Initial Stage Of Crystallization Research Articles

Information on Microenvironment in Amorphous Region of Polymer Films Revealed by PFR Method

SummaryMeasurement of the polarized fluorescence intensities of chromophores in a sample by rotating the sample around the excitation light beam, i.e., the PFR method, is very efficient for determining the three‐dimensional arrangement of the chromophores in the film. We have applied the PFR method to monitor the orientation of fluorescent species in amorphous regions of polymer films. In particular, the present paper reviews two successful studies obtained by PFR method: (i) the microenvironmental change of amorphous regions induced by uniaxially stretching of the films, and (ii) the initial stage of the cold crystallization of poly(ethylene terephthalate) films stretched uniaxially.

Formation of Helically Structured Chitin/CaCO3 Hybrids through an Approach Inspired by the Biomineralization Processes of Crustacean Cuticles.

Chitin/CaCO3 hybrids with helical structures are formed through a biomineralization-inspired crystallization process under ambient conditions. Liquid-crystalline chitin whiskers are used as helically ordered templates. The liquid-crystalline structures are stabilized by acidic polymer networks which interact with the chitin templates. The crystallization of CaCO3 is conducted by soaking the templates in the colloidal suspension of amorphous CaCO3 (ACC) at room temperature. At the initial stage of crystallization, ACC particles are introduced inside the templates, and they crystallize to CaCO3 nanocrystals. The acidic polymer networks induce CaCO3 crystallization. The characterization of the resultant hybrids reveals that they possess helical order and homogeneous hybrid structures of chitin and CaCO3 , which resemble the structure and composition of the exoskeleton of crustaceans.

Morphological Control of Anisotropic Self-Assemblies from Alternating Poly(p-dioxanone)-poly(ethylene glycol) Multiblock Copolymer Depending on the Combination Effect of Crystallization and Micellization.

A novel and facile method was developed for morphological controlling of self-assemblies prepared by crystallization induced self-assembly of crystalline-coil copolymer depending on the combination effect of crystallization and micellization. The morphological evolution of the self-assemblies of alternating poly(p-dioxanone)-block-poly(ethylene glycol) (PPDO-PEG) multiblock copolymer prepared by different solvent mixing methods in aqueous solution were investigated. "Chrysanthemum"-like and "star anise"-like self-assemblies were obtained at different rates of solvent mixing. The results suggested gradually change in solvent quality (slowly dropping water into DMF solution) leaded to a hierarchical micellization-crystallization process of core-forming PPDO blocks, and flake-like particles were formed at the initial stage of crystallization. Meanwhile, crystallization induced micellization process occurred when solvent quality changed drastically. Shuttle-like particles, which have much smaller size than those of flake-like particles, were formed at the initial stage of crystallization when quickly injecting water into DMF solution of the copolymer. Therefore, owing to the different changing rate of solvent quality, which may result in different combination effect of crystallization and micellization during self-assembly of the copolymer, PPDO-PEG self-assemblies with different hierarchical morphology in nano scale could be obtained.

Chain Trajectory and Crystallization Mechanism of a Semicrystalline Polymer in Melt- and Solution-Grown Crystals As Studied Using 13C–13C Double-Quantum NMR

The re-entrance sites, successive chain-folding number ⟨n⟩, and chain-folding fraction ⟨F⟩ of the chain-folding (CF) structure of 13C CH3-labeled isotactic poly(1-butene) (iPB1) with an weight-averaged molecular weight (⟨Mw⟩ = 37 K g/mol) in solution- and melt-grown crystals as a function of crystallization temperature (Tc) were determined using solid-state (SS) NMR. The solution- and melt-grown crystals possessed adjacent re-entry structures between the right- and left-handed stems along the (100) and (010) planes, which were invariant as a function of Tc. The adjacent re-entry structures in the former exhibited long-range order (⟨n⟩ ≥ 8) compared with that in the latter (⟨n⟩ ≥ 1.7–2). These results indicated that the concentration and entanglement of polymers play significant roles in the CF process and structural formation during the initial stage of crystallization, whereas kinetics does not. Transmission electron microscopy (TEM) revealed well-defined hexagonal and circular crystals grown from the solution state at Tc = 60 and ∼0 °C, respectively. The morphological and molecular-level structural data demonstrated that kinetics influences the structural formations of polymers differently at different length scales during crystallization. Moreover, SS-NMR, small-angle X-ray scattering (SAXS), and atomic force microscopy (AFM) indicated that the crystallinity (χc) and lamellar thickness (⟨lc⟩) of the melt-grown crystals are highly dependent on Tc, whereas in the solution-grown crystals, these parameters are independent of Tc. The experimental results and molecular dynamics, as reported in the literature, indicated that both χc and ⟨lc⟩ are primarily determined by the molecular dynamics of the stems after deposition of the chains on the growth front (late process).

Effect of Agitation on Crystallization Behavior of CaO-Al2O3-SiO2-Na2O-CaF2 Mold Fluxes with Varying Basicity

The effect of agitation on crystallization behaviors of CaO-Al2O3-SiO2-Na2O-CaF2 mold fluxes with basicity of 1.1 and 1.2 was investigated. It was found that crystallization temperatures of agitated samples were higher than those of static samples. The morphology of cuspidine shifted from dendrites to facet crystals with the decrease of temperature. The agitation was conducive to the formation of small dendritic cuspidine and could lead to crystals with smaller size. Crystalline fraction could be significantly enhanced by agitation at the initial stage of crystallization.

In Situ Detection of Calcium Phosphate Clusters in Solution and Wet Amorphous Phase by Synchrotron X-ray Absorption Near-Edge Spectroscopy at Calcium K-Edge

Calcium phosphate clusters are present in both aqueous solutions and an amorphous phase during crystallization. It is a challenging task to acquire the structural information on such clusters, owing to their small size, chemical lability, and inaccessibility to most detection techniques. Here, we demonstrate the feasibility of detecting such clusters in situ by synchrotron X-ray absorption near-edge spectroscopy at calcium K-edge, a technique that is sensitive to the short-range order in calcium coordination sphere. At the initial stage of crystallization, the most abundant clusters are detected to be Ca(η2-PO43–)2L2 (L = H2O or η1-PO43–) in solution. More reactive clusters engage in the development of an amorphous phase via growing and fusing. The amorphous phase exhibits a dual character in its short-range order: Some of its clusters are similar to hydrated calcium ions, and some others to those in crystalline hydroxyapatite. When the amorphous dissolves, the detected unit is mainly Ca(η2-PO43–)(H2O)4 i...

Probing the early stages of salt nucleation--experimental and theoretical investigations of sodium/potassium thiocyanate cluster anions.

Due to the fast solvent evaporation in electrospray ionization (ESI), the concentration of initially dilute electrolyte solutions rapidly increases to afford the formation of supersaturated droplets and generation of various pristine anhydrous salt clusters in the gas phase. The size, composition, and charge distributions of these clusters, in principle, witness the nucleation evolution in solutions. Herein, we report a microscopic study on the initial stage of nucleation and crystallization of sodium/potassium thiocyanate salt solutions simulated in the ESI process. Singly charged Mx(SCN)x+1(-), doubly charged My(SCN)y+2(2-) (M = Na, K), and triply charged Kz(SCN)z+3(3-) anion clusters (x, y, and z stand for the number of alkali atoms in the singly, doubly, and triply charged clusters, respectively) were produced via electrospray of the corresponding salt solutions and were characterized by negative ion photoelectron spectroscopy (NIPES). The vertical detachment energies (VDEs) of these sodium/potassium thiocyanate cluster anions were obtained, and theoretical calculations were carried out for the sodium thiocyanate clusters in assisting spectral identification. The measured VDEs of singly charged anions Mx(SCN)x+1(-) (M = Na and K) demonstrate that they are superhalogen anions. The existence of doubly charged anions My(SCN)y+2(2-) (y = 2x, x ≥ 4 and 3 for M = Na and K, respectively) and triply charged anions Kz(SCN)z+3(3-) (z = 3x, x ≥ 6) was initially discovered from the photoelectron spectra for those singly charged anions of Mx(SCN)x+1(-) with the same mass-to-charge ratio (m/z), and later independently confirmed by the observation of their distinct mass spectral distributions and by taking their NIPE spectra for those pure multiply charged anions with their m/z different from the singly charged species. For large clusters, multiply charged clusters were found to become preferred, but at higher temperatures, those multiply charged clusters were suppressed. The series of anion clusters investigated here range from molecular-like M1(SCN)2(-) to nano-sized K22(SCN)25(3-), providing a vivid molecular-level growth pattern reflecting the initial salt nucleation process.

Direct, single-step synthesis of hierarchical zeolites without secondary templating

Hierarchical ZSM-5 with a shell of stacked coffin-shaped crystals and a core of nanocrystal aggregates was synthesized by controlling the formation and self-assembly of zeolite precursors formed in the initial stage of crystallization. The formed hierarchical zeolite shows superior catalytic activity for reaction involving bulky molecules due to enhanced mass transport.

Crystallization Behavior of Palm Kernel Oil Monitored by <i>In-Situ</i> Focused Beam Reflectance Measurement (FBRM) and Particles Video Microscope (PVM) during Suspension Crystallization

Crystallization behavior and kinetics study of palm kernel oil (PKO) were investigated using differential scanning calorimetry (DSC) by controlling cooling and reheating rate within a certain range of temperature. The evolution of morphology and particle counts was analyzed by focused beam reflectance measurement (FBRM) and particles video microscope (PVM) at the nucleation stage during suspension crystallization. The particle counts and morphological evolution from needle-like aggregations to amorphous form from PVM were observed during the initial crystallization stage, which meant that a phase transition was likely to occur. This work can give a better understanding of complicated fat system crystallization behavior and provide some critical instructions to control fractionation process.

To the formation of aggregate structures of kidney stones

The work considers the aggregation process of calcium oxalate monohydrate crystals (whewellite) during their crystallization from aqueous solutions. The intensive crystal aggregation during the precipitation is evidenced by a decrease in the bulk concentration against an increase in the crystal size. At the initial stages of crystallization fine particles are mainly captured by larger ones in the form of substance deposition on the initiating centers: organic blobs, dead cells, and so on. During the crystallization the effect of the dominant growth of large aggregates increases; the process develops autocatalytically; fine particles disappear more rapidly than large ones, and the crystal size distribution compresses simultaneously with an increase in the average particle size.

Nanocrystallization and change in the properties of an Fe80.2P17.1Mo2.7 amorphous alloy during heat or photon treatment

The changes in the phase composition and the mechanical and magnetic properties resulting from the nanocrystallization of an Fe80.2P17.1Mo2.7 amorphous alloy activated by heat or fast photon (xenon lamp radiation) treatment are compared using X-ray diffraction, Mossbauer spectroscopy, transmission electron microscopy, and hardness measurements. The initial stages of crystallization of the amorphous alloy have been detected.

Crystallization behaviour of polymeric membrane based on polymer PVdF-HFP and Ionic liquid BMIMBF4

The crystallization behaviour of the polymer poly(vinylidenefluoride)–hexafluoropropylene (PVdF–HFP) in the presence and absence of the ionic liquid (IL) (1-butyl-3-methylimidazolium tetrafluoroborate; [BMIMBF4]) were studied by isothermal and non-isothermal crystallization processes using differential scanning calorimetry. The well-known Avrami equation is used to describe the isothermal crystallization process of pristine PVdF–HFP or PVdF–HFP + x wt% of IL BMIMBF4, where x = 10 and 30, respectively. It was found that the presence of the IL BMIMBF4 in the PVdF–HFP matrix suppresses the crystallization of the polymer PVdF–HFP, resulting in low crystal growth rates. Three kinetic methods (i.e., those of Jeziorny, Ozawa and Mo) were used to analyze the non-isothermal crystallization process. The Avrami equation modified by Jeziorny could only describe the initial stage of crystallization and the Ozawa method failed to describe the non-isothermal crystallization behavior, but Mo's method explains the results better.

Watching nucleation pathways in calcite

Crystal Nucleation The initial stage of crystallization, the formation of nuclei, is a critical process, but because of the length and time scales involved, is hard to observe. Nielsen et al. explored the crystallization of calcium carbonate, a well-studied material but one with multiple nucleation theories. Different calcium and carbonate solutions were mixed inside a fluid cell and imaged using a liquid cell inside a transmission electron microscope. Competing pathways operated during nucleation, with both the direct association of ions into nuclei from solution and the transformation of amorphous calcium carbonate into and between different crystalline polymorphs. Science , this issue p. [1158][1] [1]: /lookup/doi/10.1126/science.1254051

Effect of container shape and walls on solidification of Brownian particles in a narrow system.

We carry out Brownian dynamics simulations and study the ordering of particles under a uniform external force in a narrow system. In our previous studies [M. Sato et al., Phys. Rev. E 87, 032403 (2013); J. Phys. Soc. Jpn. 82, 084804 (2013)], we showed that the ordering of particles depends on the direction of the external force. In the studies, however, the system size and the number of particles are small, so the behaviors we observed corresponds to the motions in the initial stage of crystallization. In this paper, using a longer container and more particles, we investigate how solidification in a narrow system proceeds. We also study the effect of the shape of simulation box on the ordering of particles. When we use a rhomboid as a simulation box, the ratio of the particles with the face-centered cubic structure to those with the hexagonal close-packed structure is larger than that in a cuboid system.

Crystallization, phase evolution and corrosion of Fe-based metallic glasses: An atomic-scale structural and chemical characterization study

Understanding phase changes, including their formation and evolution, is critical for the performance of functional as well as structural materials. We analyze in detail microstructural and chemical transformations of the amorphous steel Fe50Cr15Mo14C15B6 during isothermal treatments at temperatures ranging from 550 to 800°C. By combining high-resolution transmission electron microscopy and Rietveld analyses of X-ray diffraction patterns together with the local chemical data obtained by atom probe tomography, this research provides relevant information at the atomic scale about the mechanisms of crystallization and the subsequent phases evolution. During the initial stages of crystallization a stable (Fe,Cr)23(C,B)6 precipitates as well as two metastable intermediates of M3(C,B) and the intermetallic χ-phase. When full crystallization is reached, only a percolated nano-scale Cr-rich (Fe,Cr)23(C,B)6 and Mo-rich η-Fe3Mo3C structure is detected, with no evidence to suggest that other phases appear at any subsequent time. Finally, the corrosion behavior of the developed phases is discussed from considerations of the obtained atomic information.

Epitaxial Crystal Growth of Nitratine on Calcite (10.4) Cleavage Faces at the Nanoscale

In this article, we present a study of the epitaxial growth of nitratine (NaNO3) on calcite (CaCO3) from ethanolic solutions. By using sodium nitrate saturated solutions in ethanol we were able to observe the initial stages of nitratine crystallization on calcite (10.4) cleaved surfaces with atomic force microscopy (AFM). Although the oriented epitaxial growth of nitratine crystallites on calcite is independent from the solvent used (water, ethanol, or mixtures of them), the use of ethanolic solutions saturated with respect to nitratine is preferable for surface imaging in the AFM fluid cell. Additional nanotribology AFM experiments allowed us to measure shear strengths necessary to remove crystallites of nitratine from calcite (10.4) faces. On the basis of both AFM observations and measured shear strengths, the mechanism of epitaxial growth of nitratine on calcite (10.4) is discussed.

Magnetic monitoring approach to nanocrystallization kinetics in Fe-based bulk amorphous alloy

Much of the recent metallic glass research is devoted to controlling the crystallization of amorphous precursors with the purpose of obtaining amorphous matrix nanocrystalline alloys which combine unmatched soft magnetic properties with good mechanical properties. Therefore, it is crucial to have better understanding of crystallization mechanisms and thermal dependence of nanocrystals that are formed by annealing. This study deals with the nanocrystallization kinetics of Cu-modified Fe–Co–Ni–B–Si–Nb bulk amorphous alloy using a non-conventional technique, i.e. isothermal magnetic monitoring, as applied to classical Johnson-Mehl-Avrami-Kolmogorov theory. The kinetic parameters determined via isothermal magnetic monitoring were compared with various non-isothermal approaches based on conventional thermal analysis where excellent agreement was obtained in local Avrami index and activation energy for nanocrystallization. Analyzing the local kinetics, α–(Fe,Co) nanocrystals were found to evolve through rather distinct regimes during annealing. The initial stage of crystallization is controlled by non-steady state diffusion field and transient nucleation effects, the intermediate stage is characterized by diffusion-controlled growth of crystals with negligible initial volume, and the late stage by suppressed growth kinetics due to soft-impingement diffusion and pile-up of solute atoms with slow diffusivity. Microstructural evolution of the nanocrystalline α–(Fe,Co) phase was examined by transmission electron microscopy and discussed according to the characteristics of distinct transformation regimes deduced from the kinetic analysis.

Kinetics of Isothermal Crystallization of Hydrogenated Castor Oil‐in‐Water Emulsions

AbstractKinetics of isothermal crystallization of hydrogenated castor oil in water emulsions exhibiting multiple crystal morphologies have been studied experimentally by DSC and polarized light microscopy. The induction time of nucleation increases with the increase of the isothermal temperature under which crystallization occurred. Crystal growth has been observed by microscopy showing that both crystal morphologies, fibers and rosettes, grow linearly at the initial stage of crystallization and then slow down to reach a plateau value. The Avrami model, which has been widely used in kinetics studies of triacylglycerol systems, was employed to fit experimental results at different isothermal temperatures. It was found that experimental trends could be captured by introducing the volume fraction of each type of morphology into three‐dimensional and one‐dimensional full Avrami models.

Spherulitic crystallization mechanism of a Zr-based bulk metallic glass during laser processing

Laser deposition of a Zr–Cu–Ni–Al–Nb metallic glass has been studied in an effort to understand and evaluate the challenges of fabricating metallic glass components via additive manufacturing techniques. The parent amorphous alloy crystallizes into micro-scale spherulites at heating rates up to 104 K/s during laser processing. Detailed microstructural and compositional examinations of the spherulites reveals that rapid heating suppresses phase separation and nucleation at the initial stage of crystallization, resulting in a growth-dominated crystallization behavior. The activation energy of spherulitic crystallization is estimated to be 124 kJ/mol, significantly lower than that of multiphase nanocrystallization reported elsewhere. The low activation energy of spherulitic crystallization is consistent with observations of the short-range redistribution of constituent elements at the amorphous–crystalline interfaces during growth of the spherulites.

Adhesion strength of nickel and zinc coatings with copper base electroplated in conditions of external stimulation by laser irradiance

Purpose. The investigation of laser irradiance influence on the adhesion strength of nickel and zinc coatings with copper base and the research of initial stages of crystallization for nickel and zinc films. Methodology. Electrodeposition of nickel and zinc films from the standard sulphate electrolyte solutions was carried out on the laser-electrolytic installations, built on the basis of gas discharge CO2-laser and solid ruby laser KVANT-12. The adhesion strength of metal coatings with copper base are defined not only qualitatively using the method of meshing and by means of multiple bending, but also quantitatively by means of indention of diamond pyramid into the border line between coating and base of the side section. Spectrum microanalysis of the element composition of the border line “film and base” is carried out using the electronic microscope REMMA-102-02. Findings. Laser irradiance application of the cathode region in the process of electroplating of metal coatings enables the adhesion strength improvement of coating with the base. Experimental results of adhesive strength of the films and the spectrum analysis of the element composition for the border line between film and base showed that during laser-assisted electroplating the diffusion interaction between coating elements and the base metal surface takes place. As a result of this interaction the coating metal diffuses into the base metal, forming transition diffused layer, which enhances the improvement of adhesion strength of the coatings with the base. Originality. It is found out that ion energy increase in the double electric layer during interaction with laser irradiance affects cathode supersaturation at the stage of crystallization. Hence, it also affects the penetration depth of electroplated material ions into the base metal, which leads to the adhesion strength enhancement. Practical value. On the basis of research results obtained during the laser-assisted electroplating of the structure and mechanical characteristics of nickel and zinc metal films, their connection with the laser irradiance parameters is found out. Laser irradiance application, depending on the electroplating mode (galvanostatic or potentiostatic) allows obtaining the equilibrium structure or, on the other hand, nonequilibrium structure.