016-02-01

    The effect of the electric field strength on nucleation and growth of the crystals of ammonium halides and alkali metal sulfates has been studied. The optimal electric field strength for NH4Cl and NH4Br crystals was found to be 15 kV/cm, and for NH4I, it equaled 10 kV/cm. No effect of the electric field strength on the crystal growth was found for alkali metal sulfates. This difference is analyzed in terms of the crystal growth thermodynamics. In case, when the electric field is small and the Gibbs energy is of a significant value, the influence of the electric field at the crystal growth is negligible. A method to estimate the critical radius of homogeneous nucleation of the crystal is suggested.

  18. Atomistic simulation of the homogeneous nucleation and of the growth of N2 crystallites

    NASA Astrophysics Data System (ADS)

    Leyssale, Jean-Marc; Delhommelle, Jerome; Millot, Claude

    2005-03-01

    We report on a computer simulation study of the early stages of the crystallization of molecular nitrogen. First, we study how homogeneous nucleation takes place in supercooled liquid N2 for a moderate degree of supercooling. Using the umbrella sampling technique, we determine the free energy barrier of formation for a critical nucleus of N2. We show that, in accord with Ostwald's rule of stages, the structure of the critical nucleus is predominantly that of a metastable polymorph (α-N2 for the state point investigated). We then monitor the evolution of several critical nuclei through a series of unbiased molecular dynamics trajectories. The growth of N2 crystallites is accompanied by a structural evolution toward the stable polymorph β-N2. The microscopic mechanism underlying this evolution qualitatively differs from that reported previously. We do not observe any dissolution or reorganization of the α-like core of the nucleus. On the contrary, we show that α-like and β-like blocks coexist in postcritical nuclei. We relate the structural evolution to a greater adsorption rate of β-like molecules on the surface and show that this transition actually starts well within the precritical regime. We also carefully investigate the effect of the system size on the height of the free energy barrier of nucleation and on the structure and size of the critical nucleus.

  19. The microscopic features of heterogeneous ice nucleation may affect the macroscopic morphology of atmospheric ice crystals.

    PubMed

    Cox, Stephen J; Raza, Zamaan; Kathmann, Shawn M; Slater, Ben; Michaelides, Angelos

    2013-01-01

    It is surprisingly difficult to freeze water. Almost all ice that forms under "mild" conditions (temperatures > -40 degrees C) requires the presence of a nucleating agent--a solid particle that facilitates the freezing process--such as clay mineral dust, soot or bacteria. In a computer simulation, the presence of such ice nucleating agents does not necessarily alleviate the difficulties associated with forming ice on accessible timescales. Nevertheless, in this work we present results from molecular dynamics simulations in which we systematically compare homogeneous and heterogeneous ice nucleation, using the atmospherically important clay mineral kaolinite as our model ice nucleating agent. From our simulations, we do indeed find that kaolinite is an excellent ice nucleating agent but that contrary to conventional thought, non-basal faces of ice can nucleate at the basal face of kaolinite. We see that in the liquid phase, the kaolinite surface has a drastic effect on the density profile of water, with water forming a dense, tightly bound first contact layer. Monitoring the time evolution of the water density reveals that changes away from the interface may play an important role in the nucleation mechanism. The findings from this work suggest that heterogeneous ice nucleating agents may not only enhance the ice nucleation rate, but also alter the macroscopic structure of the ice crystals that form.

  20. Toward the theory of homogeneous nucleation and its parameterization for cloud models

    NASA Astrophysics Data System (ADS)

    Khvorostyanov, Vitaly; Sassen, Kenneth

    Following the classical approach in homogeneous nucleation theory, a general but simple expression for the homogeneous freezing rate is derived with account for solution and curvature effects, and applied to the examples of ammonium sulfate and sulfuric acid solutions. After showing that this method compares well with other approaches, a parameterization suitable for use in various cloud models is discussed.

  1. Two types of amorphous protein particles facilitate crystal nucleation

    PubMed Central

    Yamazaki, Tomoya; Vekilov, Peter G.; Furukawa, Erika; Shirai, Manabu; Matsumoto, Hiroaki; Van Driessche, Alexander E. S.; Tsukamoto, Katsuo

    2017-01-01

    Nucleation, the primary step in crystallization, dictates the number of crystals, the distribution of their sizes, the polymorph selection, and other crucial properties of the crystal population. We used time-resolved liquid-cell transmission electron microscopy (TEM) to perform an in situ examination of the nucleation of lysozyme crystals. Our TEM images revealed that mesoscopic clusters, which are similar to those previously assumed to consist of a dense liquid and serve as nucleation precursors, are actually amorphous solid particles (ASPs) and act only as heterogeneous nucleation sites. Crystalline phases never form inside them. We demonstrate that a crystal appears within a noncrystalline particle assembling lysozyme on an ASP or a container wall, highlighting the role of heterogeneous nucleation. These findings represent a significant departure from the existing formulation of the two-step nucleation mechanism while reaffirming the role of noncrystalline particles. The insights gained may have significant implications in areas that rely on the production of protein crystals, such as structural biology, pharmacy, and biophysics, and for the fundamental understanding of crystallization mechanisms. PMID:28193873

  2. Improved quasi-unary nucleation model for binary H2SO4-H2O homogeneous nucleation

    NASA Astrophysics Data System (ADS)

    Yu, Fangqun

    2007-08-01

    Aerosol nucleation events have been observed at a variety of locations worldwide, and may have significant climatic and health implications. Binary homogeneous nucleation (BHN) of H2SO4 and H2O is the foundation of recently proposed nucleation mechanisms involving additional species such as ammonia, ions, and organic compounds, and it may dominate atmospheric nucleation under certain conditions. We have shown in previous work that H2SO4-H2O BHN can be treated as a quasi-unary nucleation (QUN) process involving H2SO4 in equilibrium with H2O vapor, and we have developed a self-consistent kinetic model for H2SO4-H2O nucleation. Here, the QUN approach is improved, and an analytical expression yielding H2SO4-H2O QUN rates is derived. Two independent measurements related to monomer hydration are used to constrain the equilibrium constants for this process, which reduces a major source of uncertainty. It is also shown that the capillarity approximation may lead to a large error in the calculated Gibbs free energy change for the evaporation of H2SO4 molecules from small H2SO4-H2O clusters, which affects the accuracy of predicted BHN nucleation rates. The improved QUN model—taking into account the recently measured energetics of small clusters—is thermodynamically more robust. Moreover, predicted QUN nucleation rates are in better agreement with available experimental data than rates calculated using classical H2SO4-H2O BHN theory.

  3. Chamber Design For Slow Nucleation Protein Crystal Growth

    NASA Technical Reports Server (NTRS)

    Pusey, Marc Lee

    1995-01-01

    Multiple-chamber dialysis apparatus grows protein crystals on Earth or in microgravity with minimum of intervention by technician. Use of multiple chambers provides gradation of nucleation and growth rates.

  4. Effects of shear flow on phase nucleation and crystallization

    NASA Astrophysics Data System (ADS)

    Mura, Federica; Zaccone, Alessio

    2016-04-01

    Classical nucleation theory offers a good framework for understanding the common features of new phase formation processes in metastable homogeneous media at rest. However, nucleation processes in liquids are ubiquitously affected by hydrodynamic flow, and there is no satisfactory understanding of whether shear promotes or slows down the nucleation process. We developed a classical nucleation theory for sheared systems starting from the molecular level of the Becker-Doering master kinetic equation and we analytically derived a closed-form expression for the nucleation rate. The theory accounts for the effect of flow-mediated transport of molecules to the nucleus of the new phase, as well as for the mechanical deformation imparted to the nucleus by the flow field. The competition between flow-induced molecular transport, which accelerates nucleation, and flow-induced nucleus straining, which lowers the nucleation rate by increasing the nucleation energy barrier, gives rise to a marked nonmonotonic dependence of the nucleation rate on the shear rate. The theory predicts an optimal shear rate at which the nucleation rate is one order of magnitude larger than in the absence of flow.

  5. A physically constrained classical description of the homogeneous nucleation of ice in water

    NASA Astrophysics Data System (ADS)

    Koop, Thomas; Murray, Benjamin J.

    2016-12-01

    Liquid water can persist in a supercooled state to below 238 K in the Earth's atmosphere, a temperature range where homogeneous nucleation becomes increasingly probable. However, the rate of homogeneous ice nucleation in supercooled water is poorly constrained, in part, because supercooled water eludes experimental scrutiny in the region of the homogeneous nucleation regime where it can exist only fleetingly. Here we present a new parameterization of the rate of homogeneous ice nucleation based on classical nucleation theory. In our approach, we constrain the key terms in classical theory, i.e., the diffusion activation energy and the ice-liquid interfacial energy, with physically consistent parameterizations of the pertinent quantities. The diffusion activation energy is related to the translational self-diffusion coefficient of water for which we assess a range of descriptions and conclude that the most physically consistent fit is provided by a power law. The other key term is the interfacial energy between the ice embryo and supercooled water whose temperature dependence we constrain using the Turnbull correlation, which relates the interfacial energy to the difference in enthalpy between the solid and liquid phases. The only adjustable parameter in our model is the absolute value of the interfacial energy at one reference temperature. That value is determined by fitting this classical model to a selection of laboratory homogeneous ice nucleation data sets between 233.6 K and 238.5 K. On extrapolation to temperatures below 233 K, into a range not accessible to standard techniques, we predict that the homogeneous nucleation rate peaks between about 227 and 231 K at a maximum nucleation rate many orders of magnitude lower than previous parameterizations suggest. This extrapolation to temperatures below 233 K is consistent with the most recent measurement of the ice nucleation rate in micrometer-sized droplets at temperatures of 227-232 K on very short time scales

  6. A physically constrained classical description of the homogeneous nucleation of ice in water.

    PubMed

    Koop, Thomas; Murray, Benjamin J

    2016-12-07

    Liquid water can persist in a supercooled state to below 238 K in the Earth's atmosphere, a temperature range where homogeneous nucleation becomes increasingly probable. However, the rate of homogeneous ice nucleation in supercooled water is poorly constrained, in part, because supercooled water eludes experimental scrutiny in the region of the homogeneous nucleation regime where it can exist only fleetingly. Here we present a new parameterization of the rate of homogeneous ice nucleation based on classical nucleation theory. In our approach, we constrain the key terms in classical theory, i.e., the diffusion activation energy and the ice-liquid interfacial energy, with physically consistent parameterizations of the pertinent quantities. The diffusion activation energy is related to the translational self-diffusion coefficient of water for which we assess a range of descriptions and conclude that the most physically consistent fit is provided by a power law. The other key term is the interfacial energy between the ice embryo and supercooled water whose temperature dependence we constrain using the Turnbull correlation, which relates the interfacial energy to the difference in enthalpy between the solid and liquid phases. The only adjustable parameter in our model is the absolute value of the interfacial energy at one reference temperature. That value is determined by fitting this classical model to a selection of laboratory homogeneous ice nucleation data sets between 233.6 K and 238.5 K. On extrapolation to temperatures below 233 K, into a range not accessible to standard techniques, we predict that the homogeneous nucleation rate peaks between about 227 and 231 K at a maximum nucleation rate many orders of magnitude lower than previous parameterizations suggest. This extrapolation to temperatures below 233 K is consistent with the most recent measurement of the ice nucleation rate in micrometer-sized droplets at temperatures of 227-232 K on very short time scales

  7. Kinetics of crystal nucleation and growth in Pd(40)Ni(40)P(20) glass

    NASA Technical Reports Server (NTRS)

    Drehman, A. J.; Greer, A. L.

    1984-01-01

    Samples of Pd(40)Ni(40)P(20) glass, produced by cooling the melt at 1 or 800 K/s, are heated in a differential scanning calorimeter to determine the crystallization kinetics. Optical microscopy shows that eutectic crystallization proceeds both by growth from the surface of the samples and by the growth of spherical regions around preexisting nuclei in the interior. A modified Kissinger (1957) analysis is used to obtain the activation energy for crystal growth (3.49 eV). The steady state homogeneous nucleation frequency at 590 K is about 10 million/cu m per sec. This is estimated to be the maximum nucleation frequency: it is too low to account for the observed population of quenched-in nuclei, which are therefore presumed to be heterogeneous. The major practical obstacle to glass formation in this system is heterogeneous nucleation.

  8. Fluorescence Studies of Protein Crystal Nucleation

    NASA Technical Reports Server (NTRS)

    Pusey, Marc; Sumida, John

    2000-01-01

    -association process is a function of the protein concentration relative to the saturation concentration, and observing it in dilute solution (conc. less than or equal to 10(exp -5)M) requires that the experiments be performed under low solubility conditions, i.e., low temperatures and high salt concentrations. Data from preliminary steady state FRET studies with N-terminal bound pyrene acetic acid (PAA-lys, donor, Ex 340 nm, Em 376 nm) and asp101 LY-lys as an acceptor showed a consistent trend of decreasing donor fluorescence intensity with increasing total protein concentration. The FRET data have been obtained at pH 4.6, 0.1M NaAc buffer, at 5 and 7% NaCl, 4 C. The corresponding C(sub sat) values are 0.471 and 0.362 mg/ml (approx. 3.3 and approx. 2.5 x 10(exp -5)M respectively). The donor fluorescence decrease is more pronounced at7% NaCl, consistent with the expected increased intermolecular interactions at higher salt concentrations as reflected in the lower solubility. Results from these and other ongoing studies will be discussed in conjunction with an emerging model for how tetragonal lysozyme crystals nucleate and the relevance of that model to other proteins.

  9. Fluorescence Studies of Protein Crystal Nucleation

    NASA Technical Reports Server (NTRS)

    Pusey, Marc; Sumida, John

    2000-01-01

    -association process is a function of the protein concentration relative to the saturation concentration, and observing it in dilute solution (conc. less than or equal to 10(exp -5)M) requires that the experiments be performed under low solubility conditions, i.e., low temperatures and high salt concentrations. Data from preliminary steady state FRET studies with N-terminal bound pyrene acetic acid (PAA-lys, donor, Ex 340 nm, Em 376 nm) and asp101 LY-lys as an acceptor showed a consistent trend of decreasing donor fluorescence intensity with increasing total protein concentration. The FRET data have been obtained at pH 4.6, 0.1M NaAc buffer, at 5 and 7% NaCl, 4 C. The corresponding C(sub sat) values are 0.471 and 0.362 mg/ml (approx. 3.3 and approx. 2.5 x 10(exp -5)M respectively). The donor fluorescence decrease is more pronounced at7% NaCl, consistent with the expected increased intermolecular interactions at higher salt concentrations as reflected in the lower solubility. Results from these and other ongoing studies will be discussed in conjunction with an emerging model for how tetragonal lysozyme crystals nucleate and the relevance of that model to other proteins.

  10. Theory of homogeneous nucleation - A chemical kinetic view

    NASA Technical Reports Server (NTRS)

    Yang, C. H.; Qiu, H.

    1986-01-01

    A simple function with two undetermined parameters has been used in place of the Thomson-Gibbs relation to relate the activation energy of the vaporization reaction to cluster size. The parameters are iterated to assume optimum values in numerical computation so experimental data may be correlated. Calculations show this approach closely predicts and correlates available data for water, benzene, and ethanol. The nucleation formulism is redeveloped with an emphasis on the chemical kinetic view. Surface tension of the liquid and free energy of droplet formation are not used in its derivation.

  11. Theory of homogeneous nucleation - A chemical kinetic view

    NASA Technical Reports Server (NTRS)

    Yang, C. H.; Qiu, H.

    1986-01-01

    A simple function with two undetermined parameters has been used in place of the Thomson-Gibbs relation to relate the activation energy of the vaporization reaction to cluster size. The parameters are iterated to assume optimum values in numerical computation so experimental data may be correlated. Calculations show this approach closely predicts and correlates available data for water, benzene, and ethanol. The nucleation formulism is redeveloped with an emphasis on the chemical kinetic view. Surface tension of the liquid and free energy of droplet formation are not used in its derivation.

  12. Secondary nucleation kinetcs of ammonium sulfate in a CMSMPR crystallizer

    NASA Astrophysics Data System (ADS)

    Daudey, P. J.; van Rosmalen, G. M.; de Jong, E. J.

    1990-01-01

    Secondary nucleation in suspension is most frequently modelled by an empirical "power-law" relating the nucleation rate to supersaturation and to the slurry density of the crystals already present in the solution. In this paper kinetic rate equations are developed based on a general modelling of secondary nucleation employing two mechanisms, surface breeding and mechanical breeding, each consisting of sequential steps. The specific equations gained in this way are used to determine the breeding mechanisms prevailing in suspension crystallization. Ammonium sulfate was used as a test case. For this system it is concluded that surface breeding is the predominant mechanism in both evaporation and cooling experiments.

  13. Influence of solvent polarity and supersaturation on template-induced nucleation of carbamazepine crystal polymorphs

    NASA Astrophysics Data System (ADS)

    Parambil, Jose V.; Poornachary, Sendhil K.; Tan, Reginald B. H.; Heng, Jerry Y. Y.

    2017-07-01

    Studies on the use of template surfaces to induce heterogeneous crystal nucleation have gained momentum in recent years-with potential applications in selective crystallisation of polymorphs and in the generation of seed crystals in a continuous crystallisation process. In developing a template-assisted solution crystallisation process, the kinetics of homogeneous versus heterogeneous crystal nucleation could be influenced by solute-solvent, solute-template, and solvent-template interactions. In this study, we report the effect of solvents of varying polarity on the nucleation of carbamazepine (CBZ) crystal polymorphs, a model active pharmaceutical ingredient. The experimental results demonstrate that functionalised template surfaces are effective in promoting crystallisation of either the metastable (form II) or stable (form III) polymorphs of CBZ only in moderately (methanol, ethanol, isopropanol) and low polar (toluene) solvents. A solvent with high polarity (acetonitrile) is thought to mask the template effect on heterogeneous nucleation due to strong solute-solvent and solvent-template interactions. The current study highlights that a quality-by-design (QbD) approach-considering the synergistic effects of solute concentration, solvent type, solution temperature, and template surface chemistry on crystal nucleation-is critical to the development of a template-induced crystallisation process.

  14. Heterogeneous Nucleation of Protein Crystals on Fluorinated Layered Silicate

    PubMed Central

    Ino, Keita; Udagawa, Itsumi; Iwabata, Kazuki; Takakusagi, Yoichi; Kubota, Munehiro; Kurosaka, Keiichi; Arai, Kazuhito; Seki, Yasutaka; Nogawa, Masaya; Tsunoda, Tatsuo; Mizukami, Fujio; Taguchi, Hayao; Sakaguchi, Kengo

    2011-01-01

    Here, we describe an improved system for protein crystallization based on heterogeneous nucleation using fluorinated layered silicate. In addition, we also investigated the mechanism of nucleation on the silicate surface. Crystallization of lysozyme using silicates with different chemical compositions indicated that fluorosilicates promoted nucleation whereas the silicates without fluorine did not. The use of synthesized saponites for lysozyme crystallization confirmed that the substitution of hydroxyl groups contained in the lamellae structure for fluorine atoms is responsible for the nucleation-inducing property of the nucleant. Crystallization of twelve proteins with a wide range of pI values revealed that the nucleation promoting effect of the saponites tended to increase with increased substitution rate. Furthermore, the saponite with the highest fluorine content promoted nucleation in all the test proteins regardless of their overall net charge. Adsorption experiments of proteins on the saponites confirmed that the density of adsorbed molecules increased according to the substitution rate, thereby explaining the heterogeneous nucleation on the silicate surface. PMID:21818343

  15. The decisive role of free water in determining homogenous ice nucleation behavior of aqueous solutions

    PubMed Central

    Wang, Qiang; Zhao, Lishan; Li, Chenxi; Cao, Zexian

    2016-01-01

    It is a challenging issue to quantitatively characterize how the solute and pressure affect the homogeneous ice nucleation in a supercooled solution. By measuring the glass transition behavior of solutions, a universal feature of water-content dependence of glass transition temperature is recognized, which can be used to quantify hydration water in solutions. The amount of free water can then be determined for water-rich solutions, whose mass fraction, Xf, is found to serve as a universal relevant parameter for characterizing the homogeneous ice nucleation temperature, the meting temperature of primary ice, and even the water activity of solutions of electrolytes and smaller organic molecules. Moreover, the effects of hydrated solute and pressure on ice nucleation is comparable, and the pressure, when properly scaled, can be incorporated into the universal parameter Xf. These results help establish the decisive role of free water in determining ice nucleation and other relevant properties of aqueous solutions. PMID:27225427

  16. A model description for cirrus cloud nucleation from homogeneous freezing of sulfate aerosols

    NASA Astrophysics Data System (ADS)

    Tabazadeh, Azadeh; Jensen, Eric J.; Toon, Owen B.

    1997-10-01

    Classical nucleation theory for homogeneous freezing as well as recent laboratory data are used to formulate an algorithm for ice nucleation from an aqueous sulfuric acid solution droplet A new parameterized function is derived from recent thermodynamic data to express the variation of sulfuric acid solution composition with temperature and relative humidity. This function is then used to derive critical ice nucleation parameters from recent laboratory data. The critical nucleation parameters are used in a classical nucleation theory to derive the diffusion activation energy of water molecules in a sulfuric acid solution from the measurements. The derived diffusion activation energy of water molecules in a sulfuric acid solution does not agree with the diffusion activation energy calculated from a viscous flow formulation that is commonly used in classical nucleation rate calculations. Our results show that ice nucleation in a sulfate droplet occurs when the interface energy of ice against the sulfate solution is approximately 17 dyn cm-1. We calculate that a supersaturation ratio of about 1.3 to 1.5 is required to nucleate ice from an aqueous sulfuric acid solution droplet in the temperature range of about 185 to 240 K. This supersaturation corresponds to a supercooling of a sulfate solution to about 2 to 3 K below the equilibrium condensation point of ice. Simple functions are given for estimating the nucleation point of ice in the upper troposphere. The differences between previous parameterizations and this work are discussed.

  17. Thermodynamic formulation of the barrier for heterogeneous pinned nucleation: Implication to the crossover scenarios associated with barrierless and homogeneous nucleation

    NASA Astrophysics Data System (ADS)

    Singha, Sanat K.; Das, Prasanta K.; Maiti, Biswajit

    2017-06-01

    The effect of contact line pinning on nucleation is reported using continuum thermodynamics. Based on the principle of the free-energy maximization, closed-form expressions in the dimensionless form for the free-energy of the three-phase metastable system and the thermodynamic barrier are formulated with respect to the system geometry and the substrate wettability. The condition of maximality limits the dynamic contact angle within the cluster-phase-phobic regime. The dimensionless nucleation barrier or the potency factor can be divided into two components related to the system geometry and the pinning effect. Depending on the relative value of the equilibrium and the critical dynamic contact angle, the contact line pinning can either have favorable or adverse effects. Associated pinning-depinning transition can also lead to the crossovers related to barrierless and homogeneous nucleation. Contact line tension is found to have a considerable effect during these transitional scenarios. Complete wetting transition associated with barrierless nucleation can take place due to the presence of tensile (negative) line tension. On the other hand, complete drying transition related to homogeneous nucleation can occur when line tension is compressive (positive) in nature. The pinning has a favorable effect only when the substrate wettability is within the cluster-phase-philic regime. There can be favorable, adverse, or no pinning effects when the substrate wettability is within the cluster-phase-phobic regime. Although the contact line is pinned, the minimum value of the potency factor is obtained when equilibrium and dynamic contact angles are equal.

  18. Nucleation of Salt Crystals in Clay Minerals: Molecular Dynamics Simulation.

    PubMed

    Dashtian, Hassan; Wang, Haimeng; Sahimi, Muhammad

    2017-07-20

    Nucleation of salt crystals in confined media occurs in many processes of high importance, such as injection of CO2 in geological formations for its sequestration. In particular, salt precipitation in clays, a main component of sedimentary rock, is an important phenomenon. The crystals precipitate on the pores' surface, modify the pore space morphology, and reduce its flow and transport properties. Despite numerous efforts to understand the mechanisms of nucleation of salt crystals in confined media, the effect of the clay's chemistry on the growth, distribution, and properties of the crystals is not well understood. We report the results of extensive molecular dynamics simulation of nucleation and growth of NaCl crystals in a clay pore using molecular models of two types of clay minerals, Na-montmorillonite and kaolinite. Clear evidence is presented for the nucleation of the salt crystals that indicates that the molecular structure of clay minerals affects their spatial distribution, although the nucleation mechanism is the same in both types of clays.

  19. Nucleation and Convection Effects in Protein Crystal Growth

    NASA Technical Reports Server (NTRS)

    Vekilow, Peter G.

    1998-01-01

    Our work under this grant has significantly contributed to the goals of the NASA supported protein crystallization program. We have achieved the main objectives of the proposed work, as outlined in the original proposal: (1) We have provided important insight into protein nucleation and crystal growth mechanisms to facilitate a rational approach to protein crystallization; (2) We have delineated the factors that currently limit the x-ray diffraction resolution of protein crystals, and their correlation to crystallization conditions; (3) We have developed novel technologies to study and monitor protein crystal nucleation and growth processes, in order to increase the reproducibility and yield of protein crystallization. We have published 17 papers in peer-reviewed scientific journals and books and made more than 15 invited and 9 contributed presentations of our results at international and national scientific meetings.

  20. Bubble evolution and properties in homogeneous nucleation simulations

    NASA Astrophysics Data System (ADS)

    Angélil, Raymond; Diemand, Jürg; Tanaka, Kyoko K.; Tanaka, Hidekazu

    2014-12-01

    We analyze the properties of naturally formed nanobubbles in Lennard-Jones molecular dynamics simulations of liquid-to-vapor nucleation in the boiling and the cavitation regimes. The large computational volumes provide a realistic environment at unchanging average temperature and liquid pressure, which allows us to accurately measure properties of bubbles from their inception as stable, critically sized bubbles, to their continued growth into the constant speed regime. Bubble gas densities are up to 50 % lower than the equilibrium vapor densities at the liquid temperature, yet quite close to the gas equilibrium density at the lower gas temperatures measured in the simulations: The latent heat of transformation results in bubble gas temperatures up to 25 % below those of the surrounding bulk liquid. In the case of rapid bubble growth—typical for the cavitation regime—compression of the liquid outside the bubble leads to local temperature increases of up to 5 %, likely significant enough to alter the surface tension as well as the local viscosity. The liquid-vapor bubble interface is thinner than expected from planar coexistence simulations by up to 50 % . Bubbles near the critical size are extremely nonspherical, yet they quickly become spherical as they grow. The Rayleigh-Plesset description of bubble-growth gives good agreement in the cavitation regime.

  1. Homogeneous SPC/E water nucleation in large molecular dynamics simulations.

    PubMed

    Angélil, Raymond; Diemand, Jürg; Tanaka, Kyoko K; Tanaka, Hidekazu

    2015-08-14

    We perform direct large molecular dynamics simulations of homogeneous SPC/E water nucleation, using up to ∼ 4 ⋅ 10(6) molecules. Our large system sizes allow us to measure extremely low and accurate nucleation rates, down to ∼ 10(19) cm(-3) s(-1), helping close the gap between experimentally measured rates ∼ 10(17) cm(-3) s(-1). We are also able to precisely measure size distributions, sticking efficiencies, cluster temperatures, and cluster internal densities. We introduce a new functional form to implement the Yasuoka-Matsumoto nucleation rate measurement technique (threshold method). Comparison to nucleation models shows that classical nucleation theory over-estimates nucleation rates by a few orders of magnitude. The semi-phenomenological nucleation model does better, under-predicting rates by at worst a factor of 24. Unlike what has been observed in Lennard-Jones simulations, post-critical clusters have temperatures consistent with the run average temperature. Also, we observe that post-critical clusters have densities very slightly higher, ∼ 5%, than bulk liquid. We re-calibrate a Hale-type J vs. S scaling relation using both experimental and simulation data, finding remarkable consistency in over 30 orders of magnitude in the nucleation rate range and 180 K in the temperature range.

  2. Nucleation and crystal growth in laser patterned lines in glasses

    NASA Astrophysics Data System (ADS)

    Komatsu, Takayuki; Honma, Tsuyoshi

    2016-07-01

    Laser-induced crystallization is a new method for the design and control of the crystallization of glasses and opens a new door in the study of nucleation and crystal growth in glasses. Nonlinear optical Sm-doped -BaB2O4 (-BBO) crystal lines were patterned by continuous wave Yb:YVO4 fiber laser (wavelength 1080 nm) in 8Sm2O3-42BaO-50B2O3 glass as an example, and nucleation and crystal growth behaviors in the laser-patterned bending and crossing lines were examined. It was confirmed that the growth of c-axis oriented -BBO crystals follows along the laser scanning direction even if laser scanning direction changes. The model of self-organized homo-epitaxial crystal growth was demonstrated for the orientation of -BBO crystals at the crossing point of two lines, in which the first crystal line at the crossing point acts as nucleation site for the second crystal line. This study proposes a new crystal growth technology.

  3. Twin nucleation and migration in FeCr single crystals

    SciTech Connect

    Patriarca, L.; Abuzaid, Wael; Sehitoglu, Huseyin; Maier, Hans J.; Chumlyakov, Y.

    2013-01-15

    Tension and compression experiments were conducted on body-centered cubic Fe -47.8 at pct. Cr single crystals. The critical resolved shear stress (CRSS) magnitudes for slip nucleation, twin nucleation and twin migration were established. We show that the nucleation of slip occurs at a CRSS of about 88 MPa, while twinning nucleates at a CRSS of about 191 MPa with an associated load drop. Following twin nucleation, twin migration proceeds at a CRSS that is lower than the initiation stress ( Almost-Equal-To 114-153 MPa). The experimental results of the nucleation stresses indicate that the Schmid law holds to a first approximation for the slip and twin nucleation cases, but to a lesser extent for twin migration particularly when considerable slip strains preceded twinning. The CRSSs were determined experimentally using digital image correlation (DIC) in conjunction with electron back scattering diffraction (EBSD). The DIC measurements enabled pinpointing the precise stress on the stress-strain curves where twins or slip were activated. The crystal orientations were obtained using EBSD and used to determine the activated twin and slip systems through trace analysis. - Highlights: Black-Right-Pointing-Pointer Digital image correlation allows to capture slip/twin initiation for bcc FeCr. Black-Right-Pointing-Pointer Crystal orientations from EBSD allow slip/twin system indexing. Black-Right-Pointing-Pointer Nucleation of slip always precedes twinning. Black-Right-Pointing-Pointer Twin growth is sustained with a lower stress than required for nucleation. Black-Right-Pointing-Pointer Twin-slip interactions provide high hardening at the onset of plasticity.

  4. Self Nucleation and Crystallization of Poly(vinyl alcohol)

    NASA Astrophysics Data System (ADS)

    Thomas, David; Cebe, Peggy

    Polyvinyl alcohol (PVA) is a hydrophilic, biodegradable, semi-crystalline polymer with uses ranging from textiles to medicine. Film samples of PVA were investigated to assess crystallization and melting behavior during self-nucleation experiments, and thermal degradation, using differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis, respectively. TG results show that degradation occurred at temperatures close to the observed peak melting temperature of 223 C. Using conventional DSC, PVA was heated at a rate of 10 C/min to various self-nucleation temperatures, Ts, within its melting range, briefly annealed, cooled and reheated. Three distinct crystallization regimes were observed upon cooling, depending upon self nucleation temperature. At low values of Ts, below 227 C, PVA only partially melts; residual crystal anneals while new, less perfect crystals form during cooling. Between 228 C and 234 C, PVA was found to crystallize exclusively by self-nucleation. For Ts above 235 C the PVA melts completely. Fast scanning chip-based calorimetry was used to heat and cool at 2000 K/s, to prevent degradation. Results of self nucleation experiments using fast scanning and conventional DSC will be compared. NSF DMR-1206010.

  5. Kinetic Analysis of Protein Crystal Nucleation in Gel Matrix

    PubMed Central

    Wang, Lei; Liu, Xiang-Yang

    2008-01-01

    The effect of agarose on nucleation of hen egg white lysozyme crystal was examined quantitatively using a temperature-jumping technique. For the first time, to our knowledge, the inhibition of agarose during the nucleation of lysozyme was quantified in two respects: a), the effect of increasing interfacial nucleation barrier, described by the so-called interfacial correlation parameter f(m); and b), the ratio of diffusion to interfacial kinetics obtained from dynamic surface tension measurements. It follows from a dynamic surface tension analysis that the agarose network inhibits the nucleation of lysozyme by means of an enhancement of the repulsion and interfacial structure mismatch between foreign bodies and lysozyme crystals, slowing down the diffusion process of the protein molecules and clusters toward the crystal-fluid interface and inhibiting the rearrangement of protein molecules at the interface. Our results, based on ultraviolet-visible spectroscopy, also show no evidence of the supersaturation enhancement effect in protein agarose gels. The effects of nucleation suppression and transport limitation in gels result in bigger, fewer, and perhaps better quality protein crystals. The understandings obtained in this study will improve our knowledge in controlling the crystallization of proteins and other biomolecules. PMID:18835910

  6. Extended study of molecular dynamics simulation of homogeneous vapor-liquid nucleation of water

    NASA Astrophysics Data System (ADS)

    Matsubara, Hiroki; Koishi, Takahiro; Ebisuzaki, Toshikazu; Yasuoka, Kenji

    2007-12-01

    Using the simple point charge/extended water model, we performed molecular dynamics simulations of homogeneous vapor-liquid nucleation at various values of temperature T and supersaturation S, from which the nucleation rate J, critical nucleus size n*, and the cluster formation free energy ΔG were derived. As well as providing lots of simulation data, the results were compared with theories on homogeneous nucleation, including the classical, semiphenomenological, and scaled models, but none of these gave a satisfactory explanation for our results. It was found that two main factors made the theories fail: (1) The average cluster structure including the nonspherical shape and the core structure that is not like the bulk liquid and (2) the forward rate which is larger than assumed by the theories by about one order of magnitude. The quantitative evaluation of these factors is left for future investigations.

  7. Free energy landscapes for homogeneous nucleation of ice for a monatomic water model

    NASA Astrophysics Data System (ADS)

    Reinhardt, Aleks; Doye, Jonathan P. K.

    2012-02-01

    We simulate the homogeneous nucleation of ice from supercooled liquid water at 220 K in the isobaric-isothermal ensemble using the MW monatomic water potential. Monte Carlo simulations using umbrella sampling are performed in order to determine the nucleation free energy barrier. We find the Gibbs energy profile to be relatively consistent with that predicted by classical nucleation theory; the free energy barrier to nucleation was determined to be ˜18 kBT and the critical nucleus comprised ˜85 ice particles. Growth from the supercooled liquid gives clusters that are predominantly cubic, whilst starting with a pre-formed subcritical nucleus of cubic or hexagonal ice results in the growth of predominantly that phase of ice only.

  8. Control of protein crystal nucleation around the metastable liquid–liquid phase boundary

    PubMed Central

    Galkin, Oleg; Vekilov, Peter G.

    2000-01-01

    The capability to enhance or suppress the nucleation of protein crystals opens opportunities in various fundamental and applied areas, including protein crystallography, production of protein crystalline pharmaceuticals, protein separation, and treatment of protein condensation diseases. Herein, we show that the rate of homogeneous nucleation of lysozyme crystals passes through a maximum in the vicinity of the liquid–liquid phase boundary hidden below the liquidus (solubility) line in the phase diagram of the protein solution. We found that glycerol and polyethylene glycol (which do not specifically bind to proteins) shift this phase boundary and significantly suppress or enhance the crystal nucleation rates, although no simple correlation exists between the action of polyethylene glycol on the phase diagram and the nucleation kinetics. The control mechanism does not require changes in the protein concentration, acidity, and ionicity of the solution. The effects of the two additives on the phase diagram strongly depend on their concentration, which provides opportunities for further tuning of nucleation rates. PMID:10823898

  9. Homogenous nucleation of sulfuric acid and water at close to atmospherically relevant conditions

    NASA Astrophysics Data System (ADS)

    Brus, D.; Neitola, K.; Hyvärinen, A.-P.; Petäjä, T.; Vanhanen, J.; Sipilä, M.; Paasonen, P.; Kulmala, M.; Lihavainen, H.

    2011-06-01

    In this study the homogeneous nucleation rates in the system of sulfuric acid and water were measured by using a flow tube technique. The goal was to directly compare particle formation rates obtained from atmospheric measurements with nucleation rates of freshly nucleated particles measured with particle size magnifier (PSM) which has detection efficiency of unity for particles having mobility diameter of 1.5 nm. The gas phase sulfuric acid concentration in this study was measured with the chemical ionization mass spectrometer (CIMS), commonly used in field measurements. The wall losses of sulfuric acid were estimated from measured concentration profiles along the flow tube. The initial concentrations of sulfuric acid estimated from loss measurements ranged from 108 to 3 × 109 molecules cm-3. The nucleation rates obtained in this study cover about three orders of magnitude from 10-1 to 102 cm-3 s-1 for commercial ultrafine condensation particle counter (UCPC) TSI model 3025A and from 101 to 104 cm-3 s-1 for PSM. The nucleation rates and the slopes (dlnJ/dln [H2SO4]) show satisfactory agreement when compared to empirical kinetic and activation models and the latest atmospheric nucleation data. To the best of our knowledge, this is the first experimental work providing temperature dependent nucleation rate measurements using a high efficiency particle counter with a cut-off-size of 1.5 nm together with direct measurements of gas phase sulfuric acid concentration.

  10. Surface or internal nucleation and crystallization of glass-ceramics

    NASA Astrophysics Data System (ADS)

    Höland, W.; Rheinberger, V. M.; Ritzberger, C.; Apel, E.

    2013-07-01

    Fluoroapatite (Ca5(PO4)3F) was precipitated in glass-ceramics via internal crystallization of base glasses. The crystals grew with a needle-like morphology in the direction of the crystallographic c-axis. Two different reaction mechanisms were analyzed: precipitation via a disordered primary apatite crystals and a solid state parallel reaction to rhenanite (NaCaPO4) precipitation. In contrast to the internal nucleation used in the formation of fluoroapatite, surface crystallization was induced to precipitate a phosphate-free oxyapatite of NaY9(SiO4)6O2-type. Internal nucleation and crystallization have been shown to be a very useful tool for developing high-strength lithium disilicate (Li2Si2O5) glass-ceramics. A very controlled process was conducted to transform the lithium metasilicate glass-ceramic precursor material into the final product of the lithium disilicate glass-ceramic without the major phase of the precursor material. The combination of all these methods allowed the driving forces of the internal nucleation and crystallization mechanisms to be explained. An amorphous phosphate primary phase was discovered in the process. Nucleation started at the interface between the amorphous phosphate phase and the glass matrix. The final products of all these glass-ceramics are biomaterials for dental restoration showing special optical properties, e.g. translucence and color close to dental teeth.

  11. Hard sphere crystal nucleation and growth near large spherical impurities

    NASA Astrophysics Data System (ADS)

    de Villeneuve, V. W. A.; Verboekend, D.; Dullens, R. P. A.; Aarts, D. G. A. L.; Kegel, W. K.; Lekkerkerker, H. N. W.

    2005-11-01

    We report how large spherical impurities affect the nucleation and growth of hard sphere colloidal crystals. Both the impurities and the colloids are fluorescently labelled polymethylmetacrylate particles and are dispersed in an optically and density matching solvent mixture. Crystal growth, initiated either at the impurity surface, or at the sample bottom, was studied by imaging sequences of two-dimensional xy-slices in the plane of the impurity's centre of mass with a laser scanning confocal microscope. At least two factors determine whether a large impurity can function as a seed for heterogeneous nucleation: timescales and impurity curvature. The curvature needs to be sufficiently low for crystal nuclei to form on the impurity surface. If bulk crystal growth has already approached the impurity, bulk growth is dominant over growth of crystallites on the impurity surface. Such surface crystallites eventually reorient to adapt to the overall bulk crystal symmetry.

  12. Investigating the nucleation of protein crystals with hydrostatic pressure

    NASA Astrophysics Data System (ADS)

    Kadri, A.; Damak, M.; Jenner, G.; Lorber, B.; Giegé, R.

    2003-12-01

    Hydrostatic pressure in the 0.1-75 MPa range has been used as a non-invasive tool to study the crystallization process of the tetragonal crystal form of the protein thaumatin (Mr 22 200). Crystals were prepared within agarose gel and at temperatures in the range from 283 to 303 K. The solubility, i.e. the concentration of soluble macromolecules remaining in equilibrium with the crystals, decreases when the pressure increases and when the temperature decreases. High pressure was used to probe the nucleation behaviour of thaumatin. The pressure dependence of the nucleation rate leads to an activation volume of -46.5 cm3 mol-1. It is shown that an increase in pressure decreases the enthalpy, the entropy and the free energy of crystallization of thaumatin. The data are discussed in the light of the results of crystallographic analyses and of the structure of the protein.

  13. Homogeneous ice freezing temperatures and ice nucleation rates of aqueous ammonium sulfate and aqueous levoglucosan particles for relevant atmospheric conditions.

    PubMed

    Knopf, Daniel Alexander; Lopez, Miguel David

    2009-09-28

    Homogeneous ice nucleation from micrometre-sized aqueous (NH4)2SO4 and aqueous levoglucosan particles is studied employing the optical microscope technique. A new experimental method is introduced that allows us to control the initial water activity of the aqueous droplets. Homogeneous ice freezing temperatures and ice melting temperatures of these aqueous solution droplets, 10 to 80 microm in diameter, are determined. Homogeneous ice nucleation from aqueous (NH4)2SO4 particles 5-39 wt% in concentration and aqueous levoglucosan particles with initial water activities of 0.85-0.99 yield upper limits of the homogeneous ice nucleation rate coefficients of up to 1x10(10) cm(-3) s(-1). The experimentally derived homogeneous ice freezing temperatures and upper limits of the homogeneous ice nucleation rate coefficients are compared with corresponding predictions of the water-activity-based ice nucleation theory [T. Koop, B. P. Luo, A. Tsias and T. Peter, Nature, 2000, 406, 611]. It is found that the water-activity-based ice nucleation theory can capture the experimentally derived ice freezing temperatures and homogeneous ice nucleation rate coefficients of the aqueous (NH4)2SO4 and aqueous levoglucosan particles. However, the level of agreement between experimentally derived and predicted values, in particular for homogeneous ice nucleation rate coefficients, crucially depends on the extrapolation method to obtain water activities at corresponding freezing temperatures. It is suggested that the combination of experimentally derived ice freezing temperatures and homogeneous ice nucleation rate coefficients can serve as a better validation of the water-activity-based ice nucleation theory than when compared to the observation of homogeneous ice freezing temperatures alone. The atmospheric implications with regard to the application of the water-activity-based ice nucleation theory and derivation of maximum ice particle production rates are briefly discussed.

  14. Kinetics of Nucleation and Crystal Growth in Glass Forming Melts in Microgravity

    NASA Technical Reports Server (NTRS)

    Day, Delbert E.; Ray, Chandra S.

    1999-01-01

    The following list summarizes the most important results that have been consistently reported for glass forming melts in microgravity: (1) Glass formation is enhanced for melts prepared in space; (2) Glasses prepared in microgravity are more chemically homogeneous and contain fewer and smaller chemically heterogeneous regions than identical glasses prepared on earth; (3) Heterogeneities that are deliberately introduced such as Pt particles are more uniformly distributed in a glass melted in space than in a glass melted on earth; (4) Glasses prepared in microgravity are more resistant to crystallization and have a higher mechanical strength and threshold energy for radiation damage; and (5) Glasses crystallized in space have a different microstructure, finer grains more uniformly distributed, than equivalent samples crystallized on earth. The preceding results are not only scientifically interesting, but they have considerable practical implications. These results suggest that the microgravity environment is advantageous for developing new and improved glasses and glass-ceramics that are difficult to prepare on earth. However, there is no suitable explanation at this time for why a glass melted in microgravity will be more chemically homogeneous and more resistant to crystallization than a glass melted on earth. A fundamental investigation of melt homogenization, nucleation, and crystal growth processes in glass forming melts in microgravity is important to understanding these consistently observed, but yet unexplained results. This is the objective of the present research. A lithium disilicate (Li2O.2SiO2) glass will be used for this investigation, since it is a well studied system, and the relevant thermodynamic and kinetic parameters for nucleation and crystal growth at 1-g are available. The results from this research are expected to improve our present understanding of the fundamental mechanism of nucleation and crystal growth in melts and liquids, and to lead

  15. Classical nucleation theory of homogeneous freezing of water: thermodynamic and kinetic parameters.

    PubMed

    Ickes, Luisa; Welti, André; Hoose, Corinna; Lohmann, Ulrike

    2015-02-28

    The probability of homogeneous ice nucleation under a set of ambient conditions can be described by nucleation rates using the theoretical framework of Classical Nucleation Theory (CNT). This framework consists of kinetic and thermodynamic parameters, of which three are not well-defined (namely the interfacial tension between ice and water, the activation energy and the prefactor), so that any CNT-based parameterization of homogeneous ice formation is less well-constrained than desired for modeling applications. Different approaches to estimate the thermodynamic and kinetic parameters of CNT are reviewed in this paper and the sensitivity of the calculated nucleation rate to the choice of parameters is investigated. We show that nucleation rates are very sensitive to this choice. The sensitivity is governed by one parameter - the interfacial tension between ice and water, which determines the energetic barrier of the nucleation process. The calculated nucleation rate can differ by more than 25 orders of magnitude depending on the choice of parameterization for this parameter. The second most important parameter is the activation energy of the nucleation process. It can lead to a variation of 16 orders of magnitude. By estimating the nucleation rate from a collection of droplet freezing experiments from the literature, the dependence of these two parameters on temperature is narrowed down. It can be seen that the temperature behavior of these two parameters assumed in the literature does not match with the predicted nucleation rates from the fit in most cases. Moreover a comparison of all possible combinations of theoretical parameterizations of the dominant two free parameters shows that one combination fits the fitted nucleation rates best, which is a description of the interfacial tension coming from a molecular model [Reinhardt and Doye, J. Chem. Phys., 2013, 139, 096102] in combination with the activation energy derived from self-diffusion measurements [Zobrist

  16. Kinetics of Nucleation and Crystal Growth in Glass Forming Melts in Microgravity

    NASA Technical Reports Server (NTRS)

    Day, Delbert E.; Ray, Chandra S.

    2003-01-01

    This flight definition project has the specific objective of investigating the kinetics of nucleation and crystal growth in high temperature inorganic oxide, glass forming melts in microgravity. It is related to one1 of our previous NASA projects that was concerned with glass formation for high temperature containerless melts in microgravity. The previous work culminated in two experiments which were conducted aboard the space shuttle in 1983 and 1985 and which consisted of melting (at 1500 C) and cooling levitated 6 to 8 mm diameter spherical samples in a Single Axis Acoustic Levitator (SAAL) furnace. Compared to other types of materials, there have been relatively few experiments, 6 to 8, conducted on inorganic glasses in space. These experiments have been concerned with mass transport (alkali diffusion), containerless melting, critical cooling rate for glass formation, chemical homogeneity, fiber pulling, and crystallization of glass forming melts. One of the most important and consistent findings in all of these experiments has been that the glasses prepared in microgravity are more resistant to crystallization (better glass former) and more chemically homogeneous than equivalent glasses made on earth (1g). The chemical composition of the melt appears relatively unimportant since the same general results have been reported for oxide, fluoride and chalcogenide melts. These results for space-processed glasses have important implications, since glasses with a higher resistance to crystallization or higher chemical homogeneity than those attainable on earth can significantly advance applications in areas such as fiber optics communications, high power laser glasses, and other photonic devices where glasses are the key functional materials. The classical theories for nucleation and crystal growth for a glass or melt do not contain any parameter that is directly dependent upon the g-value, so it is not readily apparent why glasses prepared in microgravity should be

  17. Sizes and spatial relationships of crystals in granitic plutons: Exploring the crystallization gaps, heterogeneous nucleation, and mechanical clustering of crystals

    NASA Astrophysics Data System (ADS)

    Špillar, V.; Dolejš, D.

    2012-04-01

    Quantitative measurements on magmatic textures provide an important insight into nucleation and growth rates as well as mechanical effects such as crystal settling and melt extraction in magma reservoirs. Crystal size distribution (CSD) measurements and spatial analysis are routinely applied to dilute volcanic suspensions but comparable data on holocrystalline multiphase plutonic rocks are uncommon. We present quantitative description of CSDs and spatial relationships for all rock-forming minerals from an intrusive suite of the Fichtelgebirge/Smrčiny granite batholith in central Europe. This composite body represents two spatially unrelated chambers, consisting of peraluminous biotite, two-mica, and tourmaline-muscovite granites, crystallized as texturally diverse batches covering equigranular, serial porphyritic, and hiatal porphyritic fine- to coarse-grained types. All granite samples exhibit straight to concave-up CSDs in the natural log of population density vs. crystal size projection. Straight CSDs were only found in fine-grained biotite-rich granites representing early crystallizing roof facies of the batholith. For all other samples, the slope decreases from -65 to nearly 0 mm-1 as grain size increases. The curvature can result from superposition of two quasilinear segments. It cannot be produced by two separate crystallization events because the population of larger grains is about 10 times more abundant by volume than the fine one. Instead, we propose that the concave-up CSDs developed in situ, with enhanced nucleation and/or reduced growth rates during the final stage of solidification. Spatial analysis and measurements of contact relationships reveal significant clustering of crystals except near the roof of the batholith. The clustering index decreases to 0.6 for the smallest crystals (random = 1), Ripley's Ľ-function reaches 0.8 mm, and the clusters are mineral sensitive: pairs of like phases appear to be more clustered than the unlike pairs. The

  18. Homogeneous nucleation and microstructure evolution in million-atom molecular dynamics simulation.

    PubMed

    Shibuta, Yasushi; Oguchi, Kanae; Takaki, Tomohiro; Ohno, Munekazu

    2015-08-27

    Homogeneous nucleation from an undercooled iron melt is investigated by the statistical sampling of million-atom molecular dynamics (MD) simulations performed on a graphics processing unit (GPU). Fifty independent instances of isothermal MD calculations with one million atoms in a quasi-two-dimensional cell over a nanosecond reveal that the nucleation rate and the incubation time of nucleation as functions of temperature have characteristic shapes with a nose at the critical temperature. This indicates that thermally activated homogeneous nucleation occurs spontaneously in MD simulations without any inducing factor, whereas most previous studies have employed factors such as pressure, surface effect, and continuous cooling to induce nucleation. Moreover, further calculations over ten nanoseconds capture the microstructure evolution on the order of tens of nanometers from the atomistic viewpoint and the grain growth exponent is directly estimated. Our novel approach based on the concept of "melting pots in a supercomputer" is opening a new phase in computational metallurgy with the aid of rapid advances in computational environments.

  19. Direct Calculation of the Rate of Homogeneous Ice Nucleation for a Molecular Model of Water

    NASA Astrophysics Data System (ADS)

    Haji-Akbari, Amir; Debenedetti, Pablo

    Ice formation is ubiquitous in nature, with important consequences in many systems and environments. However, its intrinsic kinetics and mechanism are difficult to discern with experiments. Molecular simulations of ice nucleation are also challenging due to sluggish structural relaxation and the large nucleation barriers, and direct calculations of homogeneous nucleation rates have only been achieved for mW, a monoatomic coarse-grained model of water. For the more realistic molecular models, only indirect estimates have been obtained by assuming the validity of classical nucleation theory. Here, we use a coarse-grained variant of a path sampling approach known as forward-flux sampling to perform the first direct calculation of the homogeneous nucleation rate for TIP4P/Ice, which is the most accurate water model for studying ice polymorphs. By using a novel topological order parameter, we are able to identify a freezing mechanism that involves a competition between cubic and hexagonal ice polymorphs. In this competition, cubic ice wins as its growth leads to more compact crystallites

  20. Examination of surface nucleation during the growth of long alkane crystals by molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Bourque, Alexander; Rutledge, Gregory

    2015-03-01

    Crystal growth from the melt of n-pentacontane (C50) was studied by molecular dynamics simulation using a validated united atom model. By quenching below the melting temperature of C50 (370 K), propagation of the crystal growth front into the C50 melt from a crystalline polyethylene surface was observed. By tracking the location of the midpoint in the orientational order parameter profile between the crystal and melt, crystal growth rates between 0.015-0.040 m/s were observed, for quench depths of 10 to 70 K below the melting point. In this work, surface nucleation is identified with the formation of 2D clusters of crystalline sites within layers parallel to the propagating growth front, by analogy to the formation of 3D clusters in primary, homogeneous nucleation. These surface nucleation events were tracked over several layers and numerous simulations, and a mean first passage time analysis was employed to estimate critical nucleus sizes, induction times and rates for surface nucleation. Based on new insights provided by the detailed molecular trajectories obtained from simulation, the classical theory proposed by Lauritzen and Hoffman is re-examined.

  1. Prediction of the homogeneous droplet nucleation by the density gradient theory and PC-SAFT equation of state

    NASA Astrophysics Data System (ADS)

    Planková, Barbora; Hrubý, Jan; Vinš, Václav

    2013-05-01

    We combined the density gradient theory (DGT) with the PC-SAFT and Peng-Robinson equations of state to model the homogeneous droplet nucleation and compared it to the classical nucleation theory (CNT) and experimental data. We also consider the effect of capillary waves on the surface tension. DGT predicts nucleation rates smaller than the CNT and slightly improves the temperature-dependent deviation of the predicted and experimental nucleation rates.

  2. Binary homogeneous nucleation: Temperature and relative humidity fluctuations and non-linearity

    SciTech Connect

    Easter, R.C.; Peters, L.K.

    1993-01-01

    This report discusses binary homogeneous nucleation involving H{sub 2}SO{sub 4} and water vapor is thought to be the primary mechanism for new particle formation in the marine boundary layer. Temperature, relative humidity, and partial pressure of H{sub 2}SO{sub 4} vapor are the most important parameters in fixing the binary homogeneous nucleation rate in the H{sub 2}SO{sub 4}/H{sub 2}O system. The combination of thermodynamic calculations and laboratory experiments indicates that this rate varies roughly as the tenth power of the saturation ratio of H{sub 2}SO{sub 4} vapor. Furthermore, the vapor pressure of H{sub 2}SO{sub 4} is a function of temperature, and similar dependencies of the binary homogeneous nucleation rate on relative humidity can be noted as well. These factors thus introduce strong non-linearities into the system, and fluctuations of temperature, relative humidity, and H{sub 2}SO{sub 4} vapor concentrations about mean values may strongly influence the nucleation rate measured in the atmosphere.

  3. A new method to measure homogeneous nucleation rates in shock tubes

    NASA Technical Reports Server (NTRS)

    Peters, F.

    1983-01-01

    The centered expansion wave of a shock tube is utilized to expand and supersaturate a condensable vapor in small concentration in an inert carrier gas. The supersaturated state, located at the rear of the expansion wave, is preserved for a controlled period and then terminated by a recompressing shock wave. During the period of supersaturation, condensation nuclei are formed homogeneously. The nucleation rate is measured as a function of supersaturation by a Mie-light scattering technique. The method is tested using water and the results are compared with classical nucleation theory.

  4. Two-Step Mechanism of Homogeneous Nucleation of Sickle Cell Hemoglobin Polymers

    PubMed Central

    Galkin, Oleg; Pan, Weichun; Filobelo, Luis; Hirsch, Rhoda Elison; Nagel, Ronald L.; Vekilov, Peter G.

    2007-01-01

    Sickle cell anemia is a debilitating genetic disease that affects hundreds of thousands of babies born each year worldwide. Its primary pathogenic event is the polymerization of a mutant, sickle cell, hemoglobin (HbS); and this is one of a line of diseases (Alzheimer's, Huntington's, prion, etc.) in which nucleation initiates pathophysiology. We show that the homogeneous nucleation of HbS polymers follows a two-step mechanism with metastable dense liquid clusters serving as precursor to the ordered nuclei of the HbS polymer. The evidence comes from data on the rates of fiber nucleation and growth and nucleation delay times, the interaction of fibers with polarized light, and mesoscopic metastable HbS clusters in solution. The presence of a precursor in the HbS nucleation mechanism potentially allows low-concentration solution components to strongly affect the nucleation kinetics. The variations of these concentrations in patients might account for the high variability of the disease in genetically identical patients. In addition, these components can potentially be utilized for control of HbS polymerization and treatment of the disease. PMID:17449671

  5. Homogeneous two-dimensional nucleation of guest-free silicon clathrates

    NASA Astrophysics Data System (ADS)

    Lü, Yong jun

    2015-01-01

    The difficulty in synthesizing guest-free semiconductor clathrates complicates the process of determining how these cage-like structures form. This work studies the microscopic mechanism of the nucleation of guest-free Si136 clathrate using molecular dynamics simulations with the Stillinger-Weber potential. The homogeneous nucleation of Si136, which is realized in a narrow negative pressure range before liquid cavitation, exhibits the characteristic feature of the two-dimensional (2D) mode. The critical nucleus is composed of one to two five-membered rings, and the nucleation barrier is close to 1 kBT. According to a thermodynamic model based on atomistic nucleation theory, the effective binding energy associated with the formation of 2D critical nuclei is significantly low, which is responsible for the low nucleation barrier of Si136 clathrate. In the post-nucleation period, the critical nucleus preferentially grows into a dodecahedron, and the latter continuously grows with sharing face along <1 1 0>.

  6. Homogenous nucleation of sulfuric acid and water at atmospherically relevant conditions

    NASA Astrophysics Data System (ADS)

    Brus, D.; Neitola, K.; Petäjä, T.; Vanhanen, J.; Hyvärinen, A.-P.; Sipilä, M.; Paasonen, P.; Lihavainen, H.; Kulmala, M.

    2010-11-01

    In this study the homogeneous nucleation rates of sulfuric acid and water were measured by using a flow tube technique. The goal was to directly compare particle formation rates obtained from atmospheric measurements with nucleation rates of freshly nucleated particles measured with particle size magnifier (PSM) which has detection efficiency of unity for particles having mobility diameter of 1.5 nm. The gas phase sulfuric acid concentration in this study was measured with the chemical ionization mass spectrometer (CIMS), commonly used in field measurements. The wall losses of sulfuric acid were estimated from measured concentration profiles along the flow tube. The initial concentrations of sulfuric acid estimated from loss measurements ranged from 108 to 3×109 molecules cm-3. The nucleation rates obtained in this study cover about three orders of magnitude from 10-1 to 102 cm3 s-1 for commercial ultrafine condensation particle counter (UCPC) TSI model 3025A and from 101 to 104 cm3 s-1 for PSM. The nucleation rates and the slopes (dlnJ/dln[H2SO4]) show satisfactory agreement when compared to empirical kinetic and activation models and the latest atmospheric nucleation data.

  7. Homogeneous nucleation and growth in supersaturated zinc vapor investigated by molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Römer, F.; Kraska, T.

    2007-12-01

    Homogeneous nucleation and growth of zinc from supersaturated vapor are investigated by nonequilibrium molecular dynamics simulations in the temperature range from 400to800K and for a supersaturation ranging from logS =2 to 11. Argon is added to the vapor phase as carrier gas to remove the latent heat from the forming zinc clusters. A new parametrization of the embedded atom method for zinc is employed for the interaction potential model. The simulation data are analyzed with respect to the nucleation rates and the critical cluster sizes by two different methods, namely, the threshold method of Yasuoka and Matsumoto [J. Chem. Phys. 109, 8451 (1998)] and the mean first passage time method for nucleation by Wedekind et al. [J. Chem. Phys. 126, 134103 (2007)]. The nucleation rates obtained by these methods differ approximately by one order of magnitude. Classical nucleation theory fails to describe the simulation data as well as the experimental data. The size of the critical cluster obtained by the mean first passage time method is significantly larger than that obtained from the nucleation theorem.

  8. Screening of nucleation conditions using levitated drops for protein crystallization.

    PubMed

    Santesson, Sabina; Cedergren-Zeppezauer, Eila S; Johansson, Thomas; Laurell, Thomas; Nilsson, Johan; Nilsson, Staffan

    2003-04-01

    The growth of suitable protein crystals is an essential step in the structure determination of a protein by X-ray crystallography. At present, crystals are mostly grown using trial-and-error procedures, and protocols that rapidly screen for the crystal nucleation step are rare. Presented here is an approach to minimize the consumption of precious protein material while searching for the nucleation conditions. Acoustically levitated drops of known protein concentration (0.25-1.5-microL volumes) are injected with crystallizing agents using piezoelectric flow-through dispensers (ejecting 50-100-pL droplets at 1-9000 droplets/s). A restricted number of crystallizing agents representing three classes are used: poly(ethylene glycol), salts, and the viscous alcohol 2-methyl 2,4-pentanediol. From a digitized picture of the levitated drop volume, calculations are performed giving the concentrations of all components in the drop at any time during a "precipitation experiment". Supersaturation is the prerequisite for crystal nucleation, and protein precipitation indicates high supersaturation. A light source illuminates the levitated drop, and protein precipitation is monitored using right-angle light scattering. On the basis of these intensity measurements and the volume determination, precipitation diagrams for each crystallizing agent are constructed that give the protein/crystallizing agent concentration boundaries between the minimum and the maximum detectable protein precipitation. Guided by the concentration values obtained from such plots, when approaching the supersaturation region, separate crystallization drops are mixed and allowed to equilibrate under paraffin oil. At conditions in which microcrystals can be observed, the nucleation tendency of the macromolecule is confirmed. Optimization of crystallization conditions can then follow. Proteins tested include alcohol dehydrogenase and D-serine dehydratase. Alcohol dehydrogenase, known to crystallize easily, was

  9. Shear effects on crystal nucleation in colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Cerdà, Juan J.; Sintes, Tomás; Holm, C.; Sorensen, C. M.; Chakrabarti, A.

    2008-09-01

    Extensive two-dimensional Langevin dynamics simulations are used to determine the effect of steady shear flows on the crystal nucleation kinetics of charge stabilized colloids and colloids whose pair potential possess an attractive shallow well of a few kBT ’s (attractive colloids). Results show that in both types of systems small amounts of shear speeds up the crystallization process and enhances the quality of the growing crystal significantly. Moderate shear rates, on the other hand, destroy the ordering in the system. The very high shear rate regime where a reentering transition to the ordered state could exist is not considered in this work. In addition to the crystal nucleation phenomena, the analysis of the transport properties and the characterization of the steady state regime under shear are performed.

  10. Homogeneous nucleation rate measurements of 1-propanol in helium: the effect of carrier gas pressure.

    PubMed

    Brus, David; Zdímal, Vladimír; Stratmann, Frank

    2006-04-28

    Kinetics of homogeneous nucleation in supersaturated vapor of 1-propanol was studied using an upward thermal diffusion cloud chamber. Helium was used as a noncondensable carrier gas and the influence of its pressure on observed nucleation rates was investigated. The isothermal nucleation rates were determined by a photographic method that is independent on any nucleation theory. In this method, the trajectories of growing droplets are recorded using a charge coupled device camera and the distribution of local nucleation rates is determined by image analysis. The nucleation rate measurements of 1-propanol were carried out at four isotherms 260, 270, 280, and 290 K. In addition, the pressure dependence was investigated on the isotherms 290 K (50, 120, and 180 kPa) and 280 K (50 and 120 kPa). The isotherm 270 K was measured at 25 kPa and the isotherm 260 K at 20 kPa. The experiments confirm the earlier observations from several thermal diffusion chamber investigations that the homogeneous nucleation rate of 1-propanol tends to increase with decreasing total pressure in the chamber. In order to reduce the possibility that the observed phenomenon is an experimental artifact, connected with the generally used one-dimensional description of transfer processes in the chamber, a recently developed two-dimensional model of coupled heat, mass, and momentum transfer inside the chamber was used and results of both models were compared. It can be concluded that the implementation of the two-dimensional model does not explain the observed effect. Furthermore the obtained results were compared both to the predictions of the classical theory and to the results of other investigators using different experimental devices. Plotting the experimental data on the so-called Hale plot shows that our data seem to be consistent both internally and also with the data of others. Using the nucleation theorem the critical cluster sizes were obtained from the slopes of the individual isotherms

  11. Nucleation barriers in tetrahedral liquids spanning glassy and crystallizing regimes.

    PubMed

    Saika-Voivod, Ivan; Romano, Flavio; Sciortino, Francesco

    2011-09-28

    Crystallization and vitrification of tetrahedral liquids are important both from a fundamental and a technological point of view. Here, we study via extensive umbrella sampling Monte Carlo computer simulations the nucleation barriers for a simple model for tetrahedral patchy particles in the regime where open tetrahedral crystal structures (namely, cubic and hexagonal diamond and their stacking hybrids) are thermodynamically stable. We show that by changing the angular bond width, it is possible to move from a glass-forming model to a readily crystallizing model. From the shape of the barrier we infer the role of surface tension in the formation of the crystalline clusters. Studying the trends of the nucleation barriers with the temperature and the patch width, we are able to identify an optimal value of the patch size that leads to easy nucleation. Finally, we find that the nucleation barrier is the same, within our numerical precision, for both diamond crystals and for their stacking forms. © 2011 American Institute of Physics

  12. Homogeneous nucleation of water: From vapor to supercooled droplets to ice

    NASA Astrophysics Data System (ADS)

    Wölk, J.; Wyslouzil, B. E.; Strey, R.

    2013-05-01

    We provide a brief overview of the extensive scientific research that has been conducted to determine the degree to which pure water can be supercooled and the rates at which the relevant phase transitions occur. Beginning with condensation, we present the homogeneous vapor - liquid nucleation rates measured over 20 orders of magnitude with a variety of experimental devices. Some of the experimental methods used to examine nucleation from the vapor phase can also be used to study freezing. In particular, using a supersonic nozzle (SSN) apparatus we have followed the condensation and subsequent freezing of pure water droplets by combining our normal pressure trace measurements (PTM) with both small angle Xray scattering (SAXS) and Fourier transform infrared (FTIR) spectroscopy. The time dependence of the fraction of frozen droplets yields the volume based nucleation rates for the freezing transition, 7.66ṡ1023 < Jice/cm-3s-1 < 4.23ṡ1024, confirming and extending those reported in the literature.

  13. Modelling binary homogeneous nucleation of water-sulfuric acid vapours: parameterisation for high temperature emissions.

    PubMed

    Vehkamäki, H; Kulmala, M; Lehtinen, K E J; Noppel, M

    2003-08-01

    Particles formed in the automobile exhaust might form a significant fraction of fine particles in urban air. We have developed a model and produced parametrizations for predicting the particle formation rate at exhaust conditions. We studied the formation in the mixture of water and sulfuric acid vapors and at temperatures between 300 and 400 K. A thermodynamically consistent version of the classical binary homogeneous nucleation model was used. The needed thermodynamical input data (vapor pressures, chemical activities, surface tensions, densities) are carefully investigated and utilized in thermodynamically consistent way. The obtained nucleation rates are parametrized in order to be able to use this nucleation model in aerosol dynamic models, exhaust models, or other process models. The parametrization reduces computational time at least by a factor of 500.

  14. Homogeneous nucleation and droplet growth in nitrogen. M.S. Thesis

    NASA Technical Reports Server (NTRS)

    Dotson, E. H.

    1983-01-01

    A one dimensional computer model of the homogeneous nucleation process and growth of condensate for nitrogen flows over airfoils is developed to predict the onset of condensation and thus to be able to take advantage of as much of Reynolds capability of cryogenic tunnels as possible. Homogeneous nucleation data were taken using a DFVLR CAST-10 airfoil in the 0.3-Meter Transonic Cryogenic Tunnel and are used to evaluate the classical liquid droplet theory and several proposed corrections to it. For predicting liquid nitrogen condensation effects, use of the arbitrary Tolman constant of 0.25 x 250 billionth m or the Reiss or Kikuchi correction agrees with the CAST-10 data. Because no solid nitrogen condensation were found experimentally during the CAST-10 experiments, earlier nozzle data are used to evaluate corrections to the classical liquid droplet theory in the lower temperature regime. A theoretical expression for the surface tension of solid nitrogen is developed.

  15. Crystal nucleation and glass formation in metallic alloy melts

    NASA Technical Reports Server (NTRS)

    Spaepen, F.

    1984-01-01

    Homogeneous nucleation, containerless solidification, and bulk formation of metallic glasses are discussed. Homogeneous nucleation is not a limiting factor for metallic glass formation at slow cooling rates if the reduced glass transition temperature is high enough. Such glasses can be made in bulk if heterogeneous nucleants are removed. Containerless processing eleminates potential sources of nucleants, but as drop tube experiments on the Pd-Si alloys show, the free surface may still be a very effective heterogeneous nucleant. Combination of etching and heating in vacuum or fluxing can be effective for cleaning fairly large ingots of nucleants. Reduced gravity processing has a potentially useful role in the fluxing technique, for example to keep large metallic ingots surrounded by a low density, low fluidity flux if this proved difficult under ground conditions. For systems where heterogeneous nucleants in the bulk of the ingot need gravity to segregate to the flux-metal interface, reduced gravity processing may not be appropriate for bulk glass formation.

  16. Using Microfluidics to Decouple Nucleation and Growth of Protein Crystals.

    PubMed

    Shim, Jung-Uk; Cristobal, Galder; Link, Darren R; Thorsen, Todd; Fraden, Seth

    2007-01-01

    A high throughput, low volume microfluidic device has been designed to decouple the physical processes of protein crystal nucleation and growth. This device, called the Phase Chip, is constructed out of poly(dimethylsiloxane) (PDMS) elastomer. One of the Phase Chip's innovations is to exploit surface tension forces to guide each drop to a storage chamber. We demonstrate that nanoliter water-in-oil drops of protein solutions can be rapidly stored in individual wells thereby allowing the screening of 1000 conditions while consuming a total of only 10 mug protein on a 20 cm(2) chip. Another significant advance over current microfluidic devices is that each well is in contact with a reservoir via a dialysis membrane through which only water and other low molecular weight organic solvents can pass, but not salt, polymer, or protein. This enables the concentration of all solutes in a solution to be reversibly, rapidly, and precisely varied in contrast to current methods, such as the free interface diffusion or sitting drop methods, which are irreversible. The Phase Chip operates by first optimizing conditions for nucleation by using dialysis to supersaturate the protein solution, which leads to nucleation of many small crystals. Next, conditions are optimized for crystal growth by using dialysis to reduce the protein and precipitant concentrations, which leads small crystals to dissolve while simultaneously causing only the largest ones to grow, ultimately resulting in the transformation of many small, unusable crystals into a few large ones.

  17. A Model for Tetragonal Lysozyme Crystal Nucleation and Growth

    NASA Technical Reports Server (NTRS)

    Pusey, Marc L.; Curreri, Peter A. (Technical Monitor)

    2002-01-01

    Macromolecular crystallization is a complex process, involving a system that typically has 5 or more components (macromolecule, water, buffer + counter ion, and precipitant). Whereas small molecules have only a few contacts in the crystal lattice, macromolecules generally have 10's or even 100's of contacts between molecules. These can range from hydrogen bonds (direct or water-mediated), through van der Waals, hydrophobic, salt bridges, and ion-mediated contacts. The latter interactions are stronger and require some specificity in the molecular alignment, while the others are weaker, more prevalent, and more promiscuous, i.e., can be readily broken and reformed between other sites. Formation of a consistent, ordered, 3D structure may be difficult or impossible in the absence of any or presence of too many strong interactions. Further complicating the process is the inherent structural asymmetry of monomeric (single chain) macromolecules. The process of crystal nucleation and growth involves the ordered assembly of growth units into a defined 3D lattice. We suggest that for many macromolecules, particularly those that are monomeric, this involves a preliminary solution-phase assembly process into a growth unit having some symmetry prior to addition to the lattice, recapitulating the initial stages of the nucleation process. If this model is correct then fluids and crystal growth models assuming a strictly monodisperse nutrient solution need to be revised. This model has been developed from experimental evidence based upon face growth rate, AFM, and fluorescence energy transfer data for the nucleation and growth of tetragonal lysozyme crystals.

  18. A Model for Tetragonal Lysozyme Crystal Nucleation and Growth

    NASA Technical Reports Server (NTRS)

    Pusey, Marc L.; Curreri, Peter A. (Technical Monitor)

    2002-01-01

    Macromolecular crystallization is a complex process, involving a system that typically has 5 or more components (macromolecule, water, buffer + counter ion, and precipitant). Whereas small molecules have only a few contacts in the crystal lattice, macromolecules generally have 10's or even 100's of contacts between molecules. These can range from hydrogen bonds (direct or water-mediated), through van der Waals, hydrophobic, salt bridges, and ion-mediated contacts. The latter interactions are stronger and require some specificity in the molecular alignment, while the others are weaker, more prevalent, and more promiscuous, i.e., can be readily broken and reformed between other sites. Formation of a consistent, ordered, 3D structure may be difficult or impossible in the absence of any or presence of too many strong interactions. Further complicating the process is the inherent structural asymmetry of monomeric (single chain) macromolecules. The process of crystal nucleation and growth involves the ordered assembly of growth units into a defined 3D lattice. We suggest that for many macromolecules, particularly those that are monomeric, this involves a preliminary solution-phase assembly process into a growth unit having some symmetry prior to addition to the lattice, recapitulating the initial stages of the nucleation process. If this model is correct then fluids and crystal growth models assuming a strictly monodisperse nutrient solution need to be revised. This model has been developed from experimental evidence based upon face growth rate, AFM, and fluorescence energy transfer data for the nucleation and growth of tetragonal lysozyme crystals.

  19. Cavitation in a metallic liquid: Homogeneous nucleation and growth of nanovoids

    SciTech Connect

    Cai, Y.; Wu, H. A.; Luo, S. N.

    2014-06-07

    Large-scale molecular dynamics (MD) simulations are performed to investigate homogeneous nucleation and growth of nanovoids during cavitation in liquid Cu. We characterize in detail the atomistic cavitation processes by following the temporal evolution of cavities or voids, analyze the nucleation behavior with the mean first-passage time (MFPT) and survival probability (SP) methods, and discuss the results against classical nucleation theory (CNT), the Tolman equation for surface energy, independent calculation of surface tension via integrating the stress profiles, the Johnson-Mehl-Avrami (JMA) growth law, and the power law for nucleus size distributions. Cavitation in this representative metallic liquid is a high energy barrier Poisson processes, and the steady-state nucleation rates obtained from statistical runs with the MFPT and SP methods are in agreement. The MFPT method also yields the critical nucleus size and the Zeldovich factor. Fitting with the Tolman's equation to the MD simulations yields the surface energy of a planar interface (∼0.9 J m{sup −2}) and the Tolman length (0.4–0.5 Å), and those values are in accord with those from integrating the stress profiles of a planar interface. Independent CNT predictions of the nucleation rate (10{sup 33−34} s{sup −1} m{sup −3}) and critical size (3–4 Å in radius) are in agreement with the MFPT and SP results. The JMA law can reasonably describe the nucleation and growth process. The size distribution of subcritical nuclei appears to follow a power law with an exponent decreasing with increasing tension owing to coupled nucleation and growth, and that of the supercritical nuclei becomes flattened during further stress relaxation due to void coalescence.

  20. Crystal nucleation in glass-forming alloy and pure metal melts under containerless and vibrationless conditions

    NASA Technical Reports Server (NTRS)

    Spaepen, F.; Turnbull, D.

    1982-01-01

    The undercooling behavior of large spheroids of Pd40Ni40P40 was investigated. By surface etching, supporting the specimens on a fused silica substrate, and successive heating and cooling, crystallization can be eliminated, presumable due to the removal of surface heterogeneities. By this method samples up to 3.2g with a 0.53 mm minor diameter, were made entirely glassy, except for some superficial crystals comprising less than 0.5% of the volume. These experiments show that a cooling rate of approximately 1 K/sec is adequate to avoid copious homogeneous nucleation in the alloy, and that by eliminating or reducing the effectiveness of heterogeneous nucleation sites, it is possible to form bulk samples of this metallic glass with virtually unlimited dimensions.

  1. Soot Aerosol Particles as Cloud Condensation Nuclei: from Ice Nucleation Activity to Ice Crystal Morphology

    NASA Astrophysics Data System (ADS)

    Pirim, Claire; Ikhenazene, Raouf; Ortega, Isamel Kenneth; Carpentier, Yvain; Focsa, Cristian; Chazallon, Bertrand; Ouf, François-Xavier

    2016-04-01

    Emissions of solid-state particles (soot) from engine exhausts due to incomplete fuel combustion is considered to influence ice and liquid water cloud droplet activation [1]. The activity of these aerosols would originate from their ability to be important centers of ice-particle nucleation, as they would promote ice formation above water homogeneous freezing point. Soot particles are reported to be generally worse ice nuclei than mineral dust because they activate nucleation at higher ice-supersaturations for deposition nucleation and at lower temperatures for immersion freezing than ratios usually expected for homogeneous nucleation [2]. In fact, there are still numerous opened questions as to whether and how soot's physico-chemical properties (structure, morphology and chemical composition) can influence their nucleation ability. Therefore, systematic investigations of soot aerosol nucleation activity via one specific nucleation mode, here deposition nucleation, combined with thorough structural and compositional analyzes are needed in order to establish any association between the particles' activity and their physico-chemical properties. In addition, since the morphology of the ice crystals can influence their radiative properties [3], we investigated their morphology as they grow over both soot and pristine substrates at different temperatures and humidity ratios. In the present work, Combustion Aerosol STandart soot samples were produced from propane using various experimental conditions. Their nucleation activity was studied in deposition mode (from water vapor), and monitored using a temperature-controlled reactor in which the sample's relative humidity is precisely measured with a cryo-hygrometer. Formation of water/ice onto the particles is followed both optically and spectroscopically, using a microscope coupled to a Raman spectrometer. Vibrational signatures of hydroxyls (O-H) emerge when the particle becomes hydrated and are used to characterize ice

  2. Nucleation and growth control in protein crystallization

    NASA Technical Reports Server (NTRS)

    Rosenberger, Franz; Nyce, Thomas A.; Meehan, Edward J.; Sowers, Jennifer W.; Monaco, Lisa A.

    1990-01-01

    The five topics summarized in this final report are as follows: (1) a technique for the expedient, semi-automated determination of protein solubilities as a function of temperature and application of this technique to proteins other than lysozyme; (2) a small solution cell with adjustable temperature gradients for the growth of proteins at a predetermined location through temperature programming; (3) a microscopy system with image storage and processing capability for high resolution optical studies of temperature controlled protein growth and etching kinetics; (4) growth experiments with lysozyme in thermosyphon flow ; and (5) a mathematical model for the evolution of evaporation/diffusion induced concentration gradients in the hanging drop protein crystallization technique.

  3. Exploring Carbon Nanomaterial Diversity for Nucleation of Protein Crystals

    NASA Astrophysics Data System (ADS)

    Govada, Lata; Leese, Hannah S.; Saridakis, Emmanuel; Kassen, Sean; Chain, Benny; Khurshid, Sahir; Menzel, Robert; Hu, Sheng; Shaffer, Milo S. P.; Chayen, Naomi E.

    2016-02-01

    Controlling crystal nucleation is a crucial step in obtaining high quality protein crystals for structure determination by X-ray crystallography. Carbon nanomaterials (CNMs) including carbon nanotubes, graphene oxide, and carbon black provide a range of surface topographies, porosities and length scales; functionalisation with two different approaches, gas phase radical grafting and liquid phase reductive grafting, provide routes to a range of oligomer functionalised products. These grafted materials, combined with a range of controls, were used in a large-scale assessment of the effectiveness for protein crystal nucleation of 20 different carbon nanomaterials on five proteins. This study has allowed a direct comparison of the key characteristics of carbon-based nucleants: appropriate surface chemistry, porosity and/or roughness are required. The most effective solid system tested in this study, carbon black nanoparticles functionalised with poly(ethylene glycol) methyl ether of mean molecular weight 5000, provides a novel highly effective nucleant, that was able to induce crystal nucleation of four out of the five proteins tested at metastable conditions.

  4. Exploring Carbon Nanomaterial Diversity for Nucleation of Protein Crystals

    PubMed Central

    Govada, Lata; Leese, Hannah S.; Saridakis, Emmanuel; Kassen, Sean; Chain, Benny; Khurshid, Sahir; Menzel, Robert; Hu, Sheng; Shaffer, Milo S. P.; Chayen, Naomi E.

    2016-01-01

    Controlling crystal nucleation is a crucial step in obtaining high quality protein crystals for structure determination by X-ray crystallography. Carbon nanomaterials (CNMs) including carbon nanotubes, graphene oxide, and carbon black provide a range of surface topographies, porosities and length scales; functionalisation with two different approaches, gas phase radical grafting and liquid phase reductive grafting, provide routes to a range of oligomer functionalised products. These grafted materials, combined with a range of controls, were used in a large-scale assessment of the effectiveness for protein crystal nucleation of 20 different carbon nanomaterials on five proteins. This study has allowed a direct comparison of the key characteristics of carbon-based nucleants: appropriate surface chemistry, porosity and/or roughness are required. The most effective solid system tested in this study, carbon black nanoparticles functionalised with poly(ethylene glycol) methyl ether of mean molecular weight 5000, provides a novel highly effective nucleant, that was able to induce crystal nucleation of four out of the five proteins tested at metastable conditions. PMID:26843366

  5. Polymorphism, crystal nucleation and growth in the phase-field crystal model in 2D and 3D

    NASA Astrophysics Data System (ADS)

    Tóth, Gyula I.; Tegze, György; Pusztai, Tamás; Tóth, Gergely; Gránásy, László

    2010-09-01

    We apply a simple dynamical density functional theory, the phase-field crystal (PFC) model of overdamped conservative dynamics, to address polymorphism, crystal nucleation, and crystal growth in the diffusion-controlled limit. We refine the phase diagram for 3D, and determine the line free energy in 2D and the height of the nucleation barrier in 2D and 3D for homogeneous and heterogeneous nucleation by solving the respective Euler-Lagrange (EL) equations. We demonstrate that, in the PFC model, the body-centered cubic (bcc), the face-centered cubic (fcc), and the hexagonal close-packed structures (hcp) compete, while the simple cubic structure is unstable, and that phase preference can be tuned by changing the model parameters: close to the critical point the bcc structure is stable, while far from the critical point the fcc prevails, with an hcp stability domain in between. We note that with increasing distance from the critical point the equilibrium shapes vary from the sphere to specific faceted shapes: rhombic dodecahedron (bcc), truncated octahedron (fcc), and hexagonal prism (hcp). Solving the equation of motion of the PFC model supplied with conserved noise, solidification starts with the nucleation of an amorphous precursor phase, into which the stable crystalline phase nucleates. The growth rate is found to be time dependent and anisotropic; this anisotropy depends on the driving force. We show that due to the diffusion-controlled growth mechanism, which is especially relevant for crystal aggregation in colloidal systems, dendritic growth structures evolve in large-scale isothermal single-component PFC simulations. An oscillatory effective pair potential resembling those for model glass formers has been evaluated from structural data of the amorphous phase obtained by instantaneous quenching. Finally, we present results for eutectic solidification in a binary PFC model.

  6. The mechanism of deceleration of nucleation and crystal growth by the small addition of transition metals to lithium disilicate glasses.

    PubMed

    Thieme, Katrin; Avramov, Isak; Rüssel, Christian

    2016-05-06

    The addition of small amounts of niobium or tantalum oxide to lithium disilicate glass provokes a drastic decrease of the steady-state nucleation rates and the crystal growth velocities. The viscosity of the residual glassy matrix is considered as a function of the crystallization degree in the course of a non-isothermal crystallization. For simplification, a homogeneous distribution of the added oxides in the glass matrix is assumed. While the viscosity initially decreases, it significantly increases again for higher crystallization degrees hindering crystal growth. However, it was shown that the additives are enriched at the crystal interface. Several possible reasons for the inhibition of nucleation and growth kinetics such as viscosity, interfacial energy crystal/glassy phase, thermodynamic driving force or impingement rate are discussed. Since the crystallization front is blocked by the additives the impingement rate is decreased with increasing additive concentration. Since small concentrations of Nb2O5 and Ta2O5 have a drastic effect on the nucleation, these components should be enriched at the interface crystal/glass. This will only take place, if it leads to a decrease in the interfacial energy. Since this effect alone should result in an increase of the nucleation rate, it must be overcompensated by kinetic effects.

  7. The mechanism of deceleration of nucleation and crystal growth by the small addition of transition metals to lithium disilicate glasses

    PubMed Central

    Thieme, Katrin; Avramov, Isak; Rüssel, Christian

    2016-01-01

    The addition of small amounts of niobium or tantalum oxide to lithium disilicate glass provokes a drastic decrease of the steady-state nucleation rates and the crystal growth velocities. The viscosity of the residual glassy matrix is considered as a function of the crystallization degree in the course of a non-isothermal crystallization. For simplification, a homogeneous distribution of the added oxides in the glass matrix is assumed. While the viscosity initially decreases, it significantly increases again for higher crystallization degrees hindering crystal growth. However, it was shown that the additives are enriched at the crystal interface. Several possible reasons for the inhibition of nucleation and growth kinetics such as viscosity, interfacial energy crystal/glassy phase, thermodynamic driving force or impingement rate are discussed. Since the crystallization front is blocked by the additives the impingement rate is decreased with increasing additive concentration. Since small concentrations of Nb2O5 and Ta2O5 have a drastic effect on the nucleation, these components should be enriched at the interface crystal/glass. This will only take place, if it leads to a decrease in the interfacial energy. Since this effect alone should result in an increase of the nucleation rate, it must be overcompensated by kinetic effects. PMID:27150844

  8. The interface of heterogeneous nucleation on single crystal substrates

    NASA Astrophysics Data System (ADS)

    Yang, L.; Xia, M.; Li, J.

    2016-03-01

    Under controlled nucleation process was achieved by solidifying a high purity Al droplet on a single crystal Al2O3 substrate in a high vacuum chamber. The following X-Ray Diffraction (XRD) analysis and measured undercooling prove that the nucleation was triggered by the substrate. Various lattice mismatches between new crystal and substrate (C/S) were obtained through this approach. Combining XRD patterns and high resolution transmission electron microscope analysis we found that the morphology of interface was affected by lattice misfit. An epitaxial layer was found at C/S interface with larger lattice misfit, as in Al(100)//Al2O3(0001) system. Further experiments on introduced alloying element, Sb, into liquid Al shows a suppressed epitaxial layer of Al. Chemical reaction between liquid and substrate also contributes to the formation of the interface. The nucleation of Al on the MgO substrates was actually nucleated on MgAl2O4, chemical reaction product of Al and MgO, rather than MgO.

  9. A simple apparatus for controlling nucleation and size in protein crystal growth

    NASA Technical Reports Server (NTRS)

    Gernert, Kim M.; Smith, Robert; Carter, Daniel C.

    1988-01-01

    A simple device is described for controlling vapor equilibrium in macromolecular crystallization as applied to the protein crystal growth technique commonly referred to as the 'hanging drop' method. Crystal growth experiments with hen egg white lysozyme have demonstrated control of the nucleation rate. Nucleation rate and final crystal size have been found to be highly dependent upon the rate at which critical supersaturation is approached. Slower approaches show a marked decrease in the nucleation rate and an increase in crystal size.

  10. Method and apparatus for nucleating the crystallization of undercooled materials

    DOEpatents

    Benson, David K.; Barret, Peter F.

    1989-01-01

    A method of storing and controlling a release of latent heat of transition of a phase-change material is disclosed. The method comprises trapping a crystallite of the material between two solid objects and retaining it there under high pressure by applying a force to press the two solid objects tightly together. A crystallite of the material is exposed to a quantity of the material that is in a supercooled condition to nucleate the crystallization of the supercooled material.

  11. Direct calculation of ice homogeneous nucleation rate for a molecular model of water

    PubMed Central

    Haji-Akbari, Amir; Debenedetti, Pablo G.

    2015-01-01

    Ice formation is ubiquitous in nature, with important consequences in a variety of environments, including biological cells, soil, aircraft, transportation infrastructure, and atmospheric clouds. However, its intrinsic kinetics and microscopic mechanism are difficult to discern with current experiments. Molecular simulations of ice nucleation are also challenging, and direct rate calculations have only been performed for coarse-grained models of water. For molecular models, only indirect estimates have been obtained, e.g., by assuming the validity of classical nucleation theory. We use a path sampling approach to perform, to our knowledge, the first direct rate calculation of homogeneous nucleation of ice in a molecular model of water. We use TIP4P/Ice, the most accurate among existing molecular models for studying ice polymorphs. By using a novel topological approach to distinguish different polymorphs, we are able to identify a freezing mechanism that involves a competition between cubic and hexagonal ice in the early stages of nucleation. In this competition, the cubic polymorph takes over because the addition of new topological structural motifs consistent with cubic ice leads to the formation of more compact crystallites. This is not true for topological hexagonal motifs, which give rise to elongated crystallites that are not able to grow. This leads to transition states that are rich in cubic ice, and not the thermodynamically stable hexagonal polymorph. This mechanism provides a molecular explanation for the earlier experimental and computational observations of the preference for cubic ice in the literature. PMID:26240318

  12. Direct calculation of ice homogeneous nucleation rate for a molecular model of water.

    PubMed

    Haji-Akbari, Amir; Debenedetti, Pablo G

    2015-08-25

    Ice formation is ubiquitous in nature, with important consequences in a variety of environments, including biological cells, soil, aircraft, transportation infrastructure, and atmospheric clouds. However, its intrinsic kinetics and microscopic mechanism are difficult to discern with current experiments. Molecular simulations of ice nucleation are also challenging, and direct rate calculations have only been performed for coarse-grained models of water. For molecular models, only indirect estimates have been obtained, e.g., by assuming the validity of classical nucleation theory. We use a path sampling approach to perform, to our knowledge, the first direct rate calculation of homogeneous nucleation of ice in a molecular model of water. We use TIP4P/Ice, the most accurate among existing molecular models for studying ice polymorphs. By using a novel topological approach to distinguish different polymorphs, we are able to identify a freezing mechanism that involves a competition between cubic and hexagonal ice in the early stages of nucleation. In this competition, the cubic polymorph takes over because the addition of new topological structural motifs consistent with cubic ice leads to the formation of more compact crystallites. This is not true for topological hexagonal motifs, which give rise to elongated crystallites that are not able to grow. This leads to transition states that are rich in cubic ice, and not the thermodynamically stable hexagonal polymorph. This mechanism provides a molecular explanation for the earlier experimental and computational observations of the preference for cubic ice in the literature.

  13. The Gibbs free energy of homogeneous nucleation: From atomistic nuclei to the planar limit.

    PubMed

    Cheng, Bingqing; Tribello, Gareth A; Ceriotti, Michele

    2017-09-14

    In this paper we discuss how the information contained in atomistic simulations of homogeneous nucleation should be used when fitting the parameters in macroscopic nucleation models. We show how the number of solid and liquid atoms in such simulations can be determined unambiguously by using a Gibbs dividing surface and how the free energy as a function of the number of solid atoms in the nucleus can thus be extracted. We then show that the parameters (the chemical potential, the interfacial free energy, and a Tolman correction) of a model based on classical nucleation theory can be fitted using the information contained in these free-energy profiles but that the parameters in such models are highly correlated. This correlation is unfortunate as it ensures that small errors in the computed free energy surface can give rise to large errors in the extrapolated properties of the fitted model. To resolve this problem we thus propose a method for fitting macroscopic nucleation models that uses simulations of planar interfaces and simulations of three-dimensional nuclei in tandem. We show that when the chemical potentials and the interface energy are pinned to their planar-interface values, more precise estimates for the Tolman length are obtained. Extrapolating the free energy profile obtained from small simulation boxes to larger nuclei is thus more reliable.

  14. The Gibbs free energy of homogeneous nucleation: From atomistic nuclei to the planar limit

    NASA Astrophysics Data System (ADS)

    Cheng, Bingqing; Tribello, Gareth A.; Ceriotti, Michele

    2017-09-01

    In this paper we discuss how the information contained in atomistic simulations of homogeneous nucleation should be used when fitting the parameters in macroscopic nucleation models. We show how the number of solid and liquid atoms in such simulations can be determined unambiguously by using a Gibbs dividing surface and how the free energy as a function of the number of solid atoms in the nucleus can thus be extracted. We then show that the parameters (the chemical potential, the interfacial free energy, and a Tolman correction) of a model based on classical nucleation theory can be fitted using the information contained in these free-energy profiles but that the parameters in such models are highly correlated. This correlation is unfortunate as it ensures that small errors in the computed free energy surface can give rise to large errors in the extrapolated properties of the fitted model. To resolve this problem we thus propose a method for fitting macroscopic nucleation models that uses simulations of planar interfaces and simulations of three-dimensional nuclei in tandem. We show that when the chemical potentials and the interface energy are pinned to their planar-interface values, more precise estimates for the Tolman length are obtained. Extrapolating the free energy profile obtained from small simulation boxes to larger nuclei is thus more reliable.

  15. Overview: Homogeneous nucleation from the vapor phase—The experimental science

    NASA Astrophysics Data System (ADS)

    Wyslouzil, Barbara E.; Wölk, Judith

    2016-12-01

    Homogeneous nucleation from the vapor phase has been a well-defined area of research for ˜120 yr. In this paper, we present an overview of the key experimental and theoretical developments that have made it possible to address some of the fundamental questions first delineated and investigated in C. T. R. Wilson's pioneering paper of 1897 [C. T. R. Wilson, Philos. Trans. R. Soc., A 189, 265-307 (1897)]. We review the principles behind the standard experimental techniques currently used to measure isothermal nucleation rates, and discuss the molecular level information that can be extracted from these measurements. We then highlight recent approaches that interrogate the vapor and intermediate clusters leading to particle formation, more directly.

  16. Minimum free-energy path of homogenous nucleation from the phase-field equation.

    PubMed

    Iwamatsu, Masao

    2009-06-28

    The minimum free-energy path (MFEP) is the most probable route of the nucleation process on the multidimensional free-energy surface. In this study, the phase-field equation is used as a mathematical tool to deduce the MFEP of homogeneous nucleation. We use a simple square-gradient free-energy functional with a quartic local free-energy function as an example and study the time evolution of a single nucleus placed within a metastable environment. The time integration of the phase-field equation is performed using the numerically efficient cell-dynamics method. By monitoring the evolution of the size of the nucleus and the free energy of the system simultaneously, we can easily deduce the free-energy barrier as a function of the size of the sub- and the supercritical nucleus along the MFEP.

  17. Crystal nucleation as the ordering of multiple order parameters

    NASA Astrophysics Data System (ADS)

    Russo, John; Tanaka, Hajime

    2016-12-01

    Nucleation is an activated process in which the system has to overcome a free energy barrier in order for a first-order phase transition between the metastable and the stable phases to take place. In the liquid-to-solid transition, the process occurs between phases of different symmetry, and it is thus inherently a multi-dimensional process, in which all symmetries are broken at the transition. In this Focus Article, we consider some recent studies which highlight the multi-dimensional nature of the nucleation process. Even for a single-component system, the formation of solid crystals from the metastable melt involves fluctuations of two (or more) order parameters, often associated with the decoupling of positional and orientational symmetry breaking. In other words, we need at least two order parameters to describe the free-energy of a system including its liquid and crystalline states. This decoupling occurs naturally for asymmetric particles or directional interactions, focusing here on the case of water, but we will show that it also affects spherically symmetric interacting particles, such as the hard-sphere system. We will show how the treatment of nucleation as a multi-dimensional process has shed new light on the process of polymorph selection, on the effect of external fields on the nucleation process and on glass-forming ability.

  18. Surface design for controlled crystallization: the role of surface chemistry and nanoscale pores in heterogeneous nucleation.

    PubMed

    Diao, Ying; Myerson, Allan S; Hatton, T Alan; Trout, Bernhardt L

    2011-05-03

    Current industrial practice for control of primary nucleation (nucleation from a system without pre-existing crystalline matter) during crystallization from solution involves control of supersaturation generation, impurity levels, and solvent composition. Nucleation behavior remains largely unpredictable, however, due to the presence of container surfaces, dust, dirt, and other impurities that can provide heterogeneous nucleation sites, thus making the control and scale-up of processes that depend on primary nucleation difficult. To develop a basis for the rational design of surfaces to control nucleation during crystallization from solution, we studied the role of surface chemistry and morphology of various polymeric substrates on heterogeneous nucleation using aspirin as a model compound. Nucleation induction time statistics were utilized to investigate and quantify systematically the effectiveness of polymer substrates in inducing nucleation. The nucleation induction time study revealed that poly(4-acryloylmorpholine) and poly(2-carboxyethyl acrylate), each cross-linked by divinylbenzene, significantly lowered the nucleation induction time of aspirin while the other polymers were essentially inactive. In addition, we found the presence of nanoscopic pores on certain polymer surfaces led to order-of-magnitude faster aspirin nucleation rates when compared with surfaces without pores. We studied the preferred orientation of aspirin crystals on polymer films and found the nucleation-active polymer surfaces preferentially nucleated the polar facets of aspirin, guided by hydrogen bonds. A model based on interfacial free energies was also developed which predicted the same trend of polymer surface nucleation activities as indicated by the nucleation induction times.

  19. Crystallization of isoelectrically homogeneous cholera toxin

    SciTech Connect

    Spangler, B.D.; Westbrook, E.M. )

    1989-02-07

    Past difficulty in growing good crystals of cholera toxin has prevented the study of the crystal structure of this important protein. The authors have determined that failure of cholera toxin to crystallize well has been due to its heterogeneity. They have now succeeded in overcoming the problem by isolating a single isoelectric variant of this oligomeric protein (one A subunit and five B subunits). Cholera toxin purified by their procedure readily forms large single crystals. The crystal form has been described previously. They have recorded data from native crystals of cholera toxin to 3.0-{angstrom} resolution with our electronic area detectors. With these data, they have found the orientation of a 5-fold symmetry axis within these crystals, perpendicular to the screw dyad of the crystal. They are now determining the crystal structure of cholera toxin by a combination of multiple heavy-atom isomorphous replacement and density modification techniques, making use of rotational 5-fold averaging of the B subunits.

  20. Nucleation Chemical Physics: From Vapor Phase Clusters to Crystals in Solution

    SciTech Connect

    Kathmann, Shawn M.

    2007-08-03

    Both vapor-phase clusters and condensed-phase crystals are important in a wide variety of fundamental and applied problems in chemical physics. Favorable fluctuations in a supersaturated phase generate clusters of the new phase – exactly how one defines these new clusters as distinct from the mother phase represents a continuing challenge in molecular theories of nucleation. These incipient clusters can form homogeneously within the mother phase or heterogeneously on seeds, dust, impurities, ions, or others stability-inducing atomic/molecular structures (e.g., steps, edges, vacancies, etc.). Upon reaching a critical size the clusters may grow to macroscopic dimensions if enough nucleating material is present in surrounding environment or until relaxation processes dominate bringing the phase transformation to completion. This work was supported by the Chemical and Material Sciences Division, Office of Basic Energy Sciences, Department of Energy. The Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

  1. Nucleation and Convection Effects in Protein Crystal Growth

    NASA Technical Reports Server (NTRS)

    Rosenberger, Franz

    1997-01-01

    Work during the second year under this grant (NAG8-1161) resulted in several major achievements. We have characterized protein impurities as well as microheterogeneities in the proteins hen egg white lysozyme and horse spleen apoferritin, and demonstrated the effects of these impurities on nucleation and crystallization. In particular, the purification of apoferritin resulted in crystals with an X-ray diffraction resolution of better than 1.8 A, i.e. a 1 A improvement over earlier work on the cubic form. Furthermore, we have shown, in association with studies of liquid-liquid phase separation, that depending on the growth conditions, lysozyme can produce all growth morphologies that have been observed with other proteins. Finally, in connection with our experimental and simulation work on growth step bunching, we have developed a system-dependent criterion for advantages and disadvantages of crystallization from solution under reduced gravity. In the following, these efforts are described in some detail.

  2. Nucleation kinetics, crystal growth and optical studies on lithium hydrogen oxalate monohydrate single crystal

    NASA Astrophysics Data System (ADS)

    Chandran, Senthilkumar; Paulraj, Rajesh; Ramasamy, P.

    2017-06-01

    Semi-organic lithium hydrogen oxalate monohydrate non-linear optical single crystals have been grown by slow evaporation solution technique at 40 °C. The nucleation parameters such as critical radius, interfacial tension, and critical free energy change have been evaluated using the experimental data. The solubility and the nucleation curve of the crystal at different temperatures have been analyzed. The crystal has a positive temperature coefficient of solubility. The metastable zone width and induction period have been determined for the aqueous solution growth of lithium hydrogen oxalate monohydrate. The UV-vis-NIR spectrum showed this crystal has high transparency. The photoconductivity studies indicate lithium hydrogen oxalate monohydrate has positive photoconductivity behaviour. The low etch pit density observed on (0 0 1) crystal surface and the high resolution x-ray difraction analysis indicate the good quality of the grown crystals

  3. Toward a molecular theory of homogeneous bubble nucleation: I. Equilibrium embryo definition.

    PubMed

    Torabi, Korosh; Corti, David S

    2013-10-17

    We propose an equilibrium embryo definition for homogeneous bubble nucleation within the pure component superheated Lennard-Jones liquid. The suggested embryo definition serves as an improvement to a previous (n,v) embryo model (Uline and Corti 2007). In that model, the constrained equilibrium between the bubble and the surrounding superheated liquid was maintained by placing n particles within a spherical volume v, without concern for the redundant counting of configurations and the relevance of the model to the dynamics of a nucleation process. To eliminate this redundancy, while only considering those embryos that should most likely appear at a transitional state, we now define the volume of the embryo via the use of a shell particle and only include n particles inside the volume that are deemed to be "vapor-like". The underlying free energy surface of formation of the new (n,v) embryo model is generated via Monte Carlo simulation and also approximately by a suggested density functional theory method. The resulting surface implies that small and locally confined regions of near-zero density serve as precursors initiating homogeneous bubble nucleation. Furthermore, the nonredundant counting of the embryo configurations yields a well-defined and sharp conduit in the free energy surface that directs the initially formed embryos toward the critical nucleus. We discuss how the suggested equilibrium embryo model aids in both the identification of the transitional configurations and calculation of the average number density of the critical nuclei within the superheated liquid phase, which is the focus of the companion paper (DOI 10.1021/jp404151h).

  4. Updated H2SO4-H2O binary homogeneous nucleation look-up tables

    NASA Astrophysics Data System (ADS)

    Yu, Fangqun

    2008-12-01

    The calculated rates of H2SO4-H2O binary homogeneous nucleation (BHN), which is the only nucleation mechanism currently widely used in global aerosol models, are well known to have large uncertainties. Recently, we have reduced the uncertainties in the BHN rates on the basis of a kinetic quasi-unary nucleation (KQUN) model, by taking into account the measured bonding energetics of H2SO4 monomers with hydrated sulfuric acid dimers and trimers. The uncertainties were further reduced by using two independent measurements to constrain the equilibrium constants for monomer hydration. In this paper, we present updated BHN rate look-up tables derived from the improved KQUN model which can be used by anyone to obtain the BHN rates under given conditions. The look-up tables cover a wide range of key parameters that can be found in the atmosphere and laboratory studies, and their usage significantly reduces the computational costs of the BHN rate calculations, which is critical for multidimensional modeling. The look-up tables can also be used by those involved in experiments and field measurements to quickly assess the likeliness of BHN. For quick application, one can obtain the BHN rates and properties of critical clusters by browsing through the tables. A comparison of results based on the look-up tables with those from widely used classical BHN model indicates that, in addition to several orders of magnitude difference in nucleation rates, there also exists substantial difference in the predicted numbers of sulfuric acid molecules in the critical clusters and their dependence on key parameters.

  5. Direct observation of liquid nucleus growth in homogeneous melting of colloidal crystals

    PubMed Central

    Wang, Ziren; Wang, Feng; Peng, Yi; Han, Yilong

    2015-01-01

    The growth behaviour of liquid nucleus is crucial for crystal melting, but its kinetics is difficult to predict and remains challenging in experiment. Here we directly observed the growth of individual liquid nuclei in homogeneous melting of three-dimensional superheated colloidal crystals with single-particle dynamics by video microscopy. The growth rate of nucleus at weak superheating is well fitted by generalizing the Wilson–Frenkel law of crystallization to melting and including the surface tension effects and non-spherical-shape effects. As the degree of superheating increases, the growth rate is enhanced by nucleus shape fluctuation, nuclei coalescence and multimer attachment. The results provide new guidance for the refinement of nucleation theory, especially for the poorly understood strong-superheating regime. The universal Lindemann parameter observed at the superheat limit and solid–liquid interfaces indicates a connection between homogeneous and heterogeneous melting. PMID:25897801

  6. The crystal nucleation theory revisited: The case of 2D colloidal crystals

    NASA Astrophysics Data System (ADS)

    González, A. E.; Ixtlilco-Cortés, L.

    2011-03-01

    Most of the theories and studies of crystallization and crystal nucleation consider the boundaries between the crystallites and the fluid as smooth. The crystallites are the small clusters of atoms, molecules and/or particles with the symmetry of the crystal lattice that, with a slight chance of success, would grow to form the crystal grains. In fact, in the classical nucleation theory, the crystallites are assumed to have a spherical shape (circular in 2D). As far are we are aware, there is only one experimental work [1] on colloidal crystals that founds rough surfaces for the crystallites and for the crystal grains. Motivated by this work, we performed large Kinetic Monte Carlo simulations in 2D, that would follow the eventual growing of a few crystallites to form the crystal grains. The used potential has, besides the impenetrable hard core, a soft core followed by a potential well. We found that indeed the crystallites have a fractal boundary, whose value we were able to obtain. See the figure below of a typical isolated crystallite. We were also able to obtain the critical crystallite size, measured by its number of particles, Nc, and not by any critical radius. The boundaries of the crystals above Nc also have a fractal structure but of a lower value, closer to one. Finally, we also obtained the line tension between the crystallites and the surrounding fluid, as function of temperature and particle diameter, as well as the chemical potential difference between these two phases. In the URL: www.fis.unam.mx˜˜agus˜ there are posted two movies that can be downloaded: (1) 2D_crystal_nucleation.mp4, and (2) 2D_crystal_growth.mp4, that illustrate the crystal nucleation and its further growth.

  7. Crystal growth nucleation and Fermi energy equalization of intrinsic spherical nuclei in glass-forming melts

    NASA Astrophysics Data System (ADS)

    Tournier, Robert F.

    2009-01-01

    The energy saving resulting from the equalization of Fermi energies of a crystal and its melt is added to the Gibbs free-energy change ΔG2ls associated with a crystal formation in glass-forming melts. This negative contribution being a fraction ɛ ls(T) of the fusion heat is created by the electrostatic potential energy -U0 resulting from the electron transfer from the crystal to the melt and is maximum at the melting temperature Tm in agreement with a thermodynamics constraint. The homogeneous nucleation critical temperature T2, the nucleation critical barrier ΔG2ls*/kBT and the critical radius R*2ls are determined as functions of ɛls(T). In bulk metallic glass forming melts, ɛls(T) and T2 only depend on the free-volume disappearance temperature T0l, and ɛls(Tm) is larger than 1 (T0l>Tm/3) in conventional undercooled melts ɛls(Tm) is smaller than 1 (T0l>Tm/3). Unmelted intrinsic crystals act as growth nuclei reducing ΔG2ls*/kBT and the nucleation time. The temperature-time transformation diagrams of Mg65Y10 Cu25, Zr41.2Ti13.8 Cu12.5Ni10Be22.5, Pd43Cu27 Ni10P20, Fe83B17 and Ni melts are predicted using classic nucleation models including time lags in transient nucleation, by varying the intrinsic nucleus contribution to the reduction of ΔG2ls*/kBT. The energy-saving coefficient ɛ nm(T) of an unmelted crystal of radius Rnm is reduced when Rnm LtR*2ls; ɛnm is quantified and corresponds to the first energy level of one s-electron moving in vacuum in the same spherical attractive potential -U0 despite the fact that the charge screening is built by many-body effects.

  8. Crystal growth nucleation and Fermi energy equalization of intrinsic spherical nuclei in glass-forming melts.

    PubMed

    Tournier, Robert F

    2009-02-01

    The energy saving resulting from the equalization of Fermi energies of a crystal and its melt is added to the Gibbs free-energy change ΔG2ls associated with a crystal formation in glass-forming melts. This negative contribution being a fraction ε ls(T) of the fusion heat is created by the electrostatic potential energy -U0 resulting from the electron transfer from the crystal to the melt and is maximum at the melting temperature Tm in agreement with a thermodynamics constraint. The homogeneous nucleation critical temperature T2, the nucleation critical barrier ΔG2ls∗/kBT and the critical radius R∗2ls are determined as functions of εls(T). In bulk metallic glass forming melts, εls(T) and T2 only depend on the free-volume disappearance temperature T0l, and εls(Tm) is larger than 1 (T0l>Tm/3); in conventional undercooled melts εls(Tm) is smaller than 1 (T0l>Tm/3). Unmelted intrinsic crystals act as growth nuclei reducing ΔG2ls∗/kBT and the nucleation time. The temperature-time transformation diagrams of Mg65Y10Cu25, Zr41.2Ti13.8Cu12.5Ni10Be22.5, Pd43Cu27 Ni10P20, Fe83B17 and Ni melts are predicted using classic nucleation models including time lags in transient nucleation, by varying the intrinsic nucleus contribution to the reduction of ΔG2ls∗/kBT. The energy-saving coefficient ε nm(T) of an unmelted crystal of radius Rnm is reduced when Rnm ≪R∗2ls; εnm is quantified and corresponds to the first energy level of one s-electron moving in vacuum in the same spherical attractive potential -U0 despite the fact that the charge screening is built by many-body effects.

  9. Reaction coordinates for the crystal nucleation of colloidal suspensions extracted from the reweighted path ensemble

    NASA Astrophysics Data System (ADS)

    Lechner, Wolfgang; Dellago, Christoph; Bolhuis, Peter G.

    2011-10-01

    We study the mechanisms of the homogeneous crystal nucleation from the supercooled liquid to the crystal phase in the Gaussian core model for colloidal suspensions with the aim to find optimal reaction coordinates. We introduce a set of novel collective variables based on the local structure of particles. By applying likelihood maximization of the committor function for the reweighted path ensemble constructed by replica exchange transition interface sampling, we select the optimal reaction coordinates from the set of collective variables. We find that the size of the cloud of prestructured particles surrounding the crystalline nucleus enhances the description of the transition. Further, we show that the rearrangement of the inner core of the nucleus according to Ostwald's step rule is a separate process, independent of the growth of the nucleus.

  10. Empirical relationships of homogeneous bubble nucleation, growth and coalescence in rhyolitic melt

    NASA Astrophysics Data System (ADS)

    Giachetti, T.; Gonnermann, H. M.; Gardner, J. E.; Truong, N.; Toledo, P.; Hajimirza, S.

    2015-12-01

    Decompression experiments of homogeneous nucleation, growth and coalescence of bubbles in rhyolitic melt provide new data for an empirical formulation to predict bubble number density and size from controlled experimental conditions. Samples were hydrated at 200-250 MPa and 850 °C to water contents of 5.4-6.0 wt%, followed by decompression at rates of 60-150 MPa.s-1. Samples were held at final pressures for 6-90 s, allowing for bubble growth and coalescence after decompression and nucleation. Scanning electron microscopic (SEM) images and computed tomography (CT) scans of the decompressed glasses were analyzed for size distributions of both isolated and coalesced bubbles separately. Sample porosities vary from 4% to 63%, and connected porosity is positively correlated with total porosity for samples where it is greater than approximately 35%. A steep increase in the proportion of connected bubbles is observed once the average bubble wall thickness becomes lower than approximately 2 μm. In combination with SEM, CT and bubble size distributions these results indicate that bubble coalescence is independent of bubble size. Bubble number density varies from 8.9×1011 m-3 to 4.4×1016 m-3 (melt-referenced), and is positively correlated with the degree of supersaturation (130-210 MPa), as well as initial water content. For most experiments, we do not observe any increase in bubble number density after 10-20 s, suggesting that bubble nucleation has stopped. The bubble number density does not show a systematic correlation with decompression rate.

  11. Homogeneous nucleation of ethanol and n-propanol in a shock tube

    NASA Technical Reports Server (NTRS)

    Peters, F.

    1982-01-01

    The condensation by homogeneous nucleation of ethanol (200 proof) and of n-propanol (99.98%) carried at small mole fraction in dry air (99.995%) was studied in the unsteady, isentropic expansion of a shock tube. Samples of the vapor at different partial pressures in dry air at room temperature were expanded into the liquid coexistence regime of the condensing species. A Kristler pressure transducer and Rayleigh light scattering were used to measure the pressure in the expansion and the onset of condensation. Condensation was observed at different locations between 0.15 and 1 m upstream of the diaphragm location, which correspond to different cooling rates of of the vapor samples about 50 to 10 C/ms.

  12. Homogeneous nucleation of ethanol and n-propanol in a shock tube

    NASA Technical Reports Server (NTRS)

    Peters, F.

    1982-01-01

    The condensation by homogeneous nucleation of ethanol (200 proof) and of n-propanol (99.98%) carried at small mole fraction in dry air (99.995%) was studied in the unsteady, isentropic expansion of a shock tube. Samples of the vapor at different partial pressures in dry air at room temperature were expanded into the liquid coexistence regime of the condensing species. A Kristler pressure transducer and Rayleigh light scattering were used to measure the pressure in the expansion and the onset of condensation. Condensation was observed at different locations between 0.15 and 1 m upstream of the diaphragm location, which correspond to different cooling rates of of the vapor samples about 50 to 10 C/ms.

  13. Crystal nucleation and near-epitaxial growth in nacre.

    PubMed

    Olson, Ian C; Blonsky, Adam Z; Tamura, Nobumichi; Kunz, Martin; Pokroy, Boaz; Romao, Carl P; White, Mary Anne; Gilbert, Pupa U P A

    2013-12-01

    Nacre is the iridescent inner lining of many mollusk shells, with a unique lamellar structure at the sub-micron scale, and remarkable resistance to fracture. Despite extensive studies, nacre formation mechanisms remain incompletely understood. Here we present 20-nm, 2°-resolution polarization-dependent imaging contrast (PIC) images of shells from 15 mollusk species, mapping nacre tablets and their orientation patterns. These data show where new crystal orientations appear and how similar orientations propagate as nacre grows. In all shells we found stacks of co-oriented aragonite (CaCO₃) tablets arranged into vertical columns or staggered diagonally. Near the nacre-prismatic (NP) boundary highly disordered spherulitic aragonite is nucleated. Overgrowing nacre tablet crystals are most frequently co-oriented with the underlying aragonite spherulites, or with another tablet. Away from the NP-boundary all tablets are nearly co-oriented in all species, with crystal lattice tilting, abrupt or gradual, always observed and always small (plus or minus 10°). Therefore aragonite crystal growth in nacre is near-epitaxial. Based on these data, we propose that there is one mineral bridge per tablet, and that "bridge tilting" may occur without fracturing the bridge, hence providing the seed from which the next tablet grows near-epitaxially.

  14. Mechanism of two-step vapour-crystal nucleation in a pore

    NASA Astrophysics Data System (ADS)

    van Meel, J. A.; Liu, Y.; Frenkel, D.

    2015-09-01

    We present a numerical study of the effect of hemispherical pores on the nucleation of Lennard-Jones crystals from the vapour phase. As predicted by Page and Sear, there is a narrow range of pore radii, where vapour-liquid nucleation can become a two-step process. A similar observation was made for different pore geometries by Giacomello et al. We find that the maximum nucleation rate depends on both the size and the adsorption strength of the pore. Moreover, a poe can be more effective than a planar wall with the same strength of attraction. Pore-induced vapour-liquid nucleation turns out to be the rate-limiting step for crystal nucleation. This implies that crystal nucleation can be enhanced by a judicious choice of the wetting properties of a microporous nucleating agent.

  15. A Proposed Model for Protein Crystal Nucleation and Growth

    NASA Technical Reports Server (NTRS)

    Pusey, Marc; Curreri, Peter A. (Technical Monitor)

    2002-01-01

    How does one take a molecule, strongly asymmetric in both shape and charge distribution, and assemble it into a crystal? We propose a model for the nucleation and crystal growth process for tetragonal lysozyme, based upon fluorescence, light, neutron, and X-ray scattering data, size exclusion chromatography experiments, dialysis kinetics, AFM, and modeling of growth rate data, from this and other laboratories. The first species formed is postulated to be a 'head to side' dimer. Through repeating associations involving the same intermolecular interactions this grows to a 4(sub 3) helix structure, that in turn serves as the basic unit for nucleation and subsequent crystal growth. High salt attenuates surface charges while promoting hydrophobic interactions. Symmetry facilitates subsequent helix-helix self-association. Assembly stability is enhanced when a four helix structure is obtained, with each bound to two neighbors. Only two unique interactions are required. The first are those for helix formation, where the dominant interaction is the intermolecular bridging anion. The second is the anti-parallel side-by-side helix-helix interaction, guided by alternating pairs of symmetry related salt bridges along each side. At this stage all eight unique positions of the P4(sub3)2(sub 1),2(sub 1) unit cell are filled. The process is one of a) attenuating the most strongly interacting groups, such that b) the molecules begin to self-associate in defined patterns, so that c) symmetry is obtained, which d) propagates as a growing crystal. Simple and conceptually obvious in hindsight, this tells much about what we are empirically doing when we crystallize macromolecules. By adjusting the growth parameters we are empirically balancing the intermolecular interactions, preferentially attenuating the dominant strong (for lysozyme the charged groups) while strengthening the lesser strong (hydrophobic) interactions. In the general case for proteins the lack of a singularly defined

  16. A Proposed Model for Protein Crystal Nucleation and Growth

    NASA Technical Reports Server (NTRS)

    Pusey, Marc; Curreri, Peter A. (Technical Monitor)

    2002-01-01

    How does one take a molecule, strongly asymmetric in both shape and charge distribution, and assemble it into a crystal? We propose a model for the nucleation and crystal growth process for tetragonal lysozyme, based upon fluorescence, light, neutron, and X-ray scattering data, size exclusion chromatography experiments, dialysis kinetics, AFM, and modeling of growth rate data, from this and other laboratories. The first species formed is postulated to be a 'head to side' dimer. Through repeating associations involving the same intermolecular interactions this grows to a 4(sub 3) helix structure, that in turn serves as the basic unit for nucleation and subsequent crystal growth. High salt attenuates surface charges while promoting hydrophobic interactions. Symmetry facilitates subsequent helix-helix self-association. Assembly stability is enhanced when a four helix structure is obtained, with each bound to two neighbors. Only two unique interactions are required. The first are those for helix formation, where the dominant interaction is the intermolecular bridging anion. The second is the anti-parallel side-by-side helix-helix interaction, guided by alternating pairs of symmetry related salt bridges along each side. At this stage all eight unique positions of the P4(sub3)2(sub 1),2(sub 1) unit cell are filled. The process is one of a) attenuating the most strongly interacting groups, such that b) the molecules begin to self-associate in defined patterns, so that c) symmetry is obtained, which d) propagates as a growing crystal. Simple and conceptually obvious in hindsight, this tells much about what we are empirically doing when we crystallize macromolecules. By adjusting the growth parameters we are empirically balancing the intermolecular interactions, preferentially attenuating the dominant strong (for lysozyme the charged groups) while strengthening the lesser strong (hydrophobic) interactions. In the general case for proteins the lack of a singularly defined

  17. Influence of protein solution in nucleation and optimized formulation for the growth of ARM lipase crystal

    NASA Astrophysics Data System (ADS)

    Rahman, Raja Noor Zaliha Raja Abd; Masomian, Malihe; Leow, Adam Thean Chor; Ali, Mohd Shukuri Mohamad

    2015-09-01

    ARM lipase is a thermostable and organic solvent tolerant enzyme which was highly purified prior to crystallization. The His-tagged ARM lipase was purified with immobilized metal affinity chromatography followed by anion-exchange chromatography. The effect of different salt concentrations on stability, solubility and crystal nucleation of the protein was studied. The highly purified and homogeneous ARM lipase with protein concentration of 2 mg/mL was successfully crystallized by a sitting drop, vapor diffusion method with the use of 0.1 M MES monohydrate pH 6.5 and 12% (v/v) polyethylene glycol (PEG) 20000 as precipitant. The crystallization conditions were optimized by changing the pH and concentration of the precipitant. The optimum crystallization condition was 2 mg/mL ARM lipase in 0.1 M Tris-HCl, 0.15 M NaCl, pH 8.0 protein solution, crystallized using 0.1 M Tris-HCl, pH 8.0 and 12% (v/v) PEG 20000 as precipitant.

  18. Computer simulation of heterogeneous nucleation of colloidal crystals at planar walls

    NASA Astrophysics Data System (ADS)

    Block, B. J.; Deb, D.; Schmitz, F.; Statt, A.; Tröster, A.; Winkler, A.; Zykova-Timan, T.; Virnau, P.; Binder, K.

    2014-02-01

    A mini-review of the classical theory of heterogeneous nucleation at planar walls is given, and tests by Monte Carlo simulations for simple models of colloidal suspensions exhibiting a fluid-solid transition are described. This theory (due to Turnbull) assumes sphere-cap-shaped "sessile" droplets at the substrate, and the nucleation barrier that appears in the classical theory of homogeneous nucleation then is reduced by a factor depending on the Young contact angle. Various approximations inherent in this theory are examined: curvature corrections to the interfacial free energy of small droplets; neglect of anisotropy of the surface tension between crystal and fluid; neglect of corrections due to the line tension of the three-phase contact line; continuum rather than atomistic description. Also the problem of precise identification of the particles belonging (or not) to the "droplet" is discussed, and an alternative concept of extracting droplet properties from an analysis of finite size effects on phase coexistence in finite simulation boxes is explored. While the focus of our treatment is on the Asakura-Oosawa model of colloid polymer mixtures, also simple Ising/lattice gas models are considered to test some of these questions.

  19. Crystal nucleation in glass-forming alloy and pure metal melts under containerless and vibrationless conditions

    NASA Technical Reports Server (NTRS)

    Turnbull, D.

    1979-01-01

    Crystal nucleation behavior in metallic alloys known to form glasses in melt quenching was characterized and from this characterization the possibility that massive amounts of certain alloys could be slow cooled to the glass state was assessed. Crystal nucleation behavior of pure liquid metals was examined experimentally, under containerless conditions, and theoretically.

  20. Capturing heterogeneous nucleation of nanoscale pits and subsequent crystal shrinkage during Ostwald ripening of a metal phosphate.

    PubMed

    Chung, Sung-Yoon; Kim, Young-Min; Choi, Si-Young; Kim, Jin-Gyu

    2015-01-27

    It has been generally accepted that crystal shrinkage during Ostwald ripening can be understood simply as a reverse process of crystal growth, and as a result, little attention has been paid to shrinkage behavior. The entire microstructure of polycrystalline materials, however, forms as a consequence of both growing and shrinking crystals. Thus, scrutiny of shrinking characteristics in addition to growth aspects is essential for a complete understanding of the evolution of microstructure during Ostwald ripening. By capturing real-time in situ high-resolution electron micrographs at high temperature, we herein demonstrate the shrinkage behavior of nanocrystals embedded in a solid crystalline matrix during the ripening process of a metal phosphate. Unlike typical crystal growth behavior based on two-dimensional homogeneous nucleation, heterogeneous types of nucleation with nanoscale pits at solid-solid interfaces (or crystal edges) are observed to dominantly occur during shrinkage of the crystals. The findings of this study suggest that crystal shrinkage proceeds with a lower activation energy barrier than that of crystal growth, although both crystal growth and shrinkage take place at the same time during Ostwald ripening.

  1. Report on the Implementation of Homogeneous Nucleation Scheme in MARMOT-based Phase Field Simulation

    SciTech Connect

    Li, Yulan; Hu, Shenyang Y.; Sun, Xin

    2013-09-30

    In this report, we summarized our effort in developing mesoscale phase field models for predicting precipitation kinetics in alloys during thermal aging and/or under irradiation in nuclear reactors. The first part focused on developing a method to predict the thermodynamic properties of critical nuclei such as the sizes and concentration profiles of critical nuclei, and nucleation barrier. These properties are crucial for quantitative simulations of precipitate evolution kinetics with phase field models. Fe-Cr alloy was chosen as a model alloy because it has valid thermodynamic and kinetic data as well as it is an important structural material in nuclear reactors. A constrained shrinking dimer dynamics (CSDD) method was developed to search for the energy minimum path during nucleation. With the method we are able to predict the concentration profiles of the critical nuclei of Cr-rich precipitates and nucleation energy barriers. Simulations showed that Cr concentration distribution in the critical nucleus strongly depends on the overall Cr concentration as well as temperature. The Cr concentration inside the critical nucleus is much smaller than the equilibrium concentration calculated by the equilibrium phase diagram. This implies that a non-classical nucleation theory should be used to deal with the nucleation of Cr precipitates in Fe-Cr alloys. The growth kinetics of both classical and non-classical nuclei was investigated by the phase field approach. A number of interesting phenomena were observed from the simulations: 1) a critical classical nucleus first shrinks toward its non-classical nucleus and then grows; 2) a non-classical nucleus has much slower growth kinetics at its earlier growth stage compared to the diffusion-controlled growth kinetics. 3) a critical classical nucleus grows faster at the earlier growth stage than the non-classical nucleus. All of these results demonstrated that it is critical to introduce the correct critical nuclei into phase

  2. Insights into the nucleation role of cellulose crystals during crystallization of poly(β-hydroxybutyrate).

    PubMed

    Chen, Jianxiang; Xu, Chunjiang; Wu, Defeng; Pan, Keren; Qian, Aiwen; Sha, Yulu; Wang, Li; Tong, Wei

    2015-12-10

    Cellulose crystals, including microcrystalline cellulose (MCC) and nanocrystalline cellulose (NCC), were used as the fillers to prepare green composites with poly(β-hydroxybutyrate) (PHB) by melt mixing for crystallization study. The results reveal that the spherulite morphology of PHB and its composites depends highly on the crystallization temperature, evolving from bundle shaped to ring-banded and finally to irregular or zigzag textures with increase of temperature. However, the ring-banded structure is strongly affected by the presence of cellulose crystals, and the average band space decreases evidently with the addition of MCC or NCC. Compared with PHB/MCC composite, PHB/NCC composite shows degraded spherulite structure with smaller band space and higher flocculation level of peak-to-valley height because of stronger unbalanced stresses in this system. Besides, cellulose crystals can act as good heterogeneous nucleating agent to accelerate the crystallization of PHB, which is further confirmed by the polarized optical microscopy observations and the kinetic analyses.

  3. Linear relation between TH (homogeneous ice nucleation temperature) and Tm (melting temperature) for aqueous solutions of sucrose, trehalose, and maltose

    NASA Astrophysics Data System (ADS)

    Kanno, Hitoshi; Soga, Makoto; Kajiwara, Kazuhito

    2007-08-01

    Homogeneous ice nucleation temperatures ( THs) of aqueous sucrose, trehalose, and maltose solutions were measured together with melting temperatures ( Tms). It is shown that there is a linear relation between TH and Tm for these solutions. Almost identical supercooling behavior is observed for these aqueous disaccharide solutions.

  4. Aqueous oxygen near the homogeneous nucleation limit of water: stabilization with submicron capillaries.

    PubMed

    Spears, J Richard; Prcevski, Petar; Brereton, Giles J

    2006-01-01

    Previous studies have demonstrated that the metastability threshold of aqueous oxygen (AO) is inversely dependent on the internal diameter of capillary tubes used to deliver it into blood. The hypothesis was tested herein that significantly higher thresholds are attainable with capillaries having markedly smaller dimensions (submicron) than those previously studied. Water was equilibrated with oxygen over a 0.3- to 0.7-k bar range. Inert gases (argon, helium) facilitated studies at pressures to 2.5 k bar. An argon-ion laser was used to visualize fluorescein in the liquid effluent from silica capillaries that were tapered at the distal end to a submicron internal diameter (0.5 +/- 0.3 microns). During infusion of the fluorescent effluent into host water at 21 degrees C and atmospheric pressure, integrity of the effluent and lack of microbubbles were monitored by videomicroscopy. No microbubbles were noted at AO concentrations ranging from 7.5 to 12.8 ml O2/g (0.34 to 0.68 k bar, respectively) or in the aqueous argon effluent at concentrations to 14 ml Ar/g (0.75 k bar). For aqueous helium, effluent nucleation was not observed at a mean concentration of 13 +/- 3 ml He/g (2.0 +/- 0.5 k bar), with an upper value of 15.2 ml He/g (2.4 k bar). The data represent the highest values of the tensile strength of water ever observed and approximate its theoretical homogeneous nucleation limit. Thus, remarkably high metastable concentrations of AO and other gases are attainable with the use of submicron capillaries.

  5. Competitive Growth of - -Crystals in -Nucleated Isotactic Polypropylene under Shear Flow

    SciTech Connect

    Chen, Y.; Mao, Y; Li, Z; Hsiao, B

    2010-01-01

    It has been well established that, although both shear flow and {beta}-nucleating agent could separately induce {beta}-crystals in isotactic polypropylene (iPP) in an efficient manner, their combination in fact depressed the content of {beta}-crystals when compared with quiescently crystallized {beta}-nucleated iPP. In the current study, in-situ synchrotron wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) measurements were performed to investigate this behavior. The WAXD data obtained were quantitatively analyzed to determine the independent contributions of applied shear flow and added {beta}-nucleating agent in terms of nucleation stage and subsequent {alpha}- and {beta}-crystal growth stage. In the nucleation stage, the addition of {beta}-nucleating agent increased the amount of {beta}-nuclei, while the application of shear flow and the interactions between shear and {beta}-nucleating agent enhanced the amount of {alpha}-nuclei (the amounts of {alpha}- and {beta}-nuclei were in the same order of magnitude). As a result, in the initial crystallization, {alpha}- and {beta}-crystals grew competitively, causing simultaneously increments of {alpha}- and {beta}-crystals. However, in the growth stage, the growth rate of {beta}-crystals was faster than that of {alpha}-crystals where the epitaxial growth of {beta}-crystals on {alpha}-crystals also occurred (due to more favorable isothermal crystallization temperature for {beta}-crystal growth). Consequently, the content of {beta}-crystals became dominant in the limited growth space; however, it was still less than that formed from the quiescent isothermal crystallization of {beta}-nucleated iPP. As the shear rate increased, more shear-induced {alpha}-nuclei were formed, further decreasing the amount of {beta}-crystals. Nevertheless, when shear and {beta}-nucleating agent coexisted, {beta}-crystals emerged earlier than {alpha}-crystals. The SAXS results indicated that the combination of shear

  6. Homogenization of electromagnetic crystals formed by uniaxial resonant scatterers

    NASA Astrophysics Data System (ADS)

    Belov, Pavel A.; Simovski, Constantin R.

    2005-08-01

    Dispersion properties of electromagnetic crystals formed by small uniaxial resonant scatterers (magnetic or electric) are studied using the local field approach. The goal of the study is to determine the conditions under which the homogenization of such crystals is possible. Therefore the consideration is limited to the frequency region where the wavelength in the host medium is larger than the lattice periods. It is demonstrated that, together with the known restriction for the homogenization related to the large values of the material parameters, there is an additional restriction related to their small absolute values. On the other hand, the homogenization becomes allowed in both cases of large and small material parameters for special directions of propagation. Two unusual effects inherent to the crystals under consideration are revealed: a flat isofrequency contour that allows subwavelength imaging using the canalization regime and birefringence of the extraordinary modes which can be used for beam splitting.

  7. Kinetics of Nucleation and Crystal Growth in Glass Forming Melts in Microgravity

    NASA Technical Reports Server (NTRS)

    Day, Delbert E.; Ray, Chandra S.

    2001-01-01

    This flight definition project has the specific objective of investigating the kinetics of nucleation and crystal growth in high temperature inorganic oxide, glass forming melts in microgravity. It is related to one of our previous NASA projects that was concerned with glass formation for high temperature containerless melts in microgravity. The previous work culminated in two experiments which were conducted aboard the space shuttle in 1983 and 1985 and which consisted of melting (at 1500 C) and cooling levitated 6 to 8 mm diameter spherical samples in a Single Axis Acoustic Levitator (SAAL) furnace. Compared to other types of materials, there have been relatively few experiments, 6 to 8, conducted on inorganic glasses in space. These experiments have been concerned with mass transport (alkali diffusion), containerless melting, critical cooling rate for glass formation, chemical homogeneity, fiber pulling, and crystallization of glass forming melts. One of the most important and consistent findings in all of these experiments has been that the glasses prepared in microgravity are more resistant to crystallization (better glass former) and more chemically homogeneous than equivalent glasses made on Earth (1 g). The chemical composition of the melt appears relatively unimportant since the same general results have been reported for oxide, fluoride and chalcogenide melts. These results for space-processed glasses have important implications, since glasses with a higher resistance to crystallization or higher chemical homogeneity than those attainable on Earth can significantly advance applications in areas such as fiber optics communications, high power laser glasses, and other photonic devices where glasses are the key functional materials.

  8. Kinetics of Nucleation and Crystal Growth in Glass Forming Melts in Microgravity

    NASA Technical Reports Server (NTRS)

    Day, Delbert E.; Ray, Chandra S.

    2001-01-01

    This flight definition project has the specific objective of investigating the kinetics of nucleation and crystal growth in high temperature inorganic oxide, glass forming melts in microgravity. It is related to one of our previous NASA projects that was concerned with glass formation for high temperature containerless melts in microgravity. The previous work culminated in two experiments which were conducted aboard the space shuttle in 1983 and 1985 and which consisted of melting (at 1500 C) and cooling levitated 6 to 8 mm diameter spherical samples in a Single Axis Acoustic Levitator (SAAL) furnace. Compared to other types of materials, there have been relatively few experiments, 6 to 8, conducted on inorganic glasses in space. These experiments have been concerned with mass transport (alkali diffusion), containerless melting, critical cooling rate for glass formation, chemical homogeneity, fiber pulling, and crystallization of glass forming melts. One of the most important and consistent findings in all of these experiments has been that the glasses prepared in microgravity are more resistant to crystallization (better glass former) and more chemically homogeneous than equivalent glasses made on Earth (1 g). The chemical composition of the melt appears relatively unimportant since the same general results have been reported for oxide, fluoride and chalcogenide melts. These results for space-processed glasses have important implications, since glasses with a higher resistance to crystallization or higher chemical homogeneity than those attainable on Earth can significantly advance applications in areas such as fiber optics communications, high power laser glasses, and other photonic devices where glasses are the key functional materials.

  9. Control of nucleation and growth in protein crystal growth

    NASA Technical Reports Server (NTRS)

    Rosenberger, Franz; Meehan, Edward J.

    1988-01-01

    The potential advantages of nucleation and growth control through temperature, rather than the addition of precipitants or removal of solvent, are discussed. A simple light scattering arrangement for the characterization of nucleation and growth conditions in solutions is described. The temperature dependence of the solubility of low ionic strength lysozyme solutions is applied in preliminary nucleation and growth experiments.

  10. An enthalpy landscape view of homogeneous melting in crystals.

    PubMed

    Nieves, Alex M; Sinno, Talid

    2011-08-21

    A detailed analysis of homogeneous melting in crystalline materials modeled by empirical interatomic potentials is presented using the theory of inherent structures. We show that the homogeneous melting of a perfect, infinite crystalline material can be inferred directly from the growth exponent of the inherent structure density-of-states distribution expressed as a function of formation enthalpy. Interestingly, this growth is already established by the presence of very few homogeneously nucleated point defects in the form of Frenkel pairs. This finding supports the notion that homogeneous melting is appropriately defined in terms of a one-phase theory and does not require detailed consideration of the liquid phase. We then apply this framework to the study of applied hydrostatic compression on homogeneous melting and show that the inherent structure analysis used here is able to capture the correct pressure-dependence for two crystalline materials, namely silicon and aluminum. The coupling between the melting temperature and applied pressure arises through the distribution of formation volumes for the various inherent structures.

  11. Phase-field crystal modeling of heteroepitaxy and exotic modes of crystal nucleation

    NASA Astrophysics Data System (ADS)

    Podmaniczky, Frigyes; Tóth, Gyula I.; Tegze, György; Pusztai, Tamás; Gránásy, László

    2017-01-01

    We review recent advances made in modeling heteroepitaxy, two-step nucleation, and nucleation at the growth front within the framework of a simple dynamical density functional theory, the Phase-Field Crystal (PFC) model. The crystalline substrate is represented by spatially confined periodic potentials. We investigate the misfit dependence of the critical thickness in the StranskiKrastanov growth mode in isothermal studies. Apparently, the simulation results for stress release via the misfit dislocations fit better to the PeopleBean model than to the one by Matthews and Blakeslee. Next, we investigate structural aspects of two-step crystal nucleation at high undercoolings, where an amorphous precursor forms in the first stage. Finally, we present results for the formation of new grains at the solid-liquid interface at high supersaturations/supercoolings, a phenomenon termed Growth Front Nucleation (GFN). Results obtained with diffusive dynamics (applicable to colloids) and with a hydrodynamic extension of the PFC theory (HPFC, developed for simple liquids) will be compared. The HPFC simulations indicate two possible mechanisms for GFN.

  12. The carrier gas pressure effect in a laminar flow diffusion chamber, homogeneous nucleation of n-butanol in helium.

    PubMed

    Hyvärinen, Antti-Pekka; Brus, David; Zdímal, Vladimír; Smolík, Jiri; Kulmala, Markku; Viisanen, Yrjö; Lihavainen, Heikki

    2006-06-14

    Homogeneous nucleation rate isotherms of n-butanol+helium were measured in a laminar flow diffusion chamber at total pressures ranging from 50 to 210 kPa to investigate the effect of carrier gas pressure on nucleation. Nucleation temperatures ranged from 265 to 280 K and the measured nucleation rates were between 10(2) and 10(6) cm(-3) s(-1). The measured nucleation rates decreased as a function of increasing pressure. The pressure effect was strongest at pressures below 100 kPa. This negative carrier gas effect was also temperature dependent. At nucleation temperature of 280 K and at the same saturation ratio, the maximum deviation between nucleation rates measured at 50 and 210 kPa was about three orders of magnitude. At nucleation temperature of 265 K, the effect was negligible. Qualitatively the results resemble those measured in a thermal diffusion cloud chamber. Also the slopes of the isothermal nucleation rates as a function of saturation ratio were different as a function of total pressure, 50 kPa isotherms yielded the steepest slopes, and 210 kPa isotherms the shallowest slopes. Several sources of inaccuracies were considered in the interpretation of the results: uncertainties in the transport properties, nonideal behavior of the vapor-carrier gas mixture, and shortcomings of the used mathematical model. Operation characteristics of the laminar flow diffusion chamber at both under-and over-pressure were determined to verify a correct and stable operation of the device. We conclude that a negative carrier gas pressure effect is seen in the laminar flow diffusion chamber and it cannot be totally explained with the aforementioned reasons.

  13. Two-step vapor-crystal nucleation close below triple point.

    PubMed

    van Meel, J A; Page, A J; Sear, R P; Frenkel, D

    2008-11-28

    We present the results of Monte Carlo simulations of crystal nucleation from the vapor phase. We studied the Lennard-Jones system at conditions close to, but below, the triple point. This system is expected to show surface melting. The nucleation pathway that we observe consists of two distinct steps. In the first step, a liquid droplet nucleates from the vapor. Its nucleation rate depends strongly on the vapor supersaturation. In the second step, the final crystal phase nucleates in the liquid droplet, provided that this liquid droplet exceeds a minimum size. Our simulations show that within a liquid droplet the crystal nucleation rate does not depend on the vapor supersaturation. In a recent independent study Chen et al. [J. Phys. Chem. B 112, 4069 (2008)] investigated the same phenomenon using umbrella sampling to compute free energy barriers and hence nucleation rates. We use a different numerical approach where we focus on computing the nucleation rates directly using forward-flux sampling. Our results agree with the findings of Chen et al. and both methods observe two-step nucleation. This finding indicates that this nucleation process can be described with a quasiequilibrium theory. Due to different cutoffs for the interaction potential the results cannot be compared quantitatively.

  14. Beneficial effect of solubility enhancers on protein crystal nucleation and growth.

    PubMed

    Gosavi, Rajendrakumar A; Bhamidi, Venkateswarlu; Varanasi, Sasidhar; Schall, Constance A

    2009-04-21

    Crystallizing solutions of proteins often contain various nonelectrolyte additives that arise from the purification process of proteins or from the reagents employed in the screening kits. Currently, limited knowledge exists about the influence of these additives on the mechanisms underlying the crystallization process, in particular on the nucleation stage of crystals. To address this need, we studied crystallization of two proteins, D-xylose isomerase and chicken egg-white lysozyme, in small batches and in the presence of two solubility-enhancing additives, acetonitrile and glycerol. We have also measured the nucleation rates of crystals of these proteins in the presence and in the absence of acetonitrile using the method of initial rates. With the addition of the solubility enhancers, both proteins exhibited an increase in crystal nucleation at any given supersaturation. Solubility enhancing additives appear to lower the energy barrier to nucleation by influencing the strength of attraction between the protein molecules. We have characterized the quality of D-xylose isomerase crystals by determining the crystal mosaicity, which showed considerable improvement for crystals grown in the presence of additives. When compared to the crystals of chicken egg-white lysozyme, D-xylose isomerase crystals required higher supersaturations to nucleate. We attribute this result to the large size of the D-xylose isomerase molecule, which influences the energy barrier to nucleation by increasing the surface area of the critical nucleus. Contrary to the common expectation that reagents that solubilize the protein may hinder the crystallization process, our results suggest that solubility enhancers, in fact, can have a beneficial effect on the nucleation and growth of crystals. These findings are of importance in formulating successful strategies toward crystallizing new proteins.

  15. Experiment and theory for heterogeneous nucleation of protein crystals in a porous medium

    PubMed Central

    Chayen, Naomi E.; Saridakis, Emmanuel; Sear, Richard P.

    2006-01-01

    The determination of high-resolution structures of proteins requires crystals of suitable quality. Because of the new impetus given to structural biology by structural genomics/proteomics, the problem of crystallizing proteins is becoming increasingly acute. There is therefore an urgent requirement for the development of new efficient methods to aid crystal growth. Nucleation is the crucial step that determines the entire crystallization process. Hence, the holy grail is to design a “universal nucleant,” a substrate that induces the nucleation of crystals of any protein. We report a theory for nucleation on disordered porous media and its experimental testing and validation using a mesoporous bioactive gel-glass. This material induced the crystallization of the largest number of proteins ever crystallized using a single nucleant. The combination of the model and the experimental results opens up the scope for the rational design of nucleants, leading to alternative means of controlling crystallization. PMID:16407115

  16. Experiment and theory for heterogeneous nucleation of protein crystals in a porous medium.

    PubMed

    Chayen, Naomi E; Saridakis, Emmanuel; Sear, Richard P

    2006-01-17

    The determination of high-resolution structures of proteins requires crystals of suitable quality. Because of the new impetus given to structural biology by structural genomics/proteomics, the problem of crystallizing proteins is becoming increasingly acute. There is therefore an urgent requirement for the development of new efficient methods to aid crystal growth. Nucleation is the crucial step that determines the entire crystallization process. Hence, the holy grail is to design a "universal nucleant," a substrate that induces the nucleation of crystals of any protein. We report a theory for nucleation on disordered porous media and its experimental testing and validation using a mesoporous bioactive gel-glass. This material induced the crystallization of the largest number of proteins ever crystallized using a single nucleant. The combination of the model and the experimental results opens up the scope for the rational design of nucleants, leading to alternative means of controlling crystallization.

  17. CRYSTALLIZATION OF SYNTHETIC HAEMOZOIN (β-HAEMATIN) NUCLEATED AT THE SURFACE OF LIPID PARTICLES

    PubMed Central

    Hoang, Anh N.; Ncokazi, Kanyile K.; de Villiers, Katherine A.; Wright, David W.; Egan, Timothy J.

    2010-01-01

    Summary The mechanism of formation of haemozoin, a detoxification by-product of several blood-feeding organisms including malaria parasites, has been a subject of debate; however, recent studies suggest that neutral lipids may serve as a catalyst. In this study, a model system consisting of an emulsion of neutral lipid particles was employed to investigate the formation of β-haematin, the synthetic counterpart of haemozoin, at the lipid-water interface. A solution of monoglyceride, either monostearoylglycerol (MSG) or monopalmitoylglycerol (MPG), dissolved in acetone and methanol was introduced to an aqueous surface. Fluorescence, confocal and transmission electron microscopic (TEM) imaging and dynamic light scattering analysis of samples obtained from beneath the surface confirmed the presence of homogeneous lipid particles existing in two major populations: one in the low micrometer size range and the other in the hundred nanometre range. The introduction of haem (Fe(III)PPIX) to this lipid particle system under biomimetic conditions (37 °C, pH 4.8) produced β-haematin with apparent first order kinetics and an average half life of 0.5 min. TEM of monoglycerides (MSG or MPG) extruded through a 200 nm filter with haem produced β-haematin crystals aligned and parallel to the lipid/water interface. These TEM data, together with a model system replacing the lipid with an aqueous organic solvent interface using either methyl laurate or docosane demonstrated that the OH and C=O groups are apparently necessary for efficient nucleation. This suggests that β-haematin crystallizes via epitaxial nucleation at the lipid-water interface through interaction of Fe(III)PPIX with the polar head group. Once nucleated, the crystal grows parallel to the interface until growth is terminated by the curvature of the lipid particle. The hydrophobic nature of the mature crystal favours an interior transport resulting in crystals aligned parallel to the lipid-water interface and each

  18. The homogeneous ice nucleation rate of water droplets produced in a microfluidic device and the role of temperature uncertainty.

    PubMed

    Riechers, Birte; Wittbracht, Frank; Hütten, Andreas; Koop, Thomas

    2013-04-28

    Ice nucleation was investigated experimentally in water droplets with diameters between 53 and 96 micrometres. The droplets were produced in a microfluidic device in which a flow of methyl-cyclohexane and water was combined at the T-junction of micro-channels yielding inverse (water-in-oil) emulsions consisting of water droplets with small standard deviations. In cryo-microscopic experiments we confirmed that upon cooling of such emulsion samples ice nucleation in individual droplets occurred independently of each other as required for the investigation of a stochastic process. The emulsion samples were then subjected to cooling at 1 Kelvin per minute in a differential scanning calorimeter with high temperature accuracy. From the latent heat released by freezing water droplets we inferred the volume-dependent homogeneous ice nucleation rate coefficient of water at temperatures between 236.5 and 237.9 Kelvin. A comparison of our newly derived values to existing rate coefficients from other studies suggests that the volume-dependent ice nucleation rate in supercooled water is slightly lower than previously thought. Moreover, a comprehensive error analysis suggests that absolute temperature accuracy is the single most important experimental parameter determining the uncertainty of the derived ice nucleation rates in our experiments, and presumably also in many previous experiments. Our analysis, thus, also provides a route for improving the accuracy of future ice nucleation rate measurements.

  19. Enhanced High-Temperature Ice Nucleation Ability of Crystallized Aerosol Particles after Pre-Activation at Low Temperature

    NASA Astrophysics Data System (ADS)

    Wagner, R.; Moehler, O.; Saathoff, H.; Schnaiter, M.

    2014-12-01

    The term pre-activation in heterogeneous ice nucleation describes the observation that the ice nucleation ability of solid ice nuclei may improve after they have already been involved in ice crystal formation or have been exposed to a temperature lower than 235 K. This can be explained by the retention of small ice embryos in cavities or crevices at the particle surface or by the capillary condensation and freezing of supercooled water, respectively. In recent cloud chamber experiments with crystallized aqueous ammonium sulfate, oxalic acid, and succinic acid solution droplets, we have unraveled a further pre-activation mechanism under ice subsaturated conditions which does not require the preceding growth of ice on the seed aerosol particles (Wagner, R. et al., J. Geophys. Res. Atmos., 119, doi: 10.1002/2014JD021741). First cloud expansion experiments were performed at a high temperature (267 - 244 K) where the crystallized particles did not promote any heterogeneous ice nucleation. Ice nucleation at this temperature, however, could be triggered by temporarily cooling the crystallized particles to a lower temperature. This is because upon crystallization, residuals of the aqueous solution are trapped within the crystals. These captured liquids can freeze when cooled below their respective homogeneous or heterogeneous freezing temperature, leading to the formation of ice pockets in the crystalline particles. When warmed again to the higher temperature, ice formation by the pre-activated particles occurred via depositional and deliquescence-induced ice growth, with ice active fractions ranging from 1 to 4% and 4 to 20%, respectively. Pre-activation disappeared above the eutectic temperature, which for the organic acids are close to the melting point of ice. This mechanism could therefore contribute to the very small fraction of atmospheric aerosol particles that are still ice active well above 263 K.

  20. Study of gypsum crystal nucleation and growth rates in simulated flue gas desulfurization liquors. Final report

    SciTech Connect

    Randolph, A.D.; Etherton, D.

    1981-06-01

    The kinetics of gypsum crystal nucleation and growth rates were measured in flue gas desulfurization (FGD) scrubber liquors. Variables studied were parent seed crystal size and mass; the organic additives citric acid, adipic acid, sodium dodecylbenzene sulfonate, and Calgon CL246 polyacrylic acid formulation; and pH. Citric acid produced gypsum crystals with a more favorable columnar structure. Lower pH resulted in increased nucleation rates. Stable secondary nucleation was observed in the presence of retained parent gypsum seed crystals of size >150 ..mu..m. Growth and nucleation rates were correlated using reaction kinetic models. These kinetics were then used in rigorous computer simulations to predict crystal-size distribution (CSD) with different scrubber configurations. Scrubber process configurations employing classified product removal were calculated to produce a gypsum sludge having a mean particle size up to twice as large as the particle size with unclassified operation.

  1. Mechanism for diamond nucleation and growth on single crystal copper surfaces implanted with carbon

    NASA Technical Reports Server (NTRS)

    Ong, T. P.; Xiong, Fulin; Chang, R. P. H.; White, C. W.

    1992-01-01

    The nucleation and growth of diamond crystals on single-crystal copper surfaces implanted with carbon ions is studied. Microwave plasma-enhanced chemical-vapor deposition is used for diamond growth. The single-crystal copper substrates were implanted either at room or elevated temperature with carbon ions prior to diamond nucleation. This procedure leads to the formation of a graphite film on the copper surface which greatly enhances diamond crystallite nucleation. A simple lattice model is constructed for diamond growth on graphite as 111 line (diamond) parallel to 0001 line (graphite) and 110 line (diamond) parallel to 1 1 -2 0 (graphite).

  2. Mechanism for diamond nucleation and growth on single crystal copper surfaces implanted with carbon

    NASA Technical Reports Server (NTRS)

    Ong, T. P.; Xiong, Fulin; Chang, R. P. H.; White, C. W.

    1992-01-01

    The nucleation and growth of diamond crystals on single-crystal copper surfaces implanted with carbon ions is studied. Microwave plasma-enhanced chemical-vapor deposition is used for diamond growth. The single-crystal copper substrates were implanted either at room or elevated temperature with carbon ions prior to diamond nucleation. This procedure leads to the formation of a graphite film on the copper surface which greatly enhances diamond crystallite nucleation. A simple lattice model is constructed for diamond growth on graphite as 111 line (diamond) parallel to 0001 line (graphite) and 110 line (diamond) parallel to 1 1 -2 0 (graphite).

  3. A quantitative parameter-free prediction of simulated crystal nucleation times

    SciTech Connect

    Aga, Rachel S; Morris, James R; Hoyt, Jeffrey John; Mendelev, Mikhail I.

    2006-01-01

    We present direct comparisons between simulated crystal-nucleation times and theoretical predictions using a model of aluminum, and demonstrate that a quantitative prediction can be made. All relevant thermodynamic properties of the system are known, making the agreement of our simulation data with nucleation theories free of any adjustable parameters. The role of transient nucleation is included in the classical nucleation theory approach, and shown to be necessary to understand the observed nucleation times. The calculations provide an explanation on why nucleation is difficult to observe in simulations at moderate undercoolings. Even when the simulations are significantly larger than the critical nucleus, and when simulation times are sufficiently long, at moderate undercoolings the small concentration of critical nuclei makes the probability of the nucleation low in molecular dynamics simulations.

  4. Crystal Nucleation and Growth in Mount Unzen Dacite Decompression Experiments

    NASA Astrophysics Data System (ADS)

    Almberg, L. D.; Larsen, J. F.; Eichelberger, J. C.

    2005-12-01

    Central to understanding eruption dynamics is the interplay of decompression and degassing, which triggers crystal nucleation and growth. Microlite and microphenocryst textures are an often-used tool to decipher the rates of magma ascent for specific eruptions. It is critical to determine the depth and time scale at which these processes take place to fully understand the system behavior. Conduit material retrieved from 1500 m depth from the USDP-4 at Mount Unzen, Japan provides a snap shot of a viscous magma en route to the surface and is a perfect counterpoint to compare with laboratory experiments under controlled P, T, and XH2O conditions. The core samples were identified as representing material from the 1991-1995 eruption based upon their elemental and isotopic composition and coincidence with a temperature maximum and alteration minimum (Nakada et al, ICDP Symposium, Potsdam, 2005). Three plagioclase crystal populations coexist in the spine emplaced at the conclusion of the eruption sequence in 1995, microlites (<20 μm), microphenocrysts (20-100 μm) and phenocrysts (>100 μm). Only phenocrysts and microlites are present in the samples extracted from 1500 m during drilling of the USDP-4 core. These textural differences are the focus of decompression experiments, with the purpose of replicating shallow level crystallization that may have occurred between 1500 m depth and the surface. It is possible that the microphenocrysts present in the dome lavas and absent in the conduit core could have formed at very shallow levels during magmatic ascent. Our experimental work delineates the role of decompression in controlling crystal size distributions in Unzen dacite, for comparison with the natural dome lavas and USDP-4 core samples. We conducted isothermal (870 ± 3°C) single and multi-step decompression experiments, equilibrated at 40 ± 3 MPa under water saturation and NNO conditions, and decompressed to 7.5 ± 0.5 MPa or 318 m depth. We ran such experiments for

  5. Metastability Limit for the Nucleation of NaCl Crystals in Confinement.

    PubMed

    Desarnaud, Julie; Derluyn, Hannelore; Carmeliet, Jan; Bonn, Daniel; Shahidzadeh, Noushine

    2014-03-06

    We study the spontaneous nucleation and growth of sodium chloride crystals induced by controlled evaporation in confined geometries (microcapillaries) spanning several orders of magnitude in volume. In all experiments, the nucleation happens reproducibly at a very high supersaturation S ∼ 1.6 and is independent of the size, shape, and surface properties of the microcapillary. We show from classical nucleation theory that this is expected: S ∼ 1.6 corresponds to the point where nucleation first becomes observable on experimental time scales. A consequence of the high supersaturations reached at the onset of nucleation is the very rapid growth of a single skeletal (Hopper) crystal. Experiments on porous media also reveal the formation of Hopper crystals in the entrapped liquid pockets in the porous network and consequently underline the fact that sodium chloride can easily reach high supersaturations, in spite of what is commonly assumed for this salt.

  6. Nucleation and growth of diamond on carbon-implanted single crystal copper surfaces

    SciTech Connect

    Ong, T.P.; Xiong, F.; Chang, R.P.H. ); White, C.W. )

    1992-09-01

    The nucleation and growth of diamond crystals on single crystal copper surfaces has been studied. Microwave plasma enhanced chemical vapor deposition (MPECVD) was used for diamond nucleation and growth. Prior to diamond nucleation, the single crystal copper surface is modified by carbon ion implantation at an elevated temperature ({similar to}820 {degree}C). This procedure leads to the formation of a graphite film on the copper surface, resulting in an enhancement of diamond crystallite nucleation. A simple lattice model has been constructed to describe the mechanism of diamond nucleation on graphite as {l angle}111{r angle}{sub diamond} parallel to {l angle}0001{r angle}{sub graphite} and {l angle}110{r angle}{sub diamond} parallel to {l angle}1120{r angle}{sub graphite}. This leads to a good understanding of diamond growth on carbon-implanted copper surfaces.

  7. Heterogeneous Nucleation of an n-Alkane on Tetrahedrally Coordinated Crystals.

    PubMed

    Bourque, Alexander J; Locker, C Rebecca; Rutledge, Gregory C

    2017-02-02

    Heterogeneous nucleation refers to the propensity for phase transformations to initiate preferentially on foreign surfaces, such as vessel walls, dust particles, or formulation additives. In crystallization, the form of the initial nucleus has ramifications for the crystallographic form, morphology, and properties of the resulting solid. Nevertheless, the discovery and design of nucleating agents remains a matter of trial and error because of the very small spatiotemporal scales over which the critical nucleus is formed and the extreme difficulty of examining such events empirically. Using molecular dynamics simulations, we demonstrate a method for the rapid screening of entire families of materials for activity as nucleating agents and for characterizing their mechanism of action. The method is applied to the crystallization of n-pentacontane, a model surrogate for polyethylene, on the family of tetrahedrally coordinated crystals, including diamond and silicon. A systematic variation of parameters in the interaction potential permits a comprehensive, physically based screening of nucleating agents in this class of materials, including both real and hypothetical candidates. The induction time for heterogeneous nucleation is shown to depend strongly on crystallographic registry between the nucleating agent and the critical nucleus, indicative of an epitaxial mechanism in this class of materials. Importantly, the severity of this registry requirement weakens with decreasing rigidity of the substrate and increasing strength of attraction to the surface of the nucleating agent. Employing this method, a high-throughput computational screening of nucleating agents becomes possible, facilitating the discovery of novel nucleating agents within a broad "materials genome" of possible additives.

  8. Optimization of crystal nucleation close to a metastable fluid-fluid phase transition.

    PubMed

    Wedekind, Jan; Xu, Limei; Buldyrev, Sergey V; Stanley, H Eugene; Reguera, David; Franzese, Giancarlo

    2015-06-22

    The presence of a metastable fluid-fluid critical point is thought to dramatically influence the crystallization pathway, increasing the nucleation rate by many orders of magnitude over the predictions of classical nucleation theory. We use molecular dynamics simulations to study the kinetics of crystallization in the vicinity of this metastable critical point and throughout the metastable fluid-fluid phase diagram. To quantitatively understand how the fluid-fluid phase separation affects the crystal nucleation, we evaluate accurately the kinetics and reconstruct the thermodynamic free-energy landscape of crystal formation. Contrary to expectations, we find no special advantage of the proximity of the metastable critical point on the crystallization rates. However, we find that the ultrafast formation of a dense liquid phase causes the crystallization to accelerate both near the metastable critical point and almost everywhere below the fluid-fluid spinodal line. These results unveil three different scenarios for crystallization that could guide the optimization of the process in experiments.

  9. The Effect of Solution Parameters on Lysozyme Nucleation Rates and Crystal Quality

    NASA Technical Reports Server (NTRS)

    Judge, R. A.; Snell, E. H.

    1998-01-01

    In the pursuit of strongly diffracting high quality macromolecule crystals of suitable volume, this study investigates how the formation of macromolecules in solution and their growth characteristics effect crystal volume and diffracting quality. We systematically investigated the effect of solution conditions on lysozyme nucleation rates and the volume of crystals produced. Batch crystallization plates were used in combination with a video microscope system to measure nucleation rates and crystal volume. As expected from classical nucleation theory, crystal numbers were found to increase with increases in temperature and supersaturation. Small changes in solution pH, at constant supersaturation values were found, however, to dramatically effect the number of crystals nucleated in the wells varying from 1000s to 10s in the pH range 4.0 to 5.2. Having optimized the conditions required to produce an appropriate number of crystals of a suitable volume for X-ray analysis, a large number of uniform crystals were produced under exactly the same conditions. In the X-ray analysis of more than 50 such crystals there was found a wide variation in crystal lattice parameters and data quality. The variation in X-ray quality crystal samples is thought to be related to the growth rate variation caused by growth rate dispersion seen in lysozyme crystal growth experiments.

  10. The Effect of Solution Parameters on Lysozyme Nucleation Rates and Crystal Quality

    NASA Technical Reports Server (NTRS)

    Judge, R. A.; Snell, E. H.

    1998-01-01

    In the pursuit of strongly diffracting high quality macromolecule crystals of suitable volume, this study investigates how the formation of macromolecules in solution and their growth characteristics effect crystal volume and diffracting quality. We systematically investigated the effect of solution conditions on lysozyme nucleation rates and the volume of crystals produced. Batch crystallization plates were used in combination with a video microscope system to measure nucleation rates and crystal volume. As expected from classical nucleation theory, crystal numbers were found to increase with increases in temperature and supersaturation. Small changes in solution pH, at constant supersaturation values were found, however, to dramatically effect the number of crystals nucleated in the wells varying from 1000s to 10s in the pH range 4.0 to 5.2. Having optimized the conditions required to produce an appropriate number of crystals of a suitable volume for X-ray analysis, a large number of uniform crystals were produced under exactly the same conditions. In the X-ray analysis of more than 50 such crystals there was found a wide variation in crystal lattice parameters and data quality. The variation in X-ray quality crystal samples is thought to be related to the growth rate variation caused by growth rate dispersion seen in lysozyme crystal growth experiments.

  11. Impurity effects on orientation of lysozyme crystals nucleated on fatty acid thin films

    NASA Astrophysics Data System (ADS)

    Kubo, T.; Hondoh, H.; Nakada, T.

    2008-04-01

    Commercially available lysozyme samples that have different lot numbers (E02Z04 and E05802) were crystallized on fatty acid thin films. The orientation of lysozyme crystals nucleated on the films was investigated by atomic force microscopy and optical microscopy. The numbers of lysozyme crystals with specific planes parallel to the films are different. In other words, the impurities contained in commercial lysozyme significantly affect the orientation of lysozyme crystals. Detailed analysis of the orientation distribution of the lysozyme crystals nucleated from the purified sample showed that acetic acid is one of the substances promote the epitaxy.

  12. Experimental study of homogeneous nucleation from the bismuth supersaturated vapor: evaluation of the surface tension of critical nucleus.

    PubMed

    Onischuk, A A; Vosel, S V; Borovkova, O V; Baklanov, A M; Karasev, V V; di Stasio, S

    2012-06-14

    The homogeneous nucleation of bismuth supersaturated vapor is studied in a laminar flow quartz tube nucleation chamber. The concentration, size, and morphology of outcoming aerosol particles are analyzed by a transmission electron microscope (TEM) and an automatic diffusion battery (ADB). The wall deposit morphology is studied by scanning electron microscopy. The rate of wall deposition is measured by the light absorption technique and direct weighting of the wall deposits. The confines of the nucleation region are determined in the "supersaturation cut-off" measurements inserting a metal grid into the nucleation zone and monitoring the outlet aerosol concentration response. Using the above experimental techniques, the nucleation rate, supersaturation, and nucleation temperature are measured. The surface tension of the critical nucleus and the radius of the surface of tension are determined from the measured nucleation parameters. To this aim an analytical formula for the nucleation rate is used, derived from author's previous papers based on the Gibbs formula for the work of formation of critical nucleus and the translation-rotation correction. A more accurate approach is also applied to determine the surface tension of critical drop from the experimentally measured bismuth mass flow, temperature profiles, ADB, and TEM data solving an inverse problem by numerical simulation. The simulation of the vapor to particles conversion is carried out in the framework of the explicit finite difference scheme accounting the nucleation, vapor to particles and vapor to wall deposition, and particle to wall deposition, coagulation. The nucleation rate is determined from simulations to be in the range of 10(9)-10(11) cm(-3) s(-1) for the supersaturation of Bi(2) dimers being 10(17)-10(7) and the nucleation temperature 330-570 K, respectively. The surface tension σ(S) of the bismuth critical nucleus is found to be in the range of 455-487 mN/m for the radius of the surface of

  13. Experimental study of homogeneous nucleation from the bismuth supersaturated vapor: Evaluation of the surface tension of critical nucleus

    NASA Astrophysics Data System (ADS)

    Onischuk, A. A.; Vosel, S. V.; Borovkova, O. V.; Baklanov, A. M.; Karasev, V. V.; di Stasio, S.

    2012-06-01

    The homogeneous nucleation of bismuth supersaturated vapor is studied in a laminar flow quartz tube nucleation chamber. The concentration, size, and morphology of outcoming aerosol particles are analyzed by a transmission electron microscope (TEM) and an automatic diffusion battery (ADB). The wall deposit morphology is studied by scanning electron microscopy. The rate of wall deposition is measured by the light absorption technique and direct weighting of the wall deposits. The confines of the nucleation region are determined in the "supersaturation cut-off" measurements inserting a metal grid into the nucleation zone and monitoring the outlet aerosol concentration response. Using the above experimental techniques, the nucleation rate, supersaturation, and nucleation temperature are measured. The surface tension of the critical nucleus and the radius of the surface of tension are determined from the measured nucleation parameters. To this aim an analytical formula for the nucleation rate is used, derived from author's previous papers based on the Gibbs formula for the work of formation of critical nucleus and the translation-rotation correction. A more accurate approach is also applied to determine the surface tension of critical drop from the experimentally measured bismuth mass flow, temperature profiles, ADB, and TEM data solving an inverse problem by numerical simulation. The simulation of the vapor to particles conversion is carried out in the framework of the explicit finite difference scheme accounting the nucleation, vapor to particles and vapor to wall deposition, and particle to wall deposition, coagulation. The nucleation rate is determined from simulations to be in the range of 109-1011 cm-3 s-1 for the supersaturation of Bi2 dimers being 1017-107 and the nucleation temperature 330-570 K, respectively. The surface tension σS of the bismuth critical nucleus is found to be in the range of 455-487 mN/m for the radius of the surface of tension from 0.36 to

  14. Nucleation in a Potts lattice gas model of crystallization from solution

    NASA Astrophysics Data System (ADS)

    Duff, Nathan; Peters, Baron

    2009-11-01

    Nucleation from solution is important in many pharmaceutical crystallization, biomineralization, material synthesis, and self-assembly processes. Simulation methodology has progressed rapidly for studies of nucleation in pure component and implicit solvent systems; however little progress has been made in the simulation of explicit solvent systems. The impasse stems from the inability of rare events simulation methodology to be combined with simulation techniques which maintain a constant chemical potential driving force (supersaturation) for nucleation. We present a Potts lattice gas (PLG) to aid in the development of new simulation strategies for nucleation from solution. The PLG captures common crystallization phase diagram features such as a eutectic point and solute/solvent melting points. Simulations of the PLG below the bulk solute melting temperature reveal a competition between amorphous and crystalline nuclei. As the temperature is increased toward the bulk melting temperature, the nucleation pathway changes from a one step crystalline nucleation pathway to a two step pathway, where an amorphous nucleus forms and then crystallizes. We explain these results in terms of classical nucleation theory with different size-dependant chemical potentials for the amorphous and crystalline nucleation pathways. The two step pathway may be particularly important when crystallization is favored only at postcritical sizes.

  15. Nucleation in a Potts lattice gas model of crystallization from solution.

    PubMed

    Duff, Nathan; Peters, Baron

    2009-11-14

    Nucleation from solution is important in many pharmaceutical crystallization, biomineralization, material synthesis, and self-assembly processes. Simulation methodology has progressed rapidly for studies of nucleation in pure component and implicit solvent systems; however little progress has been made in the simulation of explicit solvent systems. The impasse stems from the inability of rare events simulation methodology to be combined with simulation techniques which maintain a constant chemical potential driving force (supersaturation) for nucleation. We present a Potts lattice gas (PLG) to aid in the development of new simulation strategies for nucleation from solution. The PLG captures common crystallization phase diagram features such as a eutectic point and solute/solvent melting points. Simulations of the PLG below the bulk solute melting temperature reveal a competition between amorphous and crystalline nuclei. As the temperature is increased toward the bulk melting temperature, the nucleation pathway changes from a one step crystalline nucleation pathway to a two step pathway, where an amorphous nucleus forms and then crystallizes. We explain these results in terms of classical nucleation theory with different size-dependant chemical potentials for the amorphous and crystalline nucleation pathways. The two step pathway may be particularly important when crystallization is favored only at postcritical sizes.

  16. Volume nucleation rates for homogeneous freezing in supercooled water microdroplets: results from a combined experimental and modelling approach

    NASA Astrophysics Data System (ADS)

    Earle, M. E.; Kuhn, T.; Khalizov, A. F.; Sloan, J. J.

    2010-08-01

    Temperature-dependent volume nucleation rate coefficients for supercooled water droplets, JV(T), are derived from infrared extinction measurements in a cryogenic laminar aerosol flow tube using a microphysical model. The model inverts water and ice aerosol size distributions retrieved from experimental extinction spectra by considering the evolution of a measured initial droplet distribution via homogeneous nucleation and the exchange of vapour-phase water along a well-defined temperature profile. Experiment and model results are reported for supercooled water droplets with mean radii of 1.0, 1.7, and 2.9 μm. Values of mass accommodation coefficients for evaporation of water droplets and vapour deposition on ice particles are also determined from the model simulations. The coefficient for ice deposition was found to be 0.031 ± 0.001, while that for water evaporation was 0.054 ± 0.012. Results are considered in terms of the applicability of classical nucleation theory to the freezing of micrometre-sized droplets in cirrus clouds, with implications for the parameterization of homogeneous ice nucleation in numerical models.

  17. Volume nucleation rates for homogeneous freezing in supercooled water microdroplets: results from a combined experimental and modelling approach

    NASA Astrophysics Data System (ADS)

    Earle, M. E.; Kuhn, T.; Khalizov, A. F.; Sloan, J. J.

    2009-10-01

    Temperature-dependent volume nucleation rate coefficients for supercooled water droplets, JV(T), are derived from infrared extinction measurements in a cryogenic laminar aerosol flow tube using a microphysical model. The model inverts water and ice aerosol size distributions retrieved from experimental extinction spectra by considering the evolution of a measured initial droplet distribution via homogeneous nucleation and the exchange of vapour-phase water along a well-defined temperature profile. Experiment and model results are reported for supercooled water droplets with mode radii of 1.0, 1.7, and 2.9 μm. Values of mass accommodation coefficients for evaporation of water droplets and vapour deposition on ice particles are also determined from the model simulations. The coefficient for ice deposition was found to be approximately 0.031, while that for water evaporation was 0.054. Results are considered in terms of the applicability of classical nucleation theory to the freezing of micrometre-sized droplets in cirrus clouds, with implications for the parameterization of homogeneous ice nucleation in numerical models.

  18. In-situ observation of nucleated polymer crystallization in polyoxymethylene sandwich composites

    NASA Astrophysics Data System (ADS)

    Slouf, Miroslav; Krejcikova, Sabina; Vackova, Tatana; Kratochvil, Jaroslav; Novak, Libor

    2015-03-01

    We introduce a dynamic sandwich method, which can be used for in-situ observation and quantification of polymer crystallization nucleated by micro/nanoparticles. The method was applied on polyoxymethylene (POM) composites with three nucleating agents: talc micropowder (POM/mTalc), chalk nanopowder (POM/nChalk) and titanate nanotubes (POM/TiNT). The nucleating agents were deposited between polymer films, the resulting sandwich samples were consolidated by thermal treatment, and their microtomed cross-sections were observed during isothermal crystallization by polarized light microscopy. As the intensity of polarized light was shown to be proportional to the relative crystallinity, the PLM results could be fitted to Avrami equation and the nucleating activity of all investigated particles could be quantified by means of Avrami parameters (n, k). The crystallization half-times increased reproducibly in the following order: POM/nChalk < POM/mTalc < POM/TiNT ~ POM. For strong nucleating agents (mTalc, nChalk), the crystallization kinetics corresponded to spontaneous crystallization starting from central nucleating layer, which was verified by computer simulations. The results were also confirmed by DSC. We concluded that the sandwich method is an efficient microscopic technique for detailed evaluation of nucleating activity of arbitrary micro/nanoparticles in polymer systems.

  19. Homogeneous nucleation in vapor-liquid phase transition of Lennard-Jones fluids: a density functional theory approach.

    PubMed

    Ghosh, Satinath; Ghosh, Swapan K

    2011-01-14

    Density functional theory (DFT) with square gradient approximation for the free energy functional and a model density profile are used to obtain an analytical expression for the size-dependent free energy of formation of a liquid drop from the vapor through the process of homogeneous nucleation, without invoking the approximations used in classical nucleation theory (CNT). The density of the liquid drop in this work is not the same as the bulk liquid density but it corresponds to minimum free energy of formation of the liquid drop. The theory is applied to study the nucleation phenomena from supersaturated vapor of Lennard-Jones fluid. The barrier height predicted by this theory is significantly lower than the same in CNT which is rather high. The density at the center of the small liquid drop as obtained through optimization is less than the bulk density which is in agreement with other earlier works. Also proposed is a sharp interface limit of the proposed DFT of nucleation, which is as simple as CNT but with a modified barrier height and this modified classical nucleation theory, as we call it, is shown to lead to improved results.

  20. Kinetic Monte Carlo simulations of electrodeposition: Crossover from continuous to instantaneous homogeneous nucleation within Avrami’s law

    NASA Astrophysics Data System (ADS)

    Frank, Stefan; Rikvold, Per Arne

    2006-06-01

    The influence of lateral adsorbate diffusion on the dynamics of the first-order phase transition in a two-dimensional Ising lattice gas with attractive nearest-neighbor interactions is investigated by means of kinetic Monte Carlo simulations. For example, electrochemical underpotential deposition proceeds by this mechanism. One major difference from adsorption in vacuum surface science is that under control of the electrode potential and in the absence of mass-transport limitations, local adsorption equilibrium is approximately established. We analyze our results using the theory of Kolmogorov, Johnson and Mehl, and Avrami (KJMA), which we extend to an exponentially decaying nucleation rate. Such a decay may occur due to a suppression of nucleation around existing clusters in the presence of lateral adsorbate diffusion. Correlation functions prove the existence of such exclusion zones. By comparison with microscopic results for the nucleation rate I and the interface velocity of the growing clusters v, we can show that the KJMA theory yields the correct order of magnitude for Iv2. This is true even though the spatial correlations mediated by diffusion are neglected. The decaying nucleation rate causes a gradual crossover from continuous to instantaneous nucleation, which is complete when the decay of the nucleation rate is very fast on the time scale of the phase transformation. Hence, instantaneous nucleation can be homogeneous, producing negative minima in the two-point correlation functions. We also present in this paper an n-fold way Monte Carlo algorithm for a square lattice gas with adsorption/desorption and lateral diffusion.

  1. Nucleation kinetics and crystal growth with fluctuating rates at the intermediate stage of phase transitions

    NASA Astrophysics Data System (ADS)

    Alexandrov, D. V.; Malygin, A. P.

    2014-01-01

    Crystal growth kinetics accompanied by particle growth with fluctuating rates at the intermediate stage of phase transitions is analyzed theoretically. The integro-differential model of governing equations is solved analytically for size-independent growth rates and arbitrary dependences of the nucleation frequency on supercooling/supersaturation. Two important cases of Weber-Volmer-Frenkel-Zel'dovich and Mier nucleation kinetics are detailed. A Fokker-Plank type equation for the crystal-size density distribution function is solved explicitly.

  2. Toward a molecular theory of homogeneous bubble nucleation: II. Calculation of the number density of critical nuclei and the rate of nucleation.

    PubMed

    Torabi, Korosh; Corti, David S

    2013-10-17

    In the present paper, we develop a method to calculate the rate of homogeneous bubble nucleation within a superheated L-J liquid based on the (n,v) equilibrium embryo free energy surface introduced in the first paper (DOI: 10.1021/jp404149n). We express the nucleation rate as the product of the concentration of critical nuclei within the metastable liquid phase and the relevant forward rate coefficient. We calculate the forward rate coefficient of the critical nuclei from their average lifetime as determined from MD simulations of a large number of embryo trajectories initiated from the transitional region of the metastable liquid configuration space. Therefore, the proposed rate coefficient does not rely on any predefined reaction coordinate. In our model, the critical nuclei belong to the region of the configuration space where the committor probability is about one-half, guaranteeing the dynamical relevance of the proposed embryos. One novel characteristic of our approach is that we define a limit for the configuration space of the equilibrium metastable phase and do not include the configurations that have zero committor probability in the nucleation free energy surface. Furthermore, in order to take into account the transitional degrees of freedom of the critical nuclei, we develop a simulation-based approach for rigorously mapping the free energy of the (n,v) equilibrium embryos to the concentration of the critical nuclei within the bulk metastable liquid phase.

  3. Homogeneous sugar modification improves crystallization of measles virus hemagglutinin.

    PubMed

    Hashiguchi, Takao; Kajikawa, Mizuho; Maita, Nobuo; Takeda, Makoto; Kuroki, Kimiko; Sasaki, Kaori; Kohda, Daisuke; Yanagi, Yusuke; Maenaka, Katsumi

    2008-04-01

    Measles virus (MV) enters cells by binding to the signaling lymphocyte activation molecule (also called CD150) on the cell surface, and thus shows the lymphotropism and immunosuppressive effects. The head domain (residues Asp149 to Arg617) of the MV hemagglutinin (MV-H), the attachment protein, was produced using a transient expression system in HEK293T cells. The purified MV-H protein was heterogeneous because of a variety of complex-sugar modifications. The complex-sugar-type MV-H was crystallized successfully, and the crystals belonged to the space group P41212 with the unit cell dimension of a=b=134 A, c=100 A, but diffracted only to 3.0 A resolution. MV-H was also expressed in HEK293SGnTI(-) cells lacking the N-acetylglucosaminyltransferase I activity, which render N-linked glycans of the proteins restricted and homogeneous, producing the oligomannose, Man5GlcNAc2. The native and selenomethionyl derivative proteins of the oligomannose-type MV-H were crystallized, and the native crystals well diffracted to 2.6A resolution. Thus, homogeneous sugar modification may be useful for improved crystallization of heavily sugar-modified viral envelope proteins.

  4. Validation of homogeneous anisotropic hardening approach based on crystal plasticity

    NASA Astrophysics Data System (ADS)

    Jeong, Youngung; Barlat, Frédéric; Tomé, Carlos; Wen, Wei

    2016-10-01

    The current study investigates constitutive models at two different scales: 1) the micromechanical crystal plasticity framework using a dislocation density-based hardening model [1, 2]; 2) macroscale constitutive model based on a yield function that evolves according to the homogeneous anisotropic hardening (HAH) model [3, 4]. The polycrystalline aggregate, tuned for a low-carbon steel, is used to calculate the evolution of the yield surface during monotonic uniaxial tension. The results of the crystal plasticity model are used to train the anisotropic yield function and HAH parameters to demonstrate the flexibility of the macroscale constitutive approach. Through comparison between the two models, an improved rule for the HAH model is suggested.

  5. Using natural seeding material to generate nucleation in protein crystallization experiments.

    PubMed

    D'Arcy, Allan; Mac Sweeney, Aengus; Haber, Alexander

    2003-07-01

    The nucleation event in protein crystallization is a part of the process that is poorly controlled. It is generally accepted that the protein should be in the metastable phase for crystal growth, but for nucleation higher levels of saturation are needed. Formation of nuclei in bulk solvent requires interaction of protein molecules until a critical size of aggregate is created. In many crystallization experiments sufficiently high levels of saturation are not reached to allow this critical nucleation event to occur. If an environment can be created that favours a higher local concentration of macromolecules, the energy barrier for nucleation may be lowered. When seeds are introduced at lower levels of saturation in a crystallization experiment, nucleation may be facilitated and crystal growth initiated. In this study, the use of natural materials as stable seeds for nucleation has been investigated. The method makes it possible to introduce seeds into crystallization trials at any stage of the experiment using both microbatch and vapour-diffusion methods.

  6. Enhancement of crystal homogeneity of protein crystals under application of an external alternating current electric field

    SciTech Connect

    Koizumi, H.; Uda, S.; Fujiwara, K.; Nozawa, J.; Tachibana, M.; Kojima, K.

    2014-10-06

    X-ray diffraction rocking-curve measurements were performed on tetragonal hen egg white (HEW) lysozyme crystals grown with and without the application of an external alternating current (AC) electric field. The crystal quality was assessed by the full width at half maximum (FWHM) value for each rocking curve. For two-dimensional maps of the FWHMs measured on the 440 and the 12 12 0 reflection, the crystal homogeneity was improved under application of an external electric field at 1 MHz, compared with that without. In particular, the significant improvement of the crystal homogeneity was observed for the 12 12 0 reflection.

  7. The Effects of Thermal History on Nucleation of Tetragonal Lysozyme Crystals, or Hot Protein and Cold Nucleation

    NASA Technical Reports Server (NTRS)

    Burke, Michael; Judge, Russell; Pusey, Marc

    2000-01-01

    Chicken egg white lysozyme has a well characterized thermally driven phase transition. Between pH 4.2 and 5.2, the transition temperature, as defined by the point where the tetragonal and orthorhombic solubilities are equal, is a function of the pH, salt (precipitant) type and concentration, and most likely of the buffer concentration as well. This phase transition can be carried out with protein solution alone, prior to addition of precipitant solution. Warming a lysozyme solution above the phase transition point, then cooling it back below this point, has been shown to affect the subsequent nucleation rate, as determined by the numbers and size of crystals formed, but not the growth rate for the tetragonal crystal form . We have now measured the kinetics of this process and investigated its reversibility. The transition effects are progressive with temperature, having a half time of about 1 hour at 37C at pH 4.8. After holding a lysozyme solution at 37C (prior to addition of precipitant) for 16 hours, then cooling it back to 4C no return to the pre-warmed nucleation kinetics are observed after at least 4 weeks. Orthorhombic lysozyme crystals apparently do not undergo the flow-induced growth cessation of tetragonal lysozyme crystals. Putting the protein in the orthorhombic form does not affect the averaged face growth kinetics, only nucleation, for tetragonal crystals. This differential behaviour may be exploited to elucidate how and where flow affects the lysozyme crystal growth process. The presentation will focus on the results of these and ongoing studies in this area.

  8. The Effects of Thermal History on Nucleation of Tetragonal Lysozyme Crystals, or Hot Protein and Cold Nucleation

    NASA Technical Reports Server (NTRS)

    Burke, Michael; Judge, Russell; Pusey, Marc

    2000-01-01

    Chicken egg white lysozyme has a well characterized thermally driven phase transition. Between pH 4.2 and 5.2, the transition temperature, as defined by the point where the tetragonal and orthorhombic solubilities are equal, is a function of the pH, salt (precipitant) type and concentration, and most likely of the buffer concentration as well. This phase transition can be carried out with protein solution alone, prior to addition of precipitant solution. Warming a lysozyme solution above the phase transition point, then cooling it back below this point, has been shown to affect the subsequent nucleation rate, as determined by the numbers and size of crystals formed, but not the growth rate for the tetragonal crystal form . We have now measured the kinetics of this process and investigated its reversibility. The transition effects are progressive with temperature, having a half time of about 1 hour at 37C at pH 4.8. After holding a lysozyme solution at 37C (prior to addition of precipitant) for 16 hours, then cooling it back to 4C no return to the pre-warmed nucleation kinetics are observed after at least 4 weeks. Orthorhombic lysozyme crystals apparently do not undergo the flow-induced growth cessation of tetragonal lysozyme crystals. Putting the protein in the orthorhombic form does not affect the averaged face growth kinetics, only nucleation, for tetragonal crystals. This differential behaviour may be exploited to elucidate how and where flow affects the lysozyme crystal growth process. The presentation will focus on the results of these and ongoing studies in this area.

  9. Theoretical study of vapor-liquid homogeneous nucleation using stability analysis of a macroscopic phase.

    PubMed

    Carreón-Calderón, Bernardo

    2012-10-14

    Stability analysis is generally used to verify that the solution to phase equilibrium calculations corresponds to a stable state (minimum of the free energy). In this work, tangent plane distance analysis for stability of macroscopic mixtures is also used for analyzing the nucleation process, reconciling thus this analysis with classical nucleation theories. In the context of the revised nucleation theory, the driving force and the nucleation work are expressed as a function of the Lagrange multiplier corresponding to the mole fraction constraint from the minimization problem of stability analysis. Using a van der Waals fluid applied to a ternary mixture, Lagrange multiplier properties are illustrated. In particular, it is shown how the Lagrange multiplier value is equal to one on the binodal and spinodal curves at the same time as the driving force of nucleation vanishes on these curves. Finally, it is shown that, on the spinodal curve, the nucleation work from the revised and generalized nucleation theories are characterized by two different local minima from stability analysis, irrespective of any interfacial tension models.

  10. An improved model of homogeneous nucleation for high supersaturation conditions: aluminum vapor.

    PubMed

    Savel'ev, A M; Starik, A M

    2016-12-21

    A novel model of stationary nucleation, treating the thermodynamic functions of small clusters, has been built. The model is validated against the experimental data on the nucleation rate of water vapor obtained in a broad range of supersaturation values (S = 10-120), and, at high supersaturation values, it reproduces the experimental data much better than the traditional classical nucleation model. A comprehensive analysis of the nucleation of aluminum vapor with the usage of developed stationary and non-stationary nucleation models has been performed. It has been shown that, at some value of supersaturation, there exists a double potential nucleation barrier. It has been revealed that the existence of this barrier notably delayed the establishment of a stationary distribution of subcritical clusters. It has also been demonstrated that the non-stationary model of the present work and the model of liquid-droplet approximation predict different values of nucleation delay time, τs. In doing so, the liquid-droplet model can underestimate notably (by more than an order of magnitude) the value of τs.

  11. Crystal Nucleation in Liquids: Open Questions and Future Challenges in Molecular Dynamics Simulations

    PubMed Central

    2016-01-01

    The nucleation of crystals in liquids is one of nature’s most ubiquitous phenomena, playing an important role in areas such as climate change and the production of drugs. As the early stages of nucleation involve exceedingly small time and length scales, atomistic computer simulations can provide unique insights into the microscopic aspects of crystallization. In this review, we take stock of the numerous molecular dynamics simulations that, in the past few decades, have unraveled crucial aspects of crystal nucleation in liquids. We put into context the theoretical framework of classical nucleation theory and the state-of-the-art computational methods by reviewing simulations of such processes as ice nucleation and the crystallization of molecules in solutions. We shall see that molecular dynamics simulations have provided key insights into diverse nucleation scenarios, ranging from colloidal particles to natural gas hydrates, and that, as a result, the general applicability of classical nucleation theory has been repeatedly called into question. We have attempted to identify the most pressing open questions in the field. We believe that, by improving (i) existing interatomic potentials and (ii) currently available enhanced sampling methods, the community can move toward accurate investigations of realistic systems of practical interest, thus bringing simulations a step closer to experiments. PMID:27228560

  12. Crystal nucleation and cluster-growth kinetics in a model glass under shear.

    PubMed

    Mokshin, Anatolii V; Barrat, Jean-Louis

    2010-08-01

    Crystal nucleation and growth processes induced by an externally applied shear strain in a model metallic glass are studied by means of nonequilibrium molecular dynamics simulations, in a range of temperatures. We observe that the nucleation-growth process takes place after a transient, induction regime. The critical cluster size and the lag-time associated with this induction period are determined from a mean first-passage time analysis. The laws that describe the cluster-growth process are studied as a function of temperature and strain rate. A theoretical model for crystallization kinetics that includes the time dependence for nucleation and cluster growth is developed within the framework of the Kolmogorov-Johnson-Mehl-Avrami scenario and is compared with the molecular dynamics data. Scalings for the cluster-growth laws and for the crystallization kinetics are also proposed and tested. The observed nucleation rates are found to display a nonmonotonic strain rate dependency.

  13. Crystal nucleation and cluster-growth kinetics in a model glass under shear

    NASA Astrophysics Data System (ADS)

    Mokshin, Anatolii V.; Barrat, Jean-Louis

    2010-08-01

    Crystal nucleation and growth processes induced by an externally applied shear strain in a model metallic glass are studied by means of nonequilibrium molecular dynamics simulations, in a range of temperatures. We observe that the nucleation-growth process takes place after a transient, induction regime. The critical cluster size and the lag-time associated with this induction period are determined from a mean first-passage time analysis. The laws that describe the cluster-growth process are studied as a function of temperature and strain rate. A theoretical model for crystallization kinetics that includes the time dependence for nucleation and cluster growth is developed within the framework of the Kolmogorov-Johnson-Mehl-Avrami scenario and is compared with the molecular dynamics data. Scalings for the cluster-growth laws and for the crystallization kinetics are also proposed and tested. The observed nucleation rates are found to display a nonmonotonic strain rate dependency.

  14. Nucleation kinetics, growth and studies of β-alanine single crystals

    NASA Astrophysics Data System (ADS)

    Shanthi, D.; Selvarajan, P.; HemaDurga, K. K.; Lincy Mary Ponmani, S.

    2013-06-01

    Solubility and metastable zone width for the re-crystallized salt of β-alanine was determined. Induction period measurement for the selected supersaturation ratios at room temperature (31 °C) was carried out for supersaturated aqueous solutions of β-alanine and it is noticed that induction period decreases with increase of supersaturation ratio. The nucleation parameters such as Gibbs free energy change, radius and number of molecules of the critical nucleus, interfacial tension and the nucleation rate have been evaluated by classical nucleation theory. Single crystals of β-alanine were grown using the optimized nucleation parameters by solution method and grown crystals have been subjected to various studies like XRD studies, FTIR, optical, thermal and SHG studies.

  15. Investigation of primary nucleation phenomena of acetylsalicylic acid crystals induced by ultrasonic irradiation—ultrasonic energy needed to activate primary nucleation

    NASA Astrophysics Data System (ADS)

    Miyasaka, Etsuko; Ebihara, Satomi; Hirasawa, Izumi

    2006-09-01

    The purpose of our study is to clarify ultrasonic primary nucleation phenomena for controlling final product size by adjusting the number of primary nuclei. In our previous study, the effect of ultrasonic irradiation on the number of nuclei was investigated under the same supersaturated condition, as a result two novel phenomena were observed. First, there is a region where ultrasonic irradiation inhibits primary nucleation. Second, a specific amount of energy is needed to activate primary nucleation. From this result, it was expected that the ultrasonic energy needed to activate primary nucleation has a certain relationship to the energy necessary to form a stable nucleus. Therefore, we investigated the following: whether ultrasonic irradiation inhibits and activates primary nucleation at various degrees of supersaturation, whether final crystal size relates to the number of nuclei, and whether the ultrasonic energy needed to activate primary nucleation relates to the energy necessary to form a stable nucleus. First, we found that ultrasonic irradiation inhibits and activates primary nucleation at various supersaturated degrees. Second, we found that final crystal size increases or decreases depending on the number of nuclei. Therefore, it was indicated that ultrasonic energy could yield the desired crystal size by inducing suitable nucleation. Third, we found that the ultrasonic energy needed to activate primary nucleation decreases with a decrease in the energy necessary to form a stable nucleus. From this, we can propose criteria for determining the effect of ultrasonic irradiation on primary nucleation by showing diagrams correlating Δ Gcrit with Ecrit.

  16. Role of nearest-neighbor drops in the kinetics of homogeneous nucleation in a supersaturated vapor

    NASA Astrophysics Data System (ADS)

    Grinin, A. P.; Zhuvikina, I. A.; Kuni, F. M.; Reiss, H.

    2004-12-01

    A theory of simultaneous nucleation and drop growth in a supersaturated vapor is developed. The theory makes use of the concept of "nearest-neighbor" drops. The effect of vapor heterogeneity caused by vapor diffusion to a growing drop, formed previously, is accounted for by considering the nucleation of the nearest-neighbor drop. The diffusional boundary value problem is solved through the application of a recent theory that maintains material balance between the vapor and the drop, even though the drop boundary is a moving one. This is fundamental to the use of the proper time and space dependent vapor supersaturation in the application of nucleation theory. The conditions are formulated under which the mean distance to the nearest-neighbor drop and the mean time to its appearance can be determined reliably. Under these conditions, the mean time provides an estimate of the duration of the nucleation stage, while the mean distance provides an estimate of the number of drops formed per unit volume during the nucleation stage. It turns out, surprisingly, that these estimates agree fairly well with the predictions of the simpler and more standard approach based on the approximation that the density of the vapor phase remains uniform during the nucleation stage. Thus, as a practical matter, in many situations, the use of the simpler and less rigorous method is justified by the predictions of the more rigorous, but more complicated theory.

  17. Microstructurally-sensitive fatigue crack nucleation in Ni-based single and oligo crystals

    NASA Astrophysics Data System (ADS)

    Chen, Bo; Jiang, Jun; Dunne, Fionn P. E.

    2017-09-01

    An integrated experimental, characterisation and computational crystal plasticity study of cyclic plastic beam loading has been carried out for nickel single crystal (CMSX4) and oligocrystal (MAR002) alloys in order to assess quantitatively the mechanistic drivers for fatigue crack nucleation. The experimentally validated modelling provides knowledge of key microstructural quantities (accumulated slip, stress and GND density) at experimentally observed fatigue crack nucleation sites and it is shown that while each of these quantities is potentially important in crack nucleation, none of them in its own right is sufficient to be predictive. However, the local (elastic) stored energy density, measured over a length scale determined by the density of SSDs and GNDs, has been shown to predict crack nucleation sites in the single and oligocrystals tests. In addition, once primary nucleated cracks develop and are represented in the crystal model using XFEM, the stored energy correctly identifies where secondary fatigue cracks are observed to nucleate in experiments. This (Griffith-Stroh type) quantity also correctly differentiates and explains intergranular and transgranular fatigue crack nucleation.

  18. Local order parameters for use in driving homogeneous ice nucleation with all-atom models of water.

    PubMed

    Reinhardt, Aleks; Doye, Jonathan P K; Noya, Eva G; Vega, Carlos

    2012-11-21

    We present a local order parameter based on the standard Steinhardt-Ten Wolde approach that is capable both of tracking and of driving homogeneous ice nucleation in simulations of all-atom models of water. We demonstrate that it is capable of forcing the growth of ice nuclei in supercooled liquid water simulated using the TIP4P/2005 model using over-biassed umbrella sampling Monte Carlo simulations. However, even with such an order parameter, the dynamics of ice growth in deeply supercooled liquid water in all-atom models of water are shown to be very slow, and so the computation of free energy landscapes and nucleation rates remains extremely challenging.

  19. Some Aspects of PVT Low Supersaturation Nucleation and Contactless Crystal Growth

    NASA Technical Reports Server (NTRS)

    Grasza, K.; Palosz, W.

    1996-01-01

    The basic principles of the contactless growth of crystals from the vapor in combination with the process of low-supersaturation nucleation are discussed. The mathematical formulation of the morphological stability criterion in vapor growth systems is given and its implications for contactless growth technique are analyzed. A diagram for selection of proper temperature conditions for growth of CdTe crystals is presented.

  20. Investigation on nucleation kinetics, growth and characterization of urea oxalic acid-ferroelectric single crystal

    NASA Astrophysics Data System (ADS)

    Dhivya, R.; Ezhil Vizhi, R.; Rajan Babu, D.

    2017-06-01

    Nucleation and growth kinetics renders the information about the crystal growth process, which can be adopted to grow large size crystals. Urea oxalic acid was synthesized by slow evaporation method. Solubility was analyzed gravimetrically and it was observed that it exhibits positive temperature coefficient of solubility which is suitable for bulk growth. Metastable zonewidth was observed by adopting polythermal method. Induction period was measured by isothermal method for the saturation temperature by varying the degrees of supersaturation. Based on the classical theory of nucleation, the other nucleation parameters such as interfacial energy, Gibbs critical free energy and radius of critical nuclei were calculated. Urea oxalic acid (UOA) was synthesized and subsequently grown by a slow cooling technique. Single crystal X-ray diffraction study confirms that the crystal belongs to a monoclinic system. Dielectric analysis affirms the ferroelectric property of the material and the results were further discussed in detail.

  1. A novel approach to the theory of homogeneous and heterogeneous nucleation.

    PubMed

    Ruckenstein, Eli; Berim, Gersh O; Narsimhan, Ganesan

    2015-01-01

    A new approach to the theory of nucleation, formulated relatively recently by Ruckenstein, Narsimhan, and Nowakowski (see Refs. [7-16]) and developed further by Ruckenstein and other colleagues, is presented. In contrast to the classical nucleation theory, which is based on calculating the free energy of formation of a cluster of the new phase as a function of its size on the basis of macroscopic thermodynamics, the proposed theory uses the kinetic theory of fluids to calculate the condensation (W(+)) and dissociation (W(-)) rates on and from the surface of the cluster, respectively. The dissociation rate of a monomer from a cluster is evaluated from the average time spent by a surface monomer in the potential well as obtained from the solution of the Fokker-Planck equation in the phase space of position and momentum for liquid-to-solid transition and the phase space of energy for vapor-to-liquid transition. The condensation rates are calculated using traditional expressions. The knowledge of those two rates allows one to calculate the size of the critical cluster from the equality W(+)=W(-) as well as the rate of nucleation. The developed microscopic approach allows one to avoid the controversial application of classical thermodynamics to the description of nuclei which contain a few molecules. The new theory was applied to a number of cases, such as the liquid-to-solid and vapor-to-liquid phase transitions, binary nucleation, heterogeneous nucleation, nucleation on soluble particles and protein folding. The theory predicts higher nucleation rates at high saturation ratios (small critical clusters) than the classical nucleation theory for both solid-to-liquid as well as vapor-to-liquid transitions. As expected, at low saturation ratios for which the size of the critical cluster is large, the results of the new theory are consistent with those of the classical one. The present approach was combined with the density functional theory to account for the density

  2. The early crystal nucleation process in hard spheres shows synchronised ordering and densification

    NASA Astrophysics Data System (ADS)

    Berryman, Joshua T.; Anwar, Muhammad; Dorosz, Sven; Schilling, Tanja

    2016-12-01

    We investigate the early part of the crystal nucleation process in the hard sphere fluid using data produced by computer simulation. We find that hexagonal order manifests continuously in the overcompressed liquid, beginning approximately one diffusion time before the appearance of the first "solid-like" particle of the nucleating cluster, and that a collective influx of particles towards the nucleation site occurs simultaneously to the ordering process: the density increases leading to nucleation are generated by the same individual particle displacements as the increases in order. We rule out the presence of qualitative differences in the early nucleation process between medium and low overcompressions and also provide evidence against any separation of translational and orientational order on the relevant lengthscales.

  3. Dynamics of the phase transition boundary in the presence of nucleation and growth of crystals

    NASA Astrophysics Data System (ADS)

    Alexandrov, D. V.

    2017-08-01

    Nucleation and growth of crystals in a moving metastable layer of phase transition is analyzed theoretically. The integro-differential equations for the density distribution function and system metastability are solved analytically on the basis of a previously developed approach (Alexandrov and Malygin 2013 J. Phys. A: Math. Theor. 46 455101) in cases of the kinetic and diffusionally controlled regimes of crystal growth. The Weber-Volmer-Frenkel-Zel’dovich and Meirs nucleation kinetics are considered. It is shown that the phase transition boundary propagates with time as α\\sqrt{t}+\\varepsilon Z_1(t) , where Z_1(t)=β t7/2 and Z_1(t)=β t2 in cases of kinetic and diffusionally controlled growth regimes. The growth rate constants α and β as well as parameter ɛ are found analytically. The phase transition boundary in the presence of particle nucleation and growth moves slower than in cases without nucleation.

  4. Multiple pathways of crystal nucleation in an extremely supersaturated aqueous potassium dihydrogen phosphate (KDP) solution droplet

    PubMed Central

    Lee, Sooheyong; Wi, Haeng Sub; Jo, Wonhyuk; Cho, Yong Chan; Lee, Hyun Hwi; Jeong, Se-Young; Kim, Yong-Il; Lee, Geun Woo

    2016-01-01

    Solution studies have proposed that crystal nucleation can take more complex pathways than previously expected in classical nucleation theory, such as formation of prenucleation clusters or densified amorphous/liquid phases. These findings show that it is possible to separate fluctuations in the different order parameters governing crystal nucleation, that is, density and structure. However, a direct observation of the multipathways from aqueous solutions remains a great challenge because heterogeneous nucleation sites, such as container walls, can prevent these paths. Here, we demonstrate the existence of multiple pathways of nucleation in highly supersaturated aqueous KH2PO4 (KDP) solution using the combination of a containerless device (electrostatic levitation), and in situ micro-Raman and synchrotron X-ray scattering. Specifically, we find that, at an unprecedentedly deep level of supersaturation, a high-concentration KDP solution first transforms into a metastable crystal before reaching stability at room temperature. However, a low-concentration solution, with different local structures, directly transforms into the stable crystal phase. These apparent multiple pathways of crystallization depend on the degree of supersaturation. PMID:27791068

  5. Homogeneous bubble nucleation in water at negative pressure: A Voronoi polyhedra analysis

    NASA Astrophysics Data System (ADS)

    Abascal, Jose L. F.; Gonzalez, Miguel A.; Aragones, Juan L.; Valeriani, C.

    2013-02-01

    We investigate vapor bubble nucleation in metastable TIP4P/2005 water at negative pressure via the Mean First Passage Time (MFPT) technique using the volume of the largest bubble as a local order parameter. We identify the bubbles in the system by means of a Voronoi-based analysis of the molecular dynamics trajectories. By comparing the features of the tessellation of liquid water at ambient conditions to those of the same system with an empty cavity we are able to discriminate vapor (or interfacial) molecules from the bulk ones. This information is used to follow the time evolution of the largest bubble until the system cavitates at 280 K above and below the spinodal line. At the pressure above the spinodal line, the MFPT curve shows the expected shape for a moderately metastable liquid from which we estimate the bubble nucleation rate and the size of the critical cluster. The nucleation rate estimated using Classical Nucleation Theory turns out to be about 8 order of magnitude lower than the one we compute by means of MFPT. The behavior at the pressure below the spinodal line, where the liquid is thermodynamically unstable, is remarkably different, the MFPT curve being a monotonous function without any inflection point.

  6. Homogeneous bubble nucleation in water at negative pressure: a Voronoi polyhedra analysis.

    PubMed

    Abascal, Jose L F; Gonzalez, Miguel A; Aragones, Juan L; Valeriani, C

    2013-02-28

    We investigate vapor bubble nucleation in metastable TIP4P/2005 water at negative pressure via the Mean First Passage Time (MFPT) technique using the volume of the largest bubble as a local order parameter. We identify the bubbles in the system by means of a Voronoi-based analysis of the molecular dynamics trajectories. By comparing the features of the tessellation of liquid water at ambient conditions to those of the same system with an empty cavity we are able to discriminate vapor (or interfacial) molecules from the bulk ones. This information is used to follow the time evolution of the largest bubble until the system cavitates at 280 K above and below the spinodal line. At the pressure above the spinodal line, the MFPT curve shows the expected shape for a moderately metastable liquid from which we estimate the bubble nucleation rate and the size of the critical cluster. The nucleation rate estimated using Classical Nucleation Theory turns out to be about 8 order of magnitude lower than the one we compute by means of MFPT. The behavior at the pressure below the spinodal line, where the liquid is thermodynamically unstable, is remarkably different, the MFPT curve being a monotonous function without any inflection point.

  7. Nucleation of Crystals From Solution in Microgravity (USML-1 Glovebox (GBX) Investigation)

    NASA Technical Reports Server (NTRS)

    Kroes, Roger L.; Reiss, Donald A.; Lehoczky, Sandor L.

    1994-01-01

    A new method for initiating nucleation from solutions in microgravity which avoids nucleation on container walls and other surfaces is described. This method consists of injecting a small quantity of highly concentrated, heated solution into the interior of a lightly supersaturated, cooler host gowth solution. It was tested successfully on USML-I, producing a large number of LAP crystals whose longest dimension averaged 1 mm.

  8. Mode of action and design rules for additives that modulate crystal nucleation.

    PubMed

    Anwar, Jamshed; Boateng, Papa Kofi; Tamaki, Reiko; Odedra, Sheetal

    2009-01-01

    Molecular dynamics simulations reveal that the key factors that determine the ability of an additive to modulate crystal nucleation are the strength of its interaction with the solute, its disruptive ability (which may be based on steric, entropic, or energetic effects), and interfacial properties, along with its ability to serve as a template for nucleation (see snapshot of an emerging nucleus with a single-particle additive: black spheres).

  9. The Effect of Temperature and Solution pH on the Nucleation of Tetragonal Lysozyme Crystals

    NASA Technical Reports Server (NTRS)

    Judge, Russell A.; Jacobs, Randolph S.; Frazier, Tyralynn; Snell, Edward H.; Pusey, Marc L.

    1999-01-01

    Part of the challenge of macromolecular crystal growth for structure determination is obtaining crystals with a volume suitable for x-ray analysis. In this respect an understanding of the effect of solution conditions on macromolecule nucleation rates is advantageous. This study investigated the effects of supersaturation, temperature, and pH on the nucleation rate of tetragonal lysozyme crystals. Batch crystallization plates were prepared at given solution concentrations and incubated at set temperatures over 1 week. The number of crystals per well with their size and axial ratios were recorded and correlated with solution conditions. Crystal numbers were found to increase with increasing supersaturation and temperature. The most significant variable, however, was pH; crystal numbers changed by two orders of magnitude over the pH range 4.0-5.2. Crystal size also varied with solution conditions, with the largest crystals obtained at pH 5.2. Having optimized the crystallization conditions, we prepared a batch of crystals under the same initial conditions, and 50 of these crystals were analyzed by x-ray diffraction techniques. The results indicate that even under the same crystallization conditions, a marked variation in crystal properties exists.

  10. The effect of temperature and solution pH on the nucleation of tetragonal lysozyme crystals.

    PubMed

    Judge, R A; Jacobs, R S; Frazier, T; Snell, E H; Pusey, M L

    1999-09-01

    Part of the challenge of macromolecular crystal growth for structure determination is obtaining crystals with a volume suitable for x-ray analysis. In this respect an understanding of the effect of solution conditions on macromolecule nucleation rates is advantageous. This study investigated the effects of supersaturation, temperature, and pH on the nucleation rate of tetragonal lysozyme crystals. Batch crystallization plates were prepared at given solution concentrations and incubated at set temperatures over 1 week. The number of crystals per well with their size and axial ratios were recorded and correlated with solution conditions. Crystal numbers were found to increase with increasing supersaturation and temperature. The most significant variable, however, was pH; crystal numbers changed by two orders of magnitude over the pH range 4.0-5.2. Crystal size also varied with solution conditions, with the largest crystals obtained at pH 5.2. Having optimized the crystallization conditions, we prepared a batch of crystals under the same initial conditions, and 50 of these crystals were analyzed by x-ray diffraction techniques. The results indicate that even under the same crystallization conditions, a marked variation in crystal properties exists.

  11. The Effect of Temperature and Solution pH on the Nucleation of Tetragonal Lysozyme Crystals

    NASA Technical Reports Server (NTRS)

    Judge, Russell A.; Jacobs, Randolph S.; Frazier, Tyralynn; Snell, Edward H.; Pusey, Marc L.

    1999-01-01

    Part of the challenge of macromolecular crystal growth for structure determination is obtaining crystals with a volume suitable for x-ray analysis. In this respect an understanding of the effect of solution conditions on macromolecule nucleation rates is advantageous. This study investigated the effects of supersaturation, temperature, and pH on the nucleation rate of tetragonal lysozyme crystals. Batch crystallization plates were prepared at given solution concentrations and incubated at set temperatures over 1 week. The number of crystals per well with their size and axial ratios were recorded and correlated with solution conditions. Crystal numbers were found to increase with increasing supersaturation and temperature. The most significant variable, however, was pH; crystal numbers changed by two orders of magnitude over the pH range 4.0-5.2. Crystal size also varied with solution conditions, with the largest crystals obtained at pH 5.2. Having optimized the crystallization conditions, we prepared a batch of crystals under the same initial conditions, and 50 of these crystals were analyzed by x-ray diffraction techniques. The results indicate that even under the same crystallization conditions, a marked variation in crystal properties exists.

  12. Effect of Mannitol on Nucleation and Crystal Growth of Amorphous Flavonoids: Implications on the Formation of Nanocrystalline Solid Dispersion.

    PubMed

    Shete, Ganesh; Modi, Sameer R; Bansal, Arvind Kumar

    2015-11-01

    In this work, we studied crystallization kinetics of amorphous hesperetin (HRN) and naringenin (NRN) alone, and in 1:1 proportion with mannitol at Tg + 15 K. Crystallization rate of NRN was found to be significantly higher than HRN. Mannitol accelerated crystallization of HRN as well as NRN. NRN exhibited higher crystallization rate than HRN, in presence of mannitol, as well. Finke-Watzky model was used to deconvolute the crystallization kinetics data into nucleation and crystal growth rate constant. HRN alone had 9.56 × 10(9) times faster nucleation rate and 1.88 times slower crystal growth than NRN alone. Mannitol increased nucleation and crystal growth rate of HRN as well as NRN. In presence of mannitol, HRN possessed 1.34 × 10(10) times faster nucleation rate and 1.70 times slower crystal growth rate than NRN. Differences in crystallization behavior of HRN and NRN were explained by their thermodynamic properties.

  13. Phase field theory of interfaces and crystal nucleation in a eutectic system of fcc structure: II. Nucleation in the metastable liquid immiscibility region.

    PubMed

    Tóth, Gyula I; Gránásy, László

    2007-08-21

    In the second part of our paper, we address crystal nucleation in the metastable liquid miscibility region of eutectic systems that is always present, though experimentally often inaccessible. While this situation resembles the one seen in single component crystal nucleation in the presence of a metastable vapor-liquid critical point addressed in previous works, it is more complex because of the fact that here two crystal phases of significantly different compositions may nucleate. Accordingly, at a fixed temperature below the critical point, six different types of nuclei may form: two liquid-liquid nuclei: two solid-liquid nuclei; and two types of composite nuclei, in which the crystalline core has a liquid "skirt," whose composition falls in between the compositions of the solid and the initial liquid phases, in addition to nuclei with concentric alternating composition shells of prohibitively high free energy. We discuss crystalline phase selection via exploring/identifying the possible pathways for crystal nucleation.

  14. Effects of chitosan on the alignment, morphology and shape of calcite crystals nucleating under Langmuir monolayers

    SciTech Connect

    Kim, Kyungil; Uysal, Ahmet; Kewalramani, Sumit; Stripe, Benjamin; Dutta, Pulak

    2009-04-22

    The growth of calcium carbonate crystals under Langmuir monolayers was investigated in the presence of chitosan, a soluble derivative of chitin added to the subphase to better simulate the polyelectrolyte-containing in vivo environment. Chitosan causes distinct concentration-dependent changes in the orientation, shape and morphology of the calcite crystals nucleating under acid and sulfate monolayers. Our results suggest that polyelectrolytes may play essential roles in controlling the growth of biogenic calcite crystals.

  15. Effects of Chitosan on the Morphology and Alignment of Calcite Crystals Nucleating Under Langmuir Monolayers

    SciTech Connect

    Kim, K.; Uysal, A; Kewalramani, S; Stripe, B; Dutta, P

    2009-01-01

    The growth of calcium carbonate crystals under Langmuir monolayers was investigated in the presence of chitosan, a soluble derivative of chitin added to the subphase to better simulate the polyelectrolyte-containing in vivo environment. Chitosan causes distinct concentration-dependent changes in the orientation, shape and morphology of the calcite crystals nucleating under acid and sulfate monolayers. Our results suggest that polyelectrolytes may play essential roles in controlling the growth of biogenic calcite crystals.

  16. Nucleation of crystals from solution: classical and two-step models.

    PubMed

    Erdemir, Deniz; Lee, Alfred Y; Myerson, Allan S

    2009-05-19

    Crystallization is vital to many processes occurring in nature and in the chemical, pharmaceutical, and food industries. Notably, crystallization is an attractive isolation step for manufacturing because this single process combines both particle formation and purification. Almost all of the products based on fine chemicals, such as dyes, explosives, and photographic materials, require crystallization in their manufacture, and more than 90% of all pharmaceutical products contain bioactive drug substances and excipients in the crystalline solid state. Hence control over the crystallization process allows manufacturers to obtain products with desired and reproducible properties. We judge the quality of a crystalline product based on four main properties: size, purity, morphology, and crystal structure. The pharmaceutical industry in particular requires production of the desired crystal form (polymorph) to assure the bioavailability and stability of the drug substance. In solution crystallization, nucleation plays a decisive role in determining the crystal structure and size distribution. Therefore, understanding the fundamentals of nucleation is crucial to achieve control over these properties. Because of its analytical simplicity, researchers have widely applied classical nucleation theory to solution crystallization. However, a number of differences between theoretical predictions and experimental results suggest that nucleation of solids from solution does not proceed via the classical pathway but follows more complex routes. In this Account, we discuss the shortcomings of classical nucleation theory and review studies contributing to the development of the modern two-step model. In the two-step model that was initially proposed for protein crystallization, a sufficient-sized cluster of solute molecules forms first, followed by reorganization of that cluster into an ordered structure. In recent experimental and theoretical studies, we and other researchers have

  17. The Measurement of Sulfur Oxidation Products and Their Role in Homogeneous Nucleation

    NASA Technical Reports Server (NTRS)

    Eisele, F. L.

    1999-01-01

    An improved version of a transverse ion source was developed which uses selected ion chemical ionization mass spectrometry techniques inside of a particle nucleation flow tube. These new techniques are very unique, in that the chemical ionization is done inside of the flow tube rather than by having to remove the compounds and clusters of interest which are lost on first contact,with any surfaces. The transverse source is also unique because it allows the ion reaction time to be varied over more than an order of magnitude, which in turn makes possible the separation of ion induced cluster growth from the charging of preexisting molecular clusters. As a result of combining these unique capabilities, the first ever measurements of prenucleation molecular clusters were performed. These clusters are the intermediate stage of growth in the gas-to-particle conversion process. This new technique provides a means of observing clusters containing 2, 3, 4, ... and up to about 8 sulfuric acid molecules, where the critical cluster size under these measurement conditions was about 4 or 5. Thus, the nucleation process can now be directly observed and even growth beyond the critical cluster size can be investigated. The details of this investigation are discussed in a recently submitted paper, which is included as Appendix A. Measurements of the diffusion coefficient of sulfuric acid and sulfuric acid clustered with a water molecule have also been performed. The measurements are also discussed in more detail in another recently submitted paper which is included as Appendix B. The empirical results discussed in both of these papers provide a critical test of present nucleation theories. They also provide new hope for resolving many of the huge discrepancies between field observation and model prediction of particle nucleation. The second part of the research conducted under this project was directed towards the development of new chemical ionization techniques for measuring sulfur

  18. Homogeneous nucleation: classical formulas as asymptotic limits of the Cahn-Hilliard approach.

    PubMed

    Parra, I E; Cordero-Gracia, M; Gómez, M

    2007-02-07

    Classical expressions for the critical cluster work of formation approximate the nonclassical expressions based in the density functional theory of capillarity for the limit of low supersaturation degrees. However, the ratio between classical and nonclassical expressions for nucleation rates grows as the supersaturation degree decreases. Here, with the aim to obtain simple and more accurate expressions that approximate the modern nucleation rate formulas, an asymptotic expansion of the Cahn-Hilliard expression of the critical work of formation is developed within the limit of low supersaturation. In such asymptotic expansion, terms up to third order are retained. The ratios between the corrected classical expressions and the nonclassical ones are now decreasing for supersaturation degrees tending to zero. However, the corrected approximate formulas are as difficult to handle as the exact Cahn-Hilliard expressions. When only the two first low-order terms of the asymptotic expansion are retained, a simpler corrected classical expression is obtained but it can only approximate nonclassical expressions up to order unity. Finally, using a Becker-Doring model of nucleation, the kinetic prefactor of the critical nuclei rate of formation is modeled consistently with the Cahn-Hilliard approach to the critical work of formation.

  19. Role of Salt, Pressure, and Water Activity on Homogeneous Ice Nucleation.

    PubMed

    Espinosa, Jorge R; Soria, Guiomar D; Ramirez, Jorge; Valeriani, Chantal; Vega, Carlos; Sanz, Eduardo

    2017-09-21

    Pure water can be substantially supercooled below the melting temperature without transforming into ice. The achievable supercooling can be enhanced by adding solutes or by applying hydrostatic pressure. Avoiding ice formation is of great importance in the cryopreservation of food or biological samples. In this Letter, we investigate the similarity between the effects of pressure and salt on ice formation using a combination of state-of-the-art simulation techniques. We find that both hinder ice formation by increasing the energetic cost of creating the ice-fluid interface. Moreover, we examine the widely accepted proposal that the ice nucleation rate for different pressures and solute concentrations can be mapped through the activity of water [ Koop , L. ; Tsias , P. Nature , 2000 , 406 , 611 ]. We show that such a proposal is not consistent with the nucleation rates predicted in our simulations because it does not include all parameters affecting ice nucleation. Therefore, even though salt and pressure have a qualitatively similar effect on ice formation, they cannot be quantitatively mapped onto one another.

  20. Influence of initial conditions on homogeneous nucleation kinetics in a closed system.

    PubMed

    Kozísek, Zdenek; Demo, Pavel

    2005-10-08

    The formation of nuclei of a new phase from the supersaturated mother phase in a closed system is studied. The depletion of the mother phase due to phase transition is taken into account. Basic kinetic equations describing such process are solved numerically to determine the number density of nuclei of newly forming phase and nucleation rate. It is shown that in contrary to the standard nucleation model, when the depletion of the mother phase is not taken into account, the initial size distribution of the clusters affects considerably the nucleation process at higher supersaturations. Our model starts with the equilibrium size distribution of clusters up to various cluster sizes in the undercritical region. At lower supersaturation the formation of nuclei is similar to the standard model because of the low depletion of the mother phase. At higher supersaturation, the depletion of the mother phase plays an important role and some extremal value appears at the size distribution of nuclei, which is not observed in the standard model. The extremum in the size distribution is not a consequence of the coalescence process itself, but it is caused rather by the depletion of the mother phase during the phase transformation.

  1. The Bjerknes instability during crystal nucleation by acoustic waves

    NASA Astrophysics Data System (ADS)

    Ben Amar, Martine

    2004-05-01

    The instability of position of a growing spherical crystal in an acoustic field is studied. Due to the Bjerknes force, a spherical crystal, whose position is shifted from an antinode of pressure, moves in the acoustic field. This displacement, stable in the case of bubbles in a cavitation experiment, turns out to be unstable in the case of crystallization. This effect is studied for an arbitrary Atwood number. To cite this article: M. Ben Amar, C. R. Mecanique 332 (2004).

  2. Introducing uncertainty analysis of nucleation and crystal growth models in Process Analytical Technology (PAT) system design of crystallization processes.

    PubMed

    Samad, Noor Asma Fazli Abdul; Sin, Gürkan; Gernaey, Krist V; Gani, Rafiqul

    2013-11-01

    This paper presents the application of uncertainty and sensitivity analysis as part of a systematic model-based process monitoring and control (PAT) system design framework for crystallization processes. For the uncertainty analysis, the Monte Carlo procedure is used to propagate input uncertainty, while for sensitivity analysis, global methods including the standardized regression coefficients (SRC) and Morris screening are used to identify the most significant parameters. The potassium dihydrogen phosphate (KDP) crystallization process is used as a case study, both in open-loop and closed-loop operation. In the uncertainty analysis, the impact on the predicted output of uncertain parameters related to the nucleation and the crystal growth model has been investigated for both a one- and two-dimensional crystal size distribution (CSD). The open-loop results show that the input uncertainties lead to significant uncertainties on the CSD, with appearance of a secondary peak due to secondary nucleation for both cases. The sensitivity analysis indicated that the most important parameters affecting the CSDs are nucleation order and growth order constants. In the proposed PAT system design (closed-loop), the target CSD variability was successfully reduced compared to the open-loop case, also when considering uncertainty in nucleation and crystal growth model parameters. The latter forms a strong indication of the robustness of the proposed PAT system design in achieving the target CSD and encourages its transfer to full-scale implementation.

  3. Fragmentation, nucleation and migration of crystals and bubbles in the Bishop Tuff rhyolitic magma

    SciTech Connect

    Gualda, G.; Cook, D.L.; Chopra, R.; Qin, L.; Anderson, A.T.; Rivers, M.

    2010-12-07

    The Bishop Tuff (USA) is a large-volume, high-silica pyroclastic rhyolite. Five pumice clasts from three early stratigraphic units were studied. Size distributions were obtained using three approaches: (1) crushing, sieving and winnowing (reliable for crystals >100 {micro}m); (2) microscopy of 1 mm{sup 3} fragments (preferable for crystals <100 {micro}m); and (3) computerised X-ray microtomography of {approx}1 cm{sup 3} pumice pieces. Phenocryst fragments coated with glass are common, and the size distributions for all crystals are concave-upward, indicating that crystal fragmentation is an important magmatic process. Three groups are recognised, characterised by: (1) high-density (0.759-0.902 g cm{sup -3}), high-crystal content (14.4-15.3 wt.%) and abundant large crystals (>800 {micro}m); concave-downward size distributions for whole crystals indicate late-stage growth with limited nucleation, compatible with the slow cooling of a large, gas-saturated, stably stratified magma body; (2) low-density (0.499 g cm{sup -3}), low-crystal content (6.63 wt.%) and few large crystals; the approximately linear size distribution reveals that nucleation was locally important, perhaps close to the walls; and (3) intermediate characteristics in all respects. The volumetric fraction of bubbles inversely correlates with the number of large crystals. This is incompatible with isobaric closed-system crystallisation, but can be explained by sinking of large crystals and rise of bubbles in the magma.

  4. Hygroscopicity of nanoparticles produced from homogeneous nucleation in the CLOUD experiments

    NASA Astrophysics Data System (ADS)

    Kim, J.; Ahlm, L.; Yli-Juuti, T.; Lawler, M.; Keskinen, H.; Tröstl, J.; Schobesberger, S.; Duplissy, J.; Amorim, A.; Bianchi, F.; Donahue, N. M.; Flagan, R. C.; Hakala, J.; Heinritzi, M.; Jokinen, T.; Kürten, A.; Laaksonen, A.; Lehtipalo, K.; Miettinen, P.; Petäjä, T.; Rissanen, M. P.; Rondo, L.; Sengupta, K.; Simon, M.; Tomé, A.; Williamson, C.; Wimmer, D.; Winkler, P. M.; Ehrhart, S.; Ye, P.; Kirkby, J.; Curtius, J.; Kulmala, M.; Lehtinen, K. E. J.; Smith, J. N.; Riipinen, I.; Virtanen, A.

    2015-07-01

    Sulfuric acid, amines and oxidized organics have been found to be important compounds in the nucleation and initial growth of atmospheric particles. Because of the challenges involved in determining the chemical composition of objects with very small mass, however, the properties of the freshly nucleated particles and the detailed pathways of their formation processes are still not clear. In this study, we focus on a challenging size range, i.e. particles that have grown to diameters of 10 and 15 nm following nucleation, and measure their water uptake. Water uptake constrains their chemical composition. We use a nanometer-hygroscopicity tandem differential mobility analyzer (nano-HTDMA) at subsaturated conditions (ca. 90 % relative humidity at 293 K) to measure the hygroscopicity of particles during the seventh Cosmics Leaving OUtdoor Droplets (CLOUD7) experiments performed at CERN in 2012. In CLOUD7, the hygroscopicity of nucleated nanoparticles was measured in the presence of sulfuric acid, sulfuric acid-dimethylamine, and sulfuric acid-organics derived from α-pinene oxidation. The hygroscopicity parameter κ decreased with increasing particle size indicating decreasing acidity of particles. No clear effect of the sulfuric acid monomer concentrations on the hygroscopicities of 10 nm particles produced from sulfuric acid and dimethylamine was observed, whereas the hygroscopicity of 15 nm particles sharply decreased with decreasing sulfuric acid monomer concentrations. In particular, when the concentrations of sulfuric acid was 5.1 × 106 molecules cm-3 in the gas phase, and the dimethylamine mixing ratio was 11.8 ppt, the measured κ of 15 nm particles was 0.31 ± 0.01 close to the value reported for dimethylamine sulfate (DMAS) (κDMAS ~ 0.28). Furthermore, the difference in κ between sulfuric acid and sulfuric acid-dimethylamine experiments increased with increasing particle size. The κ values of particles in the presence of sulfuric acid and organics were

  5. Hygroscopicity of nanoparticles produced from homogeneous nucleation in the CLOUD experiments

    NASA Astrophysics Data System (ADS)

    Kim, J.; Ahlm, L.; Yli-Juuti, T.; Lawler, M.; Keskinen, H.; Tröstl, J.; Schobesberger, S.; Duplissy, J.; Amorim, A.; Bianchi, F.; Donahue, N. M.; Flagan, R. C.; Hakala, J.; Heinritzi, M.; Jokinen, T.; Kürten, A.; Laaksonen, A.; Lehtipalo, K.; Miettinen, P.; Petäjä, T.; Rissanen, M. P.; Rondo, L.; Sengupta, K.; Simon, M.; Tomé, A.; Williamson, C.; Wimmer, D.; Winkler, P. M.; Ehrhart, S.; Ye, P.; Kirkby, J.; Curtius, J.; Baltensperger, U.; Kulmala, M.; Lehtinen, K. E. J.; Smith, J. N.; Riipinen, I.; Virtanen, A.

    2016-01-01

    Sulfuric acid, amines and oxidized organics have been found to be important compounds in the nucleation and initial growth of atmospheric particles. Because of the challenges involved in determining the chemical composition of objects with very small mass, however, the properties of the freshly nucleated particles and the detailed pathways of their formation processes are still not clear. In this study, we focus on a challenging size range, i.e., particles that have grown to diameters of 10 and 15 nm following nucleation, and measure their water uptake. Water uptake is useful information for indirectly obtaining chemical composition of aerosol particles. We use a nanometer-hygroscopicity tandem differential mobility analyzer (nano-HTDMA) at subsaturated conditions (ca. 90 % relative humidity at 293 K) to measure the hygroscopicity of particles during the seventh Cosmics Leaving OUtdoor Droplets (CLOUD7) campaign performed at CERN in 2012. In CLOUD7, the hygroscopicity of nucleated nanoparticles was measured in the presence of sulfuric acid, sulfuric acid-dimethylamine, and sulfuric acid-organics derived from α-pinene oxidation. The hygroscopicity parameter κ decreased with increasing particle size, indicating decreasing acidity of particles. No clear effect of the sulfuric acid concentration on the hygroscopicity of 10 nm particles produced from sulfuric acid and dimethylamine was observed, whereas the hygroscopicity of 15 nm particles sharply decreased with decreasing sulfuric acid concentrations. In particular, when the concentration of sulfuric acid was 5.1 × 106 molecules cm-3 in the gas phase, and the dimethylamine mixing ratio was 11.8 ppt, the measured κ of 15 nm particles was 0.31 ± 0.01: close to the value reported for dimethylaminium sulfate (DMAS) (κDMAS ˜ 0.28). Furthermore, the difference in κ between sulfuric acid and sulfuric acid-imethylamine experiments increased with increasing particle size. The κ values of particles in the presence of

  6. Heterogeneous dislocation nucleation in single crystal copper-antimony solid-solution alloys

    NASA Astrophysics Data System (ADS)

    Rajgarhia, Rahul K.; Spearot, Douglas E.; Saxena, Ashok

    2009-07-01

    Molecular dynamics (MD) simulations are employed to study the partial dislocation nucleation process in single crystal copper with varying concentrations of antimony (0.0-2.0 at%Sb) under uniaxial tension. A well-established embedded-atom method potential is used to represent the Cu-Cu interactions and a recently developed Lennard-Jones potential is used for the Cu-Sb and Sb-Sb interactions. Antimony atoms are randomly distributed as substitutional defects in the Cu single crystal. MD simulations indicate that the tensile stress required for partial dislocation nucleation in the crystal decreases with increasing concentration of Sb. The strain field around Sb dopant atoms in the Cu lattice reduces the unstable stacking fault energy, which promotes heterogeneous nucleation of partial dislocations and reduces the tensile stresses required for plastic deformation. In addition, the role of Sb on the reduction in the stress required for dislocation nucleation is found to be orientation-dependent. Finally, both temperature and Sb distribution play a role in the statistical variation of the stress required for heterogeneous partial dislocation nucleation; this variation is maximum at moderate levels of Sb concentration (0.20-0.50 at%Sb).

  7. Kinetics of nucleation and crystallization in poly(e-caprolactone) (PCL)

    SciTech Connect

    Zhuravlev, Evgeny; Schmelzer, Jurn; Wunderlich, Bernhard {nmn}; Schick, Christoph

    2011-01-01

    The recently developed differential fast scanning calorimetry (DFSC) is used for a new look at the crystal growth of poly(3-caprolactone) (PCL) from 185 K, below the glass transition temperature, to 330 K, close to the equilibrium melting temperature. The DFSC allows temperature control of the sample and determination of its heat capacity using heating rates from 50 to 50,000 K/s. The crystal nucleation and crystallization halftimes were determined simultaneously. The obtained halftimes cover a range from 3 102 s (nucleation at 215 K) to 3 109 s (crystallization at 185 K). After attempting to analyze the experiments with the classical nucleation and growth model, developed for systems consisting of small molecules, a new methodology is described which addresses the specific problems of crystallization of flexible linear macromolecules. The key problems which are attempted to be resolved concern the differences between the structures of the various entities identified and their specific role in the mechanism of growth. The structures range from configurations having practically unmeasurable latent heats of ordering (nuclei) to being clearly-recognizable, ordered species with rather sharp disordering endotherms in the temperature range from the glass transition to equilibrium melting for increasingly perfect and larger crystals. The mechanisms and kinetics of growth involve also a detailed understanding of the interaction with the surrounding rigid-amorphous fraction (RAF) in dependence of crystal size and perfection.

  8. Optimization of crystal nucleation close to a metastable fluid-fluid phase transition

    PubMed Central

    Wedekind, Jan; Xu, Limei; Buldyrev, Sergey V.; Stanley, H. Eugene; Reguera, David; Franzese, Giancarlo

    2015-01-01

    The presence of a metastable fluid-fluid critical point is thought to dramatically influence the crystallization pathway, increasing the nucleation rate by many orders of magnitude over the predictions of classical nucleation theory. We use molecular dynamics simulations to study the kinetics of crystallization in the vicinity of this metastable critical point and throughout the metastable fluid-fluid phase diagram. To quantitatively understand how the fluid-fluid phase separation affects the crystal nucleation, we evaluate accurately the kinetics and reconstruct the thermodynamic free-energy landscape of crystal formation. Contrary to expectations, we find no special advantage of the proximity of the metastable critical point on the crystallization rates. However, we find that the ultrafast formation of a dense liquid phase causes the crystallization to accelerate both near the metastable critical point and almost everywhere below the fluid-fluid spinodal line. These results unveil three different scenarios for crystallization that could guide the optimization of the process in experiments PMID:26095898

  9. First passage times in homogeneous nucleation: Dependence on the total number of particles

    SciTech Connect

    Yvinec, Romain; Bernard, Samuel; Pujo-Menjouet, Laurent; Hingant, Erwan

    2016-01-21

    Motivated by nucleation and molecular aggregation in physical, chemical, and biological settings, we present an extension to a thorough analysis of the stochastic self-assembly of a fixed number of identical particles in a finite volume. We study the statistics of times required for maximal clusters to be completed, starting from a pure-monomeric particle configuration. For finite volumes, we extend previous analytical approaches to the case of arbitrary size-dependent aggregation and fragmentation kinetic rates. For larger volumes, we develop a scaling framework to study the first assembly time behavior as a function of the total quantity of particles. We find that the mean time to first completion of a maximum-sized cluster may have a surprisingly weak dependence on the total number of particles. We highlight how higher statistics (variance, distribution) of the first passage time may nevertheless help to infer key parameters, such as the size of the maximum cluster. Finally, we present a framework to quantify formation of macroscopic sized clusters, which are (asymptotically) very unlikely and occur as a large deviation phenomenon from the mean-field limit. We argue that this framework is suitable to describe phase transition phenomena, as inherent infrequent stochastic processes, in contrast to classical nucleation theory.

  10. Phase-separation induced homogeneous nucleation and growth of Cs{sub 3}LaCl{sub 6} nanoparticles in chalcohalide glass

    SciTech Connect

    Yang, Anping; Lin, Hang; Chen, Daqin; Yu, Yunlong; Wang, Yuansheng

    2014-01-01

    Graphical abstract: The phase-separation induced nucleation and growth of Cs{sub 3}LaCl{sub 6} nanocrystals has been studied for the first time. It is experimentally evidenced that the doped active rare earth ions are incorporated into the Cs{sub 3}LaCl{sub 6} nanocrystals, resulting in the intensified down- and up-conversion emissions. - Highlights: • A novel transparent glass ceramic containing Cs{sub 3}LaCl{sub 6} nanocrystals was fabricated. • Crystallization behaviors of Cs{sub 3}LaCl{sub 6} nanophase are systematically investigated. • The up-/down-conversion emissions are greatly intensified after crystallization. - Abstract: The phase-separation induced nucleation and growth of Cs{sub 3}LaCl{sub 6} nanocrystals has been studied in the GeS{sub 2}-Ga{sub 2}S{sub 3}-La{sub 2}S{sub 3}-LaCl{sub 3}-CsCl system for the first time. Remarkably, the precipitated chloride nanocrystals are spherical and distributed homogeneously in the glass matrix. Benefiting from the uniform structure, high transparency of the glass ceramic is maintained after heat treatment by reducing adverse optical scattering. As revealed by the absorption spectra and Judd–Ofelt calculations, the doped active rare earth ions are partially partitioned into the low-phonon-energy Cs{sub 3}LaCl{sub 6} nanocrystals, resulting in the decrease of the non-radiative transition probabilities and therefore intensified photoluminescence emission of Nd{sup 3+} and up-conversion one of Er{sup 3+}.

  11. Thermodynamic analysis of two-dimensional crystal growth in nucleated isotactic polypropylene

    NASA Astrophysics Data System (ADS)

    Pieruccini, M.; Marco, G. Di; Lanza, M.

    1996-08-01

    A thermodynamic model is used to describe the two-dimensional crystallization kinetics (as observed by means of a calorimeter) of polypropylene nucleated with small amounts of indigo. The customary expression of the free enthalpy associated to secondary nucleation is initially used to analyze the experimental data. A significant dependence of the apparent surface tension (either basal or lateral) of the nuclei on the concentration of indigo is pointed out. To account for this effect, a phenomenological correction to the free enthalpy of nucleation is considered afterwards, which is connected with an entropy contribution arising from the formation of the crystal-melt interface. A more detailed data analysis is then carried out in light of this model.

  12. A parameter free prediction of simulated crystal nucleation times in the Lennard-Jones system: from steady state nucleation to the transient-time regime

    SciTech Connect

    Peng, L.; Morris, James R; Aga, Rachel

    2010-01-01

    Large scale simulations of crystal nucleation from the liquid are performed using the Lennard-Jones potential, to determine the time required for nucleation. By considering both transient and finite-size effects, we successfully predict the nucleation time within order of magnitude without any parameter fitting. All necessary parameters are derived from separate, equilibrium simulations. At smaller undercoolings, large system sizes are required, not only to accommodate large critical nuclei, but also to control statistical effects that are controlled by the density of critical nuclei. Two distinct nucleation regions are observed in the simulations, which are dominated by transient time and steady state nucleation time, respectively. At deep undercoolings, we still show consistency between predicted transient times and simulated nucleation times, which suggests that the short nucleation times in simulations are due to a small barrier to nucleation, rather than spinodal transformation that have been previously predicted. We compare with similar, previous results on a model of Al, which does not show such rapid nucleation at low temperatures, and suggest that the differences are due to the behavior of the reduced barrier G*/kBT.

  13. Ice crystallization in ultrafine water-salt aerosols: nucleation, ice-solution equilibrium, and internal structure.

    PubMed

    Hudait, Arpa; Molinero, Valeria

    2014-06-04

    Atmospheric aerosols have a strong influence on Earth's climate. Elucidating the physical state and internal structure of atmospheric aqueous aerosols is essential to predict their gas and water uptake, and the locus and rate of atmospherically important heterogeneous reactions. Ultrafine aerosols with sizes between 3 and 15 nm have been detected in large numbers in the troposphere and tropopause. Nanoscopic aerosols arising from bubble bursting of natural and artificial seawater have been identified in laboratory and field experiments. The internal structure and phase state of these aerosols, however, cannot yet be determined in experiments. Here we use molecular simulations to investigate the phase behavior and internal structure of liquid, vitrified, and crystallized water-salt ultrafine aerosols with radii from 2.5 to 9.5 nm and with up to 10% moles of ions. We find that both ice crystallization and vitrification of the nanodroplets lead to demixing of pure water from the solutions. Vitrification of aqueous nanodroplets yields nanodomains of pure low-density amorphous ice in coexistence with vitrified solute rich aqueous glass. The melting temperature of ice in the aerosols decreases monotonically with an increase of solute fraction and decrease of radius. The simulations reveal that nucleation of ice occurs homogeneously at the subsurface of the water-salt nanoparticles. Subsequent ice growth yields phase-segregated, internally mixed, aerosols with two phases in equilibrium: a concentrated water-salt amorphous mixture and a spherical cap-like ice nanophase. The surface of the crystallized aerosols is heterogeneous, with ice and solution exposed to the vapor. Free energy calculations indicate that as the concentration of salt in the particles, the advance of the crystallization, or the size of the particles increase, the stability of the spherical cap structure increases with respect to the alternative structure in which a core of ice is fully surrounded by

  14. Time-evolution of grain size distributions in random nucleation and growth crystallization processes

    NASA Astrophysics Data System (ADS)

    Teran, Anthony V.; Bill, Andreas; Bergmann, Ralf B.

    2010-02-01

    We study the time dependence of the grain size distribution N(r,t) during crystallization of a d -dimensional solid. A partial differential equation, including a source term for nuclei and a growth law for grains, is solved analytically for any dimension d . We discuss solutions obtained for processes described by the Kolmogorov-Avrami-Mehl-Johnson model for random nucleation and growth (RNG). Nucleation and growth are set on the same footing, which leads to a time-dependent decay of both effective rates. We analyze in detail how model parameters, the dimensionality of the crystallization process, and time influence the shape of the distribution. The calculations show that the dynamics of the effective nucleation and effective growth rates play an essential role in determining the final form of the distribution obtained at full crystallization. We demonstrate that for one class of nucleation and growth rates, the distribution evolves in time into the logarithmic-normal (lognormal) form discussed earlier by Bergmann and Bill [J. Cryst. Growth 310, 3135 (2008)]. We also obtain an analytical expression for the finite maximal grain size at all times. The theory allows for the description of a variety of RNG crystallization processes in thin films and bulk materials. Expressions useful for experimental data analysis are presented for the grain size distribution and the moments in terms of fundamental and measurable parameters of the model.

  15. Nucleation kinetics of urea succinic acid –ferroelectric single crystal

    SciTech Connect

    Dhivya, R.; Vizhi, R. Ezhil E-mail: revizhi@gmail.com; Babu, D. Rajan

    2015-06-24

    Single crystals of Urea Succinic Acid (USA) were grown by slow cooling technique. The crystalline system was confirmed by powder X-ray diffraction. The metastable zonewidth were carried out for various temperatures i.e., 35°, 40°, 45° and 50°C. The induction period is experimentally determined and various nucleation parameters have been estimated.

  16. Effects of Pre-Existing Ice Crystals on Cirrus Clouds and Comparison between Different Ice Nucleation Parameterizations with the Community Atmosphere Model (CAM5)

    SciTech Connect

    Shi, Xiangjun; Liu, Xiaohong; Zhang, Kai

    2015-01-01

    In order to improve the treatment of ice nucleation in a more realistic manner in the Community Atmospheric Model version 5.3 (CAM5.3), the effects of preexisting ice crystals on ice nucleation in cirrus clouds are considered. In addition, by considering the in-cloud variability in ice saturation ratio, homogeneous nucleation takes place spatially only in a portion of cirrus cloud rather than in the whole area of cirrus cloud. With these improvements, the two unphysical limiters used in the representation of ice nucleation are removed. Compared to observations, the ice number concentrations and the probability distributions of ice number concentration are both improved with the updated treatment. The preexisting ice crystals significantly reduce ice number concentrations in cirrus clouds, especially at mid- to high latitudes in the upper troposphere (by a factor of ~10). Furthermore, the contribution of heterogeneous ice nucleation to cirrus ice crystal number increases considerably.Besides the default ice nucleation parameterization of Liu and Penner (2005, hereafter LP) in CAM5.3, two other ice nucleation parameterizations of Barahona and Nenes (2009, hereafter BN) and Kärcher et al. (2006, hereafter KL) are implemented in CAM5.3 for the comparison. In-cloud ice crystal number concentration, percentage contribution from heterogeneous ice nucleation to total ice crystal number, and preexisting ice effects simulated by the three ice nucleation parameterizations have similar patterns in the simulations with present-day aerosol emissions. However, the change (present-day minus pre-industrial times) in global annual mean column ice number concentration from the KL parameterization (3.24×106 m-2) is obviously less than that from the LP (8.46×106 m-2) and BN (5.62×106 m-2) parameterizations. As a result, experiment using the KL parameterization predicts a much smaller anthropogenic aerosol longwave indirect forcing (0.24 W m-2) than that using the LP (0.46 W m-2

  17. Nucleation and crystallization of tailing-based glass-ceramics by microwave heating

    NASA Astrophysics Data System (ADS)

    Li, Bao-wei; Li, Hong-xia; Zhang, Xue-feng; Jia, Xiao-lin; Sun, Zhi-chao

    2015-12-01

    The effect of microwave radiation on the nucleation and crystallization of tailing-based glass-ceramics was investigated using a 2.45 GHz multimode microwave cavity. Tailing-based glass samples were prepared from Shandong gold tailings and Guyang iron tailings utilizing a conventional glass melting technique. For comparison, the tailing-based glass samples were crystallized using two different heat-treatment methods: conventional heating and hybrid microwave heating. The nucleation and crystallization temperatures were determined by performing a differential thermal analysis of the quenched tailing-based glass. The prepared glass-ceramic samples were further characterized by Fourier transform infrared spectroscopy, X-ray diffraction, Raman spectroscopy, thermal expansion coefficient measurements, and scanning electron microscopy. The results demonstrated that hybrid microwave heating could be successfully used to crystallize the tailing-based glass, reduce the processing time, and decrease the crystallization temperature. Furthermore, the results indicated that the nucleation and crystallization mechanism of the hybrid microwave heating process slightly differs from that of the conventional heating process.

  18. A parameter-free prediction of simulated crystal nucleation times in the Lennard-Jones system: from the steady-state nucleation to the transient time regime.

    PubMed

    Peng, Lu Jian; Morris, James R; Aga, Rachel S

    2010-08-28

    Large scale simulations of crystal nucleation from the liquid are performed using the Lennard-Jones potential to determine the time required for nucleation. By considering both transient and finite-size effects, we for the first time successfully predict the nucleation time without any parameter fitting in the Lennard-Jones system. All necessary parameters are derived from separate, equilibrium simulations. At small undercoolings, large system size effects are observed. The required system size is not only determined by the size of the critical nuclei, but also the characteristic spacing between them. Two distinct nucleation regions are predicted by theory and observed by the simulations, which are dominated by the transient time and the steady-state nucleation time, respectively.

  19. The Effect of Solution Conditions on the Nucleation Kinetics of Tetragonal Lysozyme Crystals

    NASA Technical Reports Server (NTRS)

    Judge, Russell A.; Baird, James K.; Pusey, Marc L.

    1998-01-01

    An understanding of protein crystal nucleation rates and the effect of solution conditions upon them, is fundamental to the preparation of protein crystals of the desired size and shape for X-ray diffraction analysis. The ability to predict the effect of supersaturation, temperature, pH and precipitant concentration on the number and size of crystals formed is of great benefit in the pursuit of protein structure analysis. In this study we experimentally examine the effect of supersaturation, temperature, pH and sodium chloride concentration on the nucleation rate of tetragonal chicken egg white lysozyme crystals. In order to do this batch crystallization plates were prepared at given solution concentrations and incubated at three different temperatures over the period of one week. The number of crystals per well with their size and dimensions were recorded and correlated against solution conditions. Duplicate experiments indicate the reproducibility of the technique. Although it is well known that crystal numbers increase with increasing supersaturation, large changes in crystal number were also correlated against solution conditions of temperature, pH and salt concentration over the same supersaturation ranges. Analysis of these results enhance our understanding of the effect of solution conditions such as the dramatic effect that small changes in charge and ionic strength can have on the number of tetragonal lysozyme crystals that form and grow in solution.

  20. The Effect of Solution Conditions on the Nucleation Kinetics of Tetragonal Lysozyme Crystals

    NASA Technical Reports Server (NTRS)

    Judge, Russell A.; Baird, James K.; Pusey, Marc L.

    1998-01-01

    An understanding of protein crystal nucleation rates and the effect of solution conditions upon them, is fundamental to the preparation of protein crystals of the desired size and shape for X-ray diffraction analysis. The ability to predict the effect of supersaturation, temperature, pH and precipitant concentration on the number and size of crystals formed is of great benefit in the pursuit of protein structure analysis. In this study we experimentally examine the effect of supersaturation, temperature, pH and sodium chloride concentration on the nucleation rate of tetragonal chicken egg white lysozyme crystals. In order to do this batch crystallization plates were prepared at given solution concentrations and incubated at three different temperatures over the period of one week. The number of crystals per well with their size and dimensions were recorded and correlated against solution conditions. Duplicate experiments indicate the reproducibility of the technique. Although it is well known that crystal numbers increase with increasing supersaturation, large changes in crystal number were also correlated against solution conditions of temperature, pH and salt concentration over the same supersaturation ranges. Analysis of these results enhance our understanding of the effect of solution conditions such as the dramatic effect that small changes in charge and ionic strength can have on the number of tetragonal lysozyme crystals that form and grow in solution.

  1. Externally applied electric fields up to 1.6 × 10(5) V/m do not affect the homogeneous nucleation of ice in supercooled water.

    PubMed

    Stan, Claudiu A; Tang, Sindy K Y; Bishop, Kyle J M; Whitesides, George M

    2011-02-10

    The freezing of water can initiate at electrically conducting electrodes kept at a high electric potential or at charged electrically insulating surfaces. The microscopic mechanisms of these phenomena are unknown, but they must involve interactions between water molecules and electric fields. This paper investigates the effect of uniform electric fields on the homogeneous nucleation of ice in supercooled water. Electric fields were applied across drops of water immersed in a perfluorinated liquid using a parallel-plate capacitor; the drops traveled in a microchannel and were supercooled until they froze due to the homogeneous nucleation of ice. The distribution of freezing temperatures of drops depended on the rate of nucleation of ice, and the sensitivity of measurements allowed detection of changes by a factor of 1.5 in the rate of nucleation. Sinusoidal alternation of the electric field at frequencies from 3 to 100 kHz prevented free ions present in water from screening the electric field in the bulk of drops. Uniform electric fields in water with amplitudes up to (1.6 ± 0.4) × 10(5) V/m neither enhanced nor suppressed the homogeneous nucleation of ice. Estimations based on thermodynamic models suggest that fields in the range of 10(7)-10(8) V/m might cause an observable increase in the rate of nucleation.

  2. Study of experiments on condensation of nitrogen by homogeneous nucleation at states modelling those on the national transonic facility

    NASA Technical Reports Server (NTRS)

    Wegener, P. P.

    1980-01-01

    A cryogenic wind tunnel is based on the twofold idea of lowering drive power and increasing Reynolds number by operating with nitrogen near its boiling point. There are two possible types of condensation problems involved in this mode of wind tunnel operation. They concern the expansion from the nozzle supply to the test section at relatively low cooling rates, and secondly the expansion around models in the test section. This secondary expansion involves higher cooling rates and shorter time scales. In addition to these two condensation problems it is not certain what purity of nitrogen can be achieved in a large facility. Therefore, one cannot rule out condensation processes other than those of homogeneous nucleation.

  3. Application of scaling and kinetic equations to helium cluster size distributions: Homogeneous nucleation of a nearly ideal gas.

    PubMed

    Chaiken, J; Goodisman, J; Kornilov, Oleg; Peter Toennies, J

    2006-08-21

    A previously published model of homogeneous nucleation [Villarica et al., J. Chem. Phys. 98, 4610 (1993)] based on the Smoluchowski [Phys. Z. 17, 557 (1916)] equations is used to simulate the experimentally measured size distributions of 4He clusters produced in free jet expansions. The model includes only binary collisions and does not consider evaporative effects, so that binary reactive collisions are rate limiting for formation of all cluster sizes despite the need for stabilization of nascent clusters. The model represents these data very well, accounting in some cases for nearly four orders of magnitude in variation in abundance over cluster sizes ranging up to nearly 100 atoms. The success of the model may be due to particularities of 4He clusters, i.e., their very low coalescence exothermicity, and to the low temperature of 6.7 K at which the data were collected.

  4. The interfacial amorphous double layer and the homogeneous nucleation in reflow of a Sn-Zn solder on Cu substrate

    SciTech Connect

    Pan, Chien-Cheng; Lin, Kwang-Lung

    2011-05-15

    To illustrate the interfacial reaction mechanism, the Sn-Zn[Sn-8.5Zn-0.5Ag-0.01Al-0.1Ga (wt%)] solder was reflowed on Cu substrate at 250 deg. C for 15 s followed by immediate quench in liquid nitrogen. The frozen interfacial microstructure was investigated with high resolution transmission electron microscope. An amorphous double layer was formed at the interface which consists of a 5 nm pure Cu region and a Cu-Zn diffusion region. Nanocrystalline intermetallic compound (IMC) Cu{sub 5}Zn{sub 8} were observed in the Cu-Zn diffusion region. These nanocrystalline IMCs are suggested to form via a homogeneous nucleation process.

  5. Test of classical nucleation theory and mean first-passage time formalism on crystallization in the Lennard-Jones liquid

    SciTech Connect

    Lundrigan, Sarah E. M.; Saika-Voivod, Ivan

    2009-09-14

    We perform molecular dynamics (MD) and Monte Carlo computer simulations to test the ability of the recently developed formalism of mean first-passage time (MFPT) [J. Wedekind, R. Strey, and D. Reguera, J. Chem. Phys. 126, 134103 (2007); J. Wedekind and D. Reguera, J. Phys. Chem. B 112, 11060 (2008)] to characterize crystal nucleation in the Lennard-Jones liquid. We find that the nucleation rate, critical embryo size, Zeldovich factor, attachment rate, and the nucleation barrier profile obtained from MFPT all compare very well to the same quantities calculated using other methods. Furthermore, we find that the nucleation rate obtained directly through MD closely matches the prediction of classical nucleation theory.

  6. Test of classical nucleation theory and mean first-passage time formalism on crystallization in the Lennard-Jones liquid

    NASA Astrophysics Data System (ADS)

    Lundrigan, Sarah E. M.; Saika-Voivod, Ivan

    2009-09-01

    We perform molecular dynamics (MD) and Monte Carlo computer simulations to test the ability of the recently developed formalism of mean first-passage time (MFPT) [J. Wedekind, R. Strey, and D. Reguera, J. Chem. Phys. 126, 134103 (2007); J. Wedekind and D. Reguera, J. Phys. Chem. B 112, 11060 (2008)] to characterize crystal nucleation in the Lennard-Jones liquid. We find that the nucleation rate, critical embryo size, Zeldovich factor, attachment rate, and the nucleation barrier profile obtained from MFPT all compare very well to the same quantities calculated using other methods. Furthermore, we find that the nucleation rate obtained directly through MD closely matches the prediction of classical nucleation theory.

  7. Ice nucleation: elemental identification of particles in snow crystals.

    PubMed

    Parungo, F P; Pueschel, R F

    1973-06-08

    A scanning field-emission electron microscope combined with an x-ray analyzer is used to locate the ice nucleus within a three-dimensional image of a snow crystal and determine the chemical composition of the nucleus. This makes it possible to better understand the effect of nuclei in cloud seeding.

  8. Crystal nucleation of zincophosphate open frameworks in reverse micelle nanoreactors

    NASA Astrophysics Data System (ADS)

    Castagnola, Mario J.

    The synthesis of microporous zincophosphates was studied through a novel synthetic route based on reactants encapsulated in reverse micelles. The zincophosphate analog of sodalite had been previously synthesized in a reverse micelle system using Aerosol OT (AOT) as surfactant. The synthesis of open framework zincophosphates using this detergent proved unsuccessful. By studying the conventional synthesis of zincophosphates and the AOT reverse micelle aqueous environment through Raman microscopy, FTIR, NMR and XRD, it was found that the relatively high concentrations of sodium ions and the disordered structure of water present in the AOT reverse micelles prevented the synthesis of open framework structures. Based on these results, a system containing reverse micelles of the cationic surfactant dioctyldimethylammonium chloride (DODMAC) was developed. Zn 2+- and PO43--containing DODMAC reverse micelles were characterized by dynamic light scattering and conductivity measurements, indicating a rod-like shape for the former and a spherical shape for the latter reverse micelles. Combination of the two reverse micelle solutions led to the first successful reverse micelle based synthesis of the zincophosphate analog of Zeolite-X, ZnPO-X. The size of the crystals was controlled by modifying the volume ratio between the individual reagent micellar solutions. Nanocrystals of the order of 20 nm were obtained by interrupting the reaction at early stages. Studies of both the conventional aqueous and the reverse micelle based syntheses of ZnPO-X revealed that the morphology of the ZnPO-X crystals was controlled by the concentration of tetramethylammonium ions (TMA+). The ZnPO-X crystals synthesized via the reverse micelles were obtained as a single phase. Using Raman spectroscopy, it was determined that, during conventional synthesis, H+ ions promote the hydrolysis of the ZnPO-X crystals that leads to hopeite formation. Ion-exchange by monovalent cations indicated that the crystal

  9. Role of molecule flexibility on the nucleation of dislocations in molecular crystals

    NASA Astrophysics Data System (ADS)

    Munday, Lynn B.; Mitchell, Robert L.; Knap, Jaroslaw; Chung, Peter W.

    2013-10-01

    We show that a molecule's flexibility described by changes to its conformation and orientation during deformation is vital for the proper representation of dislocation nucleation in molecular crystals. This is shown for the molecular crystal hexahydro-1,3,5-trinitro-s-triazine (RDX) by comparing direct atomistic simulations to two alternate forms of a continuum dislocation nucleation model for a crack tip loaded in pure shear. The atomistic simulations show the emission of partial dislocations. These are compared to continuum dislocation nucleation models based on generalized stacking fault (GSF) energy surfaces where the molecules are allowed to be either rigid or flexible. The rigid molecules are unable to represent the partial dislocations whereas the flexible molecules agree with the direct atomistic model to within 17% of the stress intensity factor for emission of the first partial dislocation and to within 1% for the second partial. This agreement first indicates that the molecule flexibility serves a critical role in the ductile behavior of the molecular crystal and, second, the continuum dislocation nucleation model represents the correct atomistic behavior, showing two partial dislocations connected by a stacking fault, when parameterized with GSF energy surfaces that account for the molecule flexibility.

  10. Antheraea pernyi silk sericin mediating biomimetic nucleation and growth of hydroxylapatite crystals promoting bone matrix formation.

    PubMed

    Jiayao, Zhuang; Guanshan, Zhou; Jinchi, Zhang; Yuyin, Chen; Yongqiang, Zhu

    2017-03-01

    Bone biomineralization is well-regulated processes mediated by extracellular matrix proteins. The materials that can direct nucleation of hydroxylapatite (HAp) crystals and assembly of well-structured material-minerals complex are the key to mimicking the natural mineralization. This study used sericin from Antheraea pernyi (A.pernyi), non-mulberry silkworm cocoon as template to mediate nucleation of HAp crystals. Here we find out that AS (Antheraea pernyi sericin) can nucleate the formation HAp crystals in simulated body fluid verified by XRD and FTIR observations. The HAp crystals are organized into nano-rods oriented with c-axis preferentially parallel to the long axis of AS due to hydrogen bonds and electrostatic interaction and finally aggregated into HAp globule. The cell culture of human bone marrow-derived mesenchymal stem cells (BMSCs) showed that the HAp crystals mediated by AS not only stimulate cell adhesion and proliferation but also promote 0f osteogenic differentiation, suggesting that the resultant mineralized AS biomaterial has potential in promoting bone formation. Thus our work will provide significant implication on biomineralization of A. pernyi silk sericin as a potential scaffold for tissue engineering. © 2016 Wiley Periodicals, Inc.

  11. Doubled heterogeneous crystal nucleation in sediments of hard sphere binary-mass mixtures.

    PubMed

    Löwen, Hartmut; Allahyarov, Elshad

    2011-10-07

    Crystallization during the sedimentation process of a binary colloidal hard spheres mixture is explored by Brownian dynamics computer simulations. The two species are different in buoyant mass but have the same interaction diameter. Starting from a completely mixed system in a finite container, gravity is suddenly turned on, and the crystallization process in the sample is monitored. If the Peclet numbers of the two species are both not too large, crystalline layers are formed at the bottom of the cell. The composition of lighter particles in the sedimented crystal is non-monotonic in the altitude: it is first increasing, then decreasing, and then increasing again. If one Peclet number is large and the other is small, we observe the occurrence of a doubled heterogeneous crystal nucleation process. First, crystalline layers are formed at the bottom container wall which are separated from an amorphous sediment. At the amorphous-fluid interface, a secondary crystal nucleation of layers is identified. This doubled heterogeneous nucleation can be verified in real-space experiments on colloidal mixtures. © 2011 American Institute of Physics

  12. Biomineralization mechanisms: a new paradigm for crystal nucleation in organic matrices.

    PubMed

    Veis, Arthur; Dorvee, Jason R

    2013-10-01

    There is substantial practical interest in the mechanism by which the carbonated apatite of bone mineral can be initiated specifically in a matrix. The current literature is replete with studies aimed at mimicking the properties of vertebrate bone, teeth, and other hard tissues by creating organic matrices that can be mineralized in vitro and either functionally substitute for bone on a permanent basis or serve as a temporary structure that can be replaced by normal remodeling processes. A key element in this is mineralization of an implant with the matrix and mineral arranged in the proper orientations and relationships. This review examines the pathway to crystallization from a supersaturated calcium phosphate solution in vitro, focusing on the basic mechanistic questions concerning mineral nucleation and growth. Since bone and dentin mineral forms within collagenous matrices, we consider how the in vitro crystallization mechanisms might or might not be applicable to understanding the in vivo processes of biomineralization in bone and dentin. We propose that the pathway to crystallization from the calcium phosphate-supersaturated tissue fluids involves the formation of a dense liquid phase of first-layer bound-water hydrated calcium and phosphate ions in which the crystallization is nucleated. SIBLING proteins and their in vitro analogs, such as polyaspartic acids, have similar dense liquid first-layer bound-water surfaces which interact with the dense liquid calcium phosphate nucleation clusters and modulate the rate of crystallization within the bone and dentin collagen fibril matrix.

  13. Biomineralization Mechanisms: A new paradigm for crystal nucleation in organic matricies

    PubMed Central

    Veis, Arthur; Dorvee, Jason R.

    2013-01-01

    There is substantial practical interest in the mechanism by which the carbonated apatite of bone mineral can be initiated specifically in a matrix. The current literature is replete with studies aimed at mimicking the properties of vertebrate bone, teeth and other hard tissues by creating organic matrices that can be mineralized in vitro, and either functionally substitute for bone on a permanent basis, or serve as a temporary structure that can be replaced by normal remodeling processes. A key element in this is mineralization of an implant with the matrix and mineral disposed in the proper orientations and relationships. This review examines the pathway to crystallization from a supersaturated calcium phosphate solution in vitro, focusing on the basic mechanistic questions concerning mineral nucleation and growth. Since bone and dentin mineral forms within collagenous matricies we consider how the in vitro crystallization mechanisms might or might not be applicable to understanding the in vivo processes of biomineralization in bone and dentin. We propose that the pathway to crystallization from the calcium phosphate supersaturated tissue fluids involves the formation of a dense liquid phase of first-layer bound-water hydrated calcium and phosphate ions in which the crystallization is nucleated. SIBLING proteins and their in vitro analogs such as polyaspartic acids, have similar dense liquid first-layer bound water surfaces which interact with the dense liquid calcium phosphate nucleation clusters and modulate the rate of crystallization within the bone and dentin collagen fibril matrix. PMID:23241924

  14. Supercooling, ice nucleation and crystal growth: a systematic study in plant samples.

    PubMed

    Zaragotas, Dimitris; Liolios, Nikolaos T; Anastassopoulos, Elias

    2016-06-01

    This paper presents an innovative technological platform which is based on infrared video recording and is used for monitoring multiple ice nucleation events and their interactions, as they happen in 96 well microplates. Thousands of freezing curves were obtained during this study and the following freezing parameters were measured: cooling rate, nucleation point, freezing point, solidus point, degree of supercooling, duration of dendritic phase and duration of crystal growth. We demonstrate the use of this platform in the detection of ice nuclei in plant samples. Future applications of this platform may include breeding for frost tolerance, cryopreservation, frozen food technology and atmospheric sciences. Copyright © 2016 Elsevier Inc. All rights reserved.

  15. Equilibrium studies of protein aggregates and homogeneous nucleation in protein formulation.

    PubMed

    Kiese, Sylvia; Pappenberger, Astrid; Friess, Wolfgang; Mahler, Hanns-Christian

    2010-02-01

    Shaking or heat stress may induce protein aggregates. Aggregation behavior of an IgG1 stressed by shaking or heat following static storage at 5 and 25 degrees C was investigated to determine whether protein aggregates exist in equilibrium. Aggregates were detected using different analytical methods including visual inspection, turbidity, light obscuration, size exclusion chromatography, and dynamic light scattering. Significant differences were evident between shaken and heated samples upon storage. Visible and subvisible particles (insoluble aggregates), turbidity and z-average diameter decreased whilst soluble aggregate content increased in shaken samples over time. Insoluble aggregates were considered to be reversible and dissociate into soluble aggregates and both aggregate types existed in equilibrium. Heat-induced aggregates had a denatured protein structure and upon static storage, no significant change in insoluble aggregates content was shown, whilst changes in soluble aggregates content occurred. This suggested that heat-induced insoluble aggregates were irreversible and not in equilibrium with soluble aggregates. Additionally, the aggregation behavior of unstressed IgG1 after spiking with heavily aggregated material (shaken or heat stressed) was studied. The aggregation behavior was not significantly altered, independent of the spiking concentration over time. Thus, neither mechanically stressed native nor temperature-induced denatured aggregates were involved in nucleating or propagating aggregation.

  16. Engineering nanoparticle-protein associations for protein crystal nucleation and nanoparticle arrangement

    NASA Astrophysics Data System (ADS)

    Benoit, Denise N.

    Engineering the nanoparticle - protein association offers a new way to form protein crystals as well as new approaches for arrangement of nanoparticles. Central to this control is the nanoparticle surface. By conjugating polymers on the surface with controlled molecular weights many properties of the nanoparticle can be changed including its size, stability in buffers and the association of proteins with its surface. Large molecular weight poly(ethylene glycol) (PEG) coatings allow for weak associations between proteins and nanoparticles. These interactions can lead to changes in how proteins crystallize. In particular, they decrease the time to nucleation and expand the range of conditions over which protein crystals form. Interestingly, when PEG chain lengths are too short then protein association is minimized and these effects are not observed. One important feature of protein crystals nucleated with nanoparticles is that the nanoparticles are incorporated into the crystals. What results are nanoparticles placed at well-defined distances in composite protein-nanoparticle crystals. Crystals on the size scale of 10 - 100 micrometers exhibit optical absorbance, fluorescence and super paramagnetic behavior derivative from the incorporated nanomaterials. The arrangement of nanoparticles into three dimensional arrays also gives rise to new and interesting physical and chemical properties, such as fluorescence enhancement and varied magnetic response. In addition, anisotropic nanomaterials aligned throughout the composite crystal have polarization dependent optical properties.

  17. Quantum effect on the nucleation of plastic deformation carriers and destruction in crystals

    SciTech Connect

    Khon, Yury A. Kaminskii, Petr P.

    2015-10-27

    New concepts on the irreversible crystal deformation as a structure transformation caused by a change in interatomic interactions at fluctuations of the electron density under loading are described. The change in interatomic interactions lead to the excitation of dynamical displacements of atoms. A model and a theory of a deformable pristine crystal taking into account the excitation of thermally activated and dynamical displacements of atoms are suggested. New mechanisms of the nucleation of plastic deformation carriers and destruction in pristine crystals at the real value of the deforming stress are studied.

  18. Evidence from mixed hydrate nucleation for a funnel model of crystallization

    PubMed Central

    Hall, Kyle Wm.; Carpendale, Sheelagh; Kusalik, Peter G.

    2016-01-01

    The molecular-level details of crystallization remain unclear for many systems. Previous work has speculated on the phenomenological similarities between molecular crystallization and protein folding. Here we demonstrate that molecular crystallization can involve funnel-shaped potential energy landscapes through a detailed analysis of mixed gas hydrate nucleation, a prototypical multicomponent crystallization process. Through this, we contribute both: (i) a powerful conceptual framework for exploring and rationalizing molecular crystallization, and (ii) an explanation of phenomenological similarities between protein folding and crystallization. Such funnel-shaped potential energy landscapes may be typical of broad classes of molecular ordering processes, and can provide a new perspective for both studying and understanding these processes. PMID:27790987

  19. On the ice nucleation spectrum

    NASA Astrophysics Data System (ADS)

    Barahona, D.

    2012-04-01

    This work presents a novel formulation of the ice nucleation spectrum, i.e. the function relating the ice crystal concentration to cloud formation conditions and aerosol properties. The new formulation is physically-based and explicitly accounts for the dependency of the ice crystal concentration on temperature, supersaturation, cooling rate, and particle size, surface area and composition. This is achieved by introducing the concepts of ice nucleation coefficient (the number of ice germs present in a particle) and nucleation probability dispersion function (the distribution of ice nucleation coefficients within the aerosol population). The new formulation is used to generate ice nucleation parameterizations for the homogeneous freezing of cloud droplets and the heterogeneous deposition ice nucleation on dust and soot ice nuclei. For homogeneous freezing, it was found that by increasing the dispersion in the droplet volume distribution the fraction of supercooled droplets in the population increases. For heterogeneous ice nucleation the new formulation consistently describes singular and stochastic behavior within a single framework. Using a fundamentally stochastic approach, both cooling rate independence and constancy of the ice nucleation fraction over time, features typically associated with singular behavior, were reproduced. Analysis of the temporal dependency of the ice nucleation spectrum suggested that experimental methods that measure the ice nucleation fraction over few seconds would tend to underestimate the ice nuclei concentration. It is shown that inferring the aerosol heterogeneous ice nucleation properties from measurements of the onset supersaturation and temperature may carry significant error as the variability in ice nucleation properties within the aerosol population is not accounted for. This work provides a simple and rigorous ice nucleation framework where theoretical predictions, laboratory measurements and field campaign data can be

  20. On the Ice Nucleation Spectrum

    NASA Technical Reports Server (NTRS)

    Barahona, D.

    2012-01-01

    This work presents a novel formulation of the ice nucleation spectrum, i.e. the function relating the ice crystal concentration to cloud formation conditions and aerosol properties. The new formulation is physically-based and explicitly accounts for the dependency of the ice crystal concentration on temperature, supersaturation, cooling rate, and particle size, surface area and composition. This is achieved by introducing the concepts of ice nucleation coefficient (the number of ice germs present in a particle) and nucleation probability dispersion function (the distribution of ice nucleation coefficients within the aerosol population). The new formulation is used to generate ice nucleation parameterizations for the homogeneous freezing of cloud droplets and the heterogeneous deposition ice nucleation on dust and soot ice nuclei. For homogeneous freezing, it was found that by increasing the dispersion in the droplet volume distribution the fraction of supercooled droplets in the population increases. For heterogeneous ice nucleation the new formulation consistently describes singular and stochastic behavior within a single framework. Using a fundamentally stochastic approach, both cooling rate independence and constancy of the ice nucleation fraction over time, features typically associated with singular behavior, were reproduced. Analysis of the temporal dependency of the ice nucleation spectrum suggested that experimental methods that measure the ice nucleation fraction over few seconds would tend to underestimate the ice nuclei concentration. It is shown that inferring the aerosol heterogeneous ice nucleation properties from measurements of the onset supersaturation and temperature may carry significant error as the variability in ice nucleation properties within the aerosol population is not accounted for. This work provides a simple and rigorous ice nucleation framework where theoretical predictions, laboratory measurements and field campaign data can be

  1. Effects of pre-existing ice crystals on cirrus clouds and comparison between different ice nucleation parameterizations with the Community Atmosphere Model (CAM5)

    SciTech Connect

    Shi, Xiangjun; Liu, Xiaohong; Zhang, Kai

    2015-02-11

    In order to improve the treatment of ice nucleation in a more realistic manner in the Community Atmosphere Model version 5.3 (CAM5.3), the effects of pre-existing ice crystals on ice nucleation in cirrus clouds are considered. In addition, by considering the in-cloud variability in ice saturation ratio, homogeneous nucleation takes place spatially only in a portion of the cirrus cloud rather than in the whole area of the cirrus cloud. Compared to observations, the ice number concentrations and the probability distributions of ice number concentration are both improved with the updated treatment. The pre-existing ice crystals significantly reduce ice number concentrations in cirrus clouds, especially at mid- to high latitudes in the upper troposphere (by a factor of ~10). Furthermore, the contribution of heterogeneous ice nucleation to cirrus ice crystal number increases considerably.

    Besides the default ice nucleation parameterization of Liu and Penner (2005, hereafter LP) in CAM5.3, two other ice nucleation parameterizations of Barahona and Nenes (2009, hereafter BN) and Kärcher et al. (2006, hereafter KL) are implemented in CAM5.3 for the comparison. In-cloud ice crystal number concentration, percentage contribution from heterogeneous ice nucleation to total ice crystal number, and pre-existing ice effects simulated by the three ice nucleation parameterizations have similar patterns in the simulations with present-day aerosol emissions. However, the change (present-day minus pre-industrial times) in global annual mean column ice number concentration from the KL parameterization (3.24 × 106 m-2) is less than that from the LP (8.46 × 106 m-2) and BN (5.62 × 106 m-2) parameterizations. As a result, the experiment using the KL parameterization predicts a much smaller anthropogenic aerosol long-wave indirect forcing (0.24 W m-2) than that using the LP (0.46 W m−2

  2. Effects of pre-existing ice crystals on cirrus clouds and comparison between different ice nucleation parameterizations with the Community Atmosphere Model (CAM5)

    DOE PAGES

    Shi, Xiangjun; Liu, Xiaohong; Zhang, Kai

    2015-02-11

    In order to improve the treatment of ice nucleation in a more realistic manner in the Community Atmosphere Model version 5.3 (CAM5.3), the effects of pre-existing ice crystals on ice nucleation in cirrus clouds are considered. In addition, by considering the in-cloud variability in ice saturation ratio, homogeneous nucleation takes place spatially only in a portion of the cirrus cloud rather than in the whole area of the cirrus cloud. Compared to observations, the ice number concentrations and the probability distributions of ice number concentration are both improved with the updated treatment. The pre-existing ice crystals significantly reduce ice numbermore » concentrations in cirrus clouds, especially at mid- to high latitudes in the upper troposphere (by a factor of ~10). Furthermore, the contribution of heterogeneous ice nucleation to cirrus ice crystal number increases considerably. Besides the default ice nucleation parameterization of Liu and Penner (2005, hereafter LP) in CAM5.3, two other ice nucleation parameterizations of Barahona and Nenes (2009, hereafter BN) and Kärcher et al. (2006, hereafter KL) are implemented in CAM5.3 for the comparison. In-cloud ice crystal number concentration, percentage contribution from heterogeneous ice nucleation to total ice crystal number, and pre-existing ice effects simulated by the three ice nucleation parameterizations have similar patterns in the simulations with present-day aerosol emissions. However, the change (present-day minus pre-industrial times) in global annual mean column ice number concentration from the KL parameterization (3.24 × 106 m-2) is less than that from the LP (8.46 × 106 m-2) and BN (5.62 × 106 m-2) parameterizations. As a result, the experiment using the KL parameterization predicts a much smaller anthropogenic aerosol long-wave indirect forcing (0.24 W m-2) than that using the LP (0.46 W m−2) and BN (0.39 W m-2) parameterizations.« less

  3. Nucleation and crystallization kinetics of hydrated amorphous lactose above the glass transition temperature.

    PubMed

    Schmitt, E A; Law, D; Zhang, G G

    1999-03-01

    The crystallization kinetics of amorphous lactose in the presence and absence of seed crystals were investigated at 57.5% relative humidity. Isothermal crystallization studies were conducted gravimetrically in an automated vacuum moisture balance at several temperatures between 18 and 32 degrees C. The crystallization rate constants were then determined from Johnson-Mehl-Avrami (JMA) treatment and isothermal activation energies were obtained from Arrhenius plots. Based on microscopic observations, a reaction order of 3 was used for JMA analysis. The nonisothermal activation energies were determined by differential scanning calorimetry using Kissinger's analysis. Isothermal activation energies for amorphous lactose with and without seed crystals were 89.5 (+/-5.6) kJ/mol and 186.5 (+/-17.6) kJ/mol, respectively. Nonisothermal activation energies with and without seed crystals were 71 (+/-7.5) kJ/mol and 80.9 (+/-8.9) kJ/mol, respectively. The similarity of the isothermal and nonisothermal activation energies for the sample with seeds suggested that crystallization was occurring by growth from a fixed number of preexisting nuclei. Markedly different isothermal and nonisothermal activation energies in the absence of seeds suggested a site-saturated nucleation mechanism, and therefore allowed calculation of an activation energy for nucleation of 317 kJ/mol.

  4. Nucleation and convection effects in protein crystal growth

    NASA Technical Reports Server (NTRS)

    Rosenberger, Franz (Principal Investigator)

    1996-01-01

    The following activities are reported on: repartitioning of NaCl and protein impurities in lysozyme crystallization; dependence of lysozyme growth kinetics on step sources and impurities; facet morphology response to nonuniformities in nutrient and impurity supply; interactions in undersaturated and supersaturated lysozyme solutions; heterogeneity determination and purification of commercial hen egg white lysozyme; nonlinear response of layer growth dynamics in the mixed kinetics-bulk transport regime; development of a simultaneous multiangle light scattering technique; and x-ray topography of tetragonal lysozyme grown by the temperature-control technique.

  5. A Local Order Parameter-Based Method for Simulation of Free Energy Barriers in Crystal Nucleation.

    PubMed

    Eslami, Hossein; Khanjari, Neda; Müller-Plathe, Florian

    2017-03-14

    While global order parameters have been widely used as reaction coordinates in nucleation and crystallization studies, their use in nucleation studies is claimed to have a serious drawback. In this work, a local order parameter is introduced as a local reaction coordinate to drive the simulation from the liquid phase to the solid phase and vice versa. This local order parameter holds information regarding the order in the first- and second-shell neighbors of a particle and has different well-defined values for local crystallites and disordered neighborhoods but is insensitive to the type of the crystal structure. The order parameter is employed in metadynamics simulations to calculate the solid-liquid phase equilibria and free energy barrier to nucleation. Our results for repulsive soft spheres and the Lennard-Jones potential, LJ(12-6), reveal better-resolved solid and liquid basins compared with the case in which a global order parameter is used. It is also shown that the configuration space is sampled more efficiently in the present method, allowing a more accurate calculation of the free energy barrier and the solid-liquid interfacial free energy. Another feature of the present local order parameter-based method is that it is possible to apply the bias potential to regions of interest in the order parameter space, for example, on the largest nucleus in the case of nucleation studies. In the present scheme for metadynamics simulation of the nucleation in supercooled LJ(12-6) particles, unlike the cases in which global order parameters are employed, there is no need to have an estimate of the size of the critical nucleus and to refine the results with the results of umbrella sampling simulations. The barrier heights and the nucleation pathway obtained from this method agree very well with the results of former umbrella sampling simulations.

  6. Satellite Remote Sensing of the Dependence of Homogeneous Ice Nucleation on Latitude and Season

    NASA Astrophysics Data System (ADS)

    Mitchell, D. L.; Garnier, A.; Avery, M. A.; Erfani, E.

    2015-12-01

    Cirrus clouds can be thought of as belonging to one of two categories: those formed through (1) homo- and (2) heterogeneous ice nucleation (henceforth hom and het) due to the very different microphysical and radiative properties associated with these two mechanisms. Hom cirrus will form only when atmospheric ice nuclei (IN) are sufficiently low in concentration, and studies suggest that mineral dust may account for most IN globally. Hence the occurrence of hom and het cirrus is likely to depend on latitude and season as mineral dust does, making satellite remote sensing the preferred method for characterizing this occurrence. A new understanding of thermal absorption in two split-window channels renders a reinterpretation of a standard CALIPSO satellite retrieval; the effective absorption optical depth ratio or βeff. Using earlier studies and aircraft measurements in cirrus clouds, βeff is found to be tightly related to the ice particle number concentration/ice water content ratio, or N/IWC, and thresholds for hom cirrus are estimated in terms of N/IWC and βeff. When applied to cold semi-transparent cirrus clouds, we find that (1) polar cirrus (T < -38 C) occur much more often during winter than summer and (2) hom cirrus prevail at high latitudes during winter, and during spring and fall over Antarctica. The figure shows estimates of the fraction of cirrus produced by hom (where βeff > 1.15) during January and August, where green is ~ 50% and red ~ 90-100%. These high N/IWC values associated with hom cirrus occur in regions where mineral dust concentrations are predicted to be minimal. This high N/IWC condition during winter is likely to have a strong greenhouse effect that may increase high latitude temperatures by 2-5°K relative to conditions where het cirrus dominates (Storelvmo et al. 2014, Philos. Trans. A, Royal Soc.). Thus, the lack of mineral dust in the high latitudes during winter may result in a strong warming influence over these regions. Moreover

  7. Peptides of Matrix Gla Protein Inhibit Nucleation and Growth of Hydroxyapatite and Calcium Oxalate Monohydrate Crystals

    PubMed Central

    Goiko, Maria; Dierolf, Joshua; Gleberzon, Jared S.; Liao, Yinyin; Grohe, Bernd; Goldberg, Harvey A.; de Bruyn, John R.; Hunter, Graeme K.

    2013-01-01

    Matrix Gla protein (MGP) is a phosphorylated and γ-carboxylated protein that has been shown to prevent the deposition of hydroxyapatite crystals in the walls of blood vessels. MGP is also expressed in kidney and may inhibit the formation of kidney stones, which mainly consist of another crystalline phase, calcium oxalate monohydrate. To determine the mechanism by which MGP prevents soft-tissue calcification, we have synthesized peptides corresponding to the phosphorylated and γ-carboxylated sequences of human MGP in both post-translationally modified and non-modified forms. The effects of these peptides on hydroxyapatite formation and calcium oxalate crystallization were quantified using dynamic light scattering and scanning electron microscopy, respectively. Peptides YGlapS (MGP1-14: YγEpSHEpSMEpSYELNP), YEpS (YEpSHEpSMEpSYELNP), YGlaS (YγESHESMESYELNP) and SK-Gla (MGP43-56: SKPVHγELNRγEACDD) inhibited formation of hydroxyapatite in order of potency YGlapS > YEpS > YGlaS > SK-Gla. The effects of YGlapS, YEpS and YGlaS on hydroxyapatite formation were on both crystal nucleation and growth; the effect of SK-Gla was on nucleation. YGlapS and YEpS significantly inhibited the growth of calcium oxalate monohydrate crystals, while simultaneously promoting the formation of calcium oxalate dihydrate. The effects of these phosphopeptides on calcium oxalate monohydrate formation were on growth of crystals rather than nucleation. We have shown that the use of dynamic light scattering allows inhibitors of hydroxyapatite nucleation and growth to be distinguished. We have also demonstrated for the first time that MGP peptides inhibit the formation of calcium oxalate monohydrate. Based on the latter finding, we propose that MGP function not only to prevent blood-vessel calcification but also to inhibit stone formation in kidney. PMID:24265810

  8. Peptides of Matrix Gla protein inhibit nucleation and growth of hydroxyapatite and calcium oxalate monohydrate crystals.

    PubMed

    Goiko, Maria; Dierolf, Joshua; Gleberzon, Jared S; Liao, Yinyin; Grohe, Bernd; Goldberg, Harvey A; de Bruyn, John R; Hunter, Graeme K

    2013-01-01

    Matrix Gla protein (MGP) is a phosphorylated and γ-carboxylated protein that has been shown to prevent the deposition of hydroxyapatite crystals in the walls of blood vessels. MGP is also expressed in kidney and may inhibit the formation of kidney stones, which mainly consist of another crystalline phase, calcium oxalate monohydrate. To determine the mechanism by which MGP prevents soft-tissue calcification, we have synthesized peptides corresponding to the phosphorylated and γ-carboxylated sequences of human MGP in both post-translationally modified and non-modified forms. The effects of these peptides on hydroxyapatite formation and calcium oxalate crystallization were quantified using dynamic light scattering and scanning electron microscopy, respectively. Peptides YGlapS (MGP1-14: YγEpSHEpSMEpSYELNP), YEpS (YEpSHEpSMEpSYELNP), YGlaS (YγESHESMESYELNP) and SK-Gla (MGP43-56: SKPVHγELNRγEACDD) inhibited formation of hydroxyapatite in order of potency YGlapS > YEpS > YGlaS > SK-Gla. The effects of YGlapS, YEpS and YGlaS on hydroxyapatite formation were on both crystal nucleation and growth; the effect of SK-Gla was on nucleation. YGlapS and YEpS significantly inhibited the growth of calcium oxalate monohydrate crystals, while simultaneously promoting the formation of calcium oxalate dihydrate. The effects of these phosphopeptides on calcium oxalate monohydrate formation were on growth of crystals rather than nucleation. We have shown that the use of dynamic light scattering allows inhibitors of hydroxyapatite nucleation and growth to be distinguished. We have also demonstrated for the first time that MGP peptides inhibit the formation of calcium oxalate monohydrate. Based on the latter finding, we propose that MGP function not only to prevent blood-vessel calcification but also to inhibit stone formation in kidney.

  9. Evidence of Multi-step Nucleation Leading to Various Crystallization Pathways from an Fe-O-Al Melt

    PubMed Central

    Wang, G. C.; Wang, Q.; Li, S. L.; Ai, X. G.; Fan, C. G.

    2014-01-01

    The crystallization process from a solution begins with nucleation, which determines the structure and size of the resulting crystals. Further understanding of multi-pathway crystallizations from solution through two-step nucleation mechanisms is needed. This study uses density functional theory to probe the thermodynamic properties of alumina clusters at high temperature and reveals the thermodynamic relationship between these clusters and the saturation levels of dissolved oxygen and aluminum in an Fe–O–Al melt. Based on the thermodynamics of cluster formation and the experimental evidence for both excess oxygen in the Fe-O-Al melt and for alumina with a polycrystalline structure in solidified iron, we demonstrate that the appearance of various types of clusters that depends on the saturation ratio determines the nucleation steps that lead to the various crystallization pathways. Such mechanisms may also be important in nucleation and crystallization from solution. PMID:24866413

  10. Understanding Cirrus Ice Crystal Number Variability for Different Heterogeneous Ice Nucleation Spectra

    NASA Technical Reports Server (NTRS)

    Sullivan, Sylvia C.; Betancourt, Ricardo Morales; Barahona, Donifan; Nenes, Athanasios

    2016-01-01

    Along with minimizing parameter uncertainty, understanding the cause of temporal and spatial variability of the nucleated ice crystal number, Ni, is key to improving the representation of cirrus clouds in climate models. To this end, sensitivities of Ni to input variables like aerosol number and diameter provide valuable information about nucleation regime and efficiency for a given model formulation. Here we use the adjoint model of the adjoint of a cirrus formation parameterization (Barahona and Nenes, 2009b) to understand Ni variability for various ice-nucleating particle (INP) spectra. Inputs are generated with the Community Atmosphere Model version 5, and simulations are done with a theoretically derived spectrum, an empirical lab-based spectrum and two field-based empirical spectra that differ in the nucleation threshold for black carbon particles and in the active site density for dust. The magnitude and sign of Ni sensitivity to insoluble aerosol number can be directly linked to nucleation regime and efficiency of various INP. The lab-based spectrum calculates much higher INP efficiencies than field-based ones, which reveals a disparity in aerosol surface properties. Ni sensitivity to temperature tends to be low, due to the compensating effects of temperature on INP spectrum parameters; this low temperature sensitivity regime has been experimentally reported before but never deconstructed as done here.

  11. Nucleation control and separation of paracetamol polymorphs through swift cooling crystallization process

    NASA Astrophysics Data System (ADS)

    Sudha, C.; Srinivasan, K.

    2014-09-01

    Polymorphic nucleation behavior of pharmaceutical solid paracetamol has been investigated by performing swift cooling crystallization process. Saturated aqueous solution prepared at 318 K was swiftly cooled to 274 K in steps of every 1 K in the temperature range from 274 K to 313 K with uniform stirring of 100 rpm. The resultant supersaturation generated in the mother solution favours the nucleation of three different polymorphs of paracetamol. Lower supersaturation region σ=0.10-0.83 favours stable mono form I; the intermediate supersaturation region σ=0.92-1.28 favours metastable ortho form II and the higher supersaturation region σ=1.33-1.58 favours unstable form III polymorphic nucleation. Depending upon the level of supersaturation generated during swift cooling process and the corresponding solubility limit and metastable zone width (MSZW) of each polymorph, the nucleation of a particular polymorph occurs in the system. The type of polymorphs was identified by in-situ optical microscopy and the internal structure was confirmed by Powder X-ray diffraction (PXRD) study. By this novel approach, the preferred nucleation regions of all the three polymorphs of paracetamol are optimized in terms of different cooling ranges employed during the swift cooling process. Also solution mediated polymorphic transformations from unstable to mono and ortho to mono polymorphs have been studied by in-situ.

  12. Understanding cirrus ice crystal number variability for different heterogeneous ice nucleation spectra

    DOE PAGES

    Sullivan, Sylvia C.; Morales Betancourt, Ricardo; Barahona, Donifan; ...

    2016-03-03

    Along with minimizing parameter uncertainty, understanding the cause of temporal and spatial variability of the nucleated ice crystal number, Ni, is key to improving the representation of cirrus clouds in climate models. To this end, sensitivities of Ni to input variables like aerosol number and diameter provide valuable information about nucleation regime and efficiency for a given model formulation. Here we use the adjoint model of the adjoint of a cirrus formation parameterization (Barahona and Nenes, 2009b) to understand Ni variability for various ice-nucleating particle (INP) spectra. Inputs are generated with the Community Atmosphere Model version 5, and simulations are donemore » with a theoretically derived spectrum, an empirical lab-based spectrum and two field-based empirical spectra that differ in the nucleation threshold for black carbon particles and in the active site density for dust. The magnitude and sign of Ni sensitivity to insoluble aerosol number can be directly linked to nucleation regime and efficiency of various INP. The lab-based spectrum calculates much higher INP efficiencies than field-based ones, which reveals a disparity in aerosol surface properties. Ni sensitivity to temperature tends to be low, due to the compensating effects of temperature on INP spectrum parameters; this low temperature sensitivity regime has been experimentally reported before but never deconstructed as done here.« less

  13. Effects of chitosan on the alignment, morphology and shape of calcite crystals nucleating under Langmuir monolayers

    NASA Astrophysics Data System (ADS)

    Kim, Kyungil

    The mechanisms governing selective CaCO3 crystal nucleation in living organisms remain unclear. For example, nacreous layers from the inner surfaces of shells are built as brick-and-mortar complexes of plate-like aragonite single crystals and organic layers. Unstable [001] surfaces of calcite columns in prismatic layers are also stabilized by organic molecules. Biogenic calcite crystals show different morphologies compared to geological calcite minerals. Langmuir monolayers are used as structured templates in simulated biomineralization from CaCO3 supersaturated subphases. But pure or mixed Langmuir monolayers do not mimic the nucleation sites of aspartic-rich proteins found within real biominerals. It has previously been shown that there is organic-inorganic lattice relaxation in the cases of BaF2 and hydrocerussite (2PbCO3·Pb(OH) 2) nucleation under fatty (carboxylate) acid with preferred orientation of crystals, but no lattice match is observed during CaCO3 crystallization under fatty acid Langmuir monolayers. Overall, geometric influences such as structural match between the interfacial lattices and the interactions between monolayer headgroups and aqueous ions do not guarantee any well-defined orientation of CaCO3 crystallization. CaCO3 mineralization on self-assembled monolayers on metal and alloy substrates have achieved higher degrees of orientations, even though molecules in Langmuir monolayers are better ordered than in self-assembled monolayers. Until now, Langmuir monolayer experiments have emphasized only the function of the acidic proteins. To better mimic the real organic template, it is important to include the hydrophobic and polyelectrolyte characteristics of real organic templates in shells. The organic matrix in actual shells contains hydrophobic silk fibroin (which is hydrophobic) and polyelectrolytes. Some acidic proteins reside on the surface of silk fibroins. There is also semi-crystalline beta-chitin structure whose function has not been

  14. Single ice crystal measurements during nucleation experiments with the depolarization detector IODE

    NASA Astrophysics Data System (ADS)

    Nicolet, M.; Stetzer, O.; Lohmann, U.; Möhler, O.

    2008-12-01

    In order to determine the efficiency of aerosol particles of several types to nucleate ice, an Ice Optical DEpolarization detector (IODE) was developed to distinguish between water droplets and ice crystals in ice nucleation chambers. A laser beam polarized linearly (power: 50 mW, wavelength: 407 nm) is directed through the chamber. The scattered light intensity from particles is measured at a scattering angle of Θ=175° in both polarization components (parallel and perpendicular). The ratio between the perpendicular intensity over the total one gives the depolarization ratio δ. Single particle detection is possible, using a peak detection algorithm. For high particle concentrations, a real-time signal averaging method can also be run simultaneously. The IODE detector was used in connection with the Zurich ice nucleation chamber during the ICIS 2007 workshop where ice nucleation experiments were performed with several aerosol types. In presence of ice crystals, peaks were detected in both channels, generating depolarization signals. Mean values of δ ranged from 0.24 to 0.37.

  15. Single ice crystal measurements during nucleation experiments with the depolarization detector IODE

    NASA Astrophysics Data System (ADS)

    Nicolet, M.; Stetzer, O.; Lüönd, F.; Möhler, O.; Lohmann, U.

    2010-01-01

    In order to determine the efficiency of different aerosol particles to nucleate ice, an Ice Optical DEpolarization detector (IODE) was developed to distinguish between water droplets and ice crystals in ice nucleation chambers. A laser beam polarized linearly (power: 50 mW, wavelength: 407 nm) is directed through the chamber. The scattered light intensity from particles is measured at a scattering angle of Θ=175° in both polarization components (parallel and perpendicular). The ratio between the perpendicular intensity over the total one yields the depolarization ratio δ. Single particle detection is possible, using a peak detection algorithm. For high particle concentrations, a real-time signal averaging method can also be run simultaneously. The IODE detector was used in connection with the Zurich ice nucleation chamber during the ICIS 2007 workshop where ice nucleation experiments were performed with several aerosol types. In presence of ice crystals, a depolarization ratio could be measured on a particle-by-particle basis. Mean values of δ ranged from 0.24 to 0.37 and agree well with theoretical calculations.

  16. Role of clusters in nonclassical nucleation and growth of protein crystals

    PubMed Central

    Sleutel, Mike; Van Driessche, Alexander E. S.

    2014-01-01

    The development of multistep nucleation theory has spurred on experimentalists to find intermediate metastable states that are relevant to the solidification pathway of the molecule under interest. A great deal of studies focused on characterizing the so-called “precritical clusters” that may arise in the precipitation process. However, in macromolecular systems, the role that these clusters might play in the nucleation process and in the second stage of the precipitation process, i.e., growth, remains to a great extent unknown. Therefore, using biological macromolecules as a model system, we have studied the mesoscopic intermediate, the solid end state, and the relationship that exists between them. We present experimental evidence that these clusters are liquid-like and stable with respect to the parent liquid and metastable compared with the emerging crystalline phase. The presence of these clusters in the bulk liquid is associated with a nonclassical mechanism of crystal growth and can trigger a self-purifying cascade of impurity-poisoned crystal surfaces. These observations demonstrate that there exists a nontrivial connection between the growth of the macroscopic crystalline phase and the mesoscopic intermediate which should not be ignored. On the other hand, our experimental data also show that clusters existing in protein solutions can significantly increase the nucleation rate and therefore play a relevant role in the nucleation process. PMID:24449867

  17. Nucleation in Synoptically Forced Cirrostratus

    NASA Technical Reports Server (NTRS)

    Lin, R.-F.; Starr, D. OC.; Reichardt, J.; DeMott, P. J.

    2004-01-01

    Formation and evolution of cirrostratus in response to weak, uniform and constant synoptic forcing is simulated using a one-dimensional numerical model with explicit microphysics, in which the particle size distribution in each grid box is fully resolved. A series of tests of the model response to nucleation modes (homogeneous-freezing-only/heterogeneous nucleation) and heterogeneous nucleation parameters are performed. In the case studied here, nucleation is first activated in the prescribed moist layer. A continuous cloud-top nucleation zone with a depth depending on the vertical humidity gradient and one of the nucleation parameters is developed afterward. For the heterogeneous nucleation cases, intermittent nucleation zones in the mid-upper portion of the cloud form where the relative humidity is on the rise, because existent ice crystals do not uptake excess water vapor efficiently, and ice nuclei (IN) are available. Vertical resolution as fine as 1 m is required for realistic simulation of the homogeneous-freezing-only scenario, while the model resolution requirement is more relaxed in the cases where heterogeneous nucleation dominates. Bulk microphysical and optical properties are evaluated and compared. Ice particle number flux divergence, which is due to the vertical gradient of the gravity-induced particle sedimentation, is constantly and rapidly changing the local ice number concentration, even in the nucleation zone. When the depth of the nucleation zone is shallow, particle number concentration decreases rapidly as ice particles grow and sediment away from the nucleation zone. When the depth of the nucleation zone is large, a region of high ice number concentration can be sustained. The depth of nucleation zone is an important parameter to be considered in parametric treatments of ice cloud generation.

  18. Effects of crystallization and bubble nucleation on the seismic properties of magmas

    NASA Astrophysics Data System (ADS)

    Tripoli, Barbara Andrea; Cordonnier, Benoit; Zappone, Alba; Ulmer, Peter

    2016-02-01

    Seismic tomography of potentially hazardous volcanoes is a prime tool to assess the location and dimensions of magmatic reservoirs. Seismic velocities are strongly affected by processes occurring within the conduit or in the magma chamber, such as crystallization and bubble exsolution. However, the limited number of constrained measurements does not allow yet to link seismic tomography and the textural state of a particular volcanic system. In this study, we investigated a chemically simplified melt in the system CaO-Na2O-Al2O3-SiO2-H2O-CO2, which undergoes plagioclase crystallization and bubble exsolution. A Paterson-type internally heated gas pressure apparatus was employed to measure ultrasonic velocities at a constant pressure of 250 MPa and at temperature from 850 to 700°C. Magmatic processes such as crystallization, bubble nucleation, and coalescence have been recognized throughout the measurements of seismic velocities in the laboratory. Compression and shear wave velocities increase nonlinearly during crystallization. At a crystal fraction exceeding 0.45, the formation of a crystal network favors the propagation of seismic waves through magmatic liquids. However, bubble nucleation induced by crystallization leads to an increase of magma compressibility resulting in a lowering of the wave propagation velocities. These two processes occur simultaneously and have a competing influence on the seismic properties of magmas. In addition, as already observed by previous authors, when the bubble fraction is less than 0.10, the decrease in seismic velocities is more pronounced than for higher bubble fractions. The effect of bubble coalescence on elastic properties is thus lower than the effect of bubble nucleation.

  19. Bubble nucleation in magmas: a dominantly heterogeneous process?

    NASA Astrophysics Data System (ADS)

    Shea, T.; Hammer, J. E.; Brachfeld, S. A.

    2016-12-01

    The processes governing volatile exsolution, and particularly the timing of initial vapor phase nucleation with respect to depth in the conduit, control a magma's explosive potential. Experimental studies have shown that nucleation kinetics exert the dominant control on degassing efficiency in silicate melts. Homogeneous nucleation (i.e. without assistance from crystal substrates or other phases) often requires attainment of large supersaturation pressures (ΔPN, the change in pressure required for nucleation), while heterogeneous nucleation on pre-existing crystals can occur at significantly lower ΔPN (<50 MPa). Crystal-poor rhyolites have therefore been largely regarded as the type example of homogeneous bubble nucleation, disequilibrium degassing and heightened explosivity. while other less viscous magmas (dacite, phonolite, basalt) are thought to more often foster heterogeneous nucleation with variable departures from equilibrium. Distinguishing between the two nucleation mechanisms is vital for applications that employ classical nucleation theory and its derivatives: for instance, Toramaru's increasingly used decompression-rate meter (Toramaru 2006) links the number density of bubbles per unit volume melt (NV) of pyroclasts - a readily obtained textural characteristic - to rates of pressure change (dP/dt) during ascent. These formulations require an explicit or implicit decision as to whether magma degassing was dominated by homogeneous or heterogeneous nucleation. This study exploits the large number of textural datasets available for eruptions involving various magma compositions to examine the dominant nucleation mechanism in natural melts. Because Fe-Ti oxides are unrivaled in their capacity to favor heterogeneous nucleation, the absence of high concentrations of petrographically-observable Fe-Ti oxide crystals in erupted pyroclasts is often taken as an indicator that homogeneous nucleation dominated bubble vesiculation in rhyolites. This contribution

  20. Nucleation and Crystallization as Induced by Bending Stress in Lithium Silicate Glass Fibers

    NASA Technical Reports Server (NTRS)

    Reis, Signo T.; Kim, Cheol W.; Brow, Richard K.; Ray, Chandra S.

    2003-01-01

    Glass Fibers of Li2O.2SiO2 (LS2) and Li2O.1.6SiO2 (LS1.6) compositions were heated near, but below, the glass transition temperature for different times while subjected to a constant bending stress of about 1.2 GPa. The nucleation density and the crystallization tendency estimated by differential thermal analysis (DTA) of a glass sample in the vicinity of the maximum of the bending stress increased relative to that of stress-free glass fibers. LS2 glass fibers were found more resistant to nucleation and crystallization than the Ls1.6 glass fibers. These results are discussed in regards to shear thinning effects on glass stability.

  1. Mathematical modelling of nucleation and growth of crystals with buoyancy effects

    NASA Astrophysics Data System (ADS)

    Alexandrov, D. V.

    2016-04-01

    A complete analytical solution of the integro-differential model describing the nucleation of crystals and their subsequent growth in a binary system with allowance for buoyancy forces is constructed. An exact analytical solution of the Fokker-Planck-type equation for the three-parameter density distribution function is found for arbitrary nucleation kinetics. Two important cases of the Weber-Volmer-Frenkel-Zel'dovich and Meirs kinetics are considered in some detail. It is shown that the solute concentration decreases and the distribution function increases with increasing the melt supercooling (with increasing the depth of a metastable system). It is demonstrated that the distribution function attains its minimum at a certain size of crystals owing to buoyancy forces.

  2. Nucleation and Crystallization as Induced by Bending Stress in Lithium Silicate Glass Fibers

    NASA Technical Reports Server (NTRS)

    Reis, Signo T.; Kim, Cheol W.; Brow, Richard K.; Ray, Chandra S.

    2003-01-01

    Glass Fibers of Li2O.2SiO2 (LS2) and Li2O.1.6SiO2 (LS1.6) compositions were heated near, but below, the glass transition temperature for different times while subjected to a constant bending stress of about 1.2 GPa. The nucleation density and the crystallization tendency estimated by differential thermal analysis (DTA) of a glass sample in the vicinity of the maximum of the bending stress increased relative to that of stress-free glass fibers. LS2 glass fibers were found more resistant to nucleation and crystallization than the Ls1.6 glass fibers. These results are discussed in regards to shear thinning effects on glass stability.

  3. Homogeneous nucleation of water in argon. Nucleation rate computation from molecular simulations of TIP4P and TIP4P/2005 water model

    NASA Astrophysics Data System (ADS)

    Dumitrescu, Lucia R.; Smeulders, David M. J.; Dam, Jacques A. M.; Gaastra-Nedea, Silvia V.

    2017-02-01

    Molecular dynamics (MD) simulations were conducted to study nucleation of water at 350 K in argon using TIP4P and TIP4P/2005 water models. We found that the stability of any cluster, even if large, strongly depends on the energetic interactions with its vicinity, while the stable clusters change their composition almost entirely during nucleation. Using the threshold method, direct nucleation rates are obtained. Our nucleation rates are found to be 1.08 ×1027 cm-3 s-1 for TIP4P and 2.30 ×1027 cm-3 s-1 for TIP4P/2005. The latter model prescribes a faster dynamics than the former, with a nucleation rate two times larger due to its higher electrostatic charges. The non-equilibrium water densities derived from simulations and state-of-art equilibrium parameters from Vega and de Miguel [J. Chem. Phys. 126, 154707 (2007)] are used for the classical nucleation theory (CNT) prediction. The CNT overestimates our results for both water models, where TIP4P/2005 shows largest discrepancy. Our results complement earlier data at high nucleation rates and supersaturations in the Hale plot [Phys. Rev. A 33, 4156 (1986)], and are consistent with MD data on the SPC/E and the TIP4P/2005 model.

  4. Biliary microlithiasis, sludge, crystals, microcrystallization, and usefulness of assessment of nucleation time.

    PubMed

    Abeysuriya, Vasitha; Deen, Kemal I; Navarathne, Navarathne M M

    2010-06-01

    The process of microcrystallization, its sequel and the assessment of nucleation time is ignored. This systematic review aimed to highlight the importance of biliary microlithiasis, sludge, and crystals, and their association with gallstones, unexplained biliary pain, idiopathic pancreatitis, and sphincter of Oddi dysfunction. Three reviewers performed a literature search of the PubMed database. Key words used were "biliary microlithiasis", "biliary sludge", "bile crystals", "cholesterol crystallisation", "bile microscopy", "microcrystal formation of bile", "cholesterol monohydrate crystals", "nucleation time of cholesterol", "gallstone formation", "sphincter of Oddi dysfunction" and "idiopathic pancreatitis". Additional articles were sourced from references within the studies from the PubMed search. We found that biliary microcrystals account for almost all patients with gallstone disease, 7% to 79% with idiopathic pancreatitis, 83% with unexplained biliary pain, and 25% to 60% with altered biliary and pancreatic sphincter function. Overall, the detection of biliary microcrystals in gallstone disease has a sensitivity ranging from 55% to 87% and a specificity of 100%. In idiopathic pancreatitis, the presence of microcrystals ranges from 47% to 90%. A nucleation time less than 10 days in hepatic bile or ultra-filtered gallbladder bile has a specificity of 100% for cholesterol gallstone disease. Biliary crystals are associated with gallstone disease, idiopathic pancreatitis, sphincter of Oddi dysfunction, unexplained biliary pain, and post-cholecystectomy biliary pain. Pathways of cholesterol super-saturation, crystallisation, and gallstone formation have been described with scientific support. Bile microscopy is a useful method to detect microcrystals and the assessment of nucleation time is a good method of predicting the risk of cholesterol crystallisation.

  5. Experimental Study of the Low Supersaturation Nucleation in Crystal Growth by Contactless Physical Vapor Transport

    NASA Technical Reports Server (NTRS)

    Grasza, K.; Palosz, W.; Trivedi, S. B.

    1998-01-01

    The process of the development of the nuclei and of subsequent seeding in 'contactless' physical vapor transport is investigated experimentally. Consecutive stages of the Low Supersaturation Nucleation in 'contactless' geometry for growth of CdTe crystals from the vapor are shown. The effects of the temperature field, geometry of the system, and experimental procedures on the process are presented and discussed. The experimental results are found to be consistent with our earlier numerical modeling results.

  6. Temperature dependence of homogeneous nucleation rates for water: Near equivalence of the empirical fit of Wölk and Strey, and the scaled nucleation model

    NASA Astrophysics Data System (ADS)

    Hale, Barbara N.

    2005-05-01

    It is pointed out that the temperature fitting function of Wölk and Strey [J. Phys. Chem. 105, 11683 (2001)], recently shown to convert the Becker-Döring [Ann. Phys. (Leipzig) 24, 719 (1935)] nucleation rate into an expression in agreement with much of the experimental water nucleation rate data, also converts the Becker-Döring rate into a form nearly equivalent with the scaled nucleation rate model, Jscaled=Jocexp[-16πΩ3(Tc/T-1)3/3(lnS)2]. In the latter expression Joc is the inverse thermal wavelength cubed/sec, evaluated at Tc.

  7. A new experimental setup to investigate nucleation, dynamic growth and surface properties of single ice crystals

    NASA Astrophysics Data System (ADS)

    Voigtlaender, Jens; Bieligk, Henner; Niedermeier, Dennis; Clauss, Tina; Chou, Cédric; Ulanowski, Zbigniew; Stratmann, Frank

    2013-04-01

    The nucleation and growth of atmospheric ice particles is of importance for both, weather and climate. However, knowledge is still sparse, e.g. when considering the influences of ice particle surface properties on the radiative properties of clouds. Therefore, based on the experiences with our laminar flow tube chamber LACIS (Leipzig Aerosol Cloud Interaction Simulator, Stratmann et al., 2004), we developed a new device to characterize nucleation, dynamic growth and light scattering properties of a fixed single ice crystal in dependence on the prevailing thermodynamic conditions. Main part of the new setup is a thermodynamically controlled laminar flow tube with a diameter of 15 mm and a length of 1.0 m. Connected to the flow tube is a SID3-type (Small Ice Detector, Kaye et al., 2008) instrument called LISA (Leipzig Ice Scattering Apparatus), equipped with an additional optical microscope. For the investigations, a single ice nucleus (IN) with a dry size of 2-5 micrometer is attached to a thin glass fiber and positioned within the optical measuring volume of LISA. The fixed particle is exposed to the thermodynamically controlled air flow, exiting the flow tube. Two mass flow controllers adjusting a dry and a humidified gas flow are applied to control both, the temperature and the saturation ratio over a wide range. The thermodynamic conditions in the experiments were characterized using a) temperature and dew-point measurements, and b) computational fluid dynamics (CFD) calculations. Dependent on temperature and saturation ratio in the measuring volume, ice nucleation and ice crystal growth/shrinkage can occur. The optical microscope allows a time dependent visualization of the particle/ice crystal, and the LISA instrument is used to obtain 2-D light scattering patterns. Both devices together can be applied to investigate the influence of thermodynamic conditions on ice crystal growth, in particular its shape and surface properties. We successfully performed

  8. Dynamic light scattering study of inhibition of nucleation and growth of hydroxyapatite crystals by osteopontin.

    PubMed

    de Bruyn, John R; Goiko, Maria; Mozaffari, Maryam; Bator, Daniel; Dauphinee, Ron L; Liao, Yinyin; Flemming, Roberta L; Bramble, Michael S; Hunter, Graeme K; Goldberg, Harvey A

    2013-01-01

    We study the effect of isoforms of osteopontin (OPN) on the nucleation and growth of crystals from a supersaturated solution of calcium and phosphate ions. Dynamic light scattering is used to monitor the size of the precipitating particles and to provide information about their concentration. At the ion concentrations studied, immediate precipitation was observed in control experiments with no osteopontin in the solution, and the size of the precipitating particles increased steadily with time. The precipitate was identified as hydroxyapatite by X-ray diffraction. Addition of native osteopontin (nOPN) extracted from rat bone caused a delay in the onset of precipitation and reduced the number of particles that formed, but the few particles that did form grew to a larger size than in the absence of the protein. Recombinant osteopontin (rOPN), which lacks phosphorylation, caused no delay in initial calcium phosphate precipitation but severely slowed crystal growth, suggesting that rOPN inhibits growth but not nucleation. rOPN treated with protein kinase CK2 to phosphorylate the molecule (p-rOPN) produced an effect similar to that of nOPN, but at higher protein concentrations and to a lesser extent. These results suggest that phosphorylations are critical to OPN's ability to inhibit nucleation, whereas the growth of the hydroxyapatite crystals is effectively controlled by the highly acidic OPN polypeptide. This work also demonstrates that dynamic light scattering can be a powerful tool for delineating the mechanism of protein modulation of mineral formation.

  9. Dynamic Light Scattering Study of Inhibition of Nucleation and Growth of Hydroxyapatite Crystals by Osteopontin

    PubMed Central

    de Bruyn, John R.; Goiko, Maria; Mozaffari, Maryam; Bator, Daniel; Dauphinee, Ron L.; Liao, Yinyin; Flemming, Roberta L.; Bramble, Michael S.; Hunter, Graeme K.; Goldberg, Harvey A.

    2013-01-01

    We study the effect of isoforms of osteopontin (OPN) on the nucleation and growth of crystals from a supersaturated solution of calcium and phosphate ions. Dynamic light scattering is used to monitor the size of the precipitating particles and to provide information about their concentration. At the ion concentrations studied, immediate precipitation was observed in control experiments with no osteopontin in the solution, and the size of the precipitating particles increased steadily with time. The precipitate was identified as hydroxyapatite by X-ray diffraction. Addition of native osteopontin (nOPN) extracted from rat bone caused a delay in the onset of precipitation and reduced the number of particles that formed, but the few particles that did form grew to a larger size than in the absence of the protein. Recombinant osteopontin (rOPN), which lacks phosphorylation, caused no delay in initial calcium phosphate precipitation but severely slowed crystal growth, suggesting that rOPN inhibits growth but not nucleation. rOPN treated with protein kinase CK2 to phosphorylate the molecule (p-rOPN) produced an effect similar to that of nOPN, but at higher protein concentrations and to a lesser extent. These results suggest that phosphorylations are critical to OPN’s ability to inhibit nucleation, whereas the growth of the hydroxyapatite crystals is effectively controlled by the highly acidic OPN polypeptide. This work also demonstrates that dynamic light scattering can be a powerful tool for delineating the mechanism of protein modulation of mineral formation. PMID:23457612

  10. Novel Electric Nucleation Technique for Growing Large Single Crystal in Space

    NASA Technical Reports Server (NTRS)

    Abdeldayem, Hossin; Frazier, Donald O.

    1999-01-01

    We present, herein, an electrical model for growing crystals without a seed which might not be free of defects and thereby still hinder the growth of a perfect crystal in space. The system is designed to confine nucleation to a single site automatically in an under saturated solution to avoid multiple nucleation. The technique is based on the effect of electrostriction, which is the tendency of a material to become more compressed in the presence of an electric field. The system is designed to create an electrical potential well between two hyperboloid electrodes with applied voltage at low frequency. The induced potential well between the electrodes oscillates at low frequency and attracts the solute and condenses it into the region of maximum field intensity. The alternating voltage prevents molecules with intrinsic charge from being attracted to the electrodes. The continuous presence of the electric field during the duration of the experiment, provides a continuous migration of the molecules toward the trapping site. This will eliminate the creation of a depletion region around the nucleation center and will enhance the crystal growth rate. Aside from the above mentioned advantages, the system is compact, safe to operate, and inexpensive to build.

  11. Novel Electric Nucleation Technique for Growing Large Single Crystal in Space

    NASA Technical Reports Server (NTRS)

    Abdeldayem, Hossin; Frazier, Donald O.

    1999-01-01

    We present, herein, an electrical model for growing crystals without a seed which might not be free of defects and thereby still hinder the growth of a perfect crystal in space. The system is designed to confine nucleation to a single site automatically in an under saturated solution to avoid multiple nucleation. The technique is based on the effect of electrostriction, which is the tendency of a material to become more compressed in the presence of an electric field. The system is designed to create an electrical potential well between two hyperboloid electrodes with applied voltage at low frequency. The induced potential well between the electrodes oscillates at low frequency and attracts the solute and condenses it into the region of maximum field intensity. The alternating voltage prevents molecules with intrinsic charge from being attracted to the electrodes. The continuous presence of the electric field during the duration of the experiment, provides a continuous migration of the molecules toward the trapping site. This will eliminate the creation of a depletion region around the nucleation center and will enhance the crystal growth rate. Aside from the above mentioned advantages, the system is compact, safe to operate, and inexpensive to build.

  12. The laminar flow tube reactor as a quantitative tool for nucleation studies: Experimental results and theoretical analysis of homogeneous nucleation of dibutylphthalate

    SciTech Connect

    Mikheev, Vladimir B.; Laulainen, Nels S.; Barlow, Stephan E.; Knott, Michael; Ford, Ian J.

    2000-09-01

    A laminar flow tube reactor was designed and constructed to provide an accurate, quantitative measurement of a nucleation rate as a function of supersaturation and temperature. Measurements of nucleation of a supersaturated vapor of dibutylphthalate have been made for the temperature range from -30.3 to +19.1 degree sign C. A thorough analysis of the possible sources of experimental uncertainties (such as defining the correct value of the initial vapor concentration, temperature boundary conditions on the reactor walls, accuracy of the calculations of the thermodynamic parameters of the nucleation zone, and particle concentration measurement) is given. Both isothermal and the isobaric nucleation rates were measured. The experimental data obtained were compared with the measurements of other experimental groups and with theoretical predictions made on the basis of the self-consistency correction nucleation theory. Theoretical analysis, based on the first and the second nucleation theorems, is also presented. The critical cluster size and the excess of internal energy of the critical cluster are obtained. (c) 2000 American Institute of Physics.

  13. The Laminar Flow Tube Reactor as a Quantitative Tool for Nucleation Studies: Experimental Results and Theoretical Analysis of Homogeneous Nucleation of Dibutylphthalate

    SciTech Connect

    Mikheev, Vladimir B.; Laulainen, Nels S. ); Barlow, Stephan E. ); Knott, Michael; Ford, Ian J.

    1999-12-01

    A Laminar Flow Tube Reactor has been designed and constructed in order to provide an accurate, quantitative measurement of a nucleation rate as a function of supersaturation and temperature. Measurements of nucleation of a supersaturated vapor of dibutylphthalate have been made for the temperature range from -30.3 C to+19.1 C. A thorough analysis of the possible sources of experimental uncertainties (such as defining the correct value of the initial vapor concentration, temperature boundary conditions on the reactor walls, accuracy of the calculations of the thermodynamic parameters of the nucleation zone, and particle concentration measurement) has been provided. Both isothermal and the isobaric nucleation rates have been measured. The experimental data obtained have been compared with measurements of other experimental groups and with theoretical predictions made on the basis of the self-consistency correction nucleation theory. Theoretical analysis based on the first and the second nucleation theorems has been made. The critical cluster size and the excess of internal energy of the critical cluster have been obtained.

  14. Crystalline domain structure and cholesterol crystal nucleation in single hydrated DPPC:cholesterol:POPC bilayers.

    PubMed

    Ziblat, Roy; Leiserowitz, Leslie; Addadi, Lia

    2010-07-21

    Grazing incidence X-ray diffraction measurements were performed on single hydrated bilayers and monolayers of DPPC:Cholesterol:POPC at varying concentrations. There are substantial differences in the phase and structure behavior of the crystalline domains formed within the bilayers relative to the corresponding monolayers, due to interactions between the opposing leaflets. Depending on the lipid composition, these interactions led to phase separation, changes in molecular tilt angle, or formation of cholesterol crystals. In monolayers, DPPC and cholesterol form a single crystalline phase at all compositions studied. In bilayers, a second crystalline phase appears when cholesterol levels are increased: domains of cholesterol and DPPC form monolayer thick crystals where each of the lipid leaflets diffracts independently, whereas excess cholesterol forms cholesterol bilayer thick crystals at a DPPC:Chol ratio < 46:54 +/- 2 mol %. The nucleation of the cholesterol crystals occurs at concentrations relevant to the actual cell plasma membrane composition.

  15. Crystallization of aqueous inorganic-malonic acid particles: nucleation rates, dependence on size, and dependence on the ammonium-to-sulfate ratio.

    PubMed

    Parsons, Matthew T; Riffell, Jenna L; Bertram, Allan K

    2006-07-06

    Using an electrodynamic balance, we determined the relative humidity (RH) at which aqueous inorganic-malonic acid particles crystallized, with ammonium sulfate ((NH(4))(2)SO(4)), letovicite ((NH(4))(3)H(SO(4))(2)), or ammonium bisulfate (NH(4)HSO(4)) as the inorganic component. The results for (NH(4))(2)SO(4)-malonic acid particles and (NH(4))(3)H(SO(4))(2)-malonic acid particles show that malonic acid decreases the crystallization RH of the inorganic particles by less than 7% RH when the dry malonic acid mole fraction is less than 0.25. At a dry malonic acid mole fraction of about 0.5, the presence of malonic acid can decrease the crystallization RH of the inorganic particles by up to 35% RH. For the NH(4)HSO(4)-malonic acid particles, the presence of malonic acid does not significantly modify the crystallization RH of the inorganic particles for the entire range of dry malonic acid mole fractions studied; in all cases, either the particles did not crystallize or the crystallization RH was close to 0% RH. Size dependent measurements show that the crystallization RH of aqueous (NH(4))(2)SO(4) particles is not a strong function of particle volume. However, for aqueous (NH(4))(2)SO(4)-malonic acid particles (with dry malonic acid mole fraction = 0.36), the crystallization RH is a stronger function of particle volume, with the crystallization RH decreasing by 6 +/- 3% RH when the particle volume decreases by an order of magnitude. To our knowledge, these are the first size dependent measurements of the crystallization RH of atmospherically relevant inorganic-organic particles. These results suggest that for certain organic mole fractions the particle size and observation time need to be considered when extrapolating laboratory crystallization results to atmospheric scenarios. For aqueous (NH(4))(2)SO(4) particles, the homogeneous nucleation rate data are a strong function of RH, but for aqueous (NH(4))(2)SO(4)-malonic acid particles (with dry organic mole fraction = 0

  16. Process scale-up considerations for non-thermal atmospheric-pressure plasma synthesis of nanoparticles by homogenous nucleation

    NASA Astrophysics Data System (ADS)

    Cole, Jonathan; Zhang, Yao; Liu, Tianqi; Liu, Chang-jun; Mohan Sankaran, R.

    2017-08-01

    Scale-up of non-thermal atmospheric-pressure plasma reactors for the synthesis of nanoparticles by homogeneous nucleation is challenging because the active volume is typically reduced to facilitate gas breakdown, enhance discharge stability, and limit particle size and agglomeration, but thus limits throughput. Here, we introduce a dielectric barrier discharge reactor consisting of a coaxial electrode geometry for nanoparticle production that enables a simple scale-up strategy whereby increasing the outer and inner electrode diameters, the plasma volume is increased approximately linearly, while maintaining a sufficiently small electrode gap to maintain the electric field strength. We show with two test reactors that for a given residence time, the nanoparticle production rate increases linearly with volume over a range of precursor concentrations, while having minimal effect on the shape of the particle size distribution. However, our study also reveals that increasing the total gas flow rate in a smaller volume reactor leads to an enhancement of precursor conversion and a comparable production rate to a larger volume reactor. These results suggest that scale-up requires better understanding of the influence of reactor geometry on particle growth dynamics and may not always be a simple function of reactor volume.

  17. Complete thermodynamically consistent kinetic model of particle nucleation and growth: Numerical study of the applicability of the classical theory of homogeneous nucleation

    NASA Astrophysics Data System (ADS)

    Chesnokov, Evgeni N.; Krasnoperov, Lev N.

    2007-04-01

    A complete thermodynamically consistent elementary reaction kinetic model of particle nucleation and growth from supersaturated vapor was developed and numerically evaluated to determine the conditions for the steady-state regime. The model treats all processes recognized in the aerosol science (such as nucleation, condensation, evaporation, agglomeration/coagulation, etc.) as reversible elementary reactions. It includes all possible forward reactions (i.e., of monomers, dimers, trimers, etc.) together with the thermodynamically consistent reverse processes. The model is built based on the Kelvin approximation, and has two dimensionless parameters: S0—the initial supersaturation and Θ—the dimensionless surface tension. The time evolution of the size distribution function was obtained over the ranges of parameters S0 and Θ. At low initial supersaturations, S0, the steady state is established after a delay, and the steady-state distribution function corresponds to the predictions of the classical nucleation theory. At high initial supersaturations, the depletion of monomers due to condensation on large clusters starts before the establishing of the steady state. The steady state is never reached, and the classical nucleation theory is not applicable. The boundary that separates these two regimes in the two dimensionless parameter space, S0 and Θ, was determined. The model was applied to several experiments on water nucleation in an expansion chamber [J. Wolk and R. Strey, J. Phys. Chem. B 105, 11683 (2001)] and in Laval nozzle [Y. J. Kim et al., J. Phys. Chem. A 108, 4365 (2004)]. The conditions of the experiments performed using Laval nozzle (S0=40-120) were found to be close to the boundary of the non-steady-state regime. Additional calculations have shown that in the non-steady-state regime the nucleation rate is sensitive to the rate constants of the initial steps of the nucleation process, such as the monomer-monomer, monomer-dimer, etc., reactions. This

  18. Nucleation and Crystallization of Globular Proteins: What we Know and What is Missing

    NASA Technical Reports Server (NTRS)

    Rosenberger, F.; Vekilov, P. G.; Muschol, M.; Thomas, B. R.

    1996-01-01

    Recently. much progress has been made in understanding the nucleation and crystallization of globular proteins, including the formation of compositional and structural crystal defects, Insight into the interactions of (screened) protein macro-ions in solution, obtained from light scattering, small angle X-ray scattering and osmotic pressure studies. can guide the search for crystallization conditions. These studies show that the nucleation of globular proteins is governed by the same principles as that of small molecules. However, failure to account for direct and indirect (hydrodynamic) protein interactions in the solutions results in unrealistic aggregation scenarios. Microscopic studies of numerous proteins reveal that crystals grow by the attachment of growth units through the same layer-spreading mechanisms as inorganic crystals. Investigations of the growth kinetics of hen-egg-white lysozyme (HEWL) reveal non-steady behavior under steady external conditions. Long-term variations in growth rates are due to changes in step-originating dislocation groups. Fluctuations on a shorter timescale reflect the non-linear dynamics of layer growth that results from the interplay between interfacial kinetics and bulk transport. Systematic gel electrophoretic analyses suggest that most HEWL crystallization studies have been performed with material containing other proteins at percent levels. Yet, sub-percent levels of protein impurities impede growth step propagation and play a role in the formation of structural/compositional inhomogeneities. In crystal growth from highly purified HEWL solutions, however, such inhomogeneities are much weaker and form only in response to unusually large changes in growth conditions. Equally important for connecting growth conditions to crystal perfection and diffraction resolution are recent advances in structural characterization through high-resolution Bragg reflection profiling and X-ray topography.

  19. Nucleation and Crystallization of Globular Proteins: What we Know and What is Missing

    NASA Technical Reports Server (NTRS)

    Rosenberger, F.; Vekilov, P. G.; Muschol, M.; Thomas, B. R.

    1996-01-01

    Recently. much progress has been made in understanding the nucleation and crystallization of globular proteins, including the formation of compositional and structural crystal defects, Insight into the interactions of (screened) protein macro-ions in solution, obtained from light scattering, small angle X-ray scattering and osmotic pressure studies. can guide the search for crystallization conditions. These studies show that the nucleation of globular proteins is governed by the same principles as that of small molecules. However, failure to account for direct and indirect (hydrodynamic) protein interactions in the solutions results in unrealistic aggregation scenarios. Microscopic studies of numerous proteins reveal that crystals grow by the attachment of growth units through the same layer-spreading mechanisms as inorganic crystals. Investigations of the growth kinetics of hen-egg-white lysozyme (HEWL) reveal non-steady behavior under steady external conditions. Long-term variations in growth rates are due to changes in step-originating dislocation groups. Fluctuations on a shorter timescale reflect the non-linear dynamics of layer growth that results from the interplay between interfacial kinetics and bulk transport. Systematic gel electrophoretic analyses suggest that most HEWL crystallization studies have been performed with material containing other proteins at percent levels. Yet, sub-percent levels of protein impurities impede growth step propagation and play a role in the formation of structural/compositional inhomogeneities. In crystal growth from highly purified HEWL solutions, however, such inhomogeneities are much weaker and form only in response to unusually large changes in growth conditions. Equally important for connecting growth conditions to crystal perfection and diffraction resolution are recent advances in structural characterization through high-resolution Bragg reflection profiling and X-ray topography.

  20. Nucleation and growth of crystals under cirrus and polar stratospheric cloud conditions

    NASA Technical Reports Server (NTRS)

    Hallett, John; Queen, Brian; Teets, Edward; Fahey, James

    1995-01-01

    Laboratory studies examine phase changes of hygroscopic substances which occur as aerosol in stratosphere and troposphere (sodium chloride, ammonium sulfate, ammonium bisulfate, nitric acid, sulfuric acid), under controlled conditions, in samples volume 1 to 10(exp -4) ml. Crystallization of salts from supersaturated solutions is examined by slowly evaporating a solution drop on a substrate, under controlled relative humidity, until self nucleation occurs; controlled nucleation of ice in a mm capillary U-tube gives a measured ice crystallization velocity at known supercooling. Two states of crystallization occur for regions where hydrates exist. It is inferred that all of the materials readily exist as supersaturated/supercooled solutions; the degree of metastability appears to be slightly enhanced by inclusion of aircraft produced soot. The crystallization velocity is taken as a measure of viscosity. Results suggest an approach to a glass transition at high molality, supersaturation and/or supercooling within the range of atmospheric interest. It is hypothesized that surface reactions occur more readily on solidified particles - either crystalline or glass, whereas volume reactions are more important on droplets with sufficiently low viscosity and volume diffusivity. Implications are examined for optical properties of such particles in the atmosphere. In a separate experiment, crystal growth was examined in a modified thermal vapor diffusion chamber over the range of cirrus temperature (-30 to -70 C) and under controlled supersaturation and air pressure. The crystals grew at a velocity of 1-2 microns/s, thickness 60-70 micron, in the form of thin column crystals. Design criteria are given for a system to investigate particle growth down to -100 C, (PSC temperatures) where nitric acid particles can be grown under similar control and in the form of hydrate crystals.

  1. Liquid-to-crystal nucleation: A New Generation lag-time apparatus

    NASA Astrophysics Data System (ADS)

    Heneghan, Af; Haymet, Adj

    2002-03-01

    The statistics of liquid-to-crystal nucleation are examined using a new generation lag-time apparatus. A single 200 micro L sample of distilled water, both unseeded and seeded with an insoluble AgI crystal, is cooled at a constant rate, α, until the sample freezes. This cycle is repeated as many times as possible to generate the unambiguous statistics of nucleation. Our data are the times and the temperatures to nucleation for approximately 300 runs at each of five different cooling rates. The cooling rates in this experiment range from 0.01 K sec_-1 = 0.6 K min_-1 to more than an order of magnitude faster. Of interest is the functional form describing the average lag-time, <τ>, as a function of supercooling, Δ T. These data and analysis yield, from a single experiment, this average lag time, <τ>, as a function of the supercooling, Δ T. The one approximation in this analysis is easily verified by this apparatus and experiments performed thus far[1]. Comparison is made with related experiments of supercooled alloys. [1] Heneghan AF, Wilson PW, Wang GW, Haymet ADJ, Journal of Chemical Physics, 115, 7599-7608 (2001)

  2. Polymorph selection and nucleation pathway in the crystallization of Hertzian spheres

    NASA Astrophysics Data System (ADS)

    Ouyang, Wenze; Fu, Cuiliu; Sun, Zhiwei; Xu, Shenghua

    2016-10-01

    The crystallization process of Hertzian spheres is studied by means of molecular dynamics simulations in an NPT ensemble where the total number of particles N, the pressure P, and the temperature T are kept constant. It has been observed that the bond orientational ordering rather than the translational ordering (density) plays a primary role. The crystal polymorphs are determined by the state points. Under the conditions of small supercooling, the system is likely to be nucleated into crystals that have a preference for the metastable bcc structure, which can be regarded as a manifestation of the Alexander-McTague mechanism. In contrast, small nuclei are found to have a preference for fcc symmetry under conditions of a high degree of supercooling. Prestructured precursors that act as seeds and wet on the nuclei during nucleation always have a high degree of bcc-like ordering, despite different state points. The results above may provide a clue to the understanding of the crystallization process in core-softened particles.

  3. Controlled parallel crystallization of lithium disilicate and diopside using a combination of internal and surface nucleation

    NASA Astrophysics Data System (ADS)

    Rampf, Markus; Dittmer, Marc; Ritzberger, Christian; Höland, Wolfram

    2016-10-01

    In the mid-19th century, Dr. Donald Stookey identified the importance and usability of nucleating agents and mechanisms for the development of glass-ceramic materials. Today, a number of various internal and surface mechanisms as well as combinations thereof have been established in the production of glass-ceramic materials. In order to create new innovative material properties the present study focuses on the precipitation of CaMgSiO6 as a minor phase in Li2Si2O5 based glass-ceramics. In the base glass of the SiO2-Li2O-P2O5-Al2O3-K2O-MgO-CaO system P2O5 serves as nucleating agent for the internal precipitation of Li2Si2O5 crystals while a mechanical activation of the glass surface by means of ball milling is necessary to nucleate the minor CaMgSi2O6 crystal phase. For a successful precipitation of CaMgSi2O6 a minimum ratio of MgO and CaO in the range between 1.4 mol% and 2.9 mol% in the base glasses was determined. The nucleation and crystallization of both crystal phases takes place during sintering a powder compact. Dependent on the quality of the sintering process the dense Li2Si2O5-CaMgSi2O6 glass-ceramics show a mean biaxial strength of up to 392 ± 98 MPa. The microstructure of the glass-ceramics is formed by large (5-10 µm) bar like CaMgSi2O6 crystals randomly embedded in a matrix of small (≤ 0.5 µm) plate like Li2Si2O5 crystals arranged in an interlocking manner. While there is no significant influence of the minor CaMgSi2O6 phase on the strength of the material, the translucency of the material decreases upon precipitation of the minor phase.

  4. Amelogenin as a promoter of nucleation and crystal growth of apatite

    NASA Astrophysics Data System (ADS)

    Uskoković, Vuk; Li, Wu; Habelitz, Stefan

    2011-02-01

    Human dental enamel forms over a period of 2-4 years by substituting the enamel matrix, a protein gel mostly composed of a single protein, amelogenin with fibrous apatite nanocrystals. Self-assembly of amelogenin and the products of its selective proteolytic digestion are presumed to direct the growth of apatite fibers and their organization into bundles that eventually comprise the mature enamel, the hardest tissue in the mammalian body. This work aimed to establish the physicochemical and biochemical conditions for the growth of apatite crystals under the control of a recombinant amelogenin matrix (rH174) in combination with a programmable titration system. The growth of apatite substrates was initiated in the presence of self-assembling amelogenin particles. A series of constant titration rate experiments was performed that allowed for a gradual increase of the calcium and/or phosphate concentrations in the protein suspensions. We observed a significant amount of apatite crystals formed on the substrates following the titration of rH174 sols that comprised the initial supersaturation ratio equal to zero. The protein layers adsorbed onto the substrate apatite crystals were shown to act as promoters of nucleation and growth of calcium phosphates subsequently formed on the substrate surface. Nucleation lag time experiments have showed that rH174 tends to accelerate precipitation from metastable calcium phosphate solutions in proportion to its concentration. Despite their mainly hydrophobic nature, amelogenin nanospheres, the size and surface charge properties of which were analyzed using dynamic light scattering, acted as a nucleating agent for the crystallization of apatite. The biomimetic experimental setting applied in this study proves as convenient for gaining insight into the fundamental nature of the process of amelogenesis.

  5. Diffusive and martensitic nucleation kinetics in solid-solid transitions of colloidal crystals

    PubMed Central

    Peng, Yi; Li, Wei; Wang, Feng; Still, Tim; Yodh, Arjun G.; Han, Yilong

    2017-01-01

    Solid–solid transitions between crystals follow diffusive nucleation, or various diffusionless transitions, but these kinetics are difficult to predict and observe. Here we observed the rich kinetics of transitions from square lattices to triangular lattices in tunable colloidal thin films with single-particle dynamics by video microscopy. Applying a small pressure gradient in defect-free regions or near dislocations markedly transform the diffusive nucleation with an intermediate-stage liquid into a martensitic generation and oscillation of dislocation pairs followed by a diffusive nucleus growth. This transformation is neither purely diffusive nor purely martensitic as conventionally assumed but a combination thereof, and thus presents new challenges to both theory and the empirical criterion of martensitic transformations. We studied how pressure, density, grain boundary, triple junction and interface coherency affect the nucleus growth, shape and kinetic pathways. These novel microscopic kinetics cast new light on control solid–solid transitions and microstructural evolutions in polycrystals. PMID:28504246

  6. Theoretical study of production of unique glasses in space. [kinetic relationships describing nucleation and crystallization phenomena

    NASA Technical Reports Server (NTRS)

    Larsen, D. C.; Sievert, J. L.

    1975-01-01

    The potential of producing the glassy form of selected materials in the weightless, containerless nature of space processing is examined through the development of kinetic relationships describing nucleation and crystallization phenomena. Transformation kinetics are applied to a well-characterized system (SiO2), an excellent glass former (B2O3), and a poor glass former (Al2O3) by conventional earth processing methods. Viscosity and entropy of fusion are shown to be the primary materials parameters controlling the glass forming tendency. For multicomponent systems diffusion-controlled kinetics and heterogeneous nucleation effects are considered. An analytical empirical approach is used to analyze the mullite system. Results are consistent with experimentally observed data and indicate the promise of mullite as a future space processing candidate.

  7. Numerical simulations of contrail-to-cirrus transition - Part 2: Impact of initial ice crystal number, radiation, stratification, secondary nucleation and layer depth

    NASA Astrophysics Data System (ADS)

    Unterstrasser, S.; Gierens, K.

    2010-02-01

    Simulations of contrail-to-cirrus transition were performed with an LES model. In Part 1 the impact of relative humidity, temperature and vertical wind shear was explored in a detailed parametric study. Here, we study atmospheric parameters like stratification and depth of the supersaturated layer and processes which may affect the contrail evolution. We consider contrails in various radiation scenarios herein defined by the season, time of day and the presence of lower-level cloudiness which controls the radiance incident on the contrail layer. Under suitable conditions, controlled by the radiation scenario and stratification, radiative heating lifts the contrail-cirrus and prolongs its lifetime. The potential of contrail-driven secondary nucleation is investigated. We consider homogeneous nucleation and heterogeneous nucleation of preactivated soot cores released from sublimated contrail ice crystals. In our model the contrail dynamics triggered by radiative heating does not suffice to force homogeneous freezing of ambient liquid aerosol particles. Furthermore, our model results suggest that heterogeneous nucleation of preactivated soot cores is unimportant. Contrail evolution is not controlled by the depth of the supersaturated layer as long as it exceeds roughly 500 m. Deep fallstreaks however need thicker layers. A variation of the initial ice crystal number is effective during the whole evolution of a contrail. A cut of the soot particle emission by two orders of magnitude can reduce the contrail timescale by one hour and the optical thickness by a factor of 5. Hence future engines with lower soot particle emissions could potentially lead to a reduction of the climate impact of aviation.

  8. Dependence of nucleation kinetics and crystal morphology of a model protein system on ionic strength

    NASA Astrophysics Data System (ADS)

    Bhamidi, V.; Skrzypczak-Jankun, E.; Schall, C. A.

    2001-11-01

    Nucleation rate data for hen egg-white lysozyme crystallization were obtained using a particle counter. Tetragonal lysozyme crystals were expected to form at the temperature and solution conditions of these experiments: 4°C, pH 4.5 with 0.1 M sodium acetate buffer and 2-6% NaCl (w/v). The rates varied as expected, as smooth monotonic functions of supersaturation at 2%, 3% and 6% NaCl. However, at 5% NaCl, a great deal of scatter in the data was observed. At 2% and 3% NaCl, all the batches contained crystals with tetragonal morphology. At 6% NaCl, almost all of the vials contained the white powder with few or no tetragonal crystals. At 5% NaCl concentration, a mixture of tetragonal crystals and powder formed in varying proportions in all the vials as observed by visual inspection. The powdery material was examined using optical microscopy and was seen to consist of needles with regular structure and sharp, faceted edges. Powder diffraction data from these needles was inconsistent with experimental powder diffraction data from tetragonal lysozyme crystals. It is possible that at high salt and protein concentrations liquid-liquid separation occurred and yielded a crystal polymorph.

  9. Novel Design Integrating a Microwave Applicator into a Crystallizer for Rapid Temperature Cycling. A Direct Nucleation Control Study

    PubMed Central

    2017-01-01

    The control of nucleation in crystallization processes is a challenging task due to the often lacking knowledge on the process kinetics. Inflexible (predetermined) control strategies fail to grow the nucleated crystals to the desired quality because of the variability in the process conditions, disturbances, and the stochastic nature of crystal nucleation. Previously, the concept of microwave assisted direct nucleation control (DNC) was demonstrated in a laboratory setup to control the crystal size distribution in a batch crystallization process by manipulating the number of particles in the system. Rapid temperature cycling was used to manipulate the super(under)saturation and hence the number of crystals. The rapid heating response achieved with the microwave heating improved the DNC control efficiency, resulting in halving of the batch time. As an extension, this work presents a novel design in which the microwave applicator is integrated in the crystallizer, hence avoiding the external loop though the microwaves oven. DNC implemented in the 4 L unseeded crystallizer, at various count set points, resulted in strong efficiency enhancement of DNC, when compared to the performance with a slow responding system. The demonstrated crystallizer design is a basis for extending the enhanced process control opportunity to other applications. PMID:28729813

  10. Nucleation and crystallization of Na2O-2CaO-3SiO2 glass by differential thermal analysis

    NASA Technical Reports Server (NTRS)

    Xu, Xiaojie J.; Ray, Chandra S.; Day, Delbert E.

    1991-01-01

    DTA is presently used to characterize the nucleation and crystallization processes of the Na2O-2CaO-3SiO2 glass. A nucleation rate-temperaturelike curve is obtained by plotting either the reciprocal of the temperature corresponding to the crystallization peak maximum, or the height of the crystallization peak, as a function of nucleation temperature. The nucleation-temperature range for this glass composition, 550-650 C, and the maximum nucleation temperature of 600 + or - 5 C, are found to be in excellent agreement with those associated with the classical nucleation technique, followed by isothermal crystallization. It is noted that when most of the nucleation occurs during the DTA measurements, a modified Kissinger equation must be used to calculate the crystallization energy.

  11. Tetragonal Lysozyme Nucleation and Crystal Growth: The Role of the Solution Phase

    NASA Technical Reports Server (NTRS)

    Pusey, Marc L.; Forsythe, Elizabeth; Sumida, John; Maxwell, Daniel; Gorti, Sridhar

    2002-01-01

    Lysozyme, and most particularly the tetragonal form of the protein, has become the default standard protein for use in macromolecule crystal nucleation and growth studies. There is a substantial body of experimental evidence, from this and other laboratories, that strongly suggests this proteins crystal nucleation and growth is by addition of associated species that are preformed by standard reversible concentration-driven self association processes in the bulk solution. The evidence includes high resolution AFM studies of the surface packing and of growth unit size at incorporation, fluorescence resonance energy transfer measurements of intermolecular distances in dilute solution, dialysis kinetics, and modeling of the growth rate data. We have developed a selfassociation model for the proteins crystal nucleation and growth. The model accounts for the obtained crystal symmetry, explains the observed surface structures, and shows the importance of the symmetry obtained by self-association in solution to the process as a whole. Further, it indicates that nucleation and crystal growth are not distinct mechanistically, but identical, with the primary difference being the probability that the particle will continue to grow or dissolve. This model also offers a possible mechanism for fluid flow effects on the growth process and how microgravity may affect it. While a single lysozyme molecule is relatively small (M.W. = 14,400), a structured octamer in the 4(sub 3) helix configuration (the proposed average sized growth unit) would have a M.W. = 115,000 and dimensions of 5.6 x 5.6 x 7.6 nm. Direct AFM measurements of growth unit incorporation indicate that units as wide as 11.2 nm and as long as 11.4 nm commonly attach to the crystal. These measurements were made at approximately saturation conditions, and they reflect the sizes of species that both added or desorbed from the crystal surface. The larger and less isotropic the associated species the more likely that it

  12. Tetragonal Lysozyme Nucleation and Crystal Growth: The Role of the Solution Phase

    NASA Technical Reports Server (NTRS)

    Pusey, Marc L.; Forsythe, Elizabeth; Sumida, John; Maxwell, Daniel; Gorti, Sridhar

    2002-01-01

    Lysozyme, and most particularly the tetragonal form of the protein, has become the default standard protein for use in macromolecule crystal nucleation and growth studies. There is a substantial body of experimental evidence, from this and other laboratories, that strongly suggests this proteins crystal nucleation and growth is by addition of associated species that are preformed by standard reversible concentration-driven self association processes in the bulk solution. The evidence includes high resolution AFM studies of the surface packing and of growth unit size at incorporation, fluorescence resonance energy transfer measurements of intermolecular distances in dilute solution, dialysis kinetics, and modeling of the growth rate data. We have developed a selfassociation model for the proteins crystal nucleation and growth. The model accounts for the obtained crystal symmetry, explains the observed surface structures, and shows the importance of the symmetry obtained by self-association in solution to the process as a whole. Further, it indicates that nucleation and crystal growth are not distinct mechanistically, but identical, with the primary difference being the probability that the particle will continue to grow or dissolve. This model also offers a possible mechanism for fluid flow effects on the growth process and how microgravity may affect it. While a single lysozyme molecule is relatively small (M.W. = 14,400), a structured octamer in the 4(sub 3) helix configuration (the proposed average sized growth unit) would have a M.W. = 115,000 and dimensions of 5.6 x 5.6 x 7.6 nm. Direct AFM measurements of growth unit incorporation indicate that units as wide as 11.2 nm and as long as 11.4 nm commonly attach to the crystal. These measurements were made at approximately saturation conditions, and they reflect the sizes of species that both added or desorbed from the crystal surface. The larger and less isotropic the associated species the more likely that it

  13. Surface effects in nucleation and growth of smectic-B crystals in thin samples.

    PubMed

    Börzsönyi, T; Akamatsu, S

    2002-11-01

    We present an experimental study of the surface effects (interactions with the container walls) during the nucleation and growth of smectic-B (SmB) crystals from the nematic in free growth and directional solidification of a mesogenic molecule [C4H9-(C6H10)2CN] called CCH4 in thin (of thickness in the 10-microm range) samples. We follow the dynamics of the system in real time with a polarizing microscope. The inner surfaces of the glass-plate samples are coated with polymeric films, either rubbed polyimid (PI) films or mono-oriented poly(tetrafluoroethylene) (PTFE) films deposited by friction at high temperature. The orientation of the nematic and the smectic-B is planar. In PI-coated samples, the orientation effect of SmB crystals is mediated by the nematic, whereas, in PTFE-coated samples, it results from a homoepitaxy phenomenon occurring for two degenerate orientations. A recrystallization phenomenon partly destroys the initial distribution of crystal orientations. In directional solidification of polycrystals in PTFE-coated samples, a particular dynamics of faceted grain boundary grooves is at the origin of a dynamical mechanism of grain selection. Surface effects also are responsible for the nucleation of misoriented terraces on facets and the generation of lattice defects in the solid.

  14. Climate Impacts of Ice Nucleation

    NASA Technical Reports Server (NTRS)

    Gettelman, Andrew; Liu, Xiaohong; Barahona, Donifan; Lohmann, Ulrike; Chen, Celia

    2012-01-01

    Several different ice nucleation parameterizations in two different General Circulation Models (GCMs) are used to understand the effects of ice nucleation on the mean climate state, and the Aerosol Indirect Effects (AIE) of cirrus clouds on climate. Simulations have a range of ice microphysical states that are consistent with the spread of observations, but many simulations have higher present-day ice crystal number concentrations than in-situ observations. These different states result from different parameterizations of ice cloud nucleation processes, and feature different balances of homogeneous and heterogeneous nucleation. Black carbon aerosols have a small (0.06 Wm(exp-2) and not statistically significant AIE when included as ice nuclei, for nucleation efficiencies within the range of laboratory measurements. Indirect effects of anthropogenic aerosols on cirrus clouds occur as a consequence of increasing anthropogenic sulfur emissions with different mechanisms important in different models. In one model this is due to increases in homogeneous nucleation fraction, and in the other due to increases in heterogeneous nucleation with coated dust. The magnitude of the effect is the same however. The resulting ice AIE does not seem strongly dependent on the balance between homogeneous and heterogeneous ice nucleation. Regional effects can reach several Wm2. Indirect effects are slightly larger for those states with less homogeneous nucleation and lower ice number concentration in the base state. The total ice AIE is estimated at 0.27 +/- 0.10 Wm(exp-2) (1 sigma uncertainty). This represents a 20% offset of the simulated total shortwave AIE for ice and liquid clouds of 1.6 Wm(sup-2).

  15. Climate Impacts of Ice Nucleation

    SciTech Connect

    Gettelman, A.; Liu, Xiaohong; Barahona, Donifan; Lohmann, U.; Chen, Chih-Chieh

    2012-10-19

    [1] Several different ice nucleation parameterizations in two different General Circulation Models (GCMs) are used to understand the effects of ice nucleation on the mean climate state, and the Aerosol Indirect Effects (AIE) of cirrus clouds on climate. Simulations have a range of ice microphysical states that are consistent with the spread of observations, but many simulations have higher present-day ice crystal number concentrations than in-situ observations. These different states result from different parameterizations of ice cloud nucleation processes, and feature different balances of homogeneous and heterogeneous nucleation. Black carbon aerosols have a small (-0.06 Wm-2) and not statistically significant AIE when included as ice nuclei, for nucleation efficiencies within the range of laboratory measurements. Indirect effects of anthropogenic aerosols on cirrus clouds occur as a consequence of increasing anthropogenic sulfur emissions with different mechanisms important in different models. In one model this is due to increases in homogeneous nucleation fraction, and in the other due to increases in heterogeneous nucleation with coated dust. The magnitude of the effect is the same however. The resulting ice AIE does not seem strongly dependent on the balance between homogeneous and heterogeneous ice nucleation. Regional effects can reach several Wm-2. Indirect effects are slightly larger for those states with less homogeneous nucleation and lower ice number concentration in the base state. The total ice AIE is estimated at 0.27 ± 0.10 Wm-2 (1σ uncertainty). Finally, this represents a 20% offset of the simulated total shortwave AIE for ice and liquid clouds of -1.6 Wm-2.

  16. Vapor diffusion, nucleation rates and the reservoir to crystallization volume ratio.

    PubMed

    Forsythe, Elizabeth L; Maxwell, Daniel L; Pusey, Marc

    2002-10-01

    In a classical vapor diffusion crystallization, the protein solution is mixed in a 1:1 ratio with the reservoir solution, containing one or more precipitant species, after which the two are placed in an enclosed chamber. As the vapor pressure is lower for the reservoir solution, due to its higher solute concentration, there is a net transfer of water through the vapor phase from the protein droplet to the reservoir. In theory, the initial conditions in the droplet are such that the protein is in either a metastable or undersaturated state with respect to crystal nucleation. The loss of water serves to both concentrate the protein and the precipitant concentrations within the drop, bringing the protein past the metastable point to nucleation. The equilibration rate is a function of the precipitant(s) used, their concentration, the temperature, the distance between the two surfaces, and the droplet to reservoir volume ratio. For a given reservoir volume smaller droplets equilibrate faster, the rate being inversely linear with the droplet volume. In attempts to maximize the number of crystallization trials, and as crystals in the 100 - 200 micro m size range are sufficient, it has currently become standard practice to use starting droplet volumes of 2 - 4 micro l, with reservoir volumes typically in the 200 to 500 micro l range. The equilibration rates are maximized, and for most common salt concentrations and higher concentrations of polyethylene glycol (PEG) and 2-methyl-2,4-pentanediol (MPD) one can reasonably estimate that equilibration has occurred within 3 to 6 days at room temperature. Crystals appearing after this time are essentially grown under batch conditions. We experimentally find that altering the reservoir to droplet volume ratio, by changing the reservoir volume, from 50:1 (high ratio) to 5:1 (low ratio), on average increases the equilibration time by approximately 50 % when tested with solutions of 50% MPD, 1.5 M NaCl, or 30 % PEG 400. However

  17. The Effects of Impurities on Protein Crystal Growth and Nucleation: A Preliminary Study

    NASA Technical Reports Server (NTRS)

    Schall, Constance A.

    1998-01-01

    Kubota and Mullin (1995) devised a simple model to account for the effects of impurities on crystal growth of small inorganic and organic molecules in aqueous solutions. Experimentally, the relative step velocity and crystal growth of these molecules asymptotically approach zero or non-zero values with increasing concentrations of impurities. Alternatively, the step velocity and crystal growth can linearly approach zero as the impurity concentration increases. The Kubota-Mullin model assumes that the impurity exhibits Langmuirian adsorption onto the crystal surface. Decreases in step velocities and subsequent growth rates are related to the fractional coverage (theta) of the crystal surface by adsorbed impurities; theta = Kx / (I +Kx), x = mole fraction of impurity in solution. In the presence of impurities, the relative step velocity, V/Vo, and the relative growth rate of a crystal face, G/Go, are proposed to conform to the following equations: V/Vo approx. = G/Go = 1 - (alpha)(theta). The adsorption of impurity is assumed to be rapid and in quasi-equilibrium with the crystal surface sites available. When the value of alpha, an effectiveness factor, is one the growth will asymptotically approach zero with increasing concentrations of impurity. At values less than one, growth approaches a non-zero value asymptotically. When alpha is much greater than one, there will be a linear relationship between impurity concentration and growth rates. Kubota and Mullin expect alpha to decrease with increasing supersaturation and shrinking size of a two dimensional nucleus. It is expected that impurity effects on protein crystal growth will exhibit behavior similar to that of impurities in small molecule growth. A number of proteins were added to purified chicken egg white lysozyme, the effect on crystal nucleation and growth assessed.

  18. Nucleation and growth of thaumatin crystals within a gel under microgravity on STS-95 mission vs. under Earth's gravity

    NASA Astrophysics Data System (ADS)

    Lorber, B.; Giegé, R.

    2001-09-01

    In the frame of a study of the effects of microgravity on protein crystallization, tetragonal thaumatin crystals were, for the first time, prepared in agarose gel within the Advanced Protein Crystallization facility (APCF) on Space Shuttle mission STS-95 (October 1998). We have reported elsewhere that these crystals are of superior crystallographic quality, with regard to their diffraction intensity and limit as well as mosaic spread, when compared to control crystals grown on Earth [Lorber et al ., Acta Crystallogr. (1999) D55, 1491]. The analysis of images taken during the growth of these crystals under microgravity indicates that their nucleation was more synchronous than that of control crystals which were prepared simultaneously on Earth under otherwise identical conditions. Nucleation occurred essentially in the bulk of the medium and crystal growth proceeded up to 2 times faster. Crystals prepared under microgravity had better optical properties than control crystals. Experimental results give evidence of the existence of zones depleted in protein located around growing crystals. Also, they are in favor of a correlation between the better diffraction properties of these crystals and the more favorable crystallization parameters in Space. The content of individual crystals was analyzed and the results of purity analyses are presented. The advantages of crystallization in a gel under microgravity and importance of image documentation for asserting growth cessation are discussed.

  19. Crystal structure of γ-tubulin complex protein GCP4 provides insight into microtubule nucleation

    PubMed Central

    Guillet, Valérie; Knibiehler, Martine; Gregory-Pauron, Lynn; Remy, Marie-Hélène; Chemin, Cécile; Raynaud-Messina, Brigitte; Bon, Cécile; Kollman, Justin M; Agard, David A; Merdes, Andreas; Mourey, Lionel

    2013-01-01

    Microtubule nucleation in all eukaryotes involves γ-tubulin small complexes (γTuSCs) that comprise two molecules of γ-tubulin bound to γ-tubulin complex proteins (GCPs) GCP2 and GCP3. In many eukaryotes, multiple γTuSCs associate with GCP4, GCP5 and GCP6 into large γ-tubulin ring complexes (γTuRCs). Recent cryo-EM studies indicate that a scaffold similar to γTuRCs is formed by lateral association of γTuSCs, with the C-terminal regions of GCP2 and GCP3 binding γ-tubulin molecules. However, the exact role of GCPs in microtubule nucleation remains unknown. Here we report the crystal structure of human GCP4 and show that its C-terminal domain binds directly to γ-tubulin. The human GCP4 structure is the prototype for all GCPs, as it can be precisely positioned within the γTuSC envelope, revealing the nature of protein-protein interactions and conformational changes regulating nucleation activity. PMID:21725292

  20. The effect of protein–precipitant interfaces and applied shear on the nucleation and growth of lysozyme crystals

    SciTech Connect

    Reis, Nuno M.; Chirgadze, Dimitri Y.; Blundell, Tom L.; Mackley, Malcolm R.

    2009-11-01

    The nucleation of lysozyme in microbatch experiments was linked to the formation of protein–precipitant interfaces. The use of oscillatory shear allowed decreasing the nucleation rate and extending the growth period for lysozyme crystals, presumably through the control of the number of interfaces and removal of impurities or defects. This paper is concerned with the effect of protein–precipitant interfaces and externally applied shear on the nucleation and growth kinetics of hen egg-white lysozyme crystals. The early stages of microbatch crystallization of lysozyme were explored using both optical and confocal fluorescence microscopy imaging. Initially, an antisolvent (precipitant) was added to a protein drop and the optical development of the protein–precipitant interface was followed with time. In the presence of the water-soluble polymer poly(ethylene glycol) (PEG) a sharp interface was observed to form immediately within the drop, giving an initial clear separation between the lighter protein solution and the heavier precipitant. This interface subsequently became unstable and quickly developed within a few seconds into several unstable ‘fingers’ that represented regions of high concentration-gradient interfaces. Confocal microscopy demonstrated that the subsequent nucleation of protein crystals occurred preferentially in the region of these interfaces. Additional experiments using an optical shearing system demonstrated that oscillatory shear significantly decreased nucleation rates whilst extending the growth period of the lysozyme crystals. The experimental observations relating to both nucleation and growth have relevance in developing efficient and reliable protocols for general crystallization procedures and the controlled crystallization of single large high-quality protein crystals for use in X-ray crystallography.

  1. The effect of protein-precipitant interfaces and applied shear on the nucleation and growth of lysozyme crystals.

    PubMed

    Reis, Nuno M; Chirgadze, Dimitri Y; Blundell, Tom L; Mackley, Malcolm R

    2009-11-01

    This paper is concerned with the effect of protein-precipitant interfaces and externally applied shear on the nucleation and growth kinetics of hen egg-white lysozyme crystals. The early stages of microbatch crystallization of lysozyme were explored using both optical and confocal fluorescence microscopy imaging. Initially, an antisolvent (precipitant) was added to a protein drop and the optical development of the protein-precipitant interface was followed with time. In the presence of the water-soluble polymer poly(ethylene glycol) (PEG) a sharp interface was observed to form immediately within the drop, giving an initial clear separation between the lighter protein solution and the heavier precipitant. This interface subsequently became unstable and quickly developed within a few seconds into several unstable 'fingers' that represented regions of high concentration-gradient interfaces. Confocal microscopy demonstrated that the subsequent nucleation of protein crystals occurred preferentially in the region of these interfaces. Additional experiments using an optical shearing system demonstrated that oscillatory shear significantly decreased nucleation rates whilst extending the growth period of the lysozyme crystals. The experimental observations relating to both nucleation and growth have relevance in developing efficient and reliable protocols for general crystallization procedures and the controlled crystallization of single large high-quality protein crystals for use in X-ray crystallography.

  2. Homogeneous bubble nucleation in H2O- and H2O-CO2-bearing basaltic melts: Results of high temperature decompression experiments

    NASA Astrophysics Data System (ADS)

    Le Gall, Nolwenn; Pichavant, Michel

    2016-11-01

    High pressure and temperature decompression experiments were conducted to provide experimental information on the conditions of homogeneous bubble nucleation in basaltic melts. Experiments were performed on H2O- and H2O-CO2-bearing natural melts from Stromboli. Three starting volatile compositions were investigated: series #1 (4.91 wt% H2O, no CO2), series #2 (2.37-2.45 wt% H2O, 901-1011 ppm CO2) and series #3 (0.80-1.09 wt% H2O, 840-923 ppm CO2). The volatile-bearing glasses were first synthesized at 1200 °C and 200 MPa, and second continuously decompressed in the pressure range 150-25 MPa and rapidly quenched. A fast decompression rate of 78 kPa/s (or 3 m/s) was applied to limit the water loss from the glass cylinder and the formation of a H2O-depleted rim. Post-decompression glasses were characterized texturally by X-ray microtomography. The results demonstrate that homogenous bubble nucleation requires supersaturation pressures (difference between saturation pressure and pressure at which homogeneous bubble nucleation is observed, ∆ PHoN) ≤ 50-100 MPa. ∆ PHoN varies with the dissolved CO2 concentration, from ≪ 50 MPa (no CO2, series #1) to ≤ 50 MPa (872 ± 45 ppm CO2, series #3) to < 100 MPa (973 ± 63 ppm CO2, series #2). In series #1 melts, homogeneous bubble nucleation occurs as two distinct events, the first at high pressure (200 < P < 150 MPa) and the second at low pressure (50 < P < 25 MPa), just below the fragmentation level. In contrast, homogenous nucleation in series #2 and #3 melts is a continuous process. As well, chemical near-equilibrium degassing occurs in the series #1 melts, unlike in the series #2 and #3 melts which retain high CO2 concentrations even for higher vesicularities (up to 23% at 25 MPa). Thus, our experimental observations underline a significant effect of CO2 on the physical mechanisms of bubble vesiculation in basaltic melts. Our experimental decompression textures either reproduce or approach the characteristics of

  3. Nucleation, growth and characterization of semiorganic nonlinear optical crystal sodium acetate doped L-tyrosine.

    PubMed

    Arthi, D; Anbuselvi, D; Jayaraman, D; Arul Martin Mani, J; Joseph, V

    2015-02-05

    Sodium acetate doped L-tyrosine single crystal with dimensions 47×15×8 mm(3) was grown by slow evaporation solution growth technique. Nucleation kinetics of the growth of the material was studied to optimize the growth conditions. The grown doped crystal was then characterized using single crystal XRD, UV-vis-NIR, FTIR, NMR, SEM-EDAX and NLO studies. XRD study reveals that the grown crystal belongs to monoclinic system with space group P21. Lattice parameters of the grown crystals are found to be a=5.096 Å, b=8.966 Å, c=11.088 Å, α=β=90° and γ=92.035°. The transparent range of the grown crystal was measured as 260-1100 nm with 260 nm as lower cut off wavelength using UV-vis-NIR absorption spectrum and the optical band gap was evaluated as 3.24 eV from the Tauc's plot. The various functional groups were identified using FTIR spectral analysis. The thermal behavior of the title compound has been analyzed using TGA/DTA and DSC thermal curves. From the thermal study, the material is found to possess thermal stability up to 158°C. The microstructure of the grown crystal and the presence of various elements in the crystal were analyzed using SEM and EDAX techniques. NMR spectral analysis confirms the molecular structure of the grown compound. The nonlinear optical property was tested using Kurtz Perry powder technique and SHG efficiency was measured nearly same as that of KDP. Copyright © 2014 Elsevier B.V. All rights reserved.

  4. Nucleation, growth and characterization of semiorganic nonlinear optical crystal sodium acetate doped L-tyrosine

    NASA Astrophysics Data System (ADS)

    Arthi, D.; Anbuselvi, D.; Jayaraman, D.; Arul Martin Mani, J.; Joseph, V.

    2015-02-01

    Sodium acetate doped L-tyrosine single crystal with dimensions 47 × 15 × 8 mm3 was grown by slow evaporation solution growth technique. Nucleation kinetics of the growth of the material was studied to optimize the growth conditions. The grown doped crystal was then characterized using single crystal XRD, UV-vis-NIR, FTIR, NMR, SEM-EDAX and NLO studies. XRD study reveals that the grown crystal belongs to monoclinic system with space group P21. Lattice parameters of the grown crystals are found to be a = 5.096 Å, b = 8.966 Å, c = 11.088 Å, α = β = 90° and γ = 92.035°. The transparent range of the grown crystal was measured as 260-1100 nm with 260 nm as lower cut off wavelength using UV-vis-NIR absorption spectrum and the optical band gap was evaluated as 3.24 eV from the Tauc's plot. The various functional groups were identified using FTIR spectral analysis. The thermal behavior of the title compound has been analyzed using TGA/DTA and DSC thermal curves. From the thermal study, the material is found to possess thermal stability up to 158 °C. The microstructure of the grown crystal and the presence of various elements in the crystal were analyzed using SEM and EDAX techniques. NMR spectral analysis confirms the molecular structure of the grown compound. The nonlinear optical property was tested using Kurtz Perry powder technique and SHG efficiency was measured nearly same as that of KDP.

  5. Nucleation of liquid droplets and voids in a stretched Lennard-Jones fcc crystal.

    PubMed

    Baidakov, Vladimir G; Tipeev, Azat O

    2015-09-28

    The method of molecular dynamics simulation has been used to investigate the phase decay of a metastable Lennard-Jones face-centered cubic crystal at positive and negative pressures. It is shown that at high degrees of metastability, crystal decay proceeds through the spontaneous formation and growth of new-phase nuclei. It has been found that there exists a certain boundary temperature. Below this temperature, the crystal phase disintegrates as the result of formation of voids, and above, as a result of formation of liquid droplets. The boundary temperature corresponds to the temperature of cessation of a crystal-liquid phase equilibrium when the melting line comes in contact with the spinodal of the stretched liquid. The results of the simulations are interpreted in the framework of classical nucleation theory. The thermodynamics of phase transitions in solids has been examined with allowance for the elastic energy of stresses arising owing to the difference in the densities of the initial and the forming phases. As a result of the action of elastic forces, at negative pressures, the boundary of the limiting superheating (stretching) of a crystal approaches the spinodal, on which the isothermal bulk modulus of dilatation becomes equal to zero. At the boundary of the limiting superheating (stretching), the shape of liquid droplets and voids is close to the spherical one.

  6. Effect of ultrasonic irradiation on the number of acetylsalicylic acid crystals produced under the supersaturated condition and the ability of controlling the final crystal size via primary nucleation

    NASA Astrophysics Data System (ADS)

    Miyasaka, Etsuko; Kato, Yumi; Hagisawa, Minoru; Hirasawa, Izumi

    2006-03-01

    The purposes of this study were to investigate the effects of ultrasound irradiation on the number of crystals formed in an acetylsalicyclic acid crystallization process and to assess the controllability of the final product size via the number of primary nuclei. The number of crystals present after primary nucleation was counted and the relationship between the final product size and the number of crystals was examined. Additionally, the growing ASA crystals were observed, since ultrasound energy not only may control primary nucleation but may also the perfection of the crystal shape. At a high level of ultrasonic energy, ultrasound irradiation increased the average number of crystals, an effect that has been reported often; however, at a low level of ultrasonic energy it decreased the average number of crystals, and moreover, these opposing ultrasonic effects on the number of crystals interchanged at a specific energy threshold. These results reveal two novel phenomena—that there is an energy region where ultrasonic irradiation inhibits primary nucleation, and that a specific amount of ultrasonic energy is needed to activate primary nucleation. On the other hand, the final product size almost depended upon the number of primary nuclei, indicating that the final product size could be controlled via the number of crystals influenced by ultrasound irradiation. According to the photographs of crystals, they were not destroyed by the process. Therefore, it was proposed that ultrasound energy does not destroy the perfection of the crystal shape but only controls primary nucleation under the condition: both short irradiation time and low supersaturated condition.

  7. Method for preparing homogeneous single crystal ternary III-V alloys

    DOEpatents

    Ciszek, Theodore F.

    1991-01-01

    A method for producing homogeneous, single-crystal III-V ternary alloys of high crystal perfection using a floating crucible system in which the outer crucible holds a ternary alloy of the composition desired to be produced in the crystal and an inner floating crucible having a narrow, melt-passing channel in its bottom wall holds a small quantity of melt of a pseudo-binary liquidus composition that would freeze into the desired crystal composition. The alloy of the floating crucilbe is maintained at a predetermined lower temperature than the alloy of the outer crucible, and a single crystal of the desired homogeneous alloy is pulled out of the floating crucible melt, as melt from the outer crucible flows into a bottom channel of the floating crucible at a rate that corresponds to the rate of growth of the crystal.

  8. Kinetics of gypsum nucleation and crystal growth from Dead Sea brine

    NASA Astrophysics Data System (ADS)

    Reznik, Itay J.; Gavrieli, Ittai; Ganor, Jiwchar

    2009-10-01

    The Dead Sea brine is supersaturated with respect to gypsum ( Ω = 1.42). Laboratory experiments and evaluation of historical data show that gypsum nucleation and crystal growth kinetics from Dead Sea brine are both slower in comparison with solutions at a similar degree of supersaturation. The slow kinetics of gypsum precipitation in the Dead Sea brine is mainly attributed to the low solubility of gypsum which is due to the high Ca 2+/SO 42- molar ratio (115), high salinity (˜280 g/kg) and to Na + inhibition. Experiments with various clay minerals (montmorillonite, kaolinite) indicate that these minerals do not serve as crystallization seeds. In contrast, calcite and aragonite which contain traces of gypsum impurities do prompt precipitation of gypsum but at a considerable slower rate than with pure gypsum. This implies that transportation inflow of clay minerals, calcite and local crystallization of minerals in the Dead Sea does not prompt significant heterogeneous precipitation of gypsum. Based on historical analyses of the Dead Sea, it is shown that over the last decades, as inflows to the lake decreased and its salinity increased, gypsum continuously precipitated from the brine. The increasing salinity and Ca 2+/SO 42- ratio, which results from the precipitation of gypsum, lead to even slower kinetics of nucleation and crystal growth, which resulted in an increasing degree of supersaturation with respect to gypsum. Therefore, we predict that as the salinity of the Dead Sea brine continues to increase (accompanied by Dead Sea water level decline), although gypsum will continuously precipitate, the degree of supersaturation will increase furthermore due to progressively slower kinetics.

  9. Structure of finite sphere packings via exact enumeration: Implications for colloidal crystal nucleation

    NASA Astrophysics Data System (ADS)

    Hoy, Robert S.; Harwayne-Gidansky, Jared; O'Hern, Corey S.

    2012-05-01

    We analyze the geometric structure and mechanical stability of a complete set of isostatic and hyperstatic sphere packings obtained via exact enumeration. The number of nonisomorphic isostatic packings grows exponentially with the number of spheres N, and their diversity of structure and symmetry increases with increasing N and decreases with increasing hyperstaticity H≡Nc-NISO, where Nc is the number of pair contacts and NISO=3N-6. Maximally contacting packings are in general neither the densest nor the most symmetric. Analyses of local structure show that the fraction f of nuclei with order compatible with the bulk (rhcp) crystal decreases sharply with increasing N due to a high propensity for stacking faults, five- and near-fivefold symmetric structures, and other motifs that preclude rhcp order. While f increases with increasing H, a significant fraction of hyperstatic nuclei for N as small as 11 retain non-rhcp structure. Classical theories of nucleation that consider only spherical nuclei, or only nuclei with the same ordering as the bulk crystal, cannot capture such effects. Our results provide an explanation for the failure of classical nucleation theory for hard-sphere systems of N≲10 particles; we argue that in this size regime, it is essential to consider nuclei of unconstrained geometry. Our results are also applicable to understanding kinetic arrest and jamming in systems that interact via hard-core-like repulsive and short-ranged attractive interactions.

  10. Nucleation and growth of 2D covalent organic frameworks: polymerization and crystallization of COF monomers.

    PubMed

    Koo, B T; Heden, R F; Clancy, P

    2017-04-12

    We establish a theoretical foundation for understanding the nucleation and growth of 2D covalent organic frameworks (COFs) from solution. This foundation should make it easier to realize some of the unique properties of COFs in targeted applications by allowing us to understand how processing variables such as solvent choice and linkage chemistry lead to larger crystalline domains. We use free energy techniques to map out the reaction mechanisms and activation energies of three fundamental reactions that are responsible for the early stages of 2D COF nucleation for a prototypical and commonly used 2D boronate ester material, COF-5, in water and methanol solvents. We show that the presence of water and methanol greatly catalyzes the boronate ester formation reactions, lowering the activation energy barrier by about 10 kcal mol(-1) relative to an uncatalyzed reaction pathway. This is in good agreement with experimental observations by Smith and Dichtel (JACS 2014). Our crystallization studies also conclusively eliminate certain proposed mechanisms of growth, such as polymerization of large sheets followed by stacking, while strengthening the case for templated polymerization as a likely growth mechanism for COF crystals.

  11. A Fiber Optic Probe for Monitoring Protein Aggregation, Nucleation, and Crystallization

    NASA Technical Reports Server (NTRS)

    Ansari, Rafat R.; Suh, Kwang I.; Arabshahi, Alireza; Wilson, William W.; Bray, Terry L.; DeLucas, Lawrence J.

    1996-01-01

    Protein crystals are experimentally grown in hanging drops in microgravity experiments on-board the Space Shuttle orbiter. The technique of dynamic light scattering (DLS) can be used to monitor crystal growth process in hanging droplets (approx. 30 (L)) in microgravity experiments, but elaborate instrumentation and optical alignment problems have made in-situ applications difficult. In this paper we demonstrate that such experiments are now feasible. We apply a newly developed fiber optic probe to various earth and space (micro- gravity) bound protein crystallization system configurations to test its capability. These include conventional batch (cuvette or capillary) systems, hanging drop method in a six-pack hanging drop vapor diffusion apparatus (HDVDA), a modified HDVDA for temperature- induced nucleation and aggregation studies, and a newly envisioned dynamically controlled vapor diffusion system (DCVDS) configuration. Our compact system exploits the principles of DLS and offers a fast (within a few seconds) means of quantitatively and non-invasively monitoring the various growth stages of protein crystallization. In addition to DLS capability, the probe can also be used for performing single-angle static light scattering measurements. It utilizes extremely low levels of laser power (approx. few (W)) without a need of having any optical alignment and vibration isolation. The compact probe is also equipped with a miniaturized microscope for visualization of macroscopic protein crystals. This new optical diagnostic system opens up enormous opportunity for exploring new ways to grow good quality crystals suitable for x-ray crystallographic analysis and may help develop a concrete scientific basis for understanding the process of crystallization.

  12. Amphiphilic triblock copolymer-assisted synthesis of hierarchical NiCo nanoflowers by homogeneous nucleation in liquid polyols

    NASA Astrophysics Data System (ADS)

    Arief, Injamamul; Mukhopadhyay, P. K.

    2014-12-01

    Rose-like NiCo nanoflowers were synthesized by homogeneous, one-pot polyol reduction of Ni and Co-acetates in presence of an amphiphilic triblock copolymer and KOH. 1,2-propanediol was used as solvent-cum-reducing agent as no external reducing agent was found to be necessary in this process. Detailed x-ray diffraction and morphological characterizations confirmed formation of fcc hierarchical NiCo nanoflowers containing 2D nanosheet-like subunits (thickness of about 30 nm) with an average diameter of ~700 nm. Amphiphilic polymer played a pivotal role in the growth of nanorose as it favored a preferential growth of nanocrystals along a particular crystal plane as was observed in transmission electron microscopy. Effects of other parameters like use of hydrophilic polymer, surfactants, ratio of initial metal concentrations, choice of polyol media and concentration of KOH on the morphology of nanoflowers were also investigated. Room temperature magnetic studies revealed higher saturation magnetization and low coercivity (108.6 emu/g and 78.4 Oe) of nanorose. Based on LaMer model, a kinetically-controlled growth mechanism for the formation of NiCo nanorose is also proposed.

  13. A first test of the hypothesis of biogenic magnetite-based heterogeneous ice-crystal nucleation in cryopreservation.

    PubMed

    Kobayashi, Atsuko; Golash, Harry N; Kirschvink, Joseph L

    2016-06-01

    An outstanding biophysical puzzle is focused on the apparent ability of weak, extremely low-frequency oscillating magnetic fields to enhance cryopreservation of many biological tissues. A recent theory holds that these weak magnetic fields could be inhibiting ice-crystal nucleation on the nanocrystals of biological magnetite (Fe3O4, an inverse cubic spinel) that are present in many plant and animal tissues by causing them to oscillate. In this theory, magnetically-induced mechanical oscillations disrupt the ability of water molecules to nucleate on the surface of the magnetite nanocrystals. However, the ability of the magnetite crystal lattice to serve as a template for heterogeneous ice crystal nucleation is as yet unknown, particularly for particles in the 10-100 nm size range. Here we report that the addition of trace-amounts of finely-dispersed magnetite into ultrapure water samples reduces strongly the incidence of supercooling, as measured in experiments conducted using a controlled freezing apparatus with multiple thermocouples. SQUID magnetometry was used to quantify nanogram levels of magnetite in the water samples. We also report a relationship between the volume change of ice, and the degree of supercooling, that may indicate lower degassing during the crystallization of supercooled water. In addition to supporting the role of ice-crystal nucleation by biogenic magnetite in many tissues, magnetite nanocrystals could provide inexpensive, non-toxic, and non-pathogenic ice nucleating agents needed in a variety of industrial processes, as well as influencing the dynamics of ice crystal nucleation in many natural environments. Copyright © 2016 The Authors. Published by Elsevier Inc. All rights reserved.

  14. Does the homogeneous ice nucleation initiate at the surface or in the volume of super-cooled water droplets?

    NASA Astrophysics Data System (ADS)

    Benz, S.; Möhler, O.; Wagner, R.; Schnaiter, M.; Leisner, T.

    2009-04-01

    The nucleation of ice in super-cooled water droplets affects many atmospheric processes as the initiation of precipitation and radiative transfer. Water droplets are freezing due to the formation of a critical germ initiating the freezing of the whole droplet. The common quantity to describe the creation of ice is the nucleation rate J, defined as the product of the number of critical germs and the rate at which additional molecules are incorporated into a critical germ. Nucleation of ice in a super-cooled liquid is a stochastic process and depends strongly on temperature. Recently there was a discussion whether the germs of the new phase are formed preferentially near the surface or in the interior of the droplet. Experiments at the aerosol and cloud chamber AIDA of Forschungszentrum Karlsruhe were performed to assess this question. We produced clouds of super-cooled water droplets and deduced the ice nucleation rate J from simultaneously measurements of the number density and size distribution of liquid droplets, the number density of ice particles, and the temperature in the range between -36 and -37 °C. With different number densities of seed aerosol particles (sulphuric acid aerosol) we were able to vary the size of the nucleating water droplets between 4 µm and 9 µm diameter. The comparison of the results - by assumption of a volume dependent process - showed very good agreement both with data from literature gained from considerably larger droplets and with classical nucleation theory. The nucleation rates disagree from each other when converting them to surface-proportional values. This contradicts the hypothesis that a critical germ is formed preferentially near the surface of a super-cooled liquid droplet.

  15. Kinetics of Ice Nucleation Confined in Nanoporous Alumina.

    PubMed

    Suzuki, Yasuhito; Steinhart, Martin; Butt, Hans-Jürgen; Floudas, George

    2015-09-03

    The nucleation mechanism of water (heterogeneous/homogeneous) can be regulated by confinement within nanoporous alumina. The kinetics of ice nucleation is studied in confinement by employing dielectric permittivity as a probe. Both heterogeneous and homogeneous nucleation, obtained at low and high undercooling, respectively, are stochastic in nature. The temperature interval of metastability extends over ∼4 and 0.4 °C for heterogeneous and homogeneous nucleation, respectively. Nucleation within a pore is spread to all pores in the template. We have examined a possible coupling of all pores through a heat wave and a sound wave, with the latter being a more realistic scenario. In addition, dielectric spectroscopy indicates that prior to crystallization undercooled water molecules relax with an activation energy of ∼50 kJ/mol, and this process acts as precursor to ice nucleation.

  16. Synthesis of Hexagonal Boron Nitride Mono layer: Control of Nucleation and Crystal Morphology

    DOE PAGES

    Stehle, Yijing Y.; Meyer, III, Harry M.; Unocic, Raymond R.; ...

    2015-11-10

    Mono layer hexagonal boron nitride (hBN) attracts significant attention due to the potential to be used as a complementary two-dimensional dielectric in fabrication of functional 2D heterostructures. Here we investigate the growth stages of the hBN single crystals and show that hBN crystals change their shape from triangular to truncated triangular and further to hexagonal depending on copper substrate distance from the precursor. We suggest that the observed hBN crystal shape variation is affected by the ratio of boron to nitrogen active species concentrations on the copper surface inside the CVD reactor. Strong temperature dependence reveals the activation energies formore » the hBN nucleation process of similar to 5 eV and crystal growth of similar to 3.5 eV. We also show that the resulting h-BN film morphology is strongly affected by the heating method of borazane precursor and the buffer gas. Elucidation of these details facilitated synthesis of high quality large area monolayer hexagonal boron nitride by atmospheric pressure chemical vapor deposition on copper using borazane as a precursor.« less

  17. Nucleation of liquid droplets and voids in a stretched Lennard-Jones fcc crystal

    SciTech Connect

    Baidakov, Vladimir G. Tipeev, Azat O.

    2015-09-28

    The method of molecular dynamics simulation has been used to investigate the phase decay of a metastable Lennard-Jones face-centered cubic crystal at positive and negative pressures. It is shown that at high degrees of metastability, crystal decay proceeds through the spontaneous formation and growth of new-phase nuclei. It has been found that there exists a certain boundary temperature. Below this temperature, the crystal phase disintegrates as the result of formation of voids, and above, as a result of formation of liquid droplets. The boundary temperature corresponds to the temperature of cessation of a crystal–liquid phase equilibrium when the melting line comes in contact with the spinodal of the stretched liquid. The results of the simulations are interpreted in the framework of classical nucleation theory. The thermodynamics of phase transitions in solids has been examined with allowance for the elastic energy of stresses arising owing to the difference in the densities of the initial and the forming phases. As a result of the action of elastic forces, at negative pressures, the boundary of the limiting superheating (stretching) of a crystal approaches the spinodal, on which the isothermal bulk modulus of dilatation becomes equal to zero. At the boundary of the limiting superheating (stretching), the shape of liquid droplets and voids is close to the spherical one.

  18. Synthesis of Hexagonal Boron Nitride Mono layer: Control of Nucleation and Crystal Morphology

    SciTech Connect

    Stehle, Yijing Y.; Meyer, III, Harry M.; Unocic, Raymond R.; Kidder, Michelle; Polyzos, Georgios; Datskos, Panos G.; Jackson, Roderick K.; Vlassiouk, Ivan V.

    2015-11-10

    Mono layer hexagonal boron nitride (hBN) attracts significant attention due to the potential to be used as a complementary two-dimensional dielectric in fabrication of functional 2D heterostructures. Here we investigate the growth stages of the hBN single crystals and show that hBN crystals change their shape from triangular to truncated triangular and further to hexagonal depending on copper substrate distance from the precursor. We suggest that the observed hBN crystal shape variation is affected by the ratio of boron to nitrogen active species concentrations on the copper surface inside the CVD reactor. Strong temperature dependence reveals the activation energies for the hBN nucleation process of similar to 5 eV and crystal growth of similar to 3.5 eV. We also show that the resulting h-BN film morphology is strongly affected by the heating method of borazane precursor and the buffer gas. Elucidation of these details facilitated synthesis of high quality large area monolayer hexagonal boron nitride by atmospheric pressure chemical vapor deposition on copper using borazane as a precursor.

  19. Solubility and crystal nucleation in organic solvents of two polymorphs of curcumin.

    PubMed

    Liu, Jin; Svärd, Michael; Hippen, Perschia; Rasmuson, Åke C

    2015-07-01

    Two crystal polymorphs of 1,7-bis-(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione (curcumin) have been obtained by crystallization from ethanol (EtOH) solution. The polymorphs have been characterized by differential scanning calorimetry, infrared spectroscopy, and X-ray powder diffraction and shown to be the previously described forms I and III. The solubility of both polymorphs in EtOH and of one polymorph in ethyl acetate (EA) has been measured between 10°C and 50°C with a gravimetric method. Primary nucleation of curcumin from EtOH solution has been investigated in 520 constant temperature crystallization experiments in sealed, magnetically stirred vials under different conditions of supersaturation, temperature, and agitation rate. By a thermodynamic analysis of the melting data and solubility of form I, the solid-state activity is estimated from 10°C up to the melting point. The solubility is lower in EtOH than in EA, and in both solvents, a positive deviation from Raoult's law is observed. Form I has lower solubility than form III and is accordingly thermodynamically more stable over the investigated temperature interval. Extrapolation of solubility regression models indicates that there should be a low-temperature enantiotropic transition point, below which form I will be metastable. By slurry conversion experiments, it is established that this temperature is below -30°C. All nucleation experiments resulted in the stable form I. The induction time is observed to decrease with increasing agitation rate up to a certain point, and then increase with further increasing agitation rate; a trend previously observed for other compounds. By correlating the induction time data obtained at different supersaturation and temperature, the interfacial energy of form I in EtOH is estimated to be 3.0 mJ/m(2) . © 2015 Wiley Periodicals, Inc. and the American Pharmacists Association.

  20. Significant improvement of GaN crystal quality with ex-situ sputtered AlN nucleation layers

    NASA Astrophysics Data System (ADS)

    Chen, Shuo-Wei; Yang, Young; Wen, Wei-Chih; Li, Heng; Lu, Tien-Chang

    2016-03-01

    Ex-situ sputtered AlN nucleation layer has been demonstrated effective to significantly improve crystal quality and electrical properties of GaN epitaxy layers for GaN based Light-emitting diodes (LEDs). In this report, we have successfully reduced X-ray (102) FWHM from 240 to 110 arcsec, and (002) FWHM from 230 to 101 arcsec. In addition, reverse-bias voltage (Vr) increased around 20% with the sputtered AlN nucleation layer. Furthermore, output power of LEDs grown on sputtered AlN nucleation layer can be improved around 4.0% compared with LEDs which is with conventional GaN nucleation layer on pattern sapphire substrate (PSS).

  1. Epitaxy versus oriented heterogeneous nucleation of organic crystals on ionic substrates

    NASA Astrophysics Data System (ADS)

    Sarma, K. R.; Shlichta, P. J.; Wilcox, W. R.; Lefever, R. A.

    1997-04-01

    It is plausible to assume that epitaxy is a special case of heterogeneous nucleation in which a restrictive crystallographic relationship exists between substrate and deposit orientations. This would mean that epitaxial substrates should always induce a perceptible reduction in the critical supercooling for nucleation of the deposit. To test this hypothesis, the critical supercoolings of six organic compounds were measured on glass and 11 single-crystal cleaved substrates including (0001) graphite, (001) mica, (111) BaF 2, SrF 2, and CaF 2, and (100) KCl, KBr, KI, NaCl, NaF, and LiF. Reductions in supercooling (with reference to glass substrates) were checked many times for repeatability and reproducibility and shown in almost all cases to have a standard deviation of 1 C or less. Acetanilide, benzoic acid, and p-bromochlorobenzene showed a wide range of supercooling reductions and were oriented on all crystalline substrates. Naphthalene and p-dibromobenzene showed only slight supercooling reductions but were oriented on all substrates, including glass. Benzil showed strong supercooling reductions only for mica and KI but was oriented not only in these cases but also with KI, BaF 2, CaF 2, and graphite. There was little correlation between degree of lattice match and either supercooling reduction or degree of preferred orientation. These results suggest that, for the systems and geometry studied, forces such as molecular dipole binding and growth anisotropy had a stronger effect than lattice match.

  2. Mesoscopic Impurities Expose a Nucleation-Limited Regime of Crystal Growth

    NASA Astrophysics Data System (ADS)

    Sleutel, Mike; Lutsko, James F.; Maes, Dominique; Van Driessche, Alexander E. S.

    2015-06-01

    Nanoscale self-assembly is naturally subject to impediments at the nanoscale. The recently developed ability to follow processes at the molecular level forces us to resolve older, coarse-grained concepts in terms of their molecular mechanisms. In this Letter, we highlight one such example. We present evidence based on experimental and simulation data that one of the cornerstones of crystal growth theory, the Cabrera-Vermilyea model of step advancement in the presence of impurities, is based on incomplete physics. We demonstrate that the piercing of an impurity fence by elementary steps is not solely determined by the Gibbs-Thomson effect, as assumed by Cabrera-Vermilyea. Our data show that for conditions leading up to growth cessation, step retardation is dominated by the formation of critically sized fluctuations. The growth recovery of steps is counter to what is typically assumed, not instantaneous. Our observations on mesoscopic impurities for lysozyme expose a nucleation-dominated regime of growth that has not been hitherto considered, where the system alternates between zero and near-pure velocity. The time spent by the system in arrest is the nucleation induction time required for the step to amass a supercritical fluctuation that pierces the impurity fence.

  3. Application of the homogenization approximation to rough one-dimensional photonic crystals.

    PubMed

    Maskaly, Karlene Rosera; Carter, W Craig; Averitt, Richard D; Maxwell, James L

    2005-11-01

    As previously reported [Opt. Lett. 29, 2791 (2004)], one-dimensional photonic crystals exhibit a decrease in their normal reflectivity if their interfaces are not flat. We show that the homogenization approximation accurately predicts this diminished optical response by comparing results with finite-difference time-domain (FDTD) simulations applied to the same roughened structures. Within the parameter range tested (rms roughness < 20% and rms wavelengths < 100% of the photonic crystal periodicity), the homogenization approximation accurately reproduces the reflectivities obtained by the FDTD simulations, which are much more computationally expensive.

  4. Mathematical modeling of the stationary nucleation and crystallization process in supersaturated systems with a crystallizer

    NASA Astrophysics Data System (ADS)

    Makoveeva, E. V.; Malygin, A. P.; Alexandrov, D. V.

    2017-04-01

    Motivated by important industrial applications we consider the growth prosess of solid particles in a supersaturated (supercooled) system with allowance for a crystallizer. The particle-radius distribution function satisfies the second order kinetic equation supplimented by different boundary conditions. An exact steady-state analytical solution is found. We show that two different types of analytical solutions for the kinetic equation exist.

  5. Homogenous nucleation rates of n-propanol measured in the Laminar Flow Diffusion Chamber at different total pressures

    NASA Astrophysics Data System (ADS)

    Görke, Hanna; Neitola, Kimmo; Hyvärinen, Antti-Pekka; Lihavainen, Heikki; Wölk, Judith; Strey, Reinhard; Brus, David

    2014-05-01

    Nucleation rates of n-propanol were investigated in the Laminar Flow Diffusion Chamber. Nucleation temperatures between 270 and 300 K and rates between 100 and 106 cm-3 s-1 were achieved. Since earlier measurements of n-butanol and n-pentanol suggest a dependence of nucleation rates on carrier gas pressure, similar conditions were adjusted for these measurements. The obtained data fit well to results available from literature. A small positive pressure effect was found which strengthen the assumption that this effect is attributed to the carbon chain length of the n-alcohol [D. Brus, A. P. Hyvärinen, J. Wedekind, Y. Viisanen, M. Kulmala, V. Ždímal, J. Smolík, and H. Lihavainen, J. Chem. Phys. 128, 134312 (2008)] and might be less intensive for substances in the homologous series with higher equilibrium vapor pressure. A comparison with the theoretical approach by Wedekind et al. [Phys. Rev. Lett. 101, 12 (2008)] shows that the effect goes in the same direction but that the intensity is much stronger in experiments than in theory.

  6. Molecular dynamics of homogeneous nucleation in the vapor phase of Lennard-Jones. III. Effect of carrier gas pressure

    NASA Astrophysics Data System (ADS)

    Yasuoka, Kenji; Zeng, X. C.

    2007-03-01

    A molecular dynamics simulation of vapor phase nucleation has been performed with 40 000 Lennard-Jones particles for the target gas and 0-160 000 particles for the carrier gas. Three carrier gas models are adopted, including a soft-core model, a Lennard-Jones model, and a modified Lennard-Jones model in which the attractive interaction can be adjusted. The effect of the carrier-gas pressure is assessed through computing and comparing the rate of nucleation and cluster size distribution. It is found that the effect of the carrier-gas pressure can be strongly dependent on the carrier-gas model. A positive effect (enhancement of the nucleation rate) is found with the soft-core potential model, whereas negligible effect is found with the Lennard-Jones potential model. For the modified Lennard-Jones potential with a weak attractive interaction, the carrier-gas effect is positive. However, the effect is negligible with a stronger attractive interaction between the target and carrier-gas particles. A reason for the negligible effect is that the carrier-gas particles are adsorbed on the cluster surface when the density of target and carrier-gas particles are comparable. When the density of carrier-gas particles are four times that of the target particles, the carrier-gas particles tend to mix with the target particles in the clusters.

  7. Homogeneity characterization of lattice spacing of silicon single crystals by a self-referenced lattice comparator

    NASA Astrophysics Data System (ADS)

    Fujimoto, H.; Waseda, A.; Zhang, X. W.

    2011-04-01

    The homogeneity of the lattice spacings of silicon single crystals from different origins was characterized. Strain measurements were performed on single crystals from NRLM3, NRLM4 and 28Si-10Pr11 ingots, which are all used to determine the Avogadro constant. NRLM3 and NRLM4 both exhibited clear striations, whereas almost no pattern was obtained for 28Si-10Pr11. The standard deviation of the lattice spacing of the single crystal obtained from 28Si-10Pr11 was 4.7 × 10-9, which enabled the lattice spacing to be determined with a standard uncertainty of 3 × 10-9.

  8. High-throughput method for optimum solubility screening for homogeneity and crystallization of proteins

    DOEpatents

    Kim, Sung-Hou [Moraga, CA; Kim, Rosalind [Moraga, CA; Jancarik, Jamila [Walnut Creek, CA

    2012-01-31

    An optimum solubility screen in which a panel of buffers and many additives are provided in order to obtain the most homogeneous and monodisperse protein condition for protein crystallization. The present methods are useful for proteins that aggregate and cannot be concentrated prior to setting up crystallization screens. A high-throughput method using the hanging-drop method and vapor diffusion equilibrium and a panel of twenty-four buffers is further provided. Using the present methods, 14 poorly behaving proteins have been screened, resulting in 11 of the proteins having highly improved dynamic light scattering results allowing concentration of the proteins, and 9 were crystallized.

  9. Pre-ordering of interfacial water in the pathway of heterogeneous ice nucleation does not lead to a two-step crystallization mechanism

    NASA Astrophysics Data System (ADS)

    Lupi, Laura; Peters, Baron; Molinero, Valeria

    2016-12-01

    According to Classical Nucleation Theory (CNT), the transition from liquid to crystal occurs in a single activated step with a transition state controlled by the size of the crystal embryo. This picture has been challenged in the last two decades by several reports of two-step crystallization processes in which the liquid first produces pre-ordered or dense domains, within which the crystal nucleates in a second step. Pre-ordering preceding crystal nucleation has been recently reported in simulations of ice crystallization, raising the question of whether the mechanism of ice nucleation involves two steps. In this paper, we investigate the heterogeneous nucleation of ice on carbon surfaces. We use molecular simulations with efficient coarse-grained models combined with rare event sampling methods and free energy calculations to elucidate the role of pre-ordering of liquid water at the carbon surface in the reaction coordinate for heterogeneous nucleation. We find that ice nucleation proceeds through a classical mechanism, with a single barrier between liquid and crystal. The reaction coordinate that determines the crossing of the nucleation barrier is the size of the crystal nucleus, as predicted by CNT. Wetting of the critical ice nuclei within pre-ordered domains decreases the nucleation barrier, increasing the nucleation rates. The preferential pathway for crystallization involves the early creation of pre-ordered domains that are the birthplace of the ice crystallites but do not represent a minimum in the free energy pathway from liquid to ice. We conclude that a preferential pathway through an intermediate-order precursor does not necessarily result in a two-step mechanism.

  10. Molecular Dynamics Study on Nucleation Behavior and Lamellar Mergence of Polyethylene Globule Crystallization

    NASA Astrophysics Data System (ADS)

    Yang, Xiaozhen; Wang, Simiao

    2012-02-01

    The site order parameter (SOP) has been adopted to analyze various order structure formation and distribution during the crystallization of a multi-chain polyethylene globule simulated by molecular dynamics. We found that the nucleation relies on crystallinity fluctuation with increase of amplitude, and the baby nucleus in the fluctuation suddenly appears with different shape and increasing size. In the growth stage, a number of lamellar mergence was observed and their selective behaviors were suggested to be related to the orientation difference between the merging lamellae. We obtained that SOP distribution of all atoms in the system during crystallization appears with two peaks: one for the amorphous phase and the other for the crystalline phase. Mesomorphic structures with medium orders locate between the two peaks as an order promotion pathway. Obtained data show that the medium order structure fluctuates at the growth front and does not always be available; the medium order structure existing at the front is not always good for developing. It is possibly caused by chain entanglement.

  11. Thermodynamic equilibrium, metastable zone widths, and nucleation behavior in the cooling crystallization of gestodene-ethanol systems

    NASA Astrophysics Data System (ADS)

    Wang, Li-yu; Zhu, Liang; Yang, Li-bin; Wang, Yan-fei; Sha, Zuo-liang; Zhao, Xiao-yu

    2016-03-01

    A systematic investigation of nucleation behavior for the batch cooling crystallization of unseeded gestodene-ethanol solutions was carried out. The solubilities of the two polymorphs (forms I and II) of gestodene in ethanol were gravimetrically measured between 268.15 and 333.15 K under atmospheric pressure of 0.10 MPa. In addition, the metastable zone widths (MSZWs) of the gestodene-ethanol solutions were determined by the polythermal method combined with the focused beam reflectance measurement (FBRM®) technique. Moreover, polymorphic forms of the grown crystals were identified by X-ray powder diffraction (XRD) and optical microscope. Experimental results indicated that the measured MSZWs were dependent on numerous technological parameters, including cooling rate, saturation temperature, and agitation intensity. With variation of the nucleation temperature and cooling rate, forms I, II, and a mixture of the two forms were crystallized from ethanol solution. The nucleation kinetic parameters were estimated from MSZW data using the self-consistent Nývlt-like approach. Due to the high solubility of form I in ethanol at the corresponding temperature range, the stronger solute-solvent interactions confirmed that the nucleation of form I had a greater activation energy than that of form II.

  12. The nucleation of inosine: the impact of solution chemistry on the appearance of polymorphic and hydrated crystal forms.

    PubMed

    Chiarella, Renato A; Gillon, Amy L; Burton, Rebecca C; Davey, Roger J; Sadiq, Ghazala; Auffret, Anthony; Cioffi, Marina; Hunter, Christopher A

    2007-01-01

    This contribution concerns the issue of crystal nucleation in the polymorphic and hydrate forming system inosine-water. A combination of computational and experimental tools have been used to explore the relationship between solution phase inosine species and the structural synthons as found in its crystal structures. It is evident that the initial nucleation of a metastable polymorph at temperatures above 10 degrees C is directed by dimeric self-association as revealed through proton NMR. At lower temperatures a dihydrate structure becomes the most stable solid phase and in this region of the phase diagram this is the only form that appears even though the solution species remain unchanged. This can only be rationalised in terms of a combination of water binding to the solution dimers and the thermodynamic stability of the hydrate crystal structure.

  13. Comment on vapor phase homogeneous nucleation of CH 3CN and the scaling law for onset supersaturation ratios

    NASA Astrophysics Data System (ADS)

    Hale, Barbara N.; Kelly, Brendan

    1992-01-01

    We point out that the scaling law for onset vapor phase nucleation, ln Sonset ≈ 0.53 [Ω( Tc/ T-1)] 3/2, with Ω = 1.77 (from CH 3CN surface tension data) predicts the temperature dependence and approximate magnitude of CH 3CN supersaturation ratio data, S. This is contrary to the conclusions of Wright, Caldwell and El-Shall who estimate too large a value (2.14) for Ω. We note that Ω, the excess molecular surface entropy/ k, is more reliably extracted from the temperature derivative of the surface tension data.

  14. Free energy calculations along entropic pathways. I. Homogeneous vapor-liquid nucleation for atomic and molecular systems

    NASA Astrophysics Data System (ADS)

    Desgranges, Caroline; Delhommelle, Jerome

    2016-11-01

    Using the entropy S as a reaction coordinate, we determine the free energy barrier associated with the formation of a liquid droplet from a supersaturated vapor for atomic and molecular fluids. For this purpose, we develop the μ V T -S simulation method that combines the advantages of the grand-canonical ensemble, that allows for a direct evaluation of the entropy, and of the umbrella sampling method, that is well suited to the study of an activated process like nucleation. Applying this approach to an atomic system such as Ar allows us to test the method. The results show that the μ V T -S method gives the correct dependence on supersaturation of the height of the free energy barrier and of the size of the critical droplet, when compared to predictions from the classical nucleation theory and to previous simulation results. In addition, it provides insight into the relation between the entropy and droplet formation throughout this process. An additional advantage of the μ V T -S approach is its direct transferability to molecular systems, since it uses the entropy of the system as the reaction coordinate. Applications of the μ V T -S simulation method to N2 and CO2 are presented and discussed in this work, showing the versatility of the μ V T -S approach.

  15. Elimination of off-axis light leakage in a homogeneously aligned liquid crystal cell

    NASA Astrophysics Data System (ADS)

    Oh, Seung-Won; Park, Byung Wok; Yoon, Tae-Hoon

    2015-03-01

    Among various liquid crystal display modes, the in-plane switching mode exhibits the widest viewing angle because the liquid crystals are homogeneously-aligned initially and rotate within a plane parallel to the substrates when an in-plane field is applied. However, further improvement is still needed for viewing high-quality dark images from the bisector direction of the crossed polarizers. Several compensation schemes have been proposed to eliminate the off-axis light leakage in a homogeneously-aligned liquid crystal cell. Although a 100:1 iso-contrast contour at an wavelength of 550 nm can cover the entire viewing cone, light leakage at other wavelengths still remains very severe. In this paper we introduce achromatic optical compensation methods using uniaxial films to eliminate the off-axis light leakage at the dark state in homogeneously-aligned liquid crystal cell.Uniaxial films with different dispersion characteristics are used so that they can compensate one another to achieve achromatic optical compensation. The retardation values are optimized through numerical research with the aid of the Poincaré sphere.

  16. Crystal nucleation of hard spheres using molecular dynamics, umbrella sampling, and forward flux sampling: a comparison of simulation techniques.

    PubMed

    Filion, L; Hermes, M; Ni, R; Dijkstra, M

    2010-12-28

    Over the last number of years several simulation methods have been introduced to study rare events such as nucleation. In this paper we examine the crystal nucleation rate of hard spheres using three such numerical techniques: molecular dynamics, forward flux sampling, and a Bennett-Chandler-type theory where the nucleation barrier is determined using umbrella sampling simulations. The resulting nucleation rates are compared with the experimental rates of Harland and van Megen [Phys. Rev. E 55, 3054 (1997)], Sinn et al. [Prog. Colloid Polym. Sci. 118, 266 (2001)], Schätzel and Ackerson [Phys. Rev. E 48, 3766 (1993)], and the predicted rates for monodisperse and 5% polydisperse hard spheres of Auer and Frenkel [Nature 409, 1020 (2001)]. When the rates are examined in units of the long-time diffusion coefficient, we find agreement between all the theoretically predicted nucleation rates, however, the experimental results display a markedly different behavior for low supersaturation. Additionally, we examined the precritical nuclei arising in the molecular dynamics, forward flux sampling, and umbrella sampling simulations. The structure of the nuclei appears independent of the simulation method, and in all cases, the nuclei contains on average significantly more face-centered-cubic ordered particles than hexagonal-close-packed ordered particles.

  17. Nucleation of Ice

    NASA Astrophysics Data System (ADS)

    Molinero, Valeria

    2009-03-01

    The freezing of water into ice is a ubiquitous transformation in nature, yet the microscopic mechanism of homogeneous nucleation of ice has not yet been elucidated. One of the reasons is that nucleation happens in time scales that are too fast for an experimental characterization and two slow for a systematic study with atomistic simulations. In this work we use coarse-grained molecular dynamics simulations with the monatomic model of water mW[1] to shed light into the mechanism of homogeneous nucleation of ice and its relationship to the thermodynamics of supercooled water. Cooling of bulk water produces either crystalline ice or low- density amorphous ice (LDA) depending on the quenching rate. We find that ice crystallization occurs faster at temperatures close to the liquid-liquid transition, defined as the point of maximum inflection of the density with respect to the temperature. At the liquid-liquid transition, the time scale of nucleation becomes comparable to the time scale of relaxation within the liquid phase, determining --effectively- the end of the metastable liquid state. Our results imply that no ultraviscous liquid water can exist at temperatures just above the much disputed glass transition of water. We discuss how the scenario is changed when water is in confinement, and the relationship of the mechanism of ice nucleation to that of other liquids that present the same phase behavior, silicon [2] and germanium [3]. [4pt] [1] Molinero, V. & Moore, E. B. Water modeled as an intermediate element between carbon and silicon. Journal of Physical Chemistry B (2008). Online at http://pubs.acs.org/cgi- bin/abstract.cgi/jpcbfk/asap/abs/jp805227c.html [0pt] [2] Molinero, V., Sastry, S. & Angell, C. A. Tuning of tetrahedrality in a silicon potential yields a series of monatomic (metal-like) glass formers of very high fragility. Physical Review Letters 97, 075701 (2006).

  18. CO2-crystal wettability in potassic magmas: implications for eruptive dynamics in light of experimental evidence for heterogeneous nucleation

    NASA Astrophysics Data System (ADS)

    Sottili, Gianluca; Fanara, Sara; Silleni, Aurora; Palladino, Danilo M.; Schmidt, Burkhard C.

    2017-05-01

    The volatile content in magmas is fundamental for the triggering and style of volcanic eruptions. Carbon dioxide, the second most abundant volatile component in magmas after H2O, is the first to reach saturation upon ascent and depressurization. We investigate experimentally CO2-bubble nucleation in trachybasalt and trachyte melts at high temperature and high pressure (HT and HP) through wetting-angle measurements on different (sialic, mafic or oxide) phenocryst phases. The presence of crystals lowers the supersaturation required for CO2-bubble nucleation up to 37 per cent (heterogeneous nucleation, HeN), with a minor role of mineral chemistry. Different from H2O-rich systems, feldspar crystals are effective in reducing required supersaturation for bubble nucleation. Our data suggest that leucite, the dominant liquidus phase in ultrapotassic systems at shallow depth (i.e. <100 MPa), facilitates late-stage, extensive magma vesiculation through CO2HeN, which may explain the shifting of CO2-rich eruptive systems towards an apparently anomalous explosive behaviour.

  19. Polymer-templated nucleation and crystal growth of perovskite films for solar cells with efficiency greater than 21%

    NASA Astrophysics Data System (ADS)

    Bi, Dongqin; Yi, Chenyi; Luo, Jingshan; Décoppet, Jean-David; Zhang, Fei; Zakeeruddin, Shaik Mohammed; Li, Xiong; Hagfeldt, Anders; Grätzel, Michael

    2016-10-01

    The past several years have witnessed the rapid emergence of a class of solar cells based on mixed organic-inorganic halide perovskites. Today’s state-of-the-art perovskite solar cells (PSCs) employ various methods to enhance nucleation and improve the smoothness of the perovskite films formed via solution processing. However, the lack of precise control over the crystallization process creates a risk of forming unwanted defects, for example, pinholes and grain boundaries. Here, we introduce an approach to prepare perovskite films of high electronic quality by using poly(methyl methacrylate) (PMMA) as a template to control nucleation and crystal growth. We obtain shiny smooth perovskite films of excellent electronic quality, as manifested by a remarkably long photoluminescence lifetime. We realize stable PSCs with excellent reproducibility showing a power conversion efficiency (PCE) of up to 21.6% and a certified PCE of 21.02% under standard AM 1.5G reporting conditions.

  20. Ice Nucleation in Deep Convection

    NASA Technical Reports Server (NTRS)

    Jensen, Eric; Ackerman, Andrew; Stevens, David; Gore, Warren J. (Technical Monitor)

    2001-01-01

    The processes controlling production of ice crystals in deep, rapidly ascending convective columns are poorly understood due to the difficulties involved with either modeling or in situ sampling of these violent clouds. A large number of ice crystals are no doubt generated when droplets freeze at about -40 C. However, at higher levels, these crystals are likely depleted due to precipitation and detrainment. As the ice surface area decreases, the relative humidity can increase well above ice saturation, resulting in bursts of ice nucleation. We will present simulations of these processes using a large-eddy simulation model with detailed microphysics. Size bins are included for aerosols, liquid droplets, ice crystals, and mixed-phase (ice/liquid) hydrometers. Microphysical processes simulated include droplet activation, freezing, melting, homogeneous freezing of sulfate aerosols, and heterogeneous ice nucleation. We are focusing on the importance of ice nucleation events in the upper part of the cloud at temperatures below -40 C. We will show that the ultimate evolution of the cloud in this region (and the anvil produced by the convection) is sensitive to these ice nucleation events, and hence to the composition of upper tropospheric aerosols that get entrained into the convective column.

  1. Homogeneous nucleation rate measurements of 1-butanol in helium: a comparative study of a thermal diffusion cloud chamber and a laminar flow diffusion chamber.

    PubMed

    Brus, David; Hyvärinen, Antti-Pekka; Zdímal, Vladimír; Lihavainen, Heikki

    2005-06-01

    Isothermal homogeneous nucleation rates of 1-butanol were measured both in a thermal diffusion cloud chamber and in a laminar flow diffusion chamber built recently at the Institute of Chemical Process Fundamentals, Academy of Sciences of the Czech Republic, Prague, Czech Republic. The chosen system 1-butanol-helium can be studied reasonably well in both devices, in the overlapping range of temperatures. The results were compared with those found in the literature and those measured by Lihavainen in a laminar flow diffusion chamber of a similar design. The same isotherms measured with the thermal diffusion cloud chamber occur at highest saturation ratios of the three devices. Isotherms measured with the two laminar flow diffusion chambers are reasonably close together; the measurements by Lihavainen occur at lowest saturation ratios. The temperature dependences observed were similar in all three devices. The molecular content of critical clusters was calculated using the nucleation theorem and compared with the Kelvin equation. Both laminar flow diffusion chambers provided very similar sizes slightly above the Kelvin equation, whereas the thermal diffusion cloud chamber suggests critical cluster sizes significantly smaller. The results found elsewhere in the literature were in reasonable agreement with our results.

  2. Heterogeneous bubble nucleation on pyroxene and plagioclase in andesite magmas

    NASA Astrophysics Data System (ADS)

    Pleše, P.; Higgins, M.; Brun, F.; Casselman, J.; Fife, J.; Mancini, L.; Lanzafame, G.; Baker, D. R.

    2016-12-01

    Understanding bubble nucleation and growth has long been considered a key to improving our knowledge of magmatic evolution, and aiding our goal of predicting violent volcanic eruptions. The role crystals play as heterogeneous nucleation sites for bubbles has become an active area of research because they have the potential to reduce the supersaturation necessary for bubble growth. The nucleation sites of bubbles in magmas are elusive because they cannot be directly observed in natural volcanic systems. Studies are generally conducted on natural, post-eruption samples or quenched experimental charges, but both provide only a view of the final state and provide little information on how this state was achieved. We directly observed bubble nucleation and growth by 4D in-situ synchrotron X-ray tomography of bubble nucleation and growth at the Swiss Light Source. Experiments were conducted on previously prepared, hydrous, crystal-bearing andesitic melts to observe bubble nucleation and track bubble growth and movement. We collected 3D images every 0.5 s while heating hydrated melts at 1 atm. We observed that bubbles first nucleated heterogeneously at clinopyroxene/melt and near plagioclase/melt interfaces, rather than homogeneously within the melt. Heterogeneous nucleation on one oxide crystal and homogeneous nucleation within the melt occurred significantly after nucleation on the silicates. The measured bubble-crystal contact angle was not constant and decreased with time. Bubbles grew much larger than the crystals in the experiments, producing textures similar to those seen in some natural volcanic samples. Our results show that the presence of silicate phases in magmas must be taken into account when discussing bubble nucleation in magmatic systems.

  3. The crystal-fluid interfacial free energy and nucleation rate of NaCl from different simulation methods.

    PubMed

    Espinosa, Jorge R; Vega, Carlos; Valeriani, Chantal; Sanz, Eduardo

    2015-05-21

    In this work, we calculate the crystal-fluid interfacial free energy, γ(cf), for the Tosi-Fumi model of NaCl using three different simulation techniques: seeding, umbrella sampling, and mold integration. The three techniques give an orientationaly averaged γ(cf) of about 100 mJ/m(2). Moreover, we observe that the shape of crystalline clusters embedded in the supercooled fluid is spherical. Using the mold integration technique, we compute γ(cf) for four different crystal orientations. The obtained interfacial free energies range from 100 to 114 mJ/m(2), being (100) and (111) the crystal planes with the lowest and highest γ(cf), respectively. Within the accuracy of our calculations, the interfacial free energy either does not depend on temperature or changes very smoothly with it. Combining the seeding technique with classical nucleation theory, we also estimate nucleation free energy barriers and nucleation rates for a wide temperature range (800-1040 K). The obtained results compare quite well with brute force calculations and with previous results obtained with umbrella sampling [Valeriani et al., J. Chem. Phys, 122, 194501 (2005)].

  4. Role of dynamic heterogeneities in crystal nucleation kinetics in an oxide supercooled liquid

    NASA Astrophysics Data System (ADS)

    Gupta, Prabhat K.; Cassar, Daniel R.; Zanotto, Edgar D.

    2016-12-01

    The temperature at which the classical critical nucleus size is equal to the average size of the cooperatively rearranging regions (CRR) in a supercooled liquid has been referred to as a "cross-over" temperature. We show, for the first time, using published nucleation rate, viscosity, and thermo-physical data, that the cross-over temperature for the lithium disilicate melt is significantly larger than the temperature of the kinetic spinodal and is equal or close to the temperature corresponding to the maximum in the experimentally observed nucleation rates. We suggest that the abnormal decrease in nucleation rates below the cross-over temperature is most likely because, in this regime, the CRR size controls the critical nucleus size and the nucleation rate. This finding links, for the first time, measured nucleation kinetics to the dynamic heterogeneities in a supercooled liquid.

  5. Nucleation studies and characterization of potassium dihydrogen phosphate single crystals with L-arginine monohydrochloride as additive

    NASA Astrophysics Data System (ADS)

    Dhanaraj, P. V.; Mathew, Santheep K.; Rajesh, N. P.

    2008-05-01

    In the search for suitable non-linear optical (NLO) materials with higher non-linear responses and good optical, thermal, mechanical properties as well as fast growth rate, an attempt has been made to grow potassium dihydrogen phosphate (KDP) single crystals doped with L-arginine monohydrochloride (LAHCl). Slow cooling as well as slow evaporation methods were employed to grow crystals. The concentration of dopants in the mother solution varied from 1 to 10 M%. The solubility data for dopant concentration were determined and are compared with those of pure KDP. Nucleation studies show that metastable zone width of KDP is enhanced by the addition of LAHCl. The effect of additives on the growth, nucleation kinetics, structural, optical and mechanical properties has been investigated. With increasing additive concentration, the growth rate was found to increase. Vicker's microhardness study shows higher mechanical stability in LAHCl-added KDP crystals, the pure ones. Moreover, the addition of LAHCl improves the quality of the crystal surface and yields highly transparent crystals with well-defined features.

  6. The influence of homogenization process on lasing performance in polymer-nematic liquid crystal emulsions

    NASA Astrophysics Data System (ADS)

    Adamow, Alina; Sznitko, Lech; Mysliwiec, Jaroslaw

    2017-07-01

    In this letter we report on the results of studies of amplified spontaneous emission in polymer - liquid crystal emulsions based on mixtures of poly(vinyl alcohol) and 5CB nematic liquid crystal doped with three luminescent dyes: DCM, Coumarin 504 and Coumarin 540. The mixture of dyes was used in order to extend the range of stimulated emission spectra. We have investigated the emission properties of four samples with different size and distribution of liquid crystal micro droplets, controlled by the length of time exposure on ultrasounds during the homogenization process. We have designated the threshold conditions for stimulated emission occurrence and compared the emission spectra obtained below as well as above threshold conditions.

  7. Microwave effect in the fast synthesis of microporous materials: which stage between nucleation and crystal growth is accelerated by microwave irradiation?

    PubMed

    Jhung, Sung Hwa; Jin, Taihuan; Hwang, Young Kyu; Chang, Jong-San

    2007-01-01

    Microporous materials, such as silicalite-1 and VSB-5 molecular sieves, have been synthesized by both microwave irradiation (MW) and conventional electric heating (CE). The accelerated syntheses by microwave irradiation can be quantitatively investigated by various heating modes conducted in two steps such as MW-MW, MW-CE, CE-MW, and CE-CE (in the order of nucleation-crystal growth). In the case of synthesis by MW-CE or CE-MW, the heating modes were changed for the second step just after the appearance of X-ray diffraction peaks in the first step. We have quantitatively demonstrated that the microwave irradiation accelerates not only the nucleation but also crystal growth. However, the contribution to decrease the synthesis time by microwave irradiation is larger in the nucleation stage than in the step of crystal growth. The crystal size increases in the order of MW-MWcrystal growth and small crystal size observed in the synthesis from microwave-nucleated precursor can be explained in terms of the fact that the microwave-nucleated samples have higher population of nuclei with smaller size than the samples nucleated by conventional heating.

  8. Nucleation and crystallization of Ca doped basaltic glass for the production of a glass-ceramic material

    NASA Astrophysics Data System (ADS)

    Tarrago, Mariona; Royo, Irene; Garcia-Valles, Maite; Martínez, Salvador

    2016-04-01

    Sewage sludge from wastewater treatment plants is a waste with a composition roughly similar to that of a basalt. It may contain potentially toxic elements that can be inertized by vitrification. Using a glass-ceramic process, these elements will be emplaced in newly formed mineral phases. Glass-ceramic production requires an accurate knowledge of the temperatures of nucleation (TN) and crystal growth of the corresponding minerals. This work arises from the study of the addition of ions to a basaltic matrix in order to establish a model of vitrification of sewage sludge. In this case a glass-ceramic is obtained from a glass made with a basalt that has been doped with 16% CaO. Two glasses which underwent different cooling processes have been produced and compared. The first was annealed at 650oC (AG) and the second was quenched (QG). The chemical composition of the glasses is SiO2 36.11 wt%, Al2O312.19 wt%, CaO 24.44 wt%, FeO 10.06 wt%, MgO 9.19 wt%, Na2O 2.28 wt%, TiO2 2.02 wt%, K2O 1.12 wt%, P2O5 0.46 wt%. Glass transition temperature obtained by dilatometry varies from 640 oC (AG) to 700 oC (QG). The temperatures of nucleation and crystal growth of the glass have been determined by Differential Thermal Analysis (DTA). The phases formed after these treatments were identified by X-Ray Diffraction. The temperatures of exothermic and endothermic peaks measured in the quenched glass are, in average, 10 oC higher than those found for the annealed glass. The exothermic peaks provide crystallization temperatures for different phases: a first event at 857 oC corresponds to the growth of magnetite, pyroxene and nepheline, whereas a second event at 1030 oC is due to the crystallization of melilite from the reaction between previous minerals and a remaining amorphous phase. The complete melting of this system occurs at 1201 oC. This glass has been nucleated inside the DTA furnace (500-850° C/3 hours) and then heated up to 1300 oC using the fraction between 400-500μm. TN

  9. Investigating the role of solvent-solute interaction in crystal nucleation of salicylic acid from organic solvents.

    PubMed

    Khamar, Dikshitkumar; Zeglinski, Jacek; Mealey, Donal; Rasmuson, Åke C

    2014-08-20

    In previous work, it has been shown that the crystal nucleation of salicylic acid (SA) in different solvents becomes increasingly more difficult in the order: chloroform, ethyl acetate acetonitrile, acetone, methanol, and acetic acid. In the present work, vibration spectroscopy, calorimetric measurements, and density functional theory (DFT) calculations are used to reveal the underlying molecular mechanisms. Raman and infrared spectra suggest that SA exists predominately as dimers in chloroform, but in the other five solvents there is no clear evidence of dimerization. In all solvents, the shift in the SA carbonyl peak reflecting the strength in the solvent-solute interaction is quite well correlated to the nucleation ranking. This shift is corroborated by DFT calculated energies of binding one solvent molecule to the carboxyl group of SA. An even better correlation of the influence of the solvent on the nucleation is provided by DFT calculated energy of binding the complete first solvation shell to the SA molecule. These solvation shell binding energies are corroborated by the enthalpy of solvent-solute interaction as estimated from experimentally determined enthalpy of solution and calculated enthalpy of cavity formation using the scaled particle theory. The different methods reveal a consistent picture and suggest that the stronger the solvent binds to the SA molecule in solution, the slower the nucleation becomes.

  10. Effect of Pt Doping on Nucleation and Crystallization in Li2O.2SiO2 Glass: Experimental Measurements and Computer Modeling

    NASA Technical Reports Server (NTRS)

    Narayan, K. Lakshmi; Kelton, K. F.; Ray, C. S.

    1996-01-01

    Heterogeneous nucleation and its effects on the crystallization of lithium disilicate glass containing small amounts of Pt are investigated. Measurements of the nucleation frequencies and induction times with and without Pt are shown to be consistent with predictions based on the classical nucleation theory. A realistic computer model for the transformation is presented. Computed differential thermal analysis data (such as crystallization rates as a function of time and temperature) are shown to be in good agreement with experimental results. This modeling provides a new, more quantitative method for analyzing calorimetric data.

  11. Probing the homogeneity of the isotopic composition and molar mass of the ‘Avogadro’-crystal

    NASA Astrophysics Data System (ADS)

    Pramann, Axel; Lee, Kyoung-Seok; Noordmann, Janine; Rienitz, Olaf

    2015-12-01

    Improved measurements on silicon crystal samples highly enriched in the 28Si isotope (known as ‘Si28’ or AVO28 crystal material) have been carried out at PTB to investigate local isotopic variations in the original crystal. This material was used for the determination of the Avogadro constant NA and therefore plays an important role in the upcoming redefinition of the SI units kilogram and mole, using fundamental constants. Subsamples of the original crystal have been extensively studied over the past few years at the National Research Council (NRC, Canada), the National Metrology Institute of Japan (NMIJ, Japan), the National Institute of Standards and Technology (NIST, USA), the National Institute of Metrology (NIM, People’s Republic of China), and multiple times at PTB. In this study, four to five discrete, but adjacent samples were taken from three distinct axial positions of the crystal to obtain a more systematic and comprehensive understanding of the distribution of the isotopic composition and molar mass throughout the crystal. Moreover, improved state-of-the-art techniques in the experimental measurements as well as the evaluation approach and the determination of the calibration factors were utilized. The average molar mass of the measured samples is M  =  27.976 970 12(12) g mol-1 with a relative combined uncertainty uc,rel(M)  =  4.4 ×10-9. This value is in astounding agreement with the values of single samples measured and published by NIST, NMIJ, and PTB. With respect to the associated uncertainties, no significant variations in the molar mass and the isotopic composition as a function of the sample position in the boule were observed and thus could not be traced back to an inherent property of the crystal. This means that the crystal is not only ‘homogeneous’ with respect to molar mass but also has predominantly homogeneous distribution of the three stable Si isotopes.

  12. Homogeneous, core-shell, and hollow-shell ZnS colloid-based photonic crystals.

    PubMed

    Hosein, Ian D; Liddell, Chekesha M

    2007-02-27

    Ordered ZnS-based colloidal crystals from homogeneous, core-shell, and hollow building blocks were prepared via electrosteric colloid stabilization combined with a convective assembly technique. The polyelectrolyte stabilized colloids assembled into face-centered cubic arrays with the (111) face perpendicular to the substrate. Structure-property correlations were made using scanning electron microscopy, scanning transmission electron microscopy, and UV/visible/near-IR spectroscopy. Multilayer film growth, with film thickness of several micrometers, was achieved. Optical spectra showed (111) stopgaps along with pronounced higher order peaks. The spectral position of the photonic stopgap can be predicted using a volume average refractive index and the Maxwell-Garnett formula for the homogeneous and core-shell particles, respectively. This work holds the promise of harnessing ZnS for optical property engineering and enhanced photonic band gap materials.

  13. Nucleation kinetics, growth, crystalline perfection, mechanical, thermal, optical and electrical characterization of brucinium 2-carboxy-6-nitrophthalate dihydrate single crystal

    NASA Astrophysics Data System (ADS)

    Krishnan, P.; Gayathri, K.; Sivakumar, N.; Gunasekaran, S.; Anbalagan, G.

    2014-06-01

    Single crystals of brucinium 2-carboxy-6-nitrophthalate dihydrate (B2C6ND) have been grown by the slow evaporation solution technique at room temperature using water-ethanol (1:1) mixed solvent. The metastable zone width and induction period have been experimentally determined for the growth conditions. Nucleation kinetics and fundamental growth parameters such as surface free energy, critical radius and critical free energy change are also evaluated according to the experimental data. The crystal system and the lattice parameters have been confirmed by single crystal X-ray diffraction. The crystalline perfection of the grown B2C6ND crystals has been characterized by HRXRD method. Optical band gap and Urbach tail width of the sample have been studied employing UV-Vis absorption spectroscopy. The Vickers microhardness number (Hv), yield strength (σv) and stiffness constant (C11) of the grown crystal have been evaluated. The dielectric permittivity and dielectric loss of the grown B2C6ND crystal have been investigated as a function of frequency in the temperature range 313-353 K. The laser damage threshold value of B2C6ND crystal was estimated to be 2.8 GW/cm2 using a Nd:YAG laser.

  14. Homogeneous and inhomogeneous spectrum broadening in Nd3+-doped mixed vanadate crystals

    NASA Astrophysics Data System (ADS)

    Zhao, Yongguang; Yu, Haohai; Wang, Zhengping; Zhang, Huaijin; Xu, Xinguang; Wang, Jiyang

    2017-09-01

    Homogeneous and inhomogeneous spectrum broadening in Nd:LuxGd1-xVO4 series crystals were directly measured for the first time, and compared with that in the Nd:LuxY1-xVO4 and Nd:GdxY1-xVO4 crystals. Spectroscopic properties including fluorescence lifetime, spectral line width, emission peak, and stimulated emission cross section had obvious changes with the temperature increased from 77 K to 300 K, owing to the thermal phonon vibration. Compared to the pure vanadate crystals, we found these changes were more sensitive to temperature in the case of mixed crystals, in which cations (Lu, Y, and Gd) are random replaced by each other at the same lattice site. At 77 K, the thermal phonon vibration effect can be ignored and the inhomogeneous spectrum broadening that caused by disordered structure in all samplers can be calculated with the line-width of pure vanadate crystals as reference point, the corresponding values (ΔΓ(T)‧) were 2.2 nm-3.8 nm in 4F3/2 → 4I11/2 transition and 1.7 nm-2.8 nm in 4F3/2 → 4I13/2 transition. Compared to Nd:LuxY1-xVO4 and Nd:GdxY1-xVO4 series mixed crystals, the change in spectral line width with x is most obvious in the case of Nd:LuxGd1-xVO4 series crystals, which may be attributed to the larger ionic radius difference between Gd and Lu (RLu < RY < RGd).

  15. Spontaneous nucleation and growth of GaN nanowires: the fundamental role of crystal polarity.

    PubMed

    Fernández-Garrido, Sergio; Kong, Xiang; Gotschke, Tobias; Calarco, Raffaella; Geelhaar, Lutz; Trampert, Achim; Brandt, Oliver

    2012-12-12

    We experimentally investigate whether crystal polarity affects the growth of GaN nanowires in plasma-assisted molecular beam epitaxy and whether their formation has to be induced by defects. For this purpose, we prepare smooth and coherently strained AlN layers on 6H-SiC(0001) and SiC(0001̅) substrates to ensure a well-defined polarity and an absence of structural and morphological defects. On N-polar AlN, a homogeneous and dense N-polar GaN nanowire array forms, evidencing that GaN nanowires form spontaneously in the absence of defects. On Al-polar AlN, we do not observe the formation of Ga-polar GaN NWs. Instead, sparse N-polar GaN nanowires grow embedded in a Ga-polar GaN layer. These N-polar GaN nanowires are shown to be accidental in that the necessary polarity inversion is induced by the formation of Si(x)N. The present findings thus demonstrate that spontaneously formed GaN nanowires are irrevocably N-polar. Due to the strong impact of the polarity on the properties of GaN-based devices, these results are not only essential to understand the spontaneous formation of GaN nanowires but also of high technological relevance.

  16. The effect of nucleation layer thickness on the structural evolution and crystal quality of bulk GaN grown by a two-step process on cone-patterned sapphire substrate

    NASA Astrophysics Data System (ADS)

    Shang, Lin; Zhai, Guangmei; Mei, Fuhong; Jia, Wei; Yu, Chunyan; Liu, Xuguang; Xu, Bingshe

    2016-05-01

    The role of nucleation layer thickness on the GaN crystal quality grown on cone-patterned sapphire substrate (PSS) was explored. The morphologies of epitaxial GaN at different growth stages were investigated by a series of growth interruption in detail. After 10- and 15-min three-dimensional growth, the nucleation sites are very important for the bulk GaN crystal quality. They have a close relationship with the nucleation layer thickness, as confirmed through the scanning electron microscope (SEM) analysis. Nucleation sites formed mainly on patterns are bad for bulk GaN crystal quality and nucleation sites formed mainly in the trenches of PSS mounds are good for bulk GaN crystal quality, as proved by X-ray diffraction analysis. Nucleation layer thickness can effectively control the nucleation sites and thus determine the crystal quality of bulk GaN.

  17. Communication: Fourier-transform infrared probing of remarkable quantities of gas trapped in cold homogeneously nucleated nanodroplets

    NASA Astrophysics Data System (ADS)

    Uras-Aytemiz, Nevin; Devlin, J. Paul

    2013-07-01

    Studies of catalyzed all-vapor gas-hydrate formation on a sub-second timescale have been extended with a special focus on liquid-droplet compositions at the instant of hydrate crystallization. This focus has been enabled by inclusion of methanol in the all-vapor mixture. This slows droplet to gas-hydrate conversion near 200 K to a time scale suited for standard FTIR sampling. Such droplet data are sought as a guide to ongoing efforts to reduce the amount of guest catalyst required for instant formation of the gas hydrates. For the same reason, all-vapor sampling has also been extended to the generation of long-lived liquid droplets with reduced or no water content. Observations of single-solvent droplets show that surprising quantities of gas molecules are trapped during rapid droplet growth. For example, CO2 is trapped at levels near 50 mol. % in droplets of acetone, tetrahydrofuran, or trimethylene oxide formed under CO2 pressures of several Torr in a cold-chamber at 170 K. Less but significant amounts of gas are trapped at higher temperatures, or in methanol or water-methanol droplets. The droplet metastability appears to commonly lead to formation of bubbles larger than the original nanodroplets. Besides serving as a guide for the all-vapor gas-hydrate studies, the semiquantitative evidence of extensive trapping of gases is expected to have a role in future studies of atmospheric aerosols.

  18. Communication: Fourier-transform infrared probing of remarkable quantities of gas trapped in cold homogeneously nucleated nanodroplets.

    PubMed

    Uras-Aytemiz, Nevin; Devlin, J Paul

    2013-07-14

    Studies of catalyzed all-vapor gas-hydrate formation on a sub-second timescale have been extended with a special focus on liquid-droplet compositions at the instant of hydrate crystallization. This focus has been enabled by inclusion of methanol in the all-vapor mixture. This slows droplet to gas-hydrate conversion near 200 K to a time scale suited for standard FTIR sampling. Such droplet data are sought as a guide to ongoing efforts to reduce the amount of guest catalyst required for instant formation of the gas hydrates. For the same reason, all-vapor sampling has also been extended to the generation of long-lived liquid droplets with reduced or no water content. Observations of single-solvent droplets show that surprising quantities of gas molecules are trapped during rapid droplet growth. For example, CO2 is trapped at levels near 50 mol. % in droplets of acetone, tetrahydrofuran, or trimethylene oxide formed under CO2 pressures of several Torr in a cold-chamber at 170 K. Less but significant amounts of gas are trapped at higher temperatures, or in methanol or water-methanol droplets. The droplet metastability appears to commonly lead to formation of bubbles larger than the original nanodroplets. Besides serving as a guide for the all-vapor gas-hydrate studies, the semiquantitative evidence of extensive trapping of gases is expected to have a role in future studies of atmospheric aerosols.

  19. Bubble Nucleation, Coalescence and Outgassing Induced by Crystallization: Insights into Their Contribution to Seismic Properties of Magmas.

    NASA Astrophysics Data System (ADS)

    Tripoli, B. A.

    2015-12-01

    Seismic tomography of potentially hazardous volcanoes is a prime tool to assess the location and dimensions of magmatic reservoirs. Magma rheology and volcanic eruptive style are to a first order controlled by processes occurring within the conduit or in the magma chamber, such as crystallization and bubble exsolution. Seismic velocities are strongly affected by these processes, but the limited number of constrained measurements does not allow yet establishing a firm link between seismic tomography and the textural and hence rheologic state of volcanic systems. Elastic parameters of vapor-saturated, partially molten systems are thus providing fundamental information for the identification of such reservoirs under volcanoes. We investigated a chemically simplified melt analogous to trachyte, which undergoes plagioclase crystallization and bubble exsolution. A Paterson-type apparatus was employed to measure the seismic velocities at a constant pressure of 250 MPa and at a frequency of 0.1 MHz. The temperature was decreased at a rate of 0.5 or 0.1 °C/min from 850 to 700 °C and velocities were recorded every 45 minutes. In order to characterize the microstructure evolution, we conducted series of cold-seal experiments at identical pressure conditions but with rapid-quenching at each of the recorded temperatures. Magmatic processes such as crystallization, bubble nucleation and coalescence have been recognized throughout the measurements of seismic velocities in the laboratory. Compression and shear wave velocities increase non-linearly during crystallization. At crystal fraction exceeding 45 vol%, the formation of a crystal network favors the propagation of seismic waves through magmatic liquids. However, bubble nucleation induced by crystallization leads to an increase of magma compressibility resulting in a lowering of the wave propagation velocities. These two processes occurring simultaneously have thus competing effects on the seismic properties of magmas. In

  20. Anatomy of a metabentonite: nucleation and growth of illite crystals and their colescence into mixed-layer illite/smectite

    USGS Publications Warehouse

    Eberl, D.D.; Blum, A.E.; Serravezza, M.

    2011-01-01

    The illite layer content of mixed-layer illite/smectite (I/S) in a 2.5 m thick, zoned, metabentonite bed from Montana decreases regularly from the edges to the center of the bed. Traditional X-ray diffraction (XRD) pattern modeling using Markovian statistics indicated that this zonation results from a mixing in different proportions of smectite-rich R0 I/S and illite-rich R1 I/S, with each phase having a relatively constant illite layer content. However, a new method for modeling XRD patterns of I/S indicates that R0 and R1 I/S in these samples are not separate phases (in the mineralogical sense of the word), but that the samples are composed of illite crystals that have continuous distributions of crystal<