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Showing papers on "Crystallization published in 2010"


Journal ArticleDOI
TL;DR: In this article, the nonisothermal melt crystallization kinetics of poly(e-caprolactone) (PCL)/layered double hydroxide (LDH) nanocomposites were investigated with the Ozawa, Avrami, and combined Avramian-Ozawa methods.
Abstract: Poly(e-caprolactone) (PCL)/layered double hydroxide (LDH) nanocomposites were prepared success- fully via simple solution intercalation. The nonisothermal melt crystallization kinetics of neat PCL and its LDH nano- composites was investigated with the Ozawa, Avrami, and combined Avrami-Ozawa methods. The Ozawa method failed to describe the crystallization kinetics of the studied systems. The Avrami method was found to be useful for describing the nonisothermal crystallization behavior, but the parameters in this method do not have explicit meaning for nonisothermal crystallization. The combined Avrami- Ozawa method explained the nonisothermal crystallization behavior of PCL and its LDH nanocomposites effectively. The kinetic results and polarized optical microscopy obser- vations indicated that the addition of LDH could affect the mechanism of nucleation and growth of the PCL matrix. The Takhor model was used to analyze the activation ener- gies of nonisothermal crystallization. V C 2010 Wiley Periodicals,

682 citations


Journal ArticleDOI
TL;DR: The DSC screening method and classification scheme may be a useful tool to quickly assess the glass forming ability (GFA) and potential GS of new chemical entities during early drug development.

545 citations


Journal ArticleDOI
TL;DR: The elastic modulus of the nanocomposite mats increased significantly as a consequence of the reinforcing effect of CNs via the percolation network held by hydrogen bonds, but this organization-driven crystallization was limited as observed by the reduction in the degree of crystallinity of the CN-loaded composite fibers.

490 citations


Journal ArticleDOI
TL;DR: In this paper, the effects of surface silylation of cellulose nanocrystals on morphology, non-isothermal and isothermal crystallization behavior, and mechanical properties of these truly nanostructured composites were investigated.

474 citations


Journal ArticleDOI
TL;DR: In this article, high-ordered TiO2 nanotube arrays (TNs) are prepared by electrochemical anodization of titanium foil in a mixed electrolyte solution of glycerol and NH4F and then calcined at various temperatures.
Abstract: Highly ordered TiO2 nanotube arrays (TNs) are prepared by electrochemical anodization of titanium foil in a mixed electrolyte solution of glycerol and NH4F and then calcined at various temperatures The prepared samples are characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy The photocatalytic activity is evaluated by photocatalytic degradation of methyl orange (MO) aqueous solution under UV light irradiation The production of hydroxyl radicals ( OH) on the surface of UV-irradiated samples is detected by a photoluminescence (PL) technique using terephthalic acid (TA) as a probe molecule The transient photocurrent response is measured by several on–off cycles of intermittent irradiation The results show that low temperatures (below 600 °C) have no great influence on surface morphology and architecture of the TNs sample and the prepared TNs can be stable up to ca 600 °C At 800 °C, the nanotube arrays are completely destroyed and only dense rutile crystallites are observed The photocatalytic activity, formation rate of hydroxyl radicals and photocurrent of the TNs increases with increasing temperatures (from 300 to 600 °C) due to the enhancement of crystallization Especially, at 600 °C, the sample shows the highest photocatalytic activity due to its bi-phase composition, good crystallization and remaining tubular structures With further increase in the calcination temperature from 600 to 800 °C, the photocatalytic activity rapidly decreases due to the vanishing of anatase phase, collapse of nanotube structures and decrease of surface areas

399 citations


Journal ArticleDOI
TL;DR: The transformation sequence observed in biomineralization could be mainly energetically driven; the first phase deposited is hydrated ACC, which then converts to anhydrous ACC, and finally crystallizes to calcite.
Abstract: Amorphous calcium carbonate (ACC) is a metastable phase often observed during low temperature inorganic synthesis and biomineralization. ACC transforms with aging or heating into a less hydrated form, and with time crystallizes to calcite or aragonite. The energetics of transformation and crystallization of synthetic and biogenic (extracted from California purple sea urchin larval spicules, Strongylocentrotus purpuratus) ACC were studied using isothermal acid solution calorimetry and differential scanning calorimetry. Transformation and crystallization of ACC can follow an energetically downhill sequence: more metastable hydrated ACC → less metastable hydrated ACC⇒anhydrous ACC ∼ biogenic anhydrous ACC⇒vaterite → aragonite → calcite. In a given reaction sequence, not all these phases need to occur. The transformations involve a series of ordering, dehydration, and crystallization processes, each lowering the enthalpy (and free energy) of the system, with crystallization of the dehydrated amorphous material lowering the enthalpy the most. ACC is much more metastable with respect to calcite than the crystalline polymorphs vaterite or aragonite. The anhydrous ACC is less metastable than the hydrated, implying that the structural reorganization during dehydration is exothermic and irreversible. Dehydrated synthetic and anhydrous biogenic ACC are similar in enthalpy. The transformation sequence observed in biomineralization could be mainly energetically driven; the first phase deposited is hydrated ACC, which then converts to anhydrous ACC, and finally crystallizes to calcite. The initial formation of ACC may be a first step in the precipitation of calcite under a wide variety of conditions, including geological CO2 sequestration.

388 citations


Journal ArticleDOI
TL;DR: The "blob mechanism" unveiled in this work synthesizes elements of the labile cluster and local structuring hypotheses of clathrate nucleation and bears strong analogies to the two-step mechanisms of crystallization of proteins and colloids.
Abstract: The nucleation and growth of clathrate hydrates of a hydrophobic guest comparable to methane or carbon dioxide are studied by molecular dynamics simulations of two-phase systems. The crystallization proceeds in two steps: First, the guest molecules concentrate in "blobs", amorphous clusters involving multiple guest molecules in water-mediated configurations. These blobs are in dynamic equilibrium with the dilute solution and give birth to the clathrate cages that eventually transform it into an amorphous clathrate nucleus. In a second step, the amorphous clathrate transforms into crystalline clathrate. At low temperatures, the system can be arrested in the metastable amorphous clathrate phase for times sufficiently long for it to appear as an intermediate in the crystallization of clathrates. The "blob mechanism" unveiled in this work synthesizes elements of the labile cluster and local structuring hypotheses of clathrate nucleation and bears strong analogies to the two-step mechanisms of crystallization of proteins and colloids.

377 citations


Journal ArticleDOI
TL;DR: It is found that nucleation preferentially takes place in regions of high structural order via wetting effects, which reduce the crystal–liquid interfacial energy significantly and thus promotes crystal nucleation.
Abstract: Crystallization is one of the most fundamental nonequilibrium phenomena universal to a variety of materials. It has so far been assumed that a supercooled liquid is in a “homogeneous disordered state” before crystallization. Contrary to this common belief, we reveal that a supercooled colloidal liquid is actually not homogeneous, but has transient medium-range structural order. We find that nucleation preferentially takes place in regions of high structural order via wetting effects, which reduce the crystal–liquid interfacial energy significantly and thus promotes crystal nucleation. This novel scenario provides a clue to solving a long-standing mystery concerning a large discrepancy between the rigorous numerical estimation of the nucleation rate on the basis of the classical nucleation theory and the experimentally observed ones. Our finding may shed light not only on the mechanism of crystal nucleation, but also on the fundamental nature of a supercooled liquid state.

337 citations


Journal ArticleDOI
08 Jul 2010-Polymer
TL;DR: In this paper, layer-aligned poly(vinyl alcohol)/graphene nanocomposites in the form of films are prepared by reducing graphite oxide in the polymer matrix in a simple solution processing.

336 citations


Journal ArticleDOI
TL;DR: A rigorous thermodynamic approach is developed to estimate enhancement in solubility that can be achieved by conversion of a crystalline form to the amorphous form and the theoretically estimatedsolubility enhancement ratio of 7.0 for indomethacin was found to be in close agreement with the experimentally determined ratio.

331 citations


Journal ArticleDOI
TL;DR: In this paper, the effects of differently dimensional nanoparticles on the crystallization behavior of poly(l-lactide) matrices were investigated using time-resolved Fourier transform infrared spectroscopy (FTIR) and wide-angle X-ray diffraction (WAXD).
Abstract: Low-dimensional nanoparticles have a strong ability to induce the crystallization of polymer matrices. One-dimensional carbon nanotubes (CNTs) and two-dimensional graphene nanosheets (GNSs), both of which are both carbon-based nanoparticles, provide a good opportunity to investigate the effects of differently dimensional nanoparticles on the crystallization behavior of a polymer. For this purpose, respective nanocomposites of CNTs and GNSs with poly(l-lactide) (PLLA) as matrix were prepared by solution coagulation. Time-resolved Fourier-transform infrared spectroscopy (FTIR) and synchrotron wide-angle X-ray diffraction (WAXD) were performed to probe chain conformational changes and to determine the crystallization kinetics during the isothermal crystallization of the PLLA nanocomposites and neat PLLA, especially in the early stages. Both CNTs and GNSs could serve as nucleating agents in accelerating the crystallization kinetics of PLLA; however, the ability of CNTs to induce crystallization was stronger t...

Journal ArticleDOI
TL;DR: In this paper, the performance of a membrane distillation-crystallization (MDC) bench-scale plant operated on brines discharged from a seawater reverse osmosis (RO) unit was investigated.

Journal ArticleDOI
TL;DR: It was confirmed that the rate of crystallization decreases in the order US>MW>>CE, and that the accelerated syntheses under US and MW conditions are due to increased pre-exponential factors rather than decreased activation energies.
Abstract: A metal-organic framework material named MIL-53(Fe), iron terephthalate, has been synthesized sovothermally at a relatively low temperature by not only conventional electric (CE) heating, but also by irradiation under ultrasound (US) and microwave (MW) conditions to gain an understanding of the accelerated syntheses induced by US and MW. The kinetics for nucleation and crystal growth were analyzed by measuring the crystallinity of MIL-53(Fe) under various conditions. The nucleation and crystal growth rates were estimated from crystallization curves of the change in crystallinity with reaction time. The activation energies and pre-exponential factors were calculated from Arrhenius plots. It was confirmed that the rate of crystallization (both nucleation and crystal growth) decreases in the order US>MW>>CE, and that the accelerated syntheses under US and MW conditions are due to increased pre-exponential factors rather than decreased activation energies. It is suggested that physical effects such as hot spots are more important than chemical effects in the accelerated syntheses induced by US and MW irradiation. The syntheses were also conducted in two steps to understand quantitatively the acceleration induced by MW and it was found that the acceleration in crystal growth is more important than the acceleration in nucleation, even though both processes are accelerated by MW irradiation.

Journal ArticleDOI
TL;DR: In this paper, high-ordered TiO2 nanotube array (TNs) thin films were prepared by electrochemical anodization of titanium foil in a mixed electrolyte solution containing Na2SO4, H3PO4, NaF, and sodium citrate and then treated by calcination, vapor-thermal, and hydrothermal methods, respectively.
Abstract: Highly ordered TiO2 nanotube array (TNs) thin films were prepared by electrochemical anodization of titanium foil in a mixed electrolyte solution containing Na2SO4, H3PO4, NaF, and sodium citrate and then treated by calcination, vapor-thermal, and hydrothermal methods, respectively. The as-prepared samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The photocatalytic activity of the film samples was evaluated by photocatalytic degradation of methyl orange (MO) aqueous solution under UV light irradiation. The production of hydroxyl radicals (•OH) on the surface of UV-irradiated samples was detected by a photoluminescence technique using terephthalic acid as a probe molecule. The transient photocurrent response was measured by several on−off cycles of intermittent irradiation. It was found that post-treatment exhibited a great influence on the morphology, crystallization, and photocatalytic activity of TNs th...

Journal ArticleDOI
01 Aug 2010-Geology
TL;DR: In this paper, the authors explored potential mechanisms to generate compositional gaps using numerical simulations coupling crystallization kinetics and multiphase fluid dynamics of magma reservoirs, and showed that gaps are inherent to crystal fractionation for all compositions, as crystal-liquid separation takes place most efficiently within a crystallinity window of ∼50-70 vol% crystals.
Abstract: Compositional gaps are common in volcanic series worldwide. The pervasive generation of compositional gaps influences the mechanical and thermal properties of the crust, and holds clues on how our planet differentiates. We have explored potential mechanisms to generate these gaps using numerical simulations coupling crystallization kinetics and multiphase fluid dynamics of magma reservoirs. We show that gaps are inherent to crystal fractionation for all compositions, as crystal-liquid separation takes place most efficiently within a crystallinity window of ∼50–70 vol% crystals. The probability of melt extraction from a crystal residue in a cooling magma chamber is highest in this crystallinity window due to (1) enhanced melt segregation in the absence of chamber-wide convection, (2) buffering by latent heat of crystallization, and (3) diminished chamber-wall thermal gradients. This mechanical control of igneous distillation is likely to have played a dominant role in the formation of the compositionally layered Earth9s crust by allowing multiple and overlapping intrusive episodes of relatively discrete or quantized composition that become more silicic upward.

Journal ArticleDOI
TL;DR: In this article, a static mixer was used to promote homogeneous mixing of active pharmaceutical ingredient solution and antisolvent along the crystallizer to control the size of the crystals, and it was found that smaller crystals with a narrower size distribution can be obtained with the static mixers.
Abstract: Crystallization processes in the pharmaceutical industry are usually designed to obtain crystals with controlled size, shape, purity, and polymorphic form. Knowledge of the process conditions required to fabricate crystals with controlled characteristics is critical during process development. In this work, continuous crystallization of ketoconazole, flufenamic acid, and l-glutamic acid in a nonconventional plug flow crystallizer was investigated. Kenics type static mixers were used to promote homogeneous mixing of active pharmaceutical ingredient solution and antisolvent. A strategy of multiple points of addition of antisolvent along the crystallizer was evaluated to control the size of the crystals. Interestingly, it was found that crystal size can be increased or decreased with an increased number of antisolvent addition points, depending on the kinetics of the system. It was also found that smaller crystals with a narrower size distribution can be obtained with the static mixers. A model to describe t...

Journal ArticleDOI
TL;DR: In this paper, a new apparatus employing a modular, mechanically agitated gas-inducing crystallizer is used to demonstrate the capture of CO2 via hydrate crystallization, which enhances the contact of hydrate forming gases with water.

Journal ArticleDOI
TL;DR: Though the presence of cubic layers is twice as prevalent as hexagonal ones, the crystals should not be considered defective Ic as sequences with more than three adjacent cubic (or hexagonal) layers are extremely rare in the confined ice.
Abstract: The nucleation, growth, structure and melting of ice in 3 nm diameter hydrophilic nanopores are studied through molecular dynamics simulations with the mW water model. The melting temperature of water in the pore was Tporem = 223 K, 51 K lower than the melting point of bulk water in the model and in excellent agreement with experimental determinations for 3 nm silica pores. Liquid and ice coexist in equilibrium at the melting point and down to temperatures as low as 180 K. Liquid water is located at the interface of the pore wall, increasing from one monolayer at the freezing temperature, Tporef = 195 K, to two monolayers a few degrees below Tporem. Crystallization of ice in the pore occurs through homogeneous nucleation. At the freezing temperature, the critical nucleus contains ∼75 to 100 molecules, with a radius of gyration similar to the radius of the pore. The critical nuclei contain features of both cubic and hexagonal ice, although stacking of hexagonal and cubic layers is not defined until the nuclei reach ∼150 molecules. The structure of the confined ice is rich in stacking faults, in agreement with the interpretation of X-ray and neutron diffraction experiments. Though the presence of cubic layers is twice as prevalent as hexagonal ones, the crystals should not be considered defective Ic as sequences with more than three adjacent cubic (or hexagonal) layers are extremely rare in the confined ice.

Journal ArticleDOI
TL;DR: In this article, a new seeding technique (thermal seeding) was developed to strongly anchor HKUST-1 seed crystals on porous α-alumina supports, which was found critical to have both organic ligands and copper species in the seed suspension as well as to seed the crystals at elevated temperature.
Abstract: Here we report the synthesis of continuous HKUST-1 membranes on porous supports via the secondary (i.e., seeded) growth method. A new seeding technique (“thermal seeding”) was developed to strongly anchor HKUST-1 seed crystals on porous α-alumina supports. It was found critical to have both organic ligands and copper species in the seed suspension as well as to seed the crystals at elevated temperature. The HKUST-1 seed crystals on the supports were then hydrothermally grown into continuous HKUST-1 films. The formation of cracks and fractures in the films was prevented by controlling the cooling and the drying processes after crystallization. The permeation results of HKUST-1 membranes show moderate separation of hydrogen over other small gas molecules such as carbon dioxide, nitrogen, oxygen, and methane.

Journal ArticleDOI
11 Mar 2010-Polymer
TL;DR: In this paper, the crystal phase identification for polyvinylidene fluoride (PVDF) nanocomposites is discussed and clarified, based on X-ray scattering, vibrational spectra, and thermal analysis.

Journal ArticleDOI
TL;DR: In this paper, the basic concept of crystallization and some of the advances in polymer crystallization from crystals to nanocrystalline fibers are discussed. But the authors do not discuss how long interpenetrating and entangled polymer chains self-assemble into single crystals from the solution phase or melt.

Journal ArticleDOI
TL;DR: A large scale computer simulation study of crystal nucleation in hard spheres shows that a purely repulsive system (that has no metastable fluid-fluid coexistence) crystallizes via the same mechanism.
Abstract: We report on a large scale computer simulation study of crystal nucleation in hard spheres. Through a combined analysis of real- and reciprocal-space data, a picture of a two-step crystallization process is supported: First, dense, amorphous clusters form which then act as precursors for the nucleation of well-ordered crystallites. This kind of crystallization process has been previously observed in systems that interact via potentials that have an attractive as well as a repulsive part, most prominently in protein solutions. In this context the effect has been attributed to the presence of metastable fluid-fluid demixing. Our simulations, however, show that a purely repulsive system (that has no metastable fluid-fluid coexistence) crystallizes via the same mechanism.

Journal ArticleDOI
15 Oct 2010-Science
TL;DR: AFM observations are mirrored by reduced crystal yield and crystal size in the presence of L-CDME and L-CME, collectively suggesting a new pathway to the prevention of l-cystine stones by rational design of crystal growth inhibitors.
Abstract: Crystallization of L-cystine is a critical step in the pathogenesis of cystine kidney stones. Treatments for this disease are somewhat effective but often lead to adverse side effects. Real-time in situ atomic force microscopy (AFM) reveals that L-cystine dimethylester (L-CDME) and L-cystine methylester (L-CME) dramatically reduce the growth velocity of the six symmetry-equivalent {100} steps because of specific binding at the crystal surface, which frustrates the attachment of L-cystine molecules. L-CDME and L-CME produce l-cystine crystals with different habits that reveal distinct binding modes at the crystal surfaces. The AFM observations are mirrored by reduced crystal yield and crystal size in the presence of L-CDME and L-CME, collectively suggesting a new pathway to the prevention of L-cystine stones by rational design of crystal growth inhibitors.

Journal ArticleDOI
TL;DR: In this article, the influence of nitrogen concentration in metal melts on the growth processes, morphology, and defect-and-impurity structure of diamond crystals was reported, and it was found that, with increasing nitrogen concentration (CN) in the metal melt from 0.005 to 0.6 atom %, the growth of single crystal diamond is followed by formation of aggregates of block twinned crystals and then by crystallization of metastable graphite.
Abstract: In this paper, we report on the influence of nitrogen concentration in metal melts on the growth processes, morphology, and defect-and-impurity structure of diamond crystals. In two series of experiments, the concentration of nitrogen in the growth system was varied by adding Fe3N and CaCN2 to the charge; the other parameters and conditions of the growth were constant: FeNiC system, P = 5.5 GPa, T = 1400 °C, and duration of 65 h. It has been found that, with increasing nitrogen concentration (CN) in the metal melt from 0.005 to 0.6 atom %, the growth of single crystal diamond is followed by formation of aggregates of block twinned crystals and then by crystallization of metastable graphite. At the stage of single crystal growth, an increase in CN results in an increase in nitrogen impurity concentration in diamond crystals from about 200 ppm to approximately 1100 ppm, an increase in density of dislocations, twin lamellae, and internal strains, and a change in crystal morphology. Further increases in CN re...

Journal ArticleDOI
TL;DR: In this paper, nanoparticles were found to be effective nucleaging agents in cases of silica nanoparticles and oxidized multi-walled carbon nanotubes (o-MWCNTs), and the nucleation activity was calculated.

Patent
05 Mar 2010
TL;DR: In this article, the amorphous silicon film is formed using silane gas diluted with hydrogen and crystallization is attained in the crystallization process even with the continuous formation of the base film through the polysilicon film in the single film forming chamber.
Abstract: At present, a forming process of a base film through an amorphous silicon film is conducted in respective film forming chambers in order to obtain satisfactory films. When continuous formation of the base film through the amorphous silicon film is performed in a single film forming chamber with the above film formation condition, crystallization is not sufficiently attained in a crystallization process. By forming the amorphous silicon film using silane gas diluted with hydrogen, crystallization is sufficiently attained in the crystallization process even with the continuous formation of the base film through the amorphous silicon film in the single film forming chamber.


Journal ArticleDOI
TL;DR: It appears that felodipine-PVP solid dispersions are susceptible to moisture-induced immiscibility when stored at a relative humidity >or=75%.

Journal ArticleDOI
TL;DR: In this article, the structural characteristics of the calcined samples were determined by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and transmission electron microscopy (TEM).
Abstract: Crystalline, magnetic, cobalt ferrite nanoparticles were synthesized from an aqueous solution containing metal nitrates and polyvinyl pyrrolidone (PVP) as a capping agent by a thermal treatment followed by calcination at various temperatures from 673 to 923 K. The structural characteristics of the calcined samples were determined by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and transmission electron microscopy (TEM). A completed crystallization occurred at 823 and 923 K, as shown by the absence of organic absorption bands in the FT-IR spectrum. Magnetization measurements were obtained at room temperature by using a vibrating sample magnetometer (VSM), which showed that the calcined samples exhibited typical magnetic behaviors.

Journal ArticleDOI
TL;DR: It has been demonstrated that the theoretical approach does provide an accurate estimate of the maximum solubility enhancement by an amorphous drug relative to its crystalline form for structurally diverse insoluble drugs when recrystallization during dissolution is minimal.
Abstract: To quantitatively assess the solubility advantage of amorphous forms of nine insoluble drugs with a wide range of physico-chemical properties utilizing a previously reported thermodynamic approach. Thermal properties of amorphous and crystalline forms of drugs were measured using modulated differential calorimetry. Equilibrium moisture sorption uptake by amorphous drugs was measured by a gravimetric moisture sorption analyzer, and ionization constants were determined from the pH-solubility profiles. Solubilities of crystalline and amorphous forms of drugs were measured in de-ionized water at 25°C. Polarized microscopy was used to provide qualitative information about the crystallization of amorphous drug in solution during solubility measurement. For three out the nine compounds, the estimated solubility based on thermodynamic considerations was within two-fold of the experimental measurement. For one compound, estimated solubility enhancement was lower than experimental value, likely due to extensive ionization in solution and hence its sensitivity to error in pKa measurement. For the remaining five compounds, estimated solubility was about 4- to 53-fold higher than experimental results. In all cases where the theoretical solubility estimates were significantly higher, it was observed that the amorphous drug crystallized rapidly during the experimental determination of solubility, thus preventing an accurate experimental assessment of solubility advantage. It has been demonstrated that the theoretical approach does provide an accurate estimate of the maximum solubility enhancement by an amorphous drug relative to its crystalline form for structurally diverse insoluble drugs when recrystallization during dissolution is minimal.