Showing papers on "Crystallization published in 1997"
TL;DR: The preparation of a material that changes colour in response to a chemical signal by means of a change in diffraction (rather than absorption) properties is reported, anticipating that this strategy can be used to prepare ‘intelligent’ materials responsive to a wide range of analytes, including viruses.
Abstract: Chemical sensors respond to the presence of a specific analyte in a variety of ways. One of the most convenient is a change in optical properties, and in particular a visually perceptible colour change. Here we report the preparation of a material that changes colour in response to a chemical signal by means of a change in diffraction (rather than absorption) properties. Our material is a crystalline colloidal array of polymer spheres (roughly 100 nm diameter) polymerized within a hydrogel that swells and shrinks reversibly in the presence of certain analytes (here metal ions and glucose). The crystalline colloidal array diffracts light at (visible) wavelengths determined by the lattice spacing, which gives rise to an intense colour. The hydrogel contains either a molecular-recognition group that binds the analyte selectively (crown ethers for metal ions), or a molecular-recognition agent that reacts with the analyte selectively. These recognition events cause the gel to swell owing to an increased osmotic pressure, which increases the mean separation between the colloidal spheres and so shifts the Bragg peak of the diffracted light to longer wavelengths. We anticipate that this strategy can be used to prepare 'intelligent' materials responsive to a wide range of analytes, including viruses.
1,861 citations
TL;DR: Because the location of the metastable critical point can be controlled by changing the composition of the solvent, the present work suggests a systematic approach to promote protein crystallization.
Abstract: Numerical simulations of homogeneous crystal nucleation with a model for globular proteins with short-range attractive interactions showed that the presence of a metastable fluid-fluid critical point drastically changes the pathway for the formation of a crystal nucleus. Close to this critical point, the free-energy barrier for crystal nucleation is strongly reduced and hence, the crystal nucleation rate increases by many orders of magnitude. Because the location of the metastable critical point can be controlled by changing the composition of the solvent, the present work suggests a systematic approach to promote protein crystallization.
1,265 citations
TL;DR: In this article, the slow sedimentation of colloidal particles onto a patterned substrate (or template) can direct the crystallization of bulk colloidal crystals, and so permit tailoring of the lattice structure, orientation and size of the resulting crystals.
Abstract: Colloidal crystals are three-dimensional periodic structures formed from small particles suspended in solution. They have important technological uses as optical filters1–3, switches4 and materials with photonic band gaps5,6, and they also provide convenient model systems for fundamental studies of crystallization and melting7–10. Unfortunately, applications of colloidal crystals are greatly restricted by practical difficulties encountered in synthesizing large single crystals with adjustable crystal orientation11. Here we show that the slow sedimentation of colloidal particles onto a patterned substrate (or template) can direct the crystallization of bulk colloidal crystals, and so permit tailoring of the lattice structure, orientation and size of the resulting crystals: we refer to this process as 'colloidal epitaxy'. We also show that, by using silica spheres synthesized with a fluorescent core12,13, the defect structures in the colloidal crystals that result from an intentional lattice mismatch of the template can be studied by confocal microscopy14. We suggest that colloidal epitaxy will open new ways to design and fabricate materials based on colloidal crystals and also allow quantitative studies of heterogeneous crystallization in real space.
1,148 citations
TL;DR: Melting experiments on two calc-alkaline rocks, a tonalite and a granodiorite, demonstrate that shallow dehydration melting of hornblende- and biotite-bearing granitoids generates metaluminous A-type granitic melts as discussed by the authors.
Abstract: Melting experiments on two calc-alkaline rocks, a tonalite and a granodiorite, demonstrate that shallow dehydration melting of hornblende- and biotite-bearing granitoids generates metaluminous A-type granitic melts. Profuse crystallization of calcic plagioclase + orthopyroxene during low pressure ( P ≤ 4 kbar) incongruent melting explains all of the major and trace element characteristics of A-type granites (e.g., their low Al, Ca, Mg, Sr, and Eu contents, and high Ga/Al and K/Na ratios), as well as their common association with anorthositic and mangeritic rocks. The residual assemblage produced during melting of the same rocks in the deep crust ( P ≥ 8 kbar) is dominated by clinopyroxene, and, as a consequence, most of the chemical features diagnostic of A-type granites are lost. The high temperatures (>900 °C) and low H 2 O contents (≤ 4 wt%) that are characteristic of A-type magmas are adequately explained by the H 2 O-poor nature of the granitoid source materials, and require neither a granulitic nor a F-rich source. Previous attempts to explain the origin of A-type granites have focused on the nature of the source material. These experiments show that pressure of melting is at least as important as source composition in engendering A-type melts.
789 citations
TL;DR: In this article, a new and convenient approach for the nonisothermal crystallization was proposed by combining the Avrami equation with the Ozawa equation, and the kinetic parameters in this approach, the crystallization behavior of PEEKK was analyzed.
Abstract: Analysis of the nonisothermal melt and cold crystallization kinetics of poly(aryl ether ether ketone ketone) (PEEKK) was performed by using differential scanning calorimetry (DSC). The Avrami equation modified by Jeziorny could describe only the primary stage of nonisothermal crystallization of PEEKK. And, the Ozawa analysis, when applied to this polymer system, failed to describe its nonisothermal crystallization behavior. A new and convenient approach for the nonisothermal crystallization was proposed by combining the Avrami equation with the Ozawa equation. By evaluating the kinetic parameters in this approach, the crystallization behavior of PEEKK was analyzed. According to the Kissinger method, the activation energies were determined to be 189 and 328 kJ/mol for nonisothermal melt and cold crystallization, respectively.
789 citations
TL;DR: In this article, an exothermic peak at ca. 723 K in the DSC pattern was assigned to the crystallization of amorphous phase to anatase, and its heat was used to evaluate the weight fraction.
Abstract: Titanium(IV) oxide (TiO2) powders of various amorphous−anatase compositions were prepared by heat treatment (573−1073 K) of amorphous TiO2 in air and characterized by differential scanning calorimetry (DSC), powder X-ray diffraction (XRD), and BET surface area measurements. An exothermic peak at ca. 723 K in the DSC pattern was assigned to the crystallization of amorphous phase to anatase, and its heat was used to evaluate the weight fraction of amorphous phase. The fraction of anatase crystallites (f(anatase)) was calculated as the remainder after the amorphous phase and contaminated water or organic residue. The XRD data showed that the size of anatase crystallites was slightly decreased but almost constant along with the increase in f(anatase), being consistent with the small change in the BET surface area. These results suggest that each amorphous particle transforms into an anatase crystallite of similar size without sintering or crystal growth. The particles of mixture of amorphous and anatase were ...
782 citations
TL;DR: The phase boundaries for metastable liquid-liquid separation in supersaturated hen egg white lysozyme solutions with 3, 5, and 7% (wlv) NaCl at pH= 4.5 and protein concentrations c between 40 and 400 mg/ml were determined using cloud point determinations.
Abstract: Using cloud point determinations, the phase boundaries (binodals) for metastable liquid-liquid (L-L) separation in supersaturated hen egg white lysozyme solutions with 3%, 5%, and 7% (wlv) NaCl at pH= 4.5 and protein concentrations c between 40 and 400 mg/ml were determined. The critical temperature for the binodal increased approximately linearly with salt concentration. The coexisting liquid phases both remained supersaturated but differed widely in protein concentration. No salt repartitioning was observed between the initial and the two separated liquid phases. After the L-L separation, due to the presence of the high protein concentration phase, crystallization occurred much more rapidly than in the initial solution. At high initial protein concentrations, a metastable gel phase formed at temperatures above the liquid binodal. Both crystal nucleation and gel formation were accelerated in samples that had been cycled through the binodal. Solutions in the gel and L-L regions yielded various types of precipitates. Based on theoretical considerations, previous observations with other proteins, and our experimental results with lysozyme, a generic phase diagram for globular proteins is put forth. A limited region in the (T,c) plane favorable for the growth of protein single crystals is delineated.
516 citations
TL;DR: In this article, a wide supercooled liquid region before crystallization was found in Fe(Co,Ni) and Fe(Zr,Nb,Ta,Mo,W)-B systems with diameters up to 6 mm.
Abstract: New bulk amorphous alloys exhibiting a wide supercooled liquid region before crystallization were found in Fe–(Co,Ni)–(Zr,Nb,Ta)–(Mo,W)–B systems. The Tg is as high as about 870 K and the supercooled liquid region reaches 88 K. The high thermal stability of the supercooled liquid enabled the production of bulk amorphous alloys with diameters up to 6 mm. These bulk amorphous alloys exhibit a high compressive strength of 3800 MPa, high Vickers hardness of 1360, and high corrosion resistance. Besides, the amorphous alloys exhibit a high magnetic-flux density of 0.74–0.96 T, low coercivity of 1.1–3.2 A/m, high permeability exceeding 1.2×104 at 1 kHz, and low magnetostriction of about 12×10−6.
438 citations
TL;DR: In this paper, the effects of gravity on colloidal crystallization were investigated on the microgravity experiments performed on the Space Shuttle Columbia and the results showed that the f.h.c.p. component may be induced by gravity-induced stresses.
Abstract: The structure of, and transitions between, liquids, crystals and glasses have commonly been studied with the hard-sphere model1,2,3,4,5, in which the atoms are modelled as spheres that interact only through an infinite repulsion on contact. Suspensions of uniform colloidal polymer particles are good approximations to hard spheres6,7,8,9,10,11, and so provide an experimental model system for investigating hard-sphere phases. They display a crystallization transition driven by entropy alone. Because the particles are much larger than atoms, and the crystals are weakly bound, gravity plays a significant role in the formation and structure of these colloidal crystals. Here we report the results of microgravity experiments performed on the Space Shuttle Columbia to elucidate the effects of gravity on colloidal crystallization. Whereas in normal gravity colloidal crystals grown just above the volume fraction at melting show a mixture of random stacking of hexagonally close-packed planes (r.h.c.p.) and face-centred cubic (f.c.c.) packing if allowed time to settle7,8, those in microgravity exhibit the r.h.c.p. structure alone, suggesting that the f.c.c. component may be induced by gravity-induced stresses. We also see dendritic growth instabilities that are not evident in normal gravity, presumably because they are disrupted by shear-induced stresses as the crystals settle under gravity. Finally, glassy samples at high volume fraction which fail to crystallize after more than a year on Earth crystallize fully in less than two weeks in microgravity. Clearly gravity masks or alters some of the intrinsic aspects of colloidal crystallization.
401 citations
TL;DR: In this article, the authors describe the development of the four main structural components of the frozen product: a discontinuous foam, a network of partially coalesced fat surrounding the air bubbles, ice crystals and a continuous, freeze-concentrated, unfrozen aqueous solution.
328 citations
TL;DR: In this paper, the mesoporous molecular sieve MCM-41 has been used to improve the hydrothermal stability by using various salts such as sodium chloride, potassium chloride, sodium acetate, and ethylenediaminetetraacetic acid tetrasodium salt.
Abstract: Low hydrothermal stability in hot water and aqueous solutions was a critical problem for many applications of the mesoporous molecular sieve MCM-41, compared with conventional zeolites such as Y and ZSM-5. The hydrothermal stability of MCM-41 has been found to improve remarkably by using various salts such as sodium chloride, potassium chloride, sodium acetate, and ethylenediaminetetraacetic acid tetrasodium salt during the hydrothermal crystallization process performed at 370 K. High-quality MCM-41 samples obtained by using the salt effect indicated negligible structural losses as judged by X-ray diffraction during heating for 12 h in boiling water.
TL;DR: In this article, the effects of glycerol and water content on the thermal transitions of plasticized barley starch were examined using differential scanning calorimetry and it was inferred that a single phase system occurred at low water and glycerols contents, while in other cases phase separation occurred and the system was composed of starch-rich and starch-poor phases.
TL;DR: In this paper, the authors used high vacuum, containerless, electrostatic levitation process to study the undercooling and crystallization kinetics of a bulk glass forming Zr-Ti-Cu-Ni-Al alloy.
Abstract: High vacuum, containerless, electrostatic levitation process has been used to study the undercooling and crystallization kinetics of a bulk glass forming Zr-Ti-Cu-Ni-Al alloy. The oxygen impurity level in the alloy has been found to play a crucial role in the crystallization kinetics of the undercooled melt. Overheating the melt above a critical threshold temperature results in enhancement subsequent undercooling. This crucial threshold temperature is found to be a function of the overall oxygen content of the alloy direct measurement of the time-temperature-transformation (TTT) diagram for crystallization of the undercooled melt made following initial overheating above the threshold temperature show a strong dependence on overall oxygen concentration. An explanation of these observations is proposed.
TL;DR: The glass-forming ability of a Pd 4 Cu 30 Ni 10 P 20 alloy was found to increase significantly by B 2 O 3 flux treatment, as is evidenced by the decrease in the critical cooling rate from 1.57 K/s in the non-fluxed state to 0.100 K/m in the fluxed state as mentioned in this paper.
Abstract: The glass-forming ability of a Pd 4 Cu 30 Ni 10 P 20 alloy was found to increase significantly by B 2 O 3 flux treatment, as is evidenced by the decrease in the critical cooling rate from 1.57 K/s in the non-fluxed state to 0.100 K/s in the fluxed state. The flux treatment also causes the extension of the supercooled liquid region by the increase in the onset temperature of crystallization (T x ). The effect of the flux treatment is presumably due to the increase in the thermal stability of the supercooled liquid by the suppression of heterogeneous nucleation. The critical cooling rates in the non-fluxed and fluxed states for a Pd 40 Ni 40 P 20 alloy are measured to be 128 and 0.167 K/s, respectively, both of which are larger than those for the Pd-Cu-Ni-P alloy. The use of the molten Pd-Cu-Ni-P alloy subjected to the flux treatment enabled the production of bulk amorphous alloys in cylindrical forms of 50 to 72 mm in diameter and 52 to 75 mm in length. The glass transition temperature (T g ) and T x values of the bulk amorphous alloys are the same as those for the melt-spun amorphous ribbon prepared from the fluxed molten alloy. The success of synthesizing an amorphous alloy of 72 mm in diameter is encouraging both for the future development of basic science of bulk amorphous alloys and for their engineering application.
TL;DR: In this article, the authors performed a microscopy characterization of solid crystals made of monodisperse SiO2 nanometric spheres and found that for a wide range of particle diameters, the cubic phase is the only one present.
Abstract: It is well-known that stacking of hard spheres results in close-packed structures. However, until recently, it was not clear which of the various possible phases (cubic, hexagonal, mixed, or random) was the stable one. We have performed a microscopy characterization of solid crystals made of monodisperse SiO2 nanometric spheres. It was found that, for a wide range of particle diameters, the cubic phase is the only one present. This largely serves to confirm recent theoretical calculations by L. V. Woodcock which conclude that the cubic phase is the most stable one. This opens new prospects in the application of colloidal crystals to photonic band gap engineering.
TL;DR: In this article, a new procedure to fractionate ethylene/α-olefin copolymers using step-crystallization was presented, which allows melt/melt and melt/solid segregation to occur during thermal cycles that promote self-nucleation, crystallization and annealing processes.
Abstract: A new procedure to fractionate ethylene/α-olefin copolymers using DSC is presented. This procedure allows melt/melt and melt/solid segregation to occur during thermal cycles that promote self-nucleation, crystallization and annealing processes (Successive Self-Nucleation/ Annealing, SSA). The SSA has been compared with the Step-Crystallization (SC) method proposed earlier in the literature to qualitatively characterize chain branching distribution in a faster and easier way than Temperature Rising Elution Fractionation (TREF). In general, SSA produces better fractionation than SC and the DSC derived chain branching distribution by SSA can be qualitatively comparable to that obtained by TREF. The SSA technique could have important applications for the characterization of polymers that crystallize over a broad temperature range.
TL;DR: The water sorption isotherm and the crystallization rates for amorphous indomethacin were determined at 30 degrees C as a function of relative humidity (RH), along with the effects of water content on the glass transition temperature (T(g).
TL;DR: In this paper, the authors describe the numerical procedure for calculating three-dimensional profiles of temperature in a multilayer stack illuminated by a laser beam, and model the crystallization and amorphization kinetics for phase-change rewritable media.
Abstract: We describe the numerical procedure for calculating three-dimensional profiles of temperature in a multilayer stack illuminated by a laser beam, and model the crystallization and amorphization kinetics for phase-change rewritable media. Experimental methods have been used to determine indirectly the probabilities of nucleation and growth for Ge2Sb2Te5 alloy. Some of the fundamental behaviors of phase-change erasable media, such as the crystallization of as-deposited amorphous phase, amorphization of supercooled liquid, and recrystallization of quenched amorphous phase, have been illustrated based on our three-dimensional temperature calculations and the model kinetics. The calculated transient reflectance behavior of as-deposited Ge2Sb2Te5 amorphous films in a single layer and in a quadrilayer stack, as well as the erasure behavior of Ge2Sb2Te5 alloy in a quadrilayer disk are in good agreement with experimental observations.
01 Jan 1997
TL;DR: In this article, the emphasis is on the general aspects of crystallization and on practical tips concerning the source of the macromolecules, separation techniques, and crystallization conditions.
Abstract: To write about the crystallization conditions for a specific protein or nucleo-protein complex will be of no use to somebody intending to crystallize a completely different molecule or even an homologous one coming from a different organism. Therefore, the emphasis of this chapter is on the general aspects of crystallization and on practical tips concerning the source of the macromolecules, separation techniques, and crystallization conditions.
TL;DR: In this paper, textured textured WS2 and MoS2 films are obtained by the techniques of reactive sputtering and solid state reaction, as long as the substrates used are each coated with a 10-20 nm Ni layer.
TL;DR: In this article, isothermal melt crystallization of poly(L-lactide) (PLLA) has been studied in the temperature range of 90 to 135°C and a maximum in crystallization kinetic was observed around 105°C.
Abstract: Isothermal melt crystallization of poly(L-lactide) (PLLA) has been studied in the temperature range of 90 to 135°C. A maximum in crystallization kinetic was observed around 105°C. A transition from regime II to regime III is present around 115°C. The crystal morphology is a function of the degree of undercooling. At crystallization temperatures (Tc) below 105°C, further crystallization occurs upon heating; this behavior is not detected for Tc above 110°C. The analysis of the heat capacity increment at glass transition temperature (Tg) and of dielectric properties of PLLA indicates the presence of a fraction of the amorphous phase which does not relax at the Tg, and the amount of this so-called rigid amorphous phase is a function of Tc. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 911–919, 1997
TL;DR: This work establishes the potential of Bio-Beads as a simple alternative to conventional dialysis for removing detergent and for obtaining 2D crystals of integral membrane proteins useful for structure analysis by electron crystallography.
TL;DR: In this article, the effects of photodegradation on the crystallinity and melting behavior of isotactic polypropylene (PP) were investigated in the laboratory for periods of up to 48 weeks.
TL;DR: In this article, the mixture of poly(beta-hydroxybutyrate) (PHB) and poly(p-vinylphenol) (PVPh) blends were studied by differential scanning calorimetry and optical microscopy (OM).
Abstract: The miscibility and crystallization behavior of poly(beta-hydroxybutyrate) (PHB) and poly(p-vinylphenol) (PVPh) blends were studied by differential scanning calorimetry and optical microscopy (OM). The blends exhibit a single composition-dependent glass transition temperature, characteristic of miscible systems, A depression of the equilibrium melting temperature of PHB is observed. The interaction parameter values obtained from analysis of the melting point depression are of large negative values, which suggests that PHB and PVPh blends are thermodynamically miscible in the melt. Isothermal crystallization kinetics in the miscible blend system PHB/PVPh was examined by OM. The presence of the amorphous PVPh component results in a reduction in the rate of spherulite growth of PHB. The spherulite growth rate is analyzed using the Lauritzen-Hoffman model, The isothermally crystallized blends of PHB/PVPh were examined by wide-angle X-ray diffraction and smell-angle X-ray scattering (SAXS). The long period obtained from SAXS increases with the increase in PVPh component, which implies that the amorphous PVPh is squeezed into the interlamallar region of PHB.
TL;DR: In this article, the authors studied the crystallization of suspensions of sterically stabilized polymer particles, with hard-sphere-like interactions, by laser light scattering and obtained the amount of crystal, the average linear crystal dimension, the number of crystals, and the volume fraction of the crystal phase.
Abstract: The crystallization of suspensions of sterically stabilized polymer particles, with hard-sphere-like interactions, is studied by laser light scattering. Over the range of volume fractions examined, from just below melting to the glass transition, crystallization occurs by homogeneous nucleation. After the suspensions are shear melted, the intensity, position, and width of the main interlayer Bragg reflection are measured as functions of time. From these the amount of crystal, the average linear crystal dimension, the number of crystals, and the volume fraction of the crystal phase are obtained. No assumptions are made concerning the functional time dependence of nucleation or growth processes. Below the melting concentration the observed crystallization process is compatible with the classical picture of sequential nucleation and growth of isolated crystals. However, when the melting concentration is exceeded, nucleation events are correlated, nucleation is accelerated, and high nucleation rate densities suppress crystal growth. Above the melting concentration we infer, with the aid of the equations of state for the hard-sphere fluid and solid, that the first identifiable crystals are in mechanical equilibrium with the embedding fluid and, consequently, strongly compressed by it. Ensuing nucleation lags expansion of the crystal lattice.
TL;DR: In this article, the thermodynamic properties of AIN, GaN and InN are considered and the mechanisms of nucleation and growth of GaN crystals are discussed on the basis of the experimental results.
TL;DR: In this paper, the feasibility of phosphate removal from the supernatant of anaerobically digested sludge by struvite (MAP, MgNH 4 PO 4 ) crystallization in a fluidized-bed reactor (FBR) was studied.
TL;DR: In this article, a small amount of locally reversible melting and crystallization in poly(ethylene terephthalate) (PET) has been detected by temperature-modulated differential scanning calorimetry (TMDSC).
Abstract: A small amount of locally reversible melting and crystallization in poly(ethylene terephthalate) (PET) has been detected by temperature-modulated differential scanning calorimetry (TMDSC). Extended-time TMDSC was used in the quasi-isothermal mode. Studied were melt-crystallized, quenched, and a biaxially-oriented film of PET in temperature steps of 2 K from 320 to 560 K. The integral of the endothermic and exothermic latent heat contributions to the reversible melting and crystallization is less than 10% of the total heat of fusion and decreases further with time over many hours. The new observations support the concept that “molecular nucleation” is the reversible and rate-determining step in crystallization. On TMDSC, partially-melted chains remain on the surface of higher-melting crystals to permit crystallization during the cooling cycle without supercooling.
TL;DR: In this paper, the effects of water content, storage time, and glass transition (physical state) on lactose crystallization and the resultant crystal forms in skim milk powder were investigated.
TL;DR: While increasing water content increases the rate of degradation of crystalline insulin, rate constants for degradation in the amorphous solid are essentially independent of water content up to the maximum water content studied ( ≤15%).
Abstract: Purpose. Generalizations based upon behavior of small molecules have established that a crystalline solid is generally much more stable toward chemical degradation than is the amorphous solid. This study examines the validity of this generalization for proteins using biosynthetic human insulin as the model protein.