Nucleation

Distribution by Scientific Domains
Distribution within Polymers and Materials Science

Kinds of Nucleation

  • bubble nucleation
  • crack nucleation
  • crystal nucleation
  • diamond nucleation
  • heterogeneous nucleation
  • homogeneous nucleation
  • initial nucleation
  • microtubule nucleation
  • particle nucleation
  • primary nucleation
  • protein nucleation

  • Terms modified by Nucleation

  • nucleation ability
  • nucleation agent
  • nucleation center
  • nucleation density
  • nucleation effect
  • nucleation layer
  • nucleation mechanism
  • nucleation process
  • nucleation rate
  • nucleation site
  • nucleation stage
  • nucleation temperature
  • nucleation theory

  • Selected Abstracts


    Gold nanoparticles induce protein crystallization

    CRYSTAL RESEARCH AND TECHNOLOGY, Issue 6 2008
    F. Hodzhaoglu
    Abstract Nucleation of protein crystals by gold nanoparticles was observed. Lysozyme and ferritin were used as model proteins. The effect was established with uncoated gold nanoparticles and with gold nanoparticles coated by 16-mercaptodecanoic acid. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Controlled Nucleation of GaN Nanowires Grown with Molecular Beam Epitaxy

    ADVANCED FUNCTIONAL MATERIALS, Issue 17 2010
    Kris A. Bertness
    Abstract The location of GaN nanowires is controlled with essentially perfect selectivity using patterned SiNx prior to molecular beam epitaxy growth. Nanowire growth is uniform within mask openings and absent on the mask surface for over 95% of the usable area of a 76 mm diameter substrate. The diameters of the resulting nanowires are controlled by the size of the mask openings. Openings of approximately 500 nm or less produce single nanowires with symmetrically faceted tips. [source]


    In situ Mechanical Testing Reveals Periodic Buckle Nucleation and Propagation in Carbon Nanotube Bundles

    ADVANCED FUNCTIONAL MATERIALS, Issue 14 2010
    Shelby B. Hutchens
    Abstract Uniaxial compression studies are performed on 50-µm-diameter bundles of nominally vertical, intertwined carbon nanotubes grown via chemical vapor deposition from a photolithographically defined catalyst. The inhomogeneous microstructure is examined, demonstrating density and tube orientation gradients, believed to play a role in the unique periodic buckling deformation mechanism. Through in situ uniaxial compression experiments it is discovered that the characteristic bottom-to-top sequential buckling proceeds by first nucleating on the bundle surface and subsequently propagating laterally through the bundle, gradually collapsing the entire structure. The effects of strain rate are explored, and storage and loss stiffnesses are analyzed in the context of energy dissipation. [source]


    The Role of OTS Density on Pentacene and C60 Nucleation, Thin Film Growth, and Transistor Performance

    ADVANCED FUNCTIONAL MATERIALS, Issue 12 2009
    Ajay Virkar
    Abstract In organic thin film transistors (OTFTs), charge transport occurs in the first few monolayers of the semiconductor near the semiconductor/dielectric interface. Previous work has investigated the roles of dielectric surface energy, roughness, and chemical functionality on performance. However, large discrepancies in performance, even with apparently identical surface treatments, indicate that additional surface parameters must be identified and controlled in order to optimize OTFTs. Here, a crystalline, dense octadecylsilane (OTS) surface modification layer is found that promotes two-dimensional semiconductor growth. Higher mobility is consistently achieved for films deposited on crystalline OTS compared to on disordered OTS, with mobilities as high as 5.3 and 2.3,cm2,V,1,s,1 for C60 and pentacene, respectively. This is a significant step toward morphological control of organic semiconductors which is directly linked to their thin film charge carrier transport. [source]


    Cover Picture: Sequential Nucleation and Growth of Complex Nanostructured Films (Adv. Funct.

    ADVANCED FUNCTIONAL MATERIALS, Issue 3 2006
    Mater.
    Abstract A sequential nucleation and growth process has been developed to construct complex nanostructured films step-by-step from aqueous solutions, as reported by Liu, Voigt, and co-workers on p.,335. This method can be applied to a wide range of materials, and can be combined with top,down techniques to create spatially resolved micropatterns. The cover figure shows images of oriented nanowires, nanoneedles, nanotubes, nanoplates and stacked columns, wagon-wheels, hierarchical films based on wagon-wheels, hierarchically ordered mesophase silicate, and micropatterned flower-like structures. Nanostructured films with controlled architectures are desirable for many applications in optics, electronics, biology, medicine, and energy/chemical conversions. Low-temperature, aqueous chemical routes have been widely investigated for the synthesis of continuous films, and arrays of oriented nanorods and nanotubes. More recently, aqueous-phase routes have been used to produce films composed of more complex crystal structures. In this paper, we discuss recent progress in the synthesis of complex nanostructures through sequential nucleation and growth processes. We first review the use of multistage, seeded-growth methods to synthesize a wide range of nanostructures, including oriented nanowires, nanotubes, and nanoneedles, as well as laminated films, columns, and multilayer heterostructures. We then describe more recent work on the application of sequential nucleation and growth to the systematic assembly of large arrays of hierarchical, complex, oriented, and ordered crystal architectures. The multistage aqueous chemical route is shown to be applicable to several technologically important materials, and therefore may play a key role in advancing complex nanomaterials into applications. [source]


    Organic Thin-Film Transistors: Controlling Nucleation and Crystallization in Solution-Processed Organic Semiconductors for Thin-Film Transistors (Adv. Mater.

    ADVANCED MATERIALS, Issue 35 2009
    35/2009)
    The grain size in solution-processed organic semiconductor thin films for TFTs can be tuned over a range of three orders of magnitude, report Yueh-Lin Loo and co-workers on p. 3605. The process involves the addition of fractional quantities of "impurities" that are capable of seeding the crystallization of the organic semiconductor, and the control thus exerted permitted studies that correlated increasing device mobility with increasing grain size. [source]


    Controlling Nucleation and Crystallization in Solution-Processed Organic Semiconductors for Thin-Film Transistors

    ADVANCED MATERIALS, Issue 35 2009
    Stephanie S. Lee
    Three orders of magnitude is the range over which the grain size (see figure) can be tuned in solution-processed organic semiconductor thin films for TFTs. Fluorinated triethylsilyl anthradithiophene (FTES-ADT) is added in fractional amounts to seed crystallization of TES-ADT. Correlation between device mobility and grain size in the active layer is described by a composite mobility model that assumes charge-carrier traps are located at grain boundaries. [source]


    Diamond Nucleation by Carbon Transport from Buried Nanodiamond TiO2 Sol-Gel Composites

    ADVANCED MATERIALS, Issue 6 2009
    Michaël Daenen
    Diamond nucleation and growth can occur by diffusion of carbon from buried ultradispersed diamond seeds on a silicon substrate through a titanium oxide interlayer. This knowledge can improve nucleation and adhesion of thin diamond films on various substrates. [source]


    Preferential Interface Nucleation: An Expansion of the VLS Growth Mechanism for Nanowires

    ADVANCED MATERIALS, Issue 2 2009
    Brent A. Wacaser
    Abstract A review and expansion of the fundamental processes of the vapor,liquid,solid (VLS) growth mechanism for nanowires is presented. Although the focus is on nanowires, most of the concepts may be applicable to whiskers, nanotubes, and other unidirectional growth. Important concepts in the VLS mechanism such as preferred deposition, supersaturation, and nucleation are examined. Nanowire growth is feasible using a wide range of apparatuses, material systems, and growth conditions. For nanowire growth the unidirectional growth rate must be much higher than growth rates of other surfaces and interfaces. It is concluded that a general, system independent mechanism should describe why nanowires grow faster than the surrounding surfaces. This mechanism is based on preferential nucleation at the interface between a mediating material called the collector and a crystalline solid. The growth conditions used mean the probability of nucleation is low on most of the surfaces and interfaces. Nucleation at the collector-crystal interface is however different and of special significance is the edge of the collector-crystal interface where all three phases meet. Differences in nucleation due to different crystallographic interfaces can occur even in two phase systems. We briefly describe how these differences in nucleation may account for nanowire growth without a collector. Identifying the mechanism of nanowire growth by naming the three phases involved began with the naming of the VLS mechanism. Unfortunately this trend does not emphasize the important concepts of the mechanism and is only relevant to one three phase system. We therefore suggest the generally applicable term preferential interface nucleation as a replacement for these different names focusing on a unifying mechanism in nanowire growth. [source]


    The Combination of Colloid-Controlled Heterogeneous Nucleation and Polymer-Controlled Crystallization: Facile Synthesis of Separated, Uniform High-Aspect-Ratio Single-Crystalline BaCrO4 Nanofibers

    ADVANCED MATERIALS, Issue 2 2003
    S.-H. Yu
    Uniform, separated BaCrO4 single-crystalline nanofibers with high aspect ratio (>,5000, see Figure) can be fabricated at room temperature in aqueous solution using a double hydrophilic block copolymer as structure-directing agent and introducing colloidal nucleation agents. Such fibers represent a model case for advanced polymer fillers and the exploration of quasi-1D nanostructures with interesting electrical, optical, or catalytic properties. [source]


    Crystallization effects on autoclave foaming of polycarbonate using supercritical carbon dioxide

    ADVANCES IN POLYMER TECHNOLOGY, Issue 4 2006
    L. Mascia
    Abstract In this study, the conditions leading to the formation of cells and to the onset of crystallization of polycarbonate were examined with the use of supercritical carbon dioxide for the production of foams from preforms. Small plaques cut from extruded sheets were treated with supercritical carbon dioxide in an autoclave at temperatures varying from 60 to 200°C and from 4.5 to 30 MPa pressure. Visual observations and stereoscan electron microscopy examination revealed that penetration of supercritical carbon dioxide takes place via the advancing layer mechanism and that, for the particular grade of polycarbonate used in this study, the nucleation of the cells can take place at temperatures as low as 60°C. It requires, however, long treatment times and high pressures, and the growth of foam cells is severely restricted. Nucleation and growth of cells occurred much more readily at somewhat higher temperatures. With treatments at around 80°C, the onset of crystallization started to impose considerable hindrance to the formation of uniform and evenly distributed cells. This becomes increasingly evident at higher temperatures, between 100 and 180°C, owing to the formation of large spherulitic crystalline domains. A very effective nucleation and growth mechanism for the formation of cells was obtained, on the other hand, with treatments at 200°C due to the absence of crystallization phenomena. The degree of crystallinity increased with increasing treatment temperature, and the resulting morphology gave rise to two broad melting peaks. These are displaced to higher temperatures and become closer, merging into one peak with a low-temperature shoulder. These events were monitored by thermal analysis and wide-angle X-ray diffraction examinations. © 2007 Wiley Periodicals, Inc. Adv Polym Techn 25:225,235, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20075 [source]


    Nucleation and growth of myrmekite during ductile shear deformation in metagranites

    JOURNAL OF METAMORPHIC GEOLOGY, Issue 7 2006
    L. MENEGON
    Abstract Myrmekite is extensively developed along strain gradients of continuous, lower amphibolite facies shear zones in metagranites of the Gran Paradiso unit (Western Alps). To evaluate the role of stress, strain energy and fluid phase in the formation of myrmekite, we studied a sample suite consisting of weakly deformed porphyric granites (WDGs), foliated granites (FGs) representative of intermediate strains, and mylonitic granites (MGs). In the protolith, most K-feldspar is microcline with different sets of perthite lamellae and fractures. In the WDGs, abundant quartz-oligoclase myrmekite developed inside K-feldspar only along preexisting perthite lamellae and fractures oriented at a high angle to the incremental shortening direction. In the WDGs, stress played a direct role in the nucleation of myrmekites along interfaces already characterized by high stored elastic strain because of lattice mismatch between K-feldspar and albite. In the FGs and MGs, K-feldspar was progressively dismembered along the growing network of microshear zones exploiting the fine-grained recrystallized myrmekite and perthite aggregates. This was accompanied by a more pervasive fluid influx into the reaction surfaces, and myrmekite occurs more or less pervasively along all the differently oriented internal perthites and fractures independently of the kinematic framework of the shear zone. In the MGs, myrmekite forms complete rims along the outer boundary of the small K-feldspar porphyroclasts, which are almost completely free of internal reaction interfaces. Therefore, we infer that the role of fluid in the nucleation of myrmekite became increasingly important as deformation progressed and outweighed that of stress. Mass balance calculations indicate that, in Al,Si-conservative conditions, myrmekite growth was associated with a volume loss of 8.5%. This resulted in microporosity within myrmekite that enhanced the diffusion of chemical components to the reaction sites and hence the further development of myrmekite. [source]


    Fabrication of Fine Mullite Powders by Heterogeneous Nucleation and Growth Processing

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2004
    YueFeng Tang
    Heterogeneous nucleation and growth was used to prepare composite particles with homogeneous component distribution. Composite particles consisting of ,-Al2O3 cores with an outer amorphous homogeneous silica layer were prepared by heterogeneous nucleation and growth processing using an ethanol suspension containing ammonia, tetraethylorthosilicate, and ,-Al2O3. Fine mullite powders of average particle size 0.53 ,m were fabricated by calcinating the composite particles at 1500°C for 2 h. [source]


    Nucleation and Crystallization of a Lead Halide Phosphate Glass by Differential Thermal Analysis

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2002
    Hongsheng Zhao
    The nucleation and crystallization mechanisms of a lead halide phosphate glass [40P2O5·30PbBr2·30PbF2 (mol%)] were investigated by differential thermal analysis (DTA) and X-ray diffraction analysis. There were two crystalline phases in the crystallized samples: the major phase was PbP2O4, and the minor phase was PbP2O6. The average activation energy for crystallization, E, for two different particle sizes of this glass was determined to be 119 ± 4 kJ/mol by the Kissinger method and 124 ± 4 kJ/mol by the Augis,Bennett method. The Avrami constants were determined to be 1.6 and 2.5 for particle sizes of 203 and 1040 ,m, respectively, by the Ozawa equation, and 1.7 and 2.4 for particle sizes of 203 and 1040 ,m, respectively, by the Augis,Bennett equation. The decrease in the crystallization peak height in the DTA curve with increasing particle size suggested that the particles crystallize primarily by surface crystallization. A nucleation-rate type curve was determined by plotting either the reciprocal of the temperature corresponding to the crystallization peak maximum, 1/Tp, or the height of the crystallization peak, (,T)p, as a function of nucleation temperature, Tn. The temperature where nucleation can occur for this glass ranges from 360°,450°C and the maximum nucleation rate is at 420°± 10°C. [source]


    High-Temperature Oxidation Behavior of High-Purity ,-, ,-, and Mixed Silicon Nitride Ceramics

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2002
    M. Backhaus-Ricoult
    High-temperature oxidation behavior, microstructural evolution, and oxidation kinetics of additive-free ,-, ,-, and mixed silicon nitride ceramics is investigated. The oxidation rate of the ceramics depends on the allotropic ratio; best oxidation resistance is achieved for ceramics rich in ,-phase. Variations in the oxidation kinetics are directly related to average grain size and glass distribution in the oxidation scale. The oxygen contents incorporated into the Si3N4 phase before its dissolution at the oxidation front affects the local glass composition and thereby yields nucleation and growth rates of SiO2 crystallites within the glass phase and a final oxidation scale microstructure, which depend on the incorporated oxygen contents. For the ,-polymorph, the dynamic oxygen solubility is found to remain negligible; therefore, a nitrogen-rich glass forms at the oxidation front, which promotes devitrification and yields a scale with small grain size and thin intergranular glass films. ,-Si3N4 is observed to form oxygen-rich solid solutions on oxidation, which are in contact with silicon oxynitride or oxygen-rich glass. Nucleation of cristobalite in the latter is sluggish, yielding coarse-grained oxidation scales with thick intergranular glass film. [source]


    Formation Mechanism of Hydrous Zirconia Particles Produced by the Hydrolysis of ZrOCl2 Solutions: III, Kinetics Study for the Nucleation and Crystal-Growth Processes of Primary Particles

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2001
    Koji Matsui
    The formation rate and primary particle size of monoclinic, hydrous zirconia particles produced by the hydrolysis of various ZrOCl2 solutions (with and without the addition of HCl, NH4OH, NaCl, CaCl2, or AlCl3) were measured to clarify the effects of the H+ and Cl, ion concentrations on the nucleation and crystal-growth processes of primary particles of hydrous zirconia. Chemical-kinetic analyses, to which Avrami,Erofeev's equation was applied, and XRD measurements revealed that both the rate constant and the primary particle size of the hydrous zirconia decreased as the concentrations of H+ and/or Cl, ions produced by hydrolysis increased. The nucleation rate per unit of ZrOCl2 concentration and the crystal-growth rate of the primary particles of the hydrous zirconia were determined by analyzing the relationships between the rate constant and primary particle size. The nucleation rate per unit of ZrOCl2 concentration revealed almost no change and remained constant as the H+ and/or Cl, ion concentrations increased, except in the case of a slight increase for ZrOCl2 solutions with added HCl. The crystal-growth rate decreased as the H+ and/or Cl, ion concentration increased. The present kinetic analyses revealed that the decrease in rate constant with increasing H+ and/or Cl, ion concentrations resulted from the decrease in the crystal-growth rate. The decreasing tendency of the crystal-growth rate was attributed to interference with crystal growth by the Cl, ions attracted onto the particle surface through the formation of an electric double layer. The formation mechanisms for the primary particles of hydrous zirconia were determined based on the present experimental results. [source]


    Nucleation of Hydroxyapatite Crystal through Chemical Interaction with Collagen

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2000
    Sang-Hoon Rhee
    The nucleation of hydroxyapatite (HAp) crystal through chemical interaction with collagen was investigated. A collagen membrane was soaked in a supersaturated simulated body fluid (1.5 SBF) solution with ion concentrations at 1.5 times that of normal simulated body fluid (1.0 SBF). A few carbonate-containing HAp crystals were formed mostly on the edge-side of the collagen membrane after 4 weeks. In the Fourier-transform infrared spectometry (FTIR) results, the carboxylate band of the collagen membrane showed red chemical shifts after the formation of HAp crystals, which coincided well with the decrease of the calculated bond orders of the carboxylate group when chelated with a calcium ion, which emulated the first-step nucleation of HAp crystal on the carboxylate group of collagen. The result implies that the binding of a calcium ion to the carboxylate group of collagen is one of the key factors for the nucleation of HAp crystals in a 1.5 SBF solution. [source]


    Nucleation and facilitation in salt pans in Mediterranean salt marshes

    JOURNAL OF VEGETATION SCIENCE, Issue 6 2001
    A.E. Rubio-Casal
    Tutin et al. (1992) Abstract. Arthrocnemum macrostachyum is a perennial species acting as a primary colonizer of salt pans in Mediterranean high salt marshes. Salicornia ramosissima, an annual, occurs in salt pans under Arthrocnemum canopies and in open areas. The aim of this study was to analyse, in wild populations and a transplant experiment, how S. ramosissima population dynamics and growth are affected by A. macrostachyum. The environmental conditions within the patches of Arthrocnemum were less stressful than in the open areas, with lower radiation levels and salinity concentrations. In the inner areas of A. macrostachyum patches, density-dependent mortality processes of S. ramosissima seedlings led to low densities of adult individuals with greater morphological development and reproductive success than in open areas. However, at the edges of Arthrocnemum patches facilitation of seedling survival favoured high densities. Environmental stress hindered development, decreased reproduction and premature death. These results are in agreement with the general theory of factors controlling vegetation distribution that biotic interactions dominate in low stress environments, while abiotic interactions dominate under harsher environmental conditions. A. macrostachyum plays an essential role in the succession in these salt pans, facilitating seed production and stimulating nucleation processes in S. ramosissima. [source]


    Diffusion-Controlled Particle Growth and its Effects on Nucleation in Stirred Emulsion Polymerisation Reactors

    MACROMOLECULAR RAPID COMMUNICATIONS, Issue 8 2004
    Shahriar Sajjadi
    Abstract Summary: Particle formation and growth in the batch emulsion homo-polymerisation of styrene and methyl methacrylate monomers under diffusion-controlled conditions were studied. The polymerisations started with two stratified layers of a monomer and water containing an initiator and a surfactant, with the water layer being gently stirred. Because of limitations in monomer transport, the rate of particle growth was substantially reduced and as a result a large number of polymer particles formed. Schematic presentation of the highly diffusion-controlled polymerisation. [source]


    Effect of UV irradiation on type I collagen fibril formation in neutral collagen solutions

    PHOTODERMATOLOGY, PHOTOIMMUNOLOGY & PHOTOMEDICINE, Issue 3 2001
    Julian M. Menter
    Background: Collagens have the well-known ability to spontaneously self-associate to form fibrils at physiological temperature and neutral pH in vitro and in vivo. Because solar UV may photochemically alter collagen, the kinetics of fibril formation may be modified. Thus, we have begun a systematic study of the effect of various UV wavebands on fibril formation. Methods: Citrate-soluble calf skin collagen (Elastin Products) was dissolved at 0.05% in 0.5 M HOAc, dialyzed over 2 days into two changes of 0.0327 M phosphate buffer, pH 7.0 at 4 °C, and centrifuged at 48 000×g. Photolysis was carried out at 4 °C with either (a) UVC (UVG,11 lamp), (b) filtered solar-simulating radiation (SSR) or UVA (SSR or UVL,21 lamp filtered with a 2.0 mm Schott WG 345 filter). Gelation was commenced by rapidly raising the temperature from 8 °C to 33 °C. Nucleation and growth were followed by turbidimetric measurements at 400 nm. Results: UVC radiation (0,17.3 J/cm2) resulted in a dose-dependent decrease in the rate of fibril growth. Under these conditions, concomitant collagen cross-linking and degradation occurred. Fibril nucleation, a prerequisite for growth, was rapid (threshold , 2 min) and was not affected by UVC, UVA or SSR. SSR (0,1320 J/cm2) caused a small decrease in growth rate and in the degree of fibril formation. UVA radiation (0,1080 J/cm2) had a similar effect. "Direct" photochemical damage thus paralleled absorption via various collagen chromophores, with UVC>SSR,UVA. The presence of riboflavin (RF) resulted in ground-state interactions that markedly altered both nucleation and growth kinetics. Irradiation with 29.6 J/cm2 UVA in the presence of RF photosensitizer caused relatively minor additional changes in fibrillation kinetics. Conclusions: These results collectively indicate that fibril formation is markedly dependent on specific ground state interactions and relatively insensitive to nonspecific UV damage. On the other hand, fibrils thus formed from photochemically altered collagen may have altered structural properties that could have subtle but unfavorable effects on the local dermal milieu in vivo. Notwithstanding, the relative insensitivity of fibrillogenesis to non-specific photochemical damage probably represents a favorable adaptation, overall, which tends to conserve the mechanical integrity of the skin. [source]


    Nucleation, growth, and phase transformation mechanism of Ge2Sb2Te5 thin films

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 11 2009
    Eun Tae Kim
    Abstract The nucleation, growth, and metastable-to-stable phase transformation behavior of Ge2Sb2Te5 thin film were studied by means of transmission electron microscopy. The results confirm that nucleation begins at the surface of the film and proceeds by growth of grains through the thickness of film. Also, the result provides further grounds to the suggestion that some of the Ge2Sb2Te5 grains grow with an elongated grain shape to reduce interface energy between crystalline and amorphous phases at the initial stage of crystallization. We find edge dislocations in the metastable-to-stable phase transition region. We think these edge dislocations can explain the metastable-to-stable phase transformation mechanism as a result of vacancy diffusion. [source]


    Transparent diamond-on-glass micro-electrode arrays for ex-vivo neuronal study

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 9 2008
    M. Bonnauron
    Abstract We report on the fabrication of high aspect ratio diamond Micro Electrode Arrays (MEAs) grown on silicon as well as on glass substrates using an optimised nanoseeding technique and Bias Enhanced Nucleation (BEN). Such MEA systems combine high electrode reactivity and high electrical current injection limits with resiliency, biocompatibility and optical transparency of diamond surfaces. We present the technological steps for the fabrication of 2D as well as 3D diamond microelectrode arrays. The patterning issues involve the use of detonation nanodiamond particles (DND). (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Vapor-induced crystallization behavior of bisphenol-A polycarbonate

    POLYMER ENGINEERING & SCIENCE, Issue 6 2006
    Zhongyong Fan
    The effects of exposure time and vapor pressure on the crystallization behaviors of bisphenol-A polycarbonate (BAPC) films were investigated at 25°C by using differential scanning calorimetry (DSC). Double melting peaks were observed for various BAPC samples after vapor-induced crystallization. The low temperature melting peak shifted to higher temperature and became sharper with increasing exposure time, and could be assigned to defective crystals with smaller crystal size. Crystallinity and average crystal dimension normal to (020) were calculated from wide-angle X-ray diffraction spectra. A good agreement was obtained between crystallinity values obtained from WAXD and those from DSC. The morphology of crystallized samples after various exposure time periods was examined by means of polarized optical microscopy. Nucleation occurred at the initial stage of vapor-induced crystallization. Poor crystals become perfect through segment reorganization with increasing exposure time, and spherulites' growth was observed. The average diameter of spherulites increased from 2 ,m for 1 h, to 7 and 16 ,m after 3 and 56 h, respectively. POLYM. ENG. SCI., 46:729,734, 2006. © 2006 Society of Plastics Engineers [source]


    Effects of SBS on phase morphology of iPP/aPS blends

    POLYMER ENGINEERING & SCIENCE, Issue 10 2000

    The supermolecular structure of binary isotactic polypropylene/poly(styrene- b -butadiene- h -styrene) (iPP/SBS) and isotactic polypropylene/atactic polystyrene (iPP/aPS) compression molded blends and that of ternary iPP/aPS/SBS blends were studied by optical microscopy, scanning and transmission electron microscopy, wide-angle X-ray diffraction and differential scanning calorimetry. Nucleation, crystal growth, solidification and blend phase morphology are affected by the addition of amorphous components (SBS and aPS). As a compatiblizer in immiscible iPP/aPS blends, SBS formed interfacial layer between dispersed honeycomb-like aPS/SBS particles and the iPP matrix, thus influencing the crystallization process in iPP. The amount of SBS and aPS, and compatibilizing efficiency of SBS, determine the size of dispersed aPS, SBS, and aPS/SBS particles and, consequently, the final blend phase morphologies: well-developed spherulitic morphology, cross-hatched structure with blocks of sandwich lamellae and co-continuous morphology. The analysis of the relationship between the size of spherulites and dispersed particles gave the criterion relation, which showed that, in the case of a well-developed spherulitization, the spherulites should be about fourteen times larger than the incorporated dispersed particles; i.e. to be large enough to engulf dispersed inclusions without considerable disturbing of the spherulitic structure. [source]


    On the mechanism of some first-order enantiotropic solid-state phase transitions: from Simon through Ubbelohde to Mnyukh

    ACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2006
    Frank H. Herbstein
    The first (so-called) lambda transition in solids was found in the specific heat measurements for NH4Cl at 242,K by F. Simon in 1922 [Simon (1922). Ann. Phys.68, 241,280]. Analogous phenomena found in many other solids gave rise to doubts (expressed most clearly by A. R. Ubbelohde some 50 years ago) about the applicability of classical thermodynamics to some phase transitions [Ubbelohde (1956). Brit. J. Appl. Phys.7, 313,321]. However, Y. Mnyukh's studies of enantiotropic phase transitions in eight organic crystals showed that all proceed by a nucleation-and-growth mechanism [summarized in Mnyukh (2001), Fundamentals of Solid State Phase Transitions, Ferromagnetism and Ferroelectricity. 1st Books]. Nucleation is localized at defects in the parent phase; growth can be epitaxic and oriented if parent and daughter phases have closely similar structures, or random (not oriented) if there are substantial structural differences. This conclusion is supported by a critical review of Mnyukh's eight examples and other results published in the interim. It seems that Ubbelohde's invocation of `hybrid crystals' and `smeared transitions' can mostly be accounted for by lack of equilibrium in the phase-transition studies cited by him. However, the intermediate phase in 4,4,-dichlorobenzophenone appears to have structural resemblances to Ubbelohde's' `hybrid crystal'. [source]


    Template-Directed Nucleation and Growth of Inorganic Nanoparticles on DNA Scaffolds,

    ANGEWANDTE CHEMIE, Issue 45 2009
    Linda
    DNA-Origami: Eine DNA-Nanoröhre mit goldbindenden Peptiden kann zu Nanopartikeln bestimmter Größe aus löslichen chemischen Vorstufen führen. Die Peptid-DNA-Nanostruktur diente zum Aufbau einer anorganischen Nanostruktur, in der die Goldnanopartikel entlang der Oberfläche der DNA-Nanoröhre angeordnet sind (siehe Bild). Dies ist ein wichtiger Schritt hin zur Synthese programmierbarer anorganischer Materialien durch Selbstorganisation. [source]


    Heterogeneous nucleation of three-dimensional protein nanocrystals

    ACTA CRYSTALLOGRAPHICA SECTION D, Issue 5 2007
    Dilyana G. Georgieva
    Nucleation is the rate-limiting step in protein crystallization. Introducing heterogeneous substrates may in some cases lower the energy barrier for nucleation and thereby facilitate crystal growth. To date, the mechanism of heterogeneous protein nucleation remains poorly understood. In this study, the nucleating properties of fragments of human hair in crystallization experiments have been investigated. The four proteins that were tested, lysozyme, glucose isomerase, a polysaccharide-specific Fab fragment and potato serine protease inhibitor, nucleated preferentially on the hair surface. Macrocrystals and showers of tiny crystals of a few hundred nanometres thickness were obtained also under conditions that did not produce crystals in the absence of the nucleating agent. Cryo-electron diffraction showed that the nanocrystals diffracted to at least 4,Å resolution. The mechanism of heterogeneous nucleation was studied using confocal fluorescent microscopy which demonstrated that the protein is concentrated on the nucleating surface. A substantial accumulation of protein was observed on the sharp edges of the hair's cuticles, explaining the strong nucleating activity of the surface. [source]


    High Pressure Response of Rutile Polymorphs and Its Significance for Indicating the Subduction Depth of Continental Crust

    ACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 2 2008
    MENG Dawei
    Abstract: ,-PbO2 -type TiO2 (TiO2 -II) is an important index mineral for ultrahigh-pressure metamorphism. After the discovery of a natural high-pressure phase of titanium oxide with ,-PbO2 -structure in omphacite from coesite-bearing eclogite at Shima in the Dabie Mountains, China, a nano-scale (<2 nm) ,-PbO2 -type TiO2 has been identified through electron diffraction and high-resolution transmission electron microscopy in coesite-bearing jadeite quartzite at Shuanghe in the Dabie Mountains. The crystal structure is orthorhombic with lattice parameters a = 4.58times10,1 nm, b = 5.42times10,1 nm, c = 4.96times10,1 nm and space group Pbcn. The analysis results reveal that rutile {011}R twin interface is a basic structural unit of ,-PbO2 -type TiO2. Nucleation of ,-PbO2 -type TiO2 lamellae is caused by the displacement of one half of the titanium cations within the {011}R twin slab. This displacement reduces the Ti-O-Ti distance and is favored by high pressure. The identification of ,-PbO2 -type TiO2 in coesite-bearing jadeite quartzite from Shuanghe, Dabie Mountains, provides a new and powerful evidence of ultrahigh-pressure metamorphism at 4,7 GPa, 850°C-900°C, and implies a burial of continental crustal rocks to 130,200 kilometers depth or deeper. The ,-PbO2 -type TiO2 may be a useful indicator of the pressure and temperature in the diamond stability field. [source]


    Study of the Kinetics and Morphology of Gas Hydrate Formation

    CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 8 2006

    Abstract The kinetics and morphology of ethane hydrate formation were studied in a batch type reactor at a temperature of ca. 270,280,K, over a pressure range of 8.83,16.67,bar. The results of the experiments revealed that the formation kinetics were dependant on pressure, temperature, degree of supercooling, and stirring rate. Regardless of the saturation state, the primary nucleation always took place in the bulk of the water and the phase transition was always initiated at the surface of the vortex (gas-water interface). The rate of hydrate formation was observed to increase with an increase in pressure. The effect of stirring rate on nucleation and growth was emphasized in great detail. The experiments were performed at various stirring rates of 110,190,rpm. Higher rates of formation of gas hydrate were recorded at faster stirring rates. The appearance of nuclei and their subsequent growth at the interface, for different stirring rates, was explained by the proposed conceptual model of mass transfer resistances. The patterns of gas consumption rates, with changing rpm, have been visualized as due to a critical level of gas molecules in the immediate vicinity of the growing hydrate particle. Nucleation and decomposition gave a cyclic hysteresis-like phenomena. It was also observed that a change in pressure had a much greater effect on the rate of decomposition than it did on the formation rate. Morphological studies revealed that the ethane hydrate resembles thread or is cotton-like in appearance. The rate of gas consumption during nucleation, with different rpm and pressures, and the percentage decomposition at different pressures, were explained precisely for ethane hydrate. [source]


    Nucleation and Growth of Boron Nanowires on ZrB2 Particles,

    CHEMICAL VAPOR DEPOSITION, Issue 7 2006
    L. Guo
    Abstract Amorphous boron rich nanowires are grown on ZrB2 particles using diborane as the gas precursor in a CVD process under 20,Torr pressure and at 900,°C. These nanowires have uniform diameters of tens of nanometers and lengths of up to several micrometers. The boron-rich nanowires are characterized and found to be composed of boron clusters containing unit cells of icosahedral B12. A surface nucleation and growth mechanism of solid boron from vapor phase is proposed to explain the nanowire growth. The role of ZrB2 particles in the synthesis of the boron-rich nanostructures is also discussed. [source]