Showing papers on "Crystallization published in 2002"
TL;DR: The surfactant-mediated synthesis of an ordered benzene–silica hybrid material has an hexagonal array of mesopores and crystal-like pore walls that exhibit structural periodicity, and it is expected that other organosilicas and organo-metal oxides can be produced in a similar fashion, to yield a range of hierarchically ordered mesoporous solids with molecular-scale pore surface periodicity.
Abstract: Surfactant-mediated synthesis strategies are widely used to fabricate ordered mesoporous solids in the form of metal oxides, metals, carbon and hybrid organosilicas. These materials have amorphous pore walls, which could limit their practical utility. In the case of mesoporous metal oxides, efforts to crystallize the framework structure by thermal and hydrothermal treatments have resulted in crystallization of only a fraction of the pore walls. Here we report the surfactant-mediated synthesis of an ordered benzene-silica hybrid material; this material has an hexagonal array of mesopores with a lattice constant of 52.5 A, and crystal-like pore walls that exhibit structural periodicity with a spacing of 7.6 A along the channel direction. The periodic pore surface structure results from alternating hydrophilic and hydrophobic layers, composed of silica and benzene, respectively. We believe that this material is formed as a result of structure-directing interactions between the benzene-silica precursor molecules, and between the precursor molecules and the surfactants. We expect that other organosilicas and organo-metal oxides can be produced in a similar fashion, to yield a range of hierarchically ordered mesoporous solids with molecular-scale pore surface periodicity.
1,216 citations
TL;DR: In this article, a new indicator of glass-forming ability (GFA) for bulk metallic glasses (BMGs) is proposed based on crystallization processes during cooling and reheating of the supercooled liquid.
1,121 citations
Book•
01 Jan 2002
TL;DR: Solutions and Solution Properties Crystals, Crystal Growth, and Nucleation The Influence of Impurities and Solvents on Crystallization Analysis and Measurement of Crystallisation Utilizing the Population Balance Crystallizer Selection and Design Precipitation Processes Melt and Mixing:Understanding and Modelingcrystallizer mixing andsuspension flow control of crystallization processes Processes Batch and Multi-batchCrystallization:
Abstract: Solutions and Solution Properties Crystals, Crystal Growth, and Nucleation The Influence of Impurities and Solvents on Crystallization Analysis and Measurement of Crystallization Utilizing the Population Balance Crystallizer Selection and Design Precipitation Processes Melt Crystallization Crystallizer Mixing:Understanding and Modelingcrystallizer Mixing and Suspension Flow Control of Crystallization Processes Batch Crystallization Crystallization In The Pharmaceutical and Bioprocessing Industries Crystallization of Proteins Crystallization in Foods Index
889 citations
TL;DR: In this article, a review of the methods of preparation and formation of supermolecular structures in quiescent and sheared melts and the properties of the β-modification of isotactic polypropylene (β-iPP) are reviewed.
Abstract: The methods of preparation and formation of supermolecular structures in quiescent and sheared melts and the properties of the β-modification of isotactic polypropylene (β-iPP) are reviewed. The introduction of selective β-nucleants is the most reliable method for preparation of samples rich in β-modification or of pure β-iPP. The advantages and drawbacks of the known β-nucleating agents are summarized. It is emphasized that pure β-iPP can be prepared under laboratory and processing conditions in the presence of highly active and selective β-nucleants. Nevertheless, there are no literature data—apart from that of the author's groups—which evidenced unambiguously the formation of pure β-iPP. It hints at the insufficient selectivity of β-nucleants used or at the inappropriate crystallization or melting conditions applied by other scientists. The structure formation during the high-temperature hedritic crystallization is discussed comprehensively and illustrated by polarized light microscopy and scanning ele...
671 citations
TL;DR: In this article, the optical properties of polycrystalline inverse opals were modified in predictable manners by numerous methods, including tailoring the pore size, filling the pores with fluids of various refractive indices, and changing the compositions of the solid material.
Abstract: Colloidal crystal-templating methods have been used to prepare inverse opal photonic crystals of silica, mercaptopropyl-functionalized silica, titania, and zirconia. Ordered arrays of uniformly sized polymer spheres were infiltrated with fluid precursors capable of condensation or crystallization. After solidification of the material in the void spaces between the spheres, the polymer templates were removed by calcination or solvent extraction, leaving inverse replicas of the template arrays. By carefully controlling the synthetic procedures, gram-scale quantities of powdered macroporous materials exhibiting photonic crystal properties were obtained. For materials with crystalline walls (titania and zirconia), this required minimization of the size of the nanocrystalline grains. Because the periodicity introduced into the wall structure by the colloidal crystal templates was on the order of optical wavelengths, Bragg diffractions from the planes produced photonic stop bands in the visible spectra of these materials. The stop bands were manifested as brightly colored reflections and an optical filtering behavior of the materials. A crystallographic indexing of the optical spectrum of a polycrystalline inverse opal confirmed the fcc ordering of the pores. The optical properties of these materials were modified in predictable manners by numerous methods, including tailoring the pore size, filling the pores with fluids of various refractive indices, and changing the compositions of the solid material. The wavelengths of the colorful reflections (stop bands) were found to be proportional to the pore size and to vary linearly with the refractive index of the fluid filling the pores. The physical and synthetic modifications reported here allowed for the preparation of powders with optical reflections and bright colors spanning the entire visible spectrum.
492 citations
TL;DR: Transparent anatase mesoporous (MTiO2) and TiO2 nanometer thin films were prepared on soda-lime glass and fused quartz via the reverse micellar method and sol-gel method, respectively as mentioned in this paper.
Abstract: Transparent anatase mesoporous TiO2 (MTiO2) and TiO2 nanometer thin films were prepared on soda-lime glass and fused quartz via the reverse micellar method and sol–gel method, respectively. The as-prepared MTiO2 and TiO2 films were then treated by dipping them in a H2SO4 solution. The MTiO2 and TiO2 films before and after surface acid treatment were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray diffraction (XRD), BET surface area and UV–VIS spectrophotometry. The photocatalytic activity of the samples was evaluated by photocatalytic oxidation of acetone in air. It was found that MTiO2 thin films showed higher photocatalytic activity than that of the TiO2 thin films. This was attributed to the fact that MTiO2 thin films were composed of smaller monodisperse spherical particles about 15 nm and had higher specific surface areas. Furthermore, the monodispersity of TiO2 particles was beneficial to transfer and separation of photo-generated electrons and holes in the inner of and on the surface of TiO2 particle and reduced the recombination of photo-generated electrons and holes. The films deposited on quartz showed the highest photocatalytic activity because films deposited on quartz exhibited a better crystallization and had no sodium contaminant. The photocatalytic activity of MTiO2 and TiO2 thin films deposited on different substrates after treated with H2SO4 solution was significantly enhanced. Acid treatment was particularly effective for MTiO2/glass and TiO2/glass, which showed activity enhancement of four and over two times, respectively. This increase in activity has been correlated with the reduction of sodium ions and the increase in the adsorbed hydroxyl content on the surface of TiO2 films.
471 citations
TL;DR: In this article, the thermodynamics of real solutions for sodium sulfate and sodium chloride have been investigated and it was shown that dissolution of its anhydrate produces supersaturations with respect to its decahydrate capable of generating tensile hoop stresses on the order of 10-20 MPa, largely in excess of the tensile strength of almost all stones.
465 citations
TL;DR: In this paper, a melt extrusion process using maleic anhydride modified polypropylene (PP)/clay (PPCN) and organophilic clay has been used to create intercalated nanocomposites of polyethylene (PP/clay) composites.
Abstract: Intercalated nanocomposites of polypropylene (PP)/clay (PPCNs) were prepared by a melt extrusion process using maleic anhydride modified PP (PP-MA) and organophilic clay The extent of intercalation of PP-MA chains in the space between silicate galleries increased with crystallization temperature Tc and decreased as clay content increased As compared to matrix PP-MA, the dispersed clay particles in the PP-MA matrix acted as a nucleating agent and lowered the spherulite dimension with increasing clay content as revealed by light scattering experiments and polarizing optical microscopy The PPCN crystallized at high Tc showed that a certain extent of segregation of the dispersed clay particles takes place around the boundary of the spherulites (interspherulite) Extensive intercalation occurred during crystallization, especially at high Tc due to the long time for full solidification of the melt The degree of intercalation of PP-MA chains in the silicate galleries strongly depends on the time in the molte
432 citations
TL;DR: The results have shown that a material biodegradation was rapid in the beta-TCP and the CPC, but very weak in the HA, while the bone cement is degraded through a dissolution process associated with a cellular process.
Abstract: This study was undertaken to understand the biodegradation mechanisms of calcium phosphate (Ca-P) biomaterials with different crystallization. Two types of sintered Ca-P porous ceramic (HA and beta-TCP) and a Ca-P bone cement (CPC) were implanted into cavities drilled in rabbit femoral and tibiae condyles. The results have shown that a material biodegradation was rapid in the beta-TCP and the CPC, but very weak in the HA. This biodegradation presented a decrease of material volume from the periphery to the center as well as a particle formation causing phagocytosis by numerous macrophages and multinucleated giant cells in the CPC. In the beta-TCP, there was a peripheral and central decrease of material volume as well as an absence of particle formation or visible phagocytosis. The process of biodegradation is considered to be directly influenced by the type of material crystallization. The sintered bioceramics processed at a high temperature exhibit good crystallization and are primarily degraded by a process dependent on interstitial liquids. However, the bone cement is formed by physicochemical crystallization and is degraded through a dissolution process associated with a cellular process.
426 citations
TL;DR: The authors examined the melt and solid-state structures of a series of diblock copolymers containing polyethylene as the minority block, with a rubbery hydrocarbon majority block.
Abstract: We examined the melt and solid-state structures of a series of diblock copolymers containing polyethylene as the minority block, with a rubbery hydrocarbon majority block. When the interblock segregation strength during crystallization is sufficiently high (approximately 3 times the segregation strength at the order−disorder transition), crystallization can be effectively confined within spherical domains formed by microphase separation in the melt; the process is homogeneously nucleated, and the resulting kinetics are first-order (Avrami n = 1). Below this critical interblock segregation strength, crystallization disrupts the spherical microdomains, resulting in sigmoidal kinetics (n > 1). Cylinder-forming materials are more complex: there exists a range of intermediate segregation strength where crystallization is templated but not wholly confined within the nanoscale domains prescribed by microphase separation; while the melt morphology is generally retained on cooling, local distortions and connectio...
415 citations
TL;DR: In this article, the mechanism of zeolite crystallization and the role of alkali solution on the synthesis reaction were considered. And the changes in various physical and chemical properties, such as crystal structure, surface structure and cation exchange capacity, of the obtained zeolites and the dissolved amount of Si 4+ and Al 3+ in alkali solutions were investigated during the hydrothermal reaction.
TL;DR: The mechanism of hydrogen-induced crystallization of hydrogenated amorphous silicon films during post-deposition treatment with an H2 (or D2) plasma is reported, which is mediated by the insertion of H atoms into strained Si–Si bonds as the atoms diffuse through the film.
Abstract: Hydrogenated amorphous and nanocrystalline silicon films manufactured by plasma deposition techniques are used widely in electronic and optoelectronic devices1,2. The crystalline fraction and grain size of these films determines electronic and optical properties; the nanocrystal nucleation mechanism, which dictates the final film structure, is governed by the interactions between the hydrogen atoms of the plasma and the solid silicon matrix. Fundamental understanding of these interactions is important for optimizing the film structure and properties. Here we report the mechanism of hydrogen-induced crystallization of hydrogenated amorphous silicon films during post-deposition treatment with an H2 (or D2) plasma. Using molecular-dynamics simulations3,4 and infrared spectroscopy5, we show that crystallization is mediated by the insertion of H atoms into strained Si–Si bonds as the atoms diffuse through the film. This chemically driven mechanism may be operative in other covalently bonded materials, where the presence of hydrogen leads to disorder-to-order transitions.
TL;DR: In this article, the authors studied the temporal evolution of feldspar crystallization kinetics during isothermal decompression and found that slowly decompressed samples were usually further from chemical equilibrium than rapidly decompressed sample after similar durations below the initial pressure.
Abstract: [1] Experiments were conducted to study the temporal evolution of feldspar crystallization kinetics during isothermal decompression. Pinatubo dacite was held at 780°C, 220 MPa, fO2 = NNO + 2, H2O-saturated conditions for an equilibration period, decompressed to final pressures, Pf, ranging from 175 to 5 MPa, and then held for 0.3–931 hours. According to the plagioclase liquidus curve in PH2O-T space for the relevant melt composition, these decompressions impose effective undercoolings, ΔTeff, of 34–266°C. Growth of preexisting phenocrysts and newly formed sparse microlites dominate crystallization at 75 ≤ Pf < 150 MPa (ΔTeff = 34–93°C), and equilibrium crystal modes are achieved in <168 hours. Microlite nucleation is the dominant transformation process for 10 < Pf < 50 MPa (ΔTeff = 125–241°C), and chemical equilibrium is not attained by 168 hours under these conditions. Slow, steady decompressions typically produced normally zoned, euhedral, and planar-faceted feldspar crystals, although anhedral morphologies were produced at very low Pf. Contrary to expectation, slowly decompressed samples were usually further from chemical equilibrium than rapidly decompressed samples after similar durations below the initial pressure. Although counterintuitive, these trends are consistent with new constraints on the relative rates of feldspar nucleation and growth (controlled by ΔTeff and melt viscosity) experienced during each decompression path. Analysis of liquid to solid transformation kinetics using TTT-style diagrams shows that crystallization occurs most rapidly at ∼100 MPa by a crystal growth mechanism. The next most efficient crystallization conditions are at 25 MPa, in a crystal nucleation-dominated regime.
TL;DR: In this article, carbon nanotubes with octadecylamine made the tubes hydrophobic and allowed the tubes to be solubilized in an organic solvent, which promoted growth of the less-preferred beta form of crystalline polypropylene at the expense of the alpha form.
Abstract: Nonisothermal and isothermal crystallization experiments were performed on polypropylene mixed with carbon nanotubes produced by disproportionation of CO on Co-Mo catalysts. Functionalization of the nanotubes with octadecylamine made the tubes hydrophobic and allowed the tubes to be solubilized in an organic solvent. Mixing of the nanotubes with the polymer was accomplished by adding the nanotubes to a Decalin solution that contained dissolved polypropylene, followed by evaporation of the solvent. Dynamic mechanical analysis indicated very little difference in the small-strain mechanical properties between filled and unfilled polymers at the very low solid levels that were tested. By contrast, the crystallization behavior of the filled and unfilled polymer was quite different. Nanotubes promoted growth of the less-preferred beta form of crystalline polypropylene at the expense of the alpha form. In nonisothermal crystallization, the total amount of crystalline material in the sample was the same for the filled and unfilled materials. However, for isothermal crystallization experiments, the percent crystallinity in the filled materials was slightly higher. Most importantly, the rate of crystallization was substantially higher in the filled system. The results presented in this paper clearly show that carbon nanotubes nucleate crystallinity in polypropylene.
TL;DR: Bulk amorphous metal alloys as mentioned in this paper exhibit very high strength, specific strength, and elastic strain limit, along with unusual combinations of other engineering properties, and these factors, taken together with the stability of the undercooled molten alloys with respect to crystallization have enabled studies of liquid thermodynamics, rheology, atomic diffusion, and the glass transition previously not possible in metallic systems.
Abstract: During the last two decades, researchers have developed families of metal alloys that exhibit exceptional resistance to crystallization in the undercooled liquid state. Upon cooling, these alloys readily form glass or vitrify to form bulk amorphous alloys or bulk metallic glasses. The stability of the undercooled molten alloys with respect to crystallization has enabled studies of liquid thermodynamics, rheology, atomic diffusion, and the glass transition previously not possible in metallic systems. Bulk amorphous alloys exhibit very high strength, specific strength, and elastic strain limit, along with unusual combinations of other engineering properties. These factors, taken together, suggest that bulk amorphous metals will become widely used engineering materials during the next decade.
TL;DR: In this paper, the density of sputtered Ge2Sb2.74 thin films upon annealing has been precisely determined by x-ray reflection and compared to the values determined from X-ray diffraction data.
Abstract: The density of sputtered Ge2Sb2.04Te4.74 thin films upon annealing has been precisely determined by x-ray reflection and compared to the values determined from x-ray diffraction (XRD) data. The film density increases in two steps around 130 and 280 °C upon annealing up to 400 °C. These increases are consequences of phase transitions from amorphous to NaCl type and from NaCl type to hexagonal structure, respectively, as revealed by XRD. Average density values of 5.87±0.02, 6.27±0.02, and 6.39±0.02 g/cm3 were measured for the amorphous, NaCl-type, and hexagonal phases, respectively. This corresponds to density changes upon crystallization of 6.8±0.2% and 8.8±0.2% for NaCl-type and hexagonal phases, respectively. The accompanying film thickness reductions were determined to be 6.5±0.2% and 8.2±0.2%, which compares very well with the density changes. The corresponding XRD values are determined to be 6.43–6.48 and 6.48 g/cm3 for NaCl-type and the hexagonal phases, respectively. This shows that nearly void-free...
TL;DR: In this paper, the preparation and properties of polyvinylidene fluoride (PVDF)/clay nanocomposites were reported for the first time, and the composites were characterized with X-ray diffraction, differential scanning calorimetry, and dynamic mechanical analysis.
Abstract: The preparation and properties of poly(vinylidene fluoride) (PVDF)/clay nanocomposites are reported for the first time. PVDF/clay nanocomposites were prepared by melt intercalation with organophilic clay. The composites were characterized with X-ray diffraction, differential scanning calorimetry, and dynamic mechanical analysis. X-ray diffraction results indicated intercalation of the polymer into the interlayer spacing. PVDF in the nanocomposites crystallized in the β form. Differential scanning calorimetry nonisothermal curves showed an increase in the melting and crystallization temperatures along with a decrease in crystallinity, as evidenced by the melting and crystallization peaks. Isothermal crystallization studies showed an enhanced rate of crystallization with the addition of clay, as evidenced by a reduction in the crystallization time. Dynamic mechanical analysis indicated significant improvements in the storage modulus over a temperature range of −100 to 150 °C. The tan δ peak signifying the glass-transition temperature of PVDF shifted to higher temperatures. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1682–1689, 2002
TL;DR: In this article, the role of long chains in shear-induced oriented crystallization was studied by in situ rheo-optical measurements and ex situ microscopic observations, and it was shown that long chain overlap is enhanced by long chain−long chain overlap.
Abstract: The role of long chains in shear-mediated crystallization was studied by in situ rheo-optical measurements and ex situ microscopic observations. To elucidate the effects of long chains, we prepared model blends in which fractionated isotactic polypropylene (iPP) (denoted L-PP) with high molecular weight (MW) and narrow molecular weight distribution was blended with a metallocene iPP (Base-PP) with lower molecular weight. The concentration of L-PP (c) was varied ranging from 0 to twice the concentration (c*) at which L-PP coils overlap. The crystallization of all blends after cessation of transient shearing was accelerated, while the quiescent crystallization kinetics were not affected by the addition of L-PP. A distinctive change in the development of birefringence after shearing was observed when the wall shear stress (σw) exceeded a critical value (σ*). Below σ*, irrespective of c, the birefringence after transient shearing increased gradually, reaching a small value at the end of crystallization. Above σ*, a brief interval of shear induced highly oriented growth, manifested in the birefringence after cessation of flow and growing stronger and reaching a large value as crystallization proceeded. Further, the rate of growth of the birefringence exhibited a strong, nonlinear c dependence. The morphology of the skin layer showed a shish kebab type structure observed by TEM for samples subjected to stresses above σ*. The number density and thickness of shish were affected by c and changed drastically at c near the overlap concentration of the long chains. This indicates that the role of long chains in shear-induced oriented crystallization is cooperative (rather than a single chain effect), enhanced by long chain−long chain overlap.
TL;DR: Crystallization studies under nonisothermal conditions revealed that compounds with the highest entropic barriers and lowest mobilities were most difficult to crystallize, regardless of the thermodynamic driving forces.
TL;DR: In this article, a carbon-free TiO2 films with high refractive index (n=2.3 at 550 nm) were successfully obtained under an annealing temperature as low as 350 °C.
TL;DR: The synthesized carbonate- and sodium-and-carbonate-substituted hydroxyapatite powders exhibit chemical compositions and crystallinities similar to those of mineral constituents of hard tissues and therefore are promising for fabrication of bone-resembling implants.
TL;DR: In this paper, a systematic approach is developed for the in situ control of the crystal size distribution, and is applied to the aqueous crystallization of paracetamol (acetaminophen) as a model pharmaceutical system.
Abstract: A systematic approach is developed for the in situ control of the crystal size distribution, and is applied to the aqueous crystallization of paracetamol (acetaminophen) as a model pharmaceutical system. This involves the determination of the solubility curve and the metastable limit, and the operation of concentration-controlled batch crystallization. The solution concentration and the solubility curve of paracetamol in water are determined using attenuated total reflection (ATR)-Fourier transform infrared (FTIR) spectroscopy coupled with chemometrics. The metastable zone width of paracetamol is determined using laser backscattering and ATR-FTIR spectroscopy. Seeded batch crystallizations of paracetamol following a desired supersaturation profile near the metastable limit are carried out using in situ solution concentration measurements obtained from ATR-FTIR spectroscopy. The in situ chord length distributions of crystals obtained from laser backscattering are related to characteristics of the crystal s...
TL;DR: In this article, a novel nanocomposite containing polyethylene and polyhedral oligomeric silsesquioxane (POSS) nanoparticles has been characterized using wide-angle X-ray scattering (WAXS).
Abstract: A novel nanocomposite containing polyethylene and polyhedral oligomeric silsesquioxane (POSS) nanoparticles has been characterized using wide-angle X-ray scattering (WAXS). In copolymers formed between ethylene and POSS containing macromonomers, the POSS units, attached as pendant groups off the polyethylene backbones, are found to aggregate and crystallize as nanocrystals. The POSS nanoparticles in such PE-co-POSS copolymers form a lattice separate from the PE lattice with characteristic diffraction signals. From both line broadening of the diffraction maxima and also the oriented diffraction in a drawn material, we conclude that POSS crystallizes as anisotropically shaped crystallites. The presence of POSS disrupts the crystallization of polyethylene and results in less and smaller/disordered polyethylene crystallites. POSS nanocrystals are covalently connected to the PE crystallites via an intermediate disordered interfacial region. The PE crystallites are reinforced by the POSS crystallites, maintaini...
TL;DR: In this article, the synthesis of SAPO-34 molecular sieves, XRD, SEM, XRF, IR and NMR techniques were applied to monitor the crystalloid, structure and composition changes of the samples in the whole crystallization process in order to get evidence for the crystallization as well as Si incorporation mechanism of the sieves.
TL;DR: It is argued that physical factors, namely residual crystal phase and specific surface area, determine the isothermal and nonisothermal crystallization behavior of ground amorphous samples as opposed to intrinsic differences in the structure of theAmorphous phase.
TL;DR: In this article, the melting and crystallization behavior of poly(ethylene glycol) (PEG) with different molecular weights and chosen blends of PEG is investigated by means of differential scanning calorimetry (DSC) operating in dynamic mode at different heating rates.
Abstract: Melting and crystallization behaviour of poly(ethylene glycol) (PEG) with different molecular weights (from 1000 to 35 000) and chosen blends of PEG is investigated by means of differential scanning calorimetry (DSC) operating in dynamic mode at different heating rates. The influence of the molecular weight of PEG on its melting point and enthalpy of fusion is evaluated; from the DSC data the degree of crystallinity is calculated–it is found that there is an increased tendency of higher-molecular-weight PEGs towards the formation of crystalline phase owing to their lower segmental mobility and more convenient geometrical alignment. During the freezing cycle, an increase in the molecular weight of PEG causes an increase in the solidification temperature and heat of crystallization. Thermal transition data are supplemented by optical microscopy–numerous small sphere-shaped crystalline structures are observed to join together and impinge on their neighbours, forming eventually a multilayered lamellar texture. By implementing second polymeric component the polydispersity of the system increases, thus lowering the crystallization degree during preparation phase. It influences also the course of solidification by lowering the crystallization temperature, Tc. An additional effect observed in the case of the blend's freezing is associated with larger supercooling, probably due to morphological constraints and entanglements in interlamellar regions. The possible advantage of using PEG blends to replace pure components is connected with the possibility of changing the temperature range and heat associated with melting/freezing. Copyright © 2003 John Wiley & Sons, Ltd.
TL;DR: In this article, the effects of cooling rate on the macroscopic properties of a fat crystal network were studied by crystallizing anhydrous milk fat (AMF) and lard either rapidly (5 ÂC/min, Newtonian cooling) or slowly (0.1 Â C /min, stepwise cooling).
TL;DR: In this paper, the properties of three regioregular poly(3-alkyl thiophene)s (P3ATs) are studied: poly (3-hexylthiophene), poly( 3-octyl THiophene, P3OT), and poly ( 3-dodecyl thyphene) (P 3DDT).
Abstract: The crystallization properties of three regioregular poly(3-alkyl thiophene)s (P3ATs) are studied: poly(3-hexyl thiophene) (P3HT), poly(3-octyl thiophene) (P3OT), and poly(3-dodecyl thiophene) (P3DDT). The morphology of the isothermally crystallized samples is a whisker type. The values of the enthalpy of fusion of ideal crystals (ΔH), determined from the melting point depression in the polymer–diluent system, are 99, 73.6, and 52 J/g for P3HT, P3OT, and P3DDT, respectively. The values of the equilibrium melting point (T), determined from the Hoffman–Weeks extrapolation procedure, are 300, 230, and 180 °C for P3HT, P3OT, and P3DDT, respectively. From the linear extrapolation of the P3AT data, the T and ΔH values of unsubstituted polythiophene are predicted to be 400 °C and 139 J/g, respectively. The crystallization kinetics of these polymers are studied with differential scanning calorimetry, and the Avrami exponents vary between 0.6 and 1.4, indicating one-dimensional heterogeneous nucleation with linear growth. As the P3AT whiskers are produced from the chain-folding process, the Lauritzen–Hoffman growth rate theory is applied to analyze the temperature coefficient of the crystallization rate data. Graphical plots indicate a transition from regime I to regime II during isothermal crystallization for all the P3ATs studied. The fold surface energy and the work of chain folding calculated from the slopes of the graphical plots decrease with an increase in the number of carbon atoms of the side chain. The primary crystallization process of the side-chain crystallization is very fast and is attributed to the zipping effect of the main-chain crystals. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2073–2085, 2002
TL;DR: In this article, an approach that enables up to a two order of magnitude reduction in the amount of protein required and a tenfold reduction in time required for vapor-diffusion protein crystallization is reported.
Abstract: An approach that enables up to a two order of magnitude reduction in the amount of protein required and a tenfold reduction in the amount of time required for vapor-diffusion protein crystallization is reported. A prototype high-throughput automated system was used for the production of diffraction-quality crystals for a variety of proteins from a screen of 480 conditions using drop volumes as small as 20 nL. This approach results in a significant reduction in the time and cost of protein structure determination, and allows for larger and more efficient screens of crystallization parameter space. The ability to produce diffraction-quality crystals rapidly with minimal quantities of protein enables high-throughput efforts in structural genomics and structure-based drug discovery.
TL;DR: In this article, the effect of Al inclusion in HfO/sub 2/ on the crystallization temperature, leakage current, band gap, dielectric constant, and border traps was presented.
Abstract: This authors present the effect of Al inclusion in HfO/sub 2/ on the crystallization temperature, leakage current, band gap, dielectric constant, and border traps. It has been found that the crystallization temperature is significantly increased by adding Al into the HfO/sub 2/ film. With an addition of 31.7% Al, the crystallization temperature is about 400-500/spl deg/C higher than that without Al. This additional Al also results an increase of the band gap of the dielectric from 5.8 eV for HfO/sub 2/ without Al to 6.5 eV for HfAlO with 45.5% Al and a reduced dielectric constant from 19.6 for HfO/sub 2/ without Al to 7.4 for Al/sub 2/O/sub 3/ without Hf. Considering the tradeoff among the crystallization temperature, band gap, and dielectric constant, we have concluded that the optimum Al concentration is about 30% for conventional self-aligned CMOS gate processing technology.