Showing papers on "Crystallization published in 1996"
TL;DR: In this article, a review of new experimental and theoretical physical research related to the formation of polymeric membranes by phase separation of a polymer solution, and to the morphology of these membranes is presented.
1,246 citations
TL;DR: In this paper, the authors showed that soluble polyanionic proteins alone are sufficient to control the crystal phase of calcite and calcite without the need for deposition of an intervening protein sheet.
Abstract: IN the initial stages of the biomineralization of abalone shells, a primer layer of oriented calcite crystals grows on a nucleating protein sheet1,2. The deposition of this primer is followed by an abrupt transition to c-axis-oriented crystals of aragonite, another crystalline form of calcium carbonate. The formation of each of the two crystal types is accompanied by the synthesis of specific polyanionic proteins1–3, suggesting that cooperative interactions between these proteins and the inorganic ions during crystal nucleation and growth control the phase of the deposited mineral and that differential expression of the proteins allows the organism to induce phase changes. It is known that soluble shell proteins can control crystal morphology4–10, but it has been suspected that the switch in phase—from calcite to aragonite—might require the deposition of a new nucleating protein sheet. Here we describe in vitro studies of the crystallization of calcium carbonate in the presence of soluble polyanionic proteins extracted from abalone shell. We find that these proteins alone are sufficient to control the crystal phase, allowing us to switch abruptly and sequentially between aragonite and calcite without the need for deposition of an intervening protein sheet. These results show that soluble organic components can exert greater control over hierarchical biomineral growth than hitherto suspected, offering the prospect of similar phase control in materials chemistry.
1,112 citations
TL;DR: In this article, a polymer mold suitable for the formation of titanium dioxide nanotubes was obtained and the tubular structure was formed by electrochemical deposition in the mold, and the as-deposition TiO2 tubes were amorphous, but polycrystalline anatase samples were obtained after heat treatment.
Abstract: Starting from the naturally occurring structure of porous aluminum oxide, a polymer mold suitable for the formation of titanium dioxide nanotubes was obtained. The tubular structure was formed by electrochemical deposition in the mold. After dissolution of the polymer, titanium dioxide nanotubes were obtained and characterized. The “as deposited” TiO2 tubes were amorphous, but polycrystalline anatase samples of the same structure were obtained after heat treatment. The inner diameter of the tubes decreased from about 100 to 70 nm during the crystallization. A mechanism for the electrochemical deposition is proposed. Furthermore, the preparation procedure could also be applied to other semiconducting materials.
652 citations
TL;DR: In this article, several samples of poly(lactic acid) with different molecular weights and tacticity have been prepared, and some PLLA injection moulded specimens have been annealed to promote their crystallization.
Abstract: Several samples of poly(lactic acid) with different molecular weights and tacticity have been prepared, and some PLLA injection moulded specimens have been annealed to promote their crystallization. From the characterization data, poly(L-lactide) showed more interesting mechanical properties than poly(D, L-lactide), and its behavior significantly improves with crystallization. In fact, annealed specimens possess higher values of tensional and flexural modulus of elasticity, Izod impact strength, and heat resistance. The plateau region of flexural strength as a function of molecular weights appears around Mv = 35,000 for PDLLA and amorphous PLLA and at higher molecular weight, around Mv = 55,000, for crystalline PLLA. The study of temperature effect shows that at 56°C only crystalline PLLA still exhibits useful mechanical properties. © 1996 John Wiley & Sons, Inc.
541 citations
TL;DR: F Fourier-transform infrared (FTIR) spectroscopy was used to determine the rate of hydroxycarbonate apatite (HCA) formation that occurs on bioactive glass and glass-ceramic implants when exposed to simulated body fluid (SBF) solutions.
Abstract: The bioactive glass 45S5 was crystallized to 8-100 vol % of crystals by thermal treatments from 550-680 degrees C. The micro-structure of the glass-ceramics had a very uniform crystal size, ranging from 8 to 20 microns. Fourier-transform infrared (FTIR) spectroscopy was used to determine the rate of hydroxycarbonate apatite (HCA) formation that occurs on bioactive glass and glass-ceramic implants when exposed to simulated body fluid (SBF) solutions. Crystallization did not inhibit development of a crystalline HCA layer, but the onset time of crystallization increased from 10 h for the parent glass to 22 h for 100% crystallized glass-ceramic. The rate of surface reactions was slower when the percentage of crystallization was > or = 60%.
527 citations
490 citations
TL;DR: In this paper, a low temperature crystallization method for poly-Si TFTs was developed: Metal-Induced Lateral Crystallization (MILC), where the a-Si film in the channel area was laterally crystallized from the source/drain area, on which an ultrathin nickel layer was deposited before annealing.
Abstract: A new low temperature crystallization method for poly-Si TFTs was developed: Metal-Induced Lateral Crystallization (MILC). The a-Si film in the channel area of a TFT was laterally crystallized from the source/drain area, on which an ultrathin nickel layer was deposited before annealing. The a-channel poly-Si TFTs fabricated at 500/spl deg/C by MILC showed a mobility of 121 cm/sup 2//V/spl middot/s, a threshold voltage of 1.2 V, and an on/off current ratio of higher than 10/sup 6/. These electrical properties are much better than TFTs fabricated by conventional crystallization at 600/spl deg/C.
477 citations
TL;DR: Crystallization of PD6S is substantially hindered in ultrathin films, in which a critical thickness of 150 angstroms is needed for crystalline morphology to exist and in which the rate of crystallization is initially slow but increases rapidly as the film approaches 500Angstroms in thickness.
Abstract: The molecular organization in ultrathin polymer films (thicknesses less than 1000 angstroms) and thin polymer films (thicknesses between 1000 and 10,000 angstroms) may differ substantially from that of bulk polymers, which can lead to important differences in resulting thermophysical properties. Such constrained geometry films have been fabricated from amorphous poly(3-methyl-4-hydroxy styrene) (PMHS) and semicrystalline poly(di-n-hexyl silane) (PD6S) by means of spin-casting. The residual solvent content is substantially greater in ultrathin PMHS films, which suggests a higher glass transition temperature that results from a stronger hydrogen-bonded network as compared with that in thicker films. Crystallization of PD6S is substantially hindered in ultrathin films, in which a critical thickness of 150 angstroms is needed for crystalline morphology to exist and in which the rate of crystallization is initially slow but increases rapidly as the film approaches 500 angstroms in thickness.
449 citations
TL;DR: In this paper, it was shown that shear-induced crystallization of isotactic polypropylene (iPP) homo-, block, and random copolymers is associated with the development of α-row-nuclei.
Abstract: Shear-induced crystallization of isotactic polypropylene (iPP) homo-, block, and random copolymers was studied and compared to that in quiescent melt. It was evidenced by means of the thermo-optical technique that melt-shearing, caused by fiber pulling, is associated with the development of α-row-nuclei. The surface of the in situ formed α-row-nuclei may induce the growth of the β-modification of iPP resulting in a cylindrite of polymorphous composition. The polymorphous composition is controlled by the temperature-dependent relative growth rate of the α- and β-iPP for which a model explanation was given. The β-nucleation ability of the α-row-nuclei is lost by melt-shearing at high temperature or remelting. This was attributed to a coverage of the β-nuclei by the α-phase. The structural memory of the supermolecular structures was studied in repeated melting and crystallization cycles and discussed. It was found that the quality of the fiber did not influence the mechanisms concluded. The shear-induced crystallization of propylene block copolymers was highly analogous to the homopolymers. In case of the random copolymers, however, crystallization in sheared melt resulted in an α-cylindritic structure, because for propylene random copolymers the growth rate of the α-modification is always higher than that of the β. It was also demonstrated that the mechanism of shear-induced crystallization was unaffected when the crystallizing PP melt contained selective β-nucleants. © 1996 John Wiley & Sons, Inc.
419 citations
TL;DR: The ability of tristearin, tripalmitin, trimyristin and trilaurin to form solid lipid nanoparticles after melt-homogenization is investigated by DSC and X-ray diffraction.
375 citations
TL;DR: The crystallization boundaries of small, attractive particles are found to be identical when interactions are modeled as adhesive hard spheres and it is concluded that solubility is insensitive to interaction details and various colloidal particles will only display equilibrium colloidal fluid and colloidal crystal equilibrium phases.
Abstract: The crystallization boundaries of small, attractive particles are found to be identical when interactions are modeled as adhesive hard spheres. Based on experimental results and the attraction range, we conclude that solubility is insensitive to interaction details and various colloidal particles will only display equilibrium colloidal fluid and colloidal crystal equilibrium phases. This study provides a basis for the observations of George and Wilson [Acta Crystallogr. D 50, 361 (1994)] who suggest using second virial coefficient measurements to identify protein crystallization conditions.
TL;DR: In this paper, the authors used the nonlinear Avrami equation and Hoffman-Lauritzen equation to fit poly(L-lactide-co-meso lactide) copolymers.
Abstract: The crystallization kinetics of poly(L-lactide-co-meso-lactide) were determined over a range of 0% to 9% mesolactide. The kinetics were fit to the nonlinear Avrami equation and then to the Hoffman–Lauritzen equation modified for optical copolymers. The theory was found to fit the data well. The crystallization half-time was found to increase about 40% for every 1 wt % meso-lactide in the polymerization mixture. The change in crystallization rate is driven mainly by the reduction in melting point for the copolymers. The copolymer crystallization kinetics were also determined in the presence of talc, a nucleating agent for polylactide. The theory again fit the data well, using the same growth parameters and accounting for the talc only through the nucleation density term. © 1996 John Wiley & Sons, Inc.
TL;DR: In this paper, copolymerization of poly(lactide)s with different optical purities (OP) was studied from the melt over a wide range of annealing temperatures using differential scanning calorimetry and polarizing microscopy.
Abstract: Poly(lactide)s (PLA) with different optical purities (OP) were synthesized by copolymerization of D-lactide and L-lactide. Crystallization of D- and L-lactide-rich copolymers before and after 1 : 1 blending was studied from the melt over a wide range of annealing temperatures (Ta) using differential scanning calorimetry and polarizing microscopy. Melting temperature and crystallinity increased with an increase in OP for both the non-blended and the 1 : 1 blended PLAs and they lost their crystallizability when their OP became smaller than 76%, suggesting that the critical isotactic sequence length of PLA for crystallization was approximately 15 isotactic lactate units. Normal spherulite formation was observed for both the non-blended and the blended PLAs even when the OP of PLAs decreased to 76%, whereas the spherulitic size of the non-blended PLAs was larger than that of the 1 : 1 blended PLAs when compared at the same OP and Ta. The highest Ta for crystallization increased with increasing OP and was higher for the 1 : 1 blended PLAs than for the non-blended PLAs at a fixed OP, indicating that the crystallizable Ta range was extended to higher temperature by blending D- and L-lactide-rich PLAs. This is ascribed to stereocomplex (racemic crystallites) formation at high Ta from the 1 : 1 blended PLAs. Based on these results, the phase diagram for crystallization was depicted for the non-blended and the 1 : 1 blended PLAs.
TL;DR: Thermodynamics of the polymer/solvent pair has a decisive effect on the final macroporous foams, as shown by the dependence of their porosity, density, porous morphology, and mechanical behavior on molecular weight and crystallinity of polylactide and concentration of the original solutions.
Abstract: Potential of thermally induced phase separation as a porogen technique has been studied in an effort to produce a surgical implant suitable for cell transplantation. Emphasis has been placed on the liquid-liquid phase separation of solutions of amorphous poly DL-lactide and semicrystalline poly L-lactide in an 87/13 dioxane/water mixture. The related temperature/composition phase diagrams have been set up by turbidimetry, and the possible occurrence of a gel has been discussed. Freeze-drying of some phase-separated polylactide solutions can produce flexible and tough foams with an isotropic morphology. Interconnected pores of 1-10 microns in diameter are expected to result from the spinodal decomposition of the polylactide solutions with formation of co-continuous phases. Thermodynamics of the polymer/solvent pair has a decisive effect on the final macroporous foams, as shown by the dependence of their porosity, density, porous morphology, and mechanical behavior on molecular weight and crystallinity of polylactide and concentration of the original solutions. On the basis of the foam characteristics, potential of the liquid-liquid phase separation (spinodal decomposition) has been compared with the solid/liquid phase separation (solvent crystallization) as a porogen technique.
TL;DR: The structural characteristics of aqueous solutions of Pluronic triblock copolymers of poly(ethylene oxide) - poly(propylene oxide), poly(methylene oxide), PEO - PPO - PEO, and their self-associated assemblies are reviewed in this article.
Abstract: The structural characteristics of aqueous solutions of the Pluronic triblock copolymers of poly(ethylene oxide) - poly(propylene oxide) - poly(ethylene oxide), PEO - PPO - PEO, and their self-associated assemblies are reviewed. It is shown by small-angle neutron scattering that at low temperatures and/or concentration the individual copolymers exist in solution as individual unimers. Thermodynamically stable micelles are formed with increasing copolymer concentration and/or temperature. The unimer-to-micelle transition is not sharp, however. Micelles of well defined spherical shape and size coexist with unimers over a relatively wide temperature/concentration range. The micellar volume fraction increases accordingly with increasing temperature, increasing copolymer concentration and decreasing hydrostatic pressure. The copolymer suspension undergoes as a result a transition from a Newtonian liquid to a soft solid material when the micellar volume fraction crosses the critical value for hard-sphere crystallization. Crystallographic investigations on shear-aligned monodomain samples prove that the micelles in the solid phase are organized on a body-centred cubic lattice. As a result of an increasing micellar size upon increasing the temperature, the micelles themselves undergo a sphere-to-rod transition at elevated temperatures. In a shear field these rod-like micelles form a macroscopic nematic phase for low copolymer concentration, and a hexagonal solid phase for higher concentrations. For even higher concentrations, lamellar phases are observed: one lamellar type which is still governed by the hydrophobic interactions, and one type which appears as a result of crystallization of the PEO blocks.
TL;DR: In this article, the effect of finite size on the solidification of o-terphenyl and benzyl alcohol confined in model controlled pore glass (CPG) materials is described.
Abstract: The effect of finite size on the solidification of o-terphenyl and benzyl alcohol confined in model controlled pore glass (CPG) materials is described. These two organic liquids form either amorphous glasses or crystalline solids in the bulk upon cooling, depending on the rate of cooling and other factors. The solidification behavior of the liquid in the pores was studied as a function of pore diameter (4−73 nm), chemical surface treatment of the CPG and the degree of pore filling, by differential scanning calorimetry (DSC). We observe that the glass transition, Tg, shifts to a lower temperature as pore size decreases. This shift is independent of the degree of pore filling for both o-terphenyl and benzyl alcohol, suggesting that a reduction in bulk density or a negative pressure effect is not the cause of the observed shift. The crystallization behavior of o-terphenyl and benzyl alcohol is also altered by confinement and strongly depends on the pore size and degree of pore filling.
TL;DR: In this article, a number of multicomponent alloy families have been investigated in which the liquid alloys form metallic glass at cooling rates below 1000 K/s and as low as 1 k/s or less.
Abstract: During the past several years, a number of multicomponent alloy families have been investigated in which the liquid alloys form metallic glass at cooling rates below 1000 K/s and as low as 1 K/s or less. These ``bulk`` metallic glass forming alloys have been cast from the melt into glass samples with the smallest dimension ranging from millimeters to centimeters. The undercooled liquid alloys show remarkable resistance to crystallization permitting studies of thermal and physical properties, the glass transition, and crystallization behavior of the melt over previously inaccessible temperatures in the deeply undercooled region. One group of these alloys, which includes the Zr-Ti-Ni-Cu-Be and Zr-Ti-Ni-Cu systems, has been extensively investigated in our laboratory. Results of atomic diffusion and viscosity measurements, crystallization behavior and TTT-diagrams, and studies of liquid phase separation in the deeply undercooled liquid have been carried out and will be discussed. Engineering properties and potential applications of these bulk glasses will be briefly mentioned. (orig.)
TL;DR: In this article, the effects of polymer concentration, chain stereoregularity, polymer molecular weight and cooling rate have been investigated in connection with the porous morphology and physicomechanical characteristics of the final foams.
TL;DR: It was found that with increasing surfactant-to-metal ratios, new hexagonal P63/mmc and layered and layered Nb-TMS4 phases could be formed, while increasing the Surfactant chain length led to a new cubic phase (Nb- TMS3).
Abstract: A systematic study of the factors governing the formation of Nb-TMS1, a niobium-based mesoporous hexagonally-packed transition metal oxide molecular sieve, is reported. The synthesis of this material was achieved through a novel ligand-assisted liquid crystal templating mechanism in which a discrete covalent bond is used to direct the templating interaction between the organic and inorganic phases. In general, the synthesis of Nb-TMS1 is more strongly affected by starting conditions such as temperature, surfactant-to-metal ratio, pH, and solvent than by temperature and time of aging after the initial hydrolysis step. The results also show that Nb-TMS1 can be synthesized under conditions which strongly disfavor the formation of micelles. This suggests that Nb-TMS1 is formed via a mechanism involving self-assembly with concomitant condensation. It was found that with increasing surfactant-to-metal ratios, new hexagonal P63/mmc (Nb-TMS2) and layered (Nb-TMS4) phases could be formed, while increasing the surfactant chain length led to a new cubic phase (Nb-TMS3). Crystals of Nb-TMS1 of up to several mm in dimensions were also grown. These crystals are larger than the biggest mesoporous crystals reported by a factor of 3 orders of magnitude. These crystals retain their structure on micelle removal by acid treatment and are thus of great interest as hosts for quantum wires.
TL;DR: In this paper, the authors studied the growth of calcite and aragonite under controlled supersaturation conditions by the counter diffusion of Ca2+ and CO32- ions through a column of silica gel.
Abstract: Morphological development of calcite crystals is related to supersaturation conditions during growth. Crystallization of calcium carbonate (calcite and aragonite) as well as Mg-calcite was studied under controlled supersaturation conditions by the counter diffusion of Ca2+ and CO32- ions through a porous transport medium (a column of silica gel). Under our experimental conditions, where ion transport is constrained to be diffusion controlled, nucleation and growth take place under conditions of high supersaturation, the actual threshold value of the supersaturation depending on the supersaturation gradient. In the pure CaCO3 system, calcite grows at lower supersaturation than aragonite. The calcite develops relatively simple rhombohedra whil the aragonite grows as spherulites. Presence of Mg2+ in the interstitial fluid inhibits nucleation, increasing the threshold supersaturation at which crystallization begins. The resulting Mg-calcite crystals show a range of morphologies depending on the Mg content and the supersaturation at the point of crystallization. At high values of supersaturation, up to 15 mol % MgCO3 is incorporated into the calcite and the crystals form spheres. At lower supersaturations, Mg content decreases and morphologies change progressively through a well-defined and reproducible sequence from spheres to dumbbell-like forms to wheat-sheaf-like bundles and eventually single crystals with steep rhombohedral faces. The crystals are compositionally zoned, showing both sector and oscillatory zoning. The compositional evol tion is related to the supersaturation and interface roughness during crystal growth.
TL;DR: In this paper, the results of morphological studies during long time melt crystallization and subsequent melting in poly(aryl ether ether ketone) (PEEK) were monitored via small angle X-ray scattering (SAXS).
Abstract: In this paper, we present results of morphological studies during long time melt crystallization and subsequent melting in poly(aryl ether ether ketone) (PEEK). Morphological changes were monitored via small angle X-ray scattering (SAXS). SAXS data were analyzed via a combination of the correlation and interface distribution functions. Our analysis indicates the following: (1) The semicrystalline morphology is best described by a three-phase, dual lamellar stack model. Stacks of a finite number of lamellae and interlamellar amorphous layers are separated from each other by interstack regions of amorphous material (liquid pockets). (2) Secondary crystallization occurs via the formation of secondary lamellar stacks within the liquid pockets. Secondary lamellae are thinner than primary lamellae (70 A vs 120 A), and the amorphous layer thicknesses are about 47 A in both stacks. (3) The low endotherm observed during a heating scan is associated with the melting of the secondary lamellae. (4) At room temperatu...
TL;DR: In this paper, the authors consider that registered names, trademarks, etc. are not to be considered unprotected by law, even without soecific indications thereof, and they propose an approach to protect them.
Abstract: Registered names, trademarks, etc. used in this journal, even without soecific. indications thereof. are not to be considered unprotected by law. Printed in the Federal Republic of Germany
TL;DR: A model for crystallization over long timescales is described that can be applied to a wide range of impure water ices under typical astrophysical conditions if the fragility factor D, which describes the viscosity behavior, can be estimated.
Abstract: Electron diffraction studies of vapor-deposited water ice have characterized the dynamical structural changes during crystallization that affect volatile retention in cometary materials. Crystallization is found to occur by nucleation of small domains, while leaving a significant part of the amorphous material in a slightly more relaxed amorphous state that coexists metastably with cubic crystalline ice. The onset of the amorphous relaxation is prior to crystallization and coincides with the glass transition. Above the glass transition temperature, the crystallization kinetics are consistent with the amorphous solid becoming a "strong" viscous liquid. The amorphous component can effectively retain volatiles during crystallization if the volatile concentration is approximately 10% or less. For higher initial impurity concentrations, a significant amount of impurities is released during crystallization, probably because the impurities are trapped on the surfaces of micropores. A model for crystallization over long timescales is described that can be applied to a wide range of impure water ices under typical astrophysical conditions if the fragility factor D, which describes the viscosity behavior, can be estimated.
TL;DR: In this article, a new method for modeling fractional crystallization processes that involve olivine (ol), plagioclase (plag) and augite (aug) is presented.
Abstract: A new method for modeling fractional crystallization processes that involve olivine (ol), plagioclase (plag) and augite (aug) is presented. This crystallization assemblage is the major control on the chemical variations in mid-ocean ridge basalts. The compositional and temperature variations in ol-plag-aug saturated basalts over a range of pressures are described using empirical expressions. A data base of 190 experiments in natural and basalt-analog chemical systems is used to describe temperature, Al, Ca and Mg molar fractions as functions of Si, Fe, Na, Ti and K molar fractions and pressure. Increases in the abundances of Na and K cause Ca and Mg abundances to decrease and Al abundance to increase in ol-plag-aug saturated melts. The equations can be used to predict pressure and temperature and thus provide a useful thermobarometer. A model is described to calculate ol-plag-aug fractional crystallization as a function of pressure and melt composition, using melt and augite models developed here, combined with existing models for olivine-melt and plagioclase-melt equilibria. We compare the fractional crystallization sequence of ALV-2004-3-1 predicted from the models presented in this paper, Langmuir et al. (1992) modified by Reynolds (1995), Ghiorso and Sack (1995) and Ariskin et al. (1993) at 0.001 and 4 kbar. As an example the model is applied to estimate pressure of crystallization of glasses from the east flank of the East Pacific Rise at 11°45′N.
TL;DR: In this paper, the adhesive hard sphere potential was used to model protein interactions, and a lysozyme phase boundary was constructed from solubility and osmotic second virial coefficient measurements.
TL;DR: In this article, the long period of the lamellar structure decreases as x-1 (x is the number of PDP molecules per P4VP repeat unit) in complete contrast to similar polyelectrolyte systems.
Abstract: Properly selected hydrogen bonding suffices to induce mesomorphic structures in mixtures of flexible polymers and nonmesogenic surfactants. For poly(4-vinylpyridine)−3-pentadecylphenol (P4VP(PDP)x) complexes, the long period of the lamellar structure decreases as x-1 (x is the number of PDP molecules per P4VP repeat unit) in complete contrast to similar polyelectrolyte systems. Upon cooling from 80 °C to the room temperature, the long period gradually increases and levels off at around 30 °C at a value which is approximately 4 A above the starting value. After an induction time, a structural transformation occurs in the highly complexed samples, due to the crystallization of the alkyl side chains. It is accompanied by a sudden decrease in the long period of approximately 5 A. However, the structure is not stable and after an additional induction time both structures are present in the samples. Arguments to explain most of the observed phenomena will be given.
TL;DR: In this paper, small angle neutron scattering (SANS), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC) was used to study primary crystallization and decomposition in the bulk amorphous alloy Ar41.2Ti13.8Cu12.5Ni10Be22.5
Abstract: Primary crystallization and decomposition in the bulk amorphous alloy Ar41.2Ti13.8Cu12.5Ni10Be22.5 have been studied by small angle neutron scattering (SANS), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). SANS data of samples annealed isothermally at 623 K exhibit an interference peak centered at q=0.46 nm(^-1) after an incubation time of about 100 min. TEM and DSC investigations confirm that the respective periodic variation in the scattering length density is due to the formation of nanocrystals embedded in the amorphous matrix. These observations suggest that during the incubation time a chemical decomposition process occurs and the related periodic composition fluctuations give rise to the observed periodic arrangement of the nanocrystals.
TL;DR: In this article, the miscibility, crystallization and morphology of poly(β-hydroxybutyrate) (PHB)/poly(d,l-lactide) (PLA) blends were investigated by means of differential scanning calorimetry, polarizing optical microscopy and scanning electron microscopy studies.
TL;DR: In this paper, the orientation of the PE stems was deduced from the orientations of peaks in the WAXS pattern with respect to those in the SAXS to be parallel to the lamellar interface for symmetric diblocks containing poly(ethylene) (PE) and either a rubbery or glassy amorphous block.
Abstract: Crystallization in oriented diblock copolymers containing poly(ethylene) (PE) has been investigated using simultaneous small-angle and wide-angle X-ray scattering (SAXS/WAXS). The orientation of the crystallized PE stems was deduced from the orientation of peaks in the WAXS pattern with respect to those in the SAXS to be parallel to the lamellar interface for symmetric diblocks containing PE and either a rubbery or glassy amorphous block. For a symmetric diblock with a poly(vinylcyclohexane) block that is glassy at room temperature we observe diffuse scattering parallel to the meridian in the SAXS pattern that is consistent with lateral correlations between PE crystallites within the layers of semicrystalline PE. In contrast, in all the samples containing an amorphous component, PE crystallization occurred with no lateral positional correlations of crystallites. Crystallization in asymmetric diblocks with compositions fPE = 0.35 and 0.46 was also investigated. It was found that a lamellar structure is the stable solid structure and that this melts epitaxially to a hexagonal-packed cylinder structure in the fPE = 0.35 sample. For the fPE = 0.46 sample that forms a perforated layer phase in the melt, chain-folded PE stems were found to be parallel to the lamellar interface, as for the symmetric diblocks.
TL;DR: In this paper, a single-layer germanium-antimony-tellurium (Ge-Sb-Te) ternary amorphous thin film as a single layer or sandwiched between various dielectric films, such as silicon dioxide (SiO2), siricon nitride (Si3N4), tantalum oxide (Ta2O5), zinc sulfide (ZnS), and ZnS−20 m...
Abstract: Crystallization processes were studied for germanium–antimony–tellurium (Ge–Sb–Te) ternary amorphous thin film as a single layer or sandwiched between various dielectric films, such as silicon dioxide (SiO2), siricon nitride (Si3N4), tantalum oxide (Ta2O5), zinc sulfide (ZnS), and ZnS–20 mol % SiO2. The processes were analyzed quantitatively, based on transmittance changes in Ge–Sb–Te films heated either exothermally or isothermally. Both Kissinger equation and Johnson–Mehl–Avrami kinetic analysis were adopted to estimate activation energy and the reaction order of the processes. Ge–Sb–Te single‐layer amorphous film crystallized in two stages, nucleation and crystal growth. These two processes can be distinguished by exothermal crystallization patterns. By sandwiching this film into dielectric films, crystallization activation energy increases and the nucleation processes are affected. The Si3N4 and Ta2O5 dielectric films accelerate the nucleation, while the SiO2 films inhibit it, and the ZnS and ZnS–20 m...