Crystallization

Distribution by Scientific Domains
Distribution within Chemistry

Kinds of Crystallization

  • cold crystallization
  • cooling crystallization
  • fractional crystallization
  • isothermal crystallization
  • melt crystallization
  • membrane-protein crystallization
  • non-isothermal crystallization
  • polymer crystallization
  • preferential crystallization
  • protein crystallization
  • reactive crystallization
  • situ crystallization
  • successful crystallization
  • surface crystallization

  • Terms modified by Crystallization

  • crystallization ability
  • crystallization age
  • crystallization behavior
  • crystallization behaviour
  • crystallization buffer
  • crystallization condition
  • crystallization data
  • crystallization drop
  • crystallization experiment
  • crystallization history
  • crystallization image
  • crystallization kinetics
  • crystallization mechanism
  • crystallization method
  • crystallization peak
  • crystallization phenomenoN
  • crystallization procedure
  • crystallization process
  • crystallization property
  • crystallization rate
  • crystallization screen
  • crystallization screening
  • crystallization solution
  • crystallization structure
  • crystallization studies
  • crystallization system
  • crystallization technique
  • crystallization techniques
  • crystallization technology
  • crystallization temperature
  • crystallization time
  • crystallization trials

  • Selected Abstracts


    Crystallization for the Downstream Processing of Proteins

    ENGINEERING IN LIFE SCIENCES (ELECTRONIC), Issue 3 2005
    S. Schmidt
    Abstract Protein crystallization offers great potential in downstream processing of pharmaceutical protein active ingredients. The advantages, which are well known and widely utilized in low-molecular weight crystallization, can also be expected to be found to some extent in protein crystallization. However, there is still a marked need for improvement in two main areas of protein processing, namely, in crystallization from impure solutions and scale-up. [source]


    Microstructure of fat crystallizing on a collagenous surface

    EUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 9 2005
    Michael A. Rogers
    Abstract The effect of surface quality on fat crystallization was examined for glass and gelatin surfaces using three-dimensional polarized light microscopy in an attempt to develop a model system for how fat may crystallize in arteries. A mixture of the high-melting fraction of milk fat and triolein was crystallized from 60,C to 30,C at a rate of 0.5,C/min on both glass and gelatin surfaces. Crystallization of fat on the gelatin surface led to an increase in the amount of nucleation and resulted in a more even distribution of crystal mass than crystallization on the glass surface. No evidence of crystal precipitation or glass surface crystallization was evident. We postulate that the gelatin acted as a template for nucleation. Similar trends were identified using fractal analysis. Fat crystallized on gelatin had a higher fractal dimension than fat crystallized on glass. [source]


    Back Cover: Fundamentals of Metal-induced Crystallization of Amorphous Semiconductors (Adv. Eng.

    ADVANCED ENGINEERING MATERIALS, Issue 3 2009
    Mater.
    The Backcover shows a covering layer of aluminum lowers the crystallization temperature of amorphous silicon (a-Si). First the a-Si covers ("wets") the grain boundaries in the aluminum layer (Al). Once the wetting a-Si film has reached a critical thickness, crystallization starts at the grain boundaries. More details can be found in the article by E. J. Mittemeijer on page 131. [source]


    Fundamentals of Metal-induced Crystallization of Amorphous Semiconductors

    ADVANCED ENGINEERING MATERIALS, Issue 3 2009
    Zumin Wang
    Abstract A general, quantitative model has been developed that provides fundamental understanding of the metal-induced crystallization (MIC) of amorphous semiconductors. Interface thermodynamics has been shown to play a decisive role for the whether or not occurrence of MIC. The model has been employed to predict the MIC temperature for various metal/amorphous-semiconductor systems. A consequence of the model is the prediction that the thickness of an ultrathin, pure Al film put on the top of an amorphous Si layer can be used as a very accurate tool to tune the crystallization temperature of amorphous Si. These theoretical predictions have been confirmed experimentally. The fundamental understanding reached may lead to pronounced technological progress in the low-temperature manufacturing of crystalline-Si-based devices deposited on cheap and flexible substrates such as glasses, plastics, and possibly even papers. [source]


    Crystallization of Highly Supercooled Silicate Melts

    ADVANCED ENGINEERING MATERIALS, Issue 12 2006
    M. Roskosz
    Crystallization of liquids in the system CaO-MgO-Al2O3 -SiO2 at one atmosphere has been studied at temperatures between the glass transition (Tg) and the solidus. To determine the textures, compositions and unit-cell parameters of the crystalline phases, the authors have characterized the experimental charges over a wide range of length scales by scanning and transmission electron microscopy, electron microprobe analyses, X-ray diffraction, and Raman spectroscopy. With increasing temperature, crystals tend to reach the equilibrium composition, but the relative importance of thermodynamic and kinetic factors is a single function of T - Tg, regardless of liquid composition. This feature is of considerable practical interest as it provides the possibility, not only to predict, but also to control the composition of the crystallizing phases. [source]


    Time,Temperature,Transformation (TTT) Diagrams for Crystallization of Metal Oxide Thin Films

    ADVANCED FUNCTIONAL MATERIALS, Issue 17 2010
    Jennifer L. M. Rupp
    Abstract Time,temperature,transformation (TTT) diagrams are proposed for the crystallization of amorphous metal oxide thin films and their specific characteristics are discussed in comparison to glass-based materials, such as glass-ceramics and metallic glasses. The films crystallize from amorphous to full crystallinity in the solid state. As an example the crystallization kinetics for a single-phase metal oxide, ceria, and its gadolinia solid solutions are reported made by the precipitation thin-film method spray pyrolysis. The crystallization of an amorphous metal oxide thin film generally follows the Lijschitz,Sletow,Wagner (LSW) Ostwald ripening theory: Below the percolation threshold of 20 vol% single grains crystallize in the amorphous phase and low crystallization rates are measured. In this state no impact of solute on crystallization is measurable. Once the grains form primary clusters above the threshold the solute slows down crystallization (and grain growth) thus shifting the TTT curves of the doped ceria films to longer times and higher temperatures in comparison to undoped ceria. Current views on crystallization of metal oxide thin films, the impact of solute dragging, and primary TTT diagrams are discussed. Finally, examples on how to use these TTT diagrams for better thermokinetic engineering of metal oxide thin films for MEMS are given, for example, for micro-Solid Oxide Fuel Cells and resistive sensors. In these examples the electrical properties depend on the degree of crystallinity and, thereby, on the TTT conditions. [source]


    Biomineralization: Mussel-Inspired Polydopamine Coating as a Universal Route to Hydroxyapatite Crystallization (Adv. Funct.

    ADVANCED FUNCTIONAL MATERIALS, Issue 13 2010
    Mater.
    A universal biomineralization approach that can integrate hydroxyapatites on virtually any type and shape of substrate is presented. H. Lee, C. B. Park, and co-workers show on page 2132 that polydopamine, a catecholamine surface modifier inspired by adhesive proteins found in mussels, enriches calcium ions at the interface, facilitating the formation of biomimetic hydroxyapatite crystals. [source]


    Mussel-Inspired Polydopamine Coating as a Universal Route to Hydroxyapatite Crystallization

    ADVANCED FUNCTIONAL MATERIALS, Issue 13 2010
    Jungki Ryu
    Abstract Bone tissue is a complex biocomposite material with a variety of organic (e.g., proteins, cells) and inorganic (e.g., hydroxyapatite crystals) components hierarchically organized with nano/microscale precision. Based on the understanding of such hierarchical organization of bone tissue and its unique mechanical properties, efforts are being made to mimic these organic,inorganic hybrid biocomposites. A key factor for the successful designing of complex, hybrid biomaterials is the facilitation and control of adhesion at the interfaces, as many current synthetic biomaterials are inert, lacking interfacial bioactivity. In this regard, researchers have focused on controlling the interface by surface modifications, but the development of a simple, unified way to biofunctionalize diverse organic and inorganic materials remains a critical challenge. Here, a universal biomineralization route, called polydopamine-assisted hydroxyapatite formation (pHAF), that can be applied to virtually any type and morphology of scaffold materials is demonstrated. Inspired by the adhesion mechanism of mussels, the pHAF method can readily integrate hydroxyapatites on ceramics, noble metals, semiconductors, and synthetic polymers, irrespective of their size and morphology (e.g., porosity and shape). Surface-anchored catecholamine moieties in polydopamine enriches the interface with calcium ions, facilitating the formation of hydroxyapatite crystals that are aligned to the c -axes, parallel to the polydopamine layer as observed in natural hydroxyapatites in mineralized tissues. This universal surface biomineralization can be an innovative foundation for future tissue engineering. [source]


    Crystallization and Grain Growth Kinetics for Precipitation-Based Ceramics: A Case Study on Amorphous Ceria Thin Films from Spray Pyrolysis

    ADVANCED FUNCTIONAL MATERIALS, Issue 21 2009
    Jennifer L. M. Rupp
    No abstract is available for this article. [source]


    Crystallization and Grain Growth Kinetics for Precipitation-Based Ceramics: A Case Study on Amorphous Ceria Thin Films from Spray Pyrolysis

    ADVANCED FUNCTIONAL MATERIALS, Issue 17 2009
    Jennifer L. M. Rupp
    Abstract The introductory part reviews the impact of thin film fabrication, precipitation versus vacuum-based methods, on the initial defect state of the material and microstructure evolution to amorphous, biphasic amorphous-nanocrystalline, and fully nanocrystalline metal oxides. In this study, general rules for the kinetics of nucleation, crystallization, and grain growth of a pure single-phase metal oxide thin film made by a precipitation-based technique from a precursor with one single organic solvent are discussed. For this a complete case study on the isothermal and non-isothermal microstructure evolution of dense amorphous ceria thin films fabricated by spray pyrolysis is conducted. A general model is established and comparison of these thin film microstructure evolution to kinetics of classical glass-ceramics or metallic glasses is presented. Knowledge on thermal microstructure evolution of originally amorphous precipitation-based metal oxide thin films allows for their introduction and distinctive microstructure engineering in devices-based on microelectromechanical (MEMS) technology such as solar cells, capacitors, sensors, micro-solid oxide fuel cells, or oxygen separation membranes on Si-chips. [source]


    Directed Helical Growth: A Spring-Like Behavior of Chiral Block Copolymer with Helical Nanostructure Driven by Crystallization (Adv. Funct.

    ADVANCED FUNCTIONAL MATERIALS, Issue 3 2009
    Mater.
    Crystalline helices (PLLA crystallization directed by helical confined microdomains) and crystalline cylinders (phase transformation of helical nano structures dictated by crystallization) are obtained by controlling the crystallization temperature of PLLA with respect to the glass transition temperature of PS in PS-PLLA block copolymers; this process is described by J.-W. Chiang et al. on page 448. A spring-like behavior of the PLLA helical nanostructures embedded in the PS matrix can be driven by crystallization, so as to dictate the transformation of the helices, resulting in crystalline cylinders that might represent a possible avenue for the design of switchable large-strain actuators. [source]


    A Spring-Like Behavior of Chiral Block Copolymer with Helical Nanostructure Driven by Crystallization

    ADVANCED FUNCTIONAL MATERIALS, Issue 3 2009
    Yeo-Wan Chiang
    Abstract The crystallization of helical nanostructure resulting from the self-assembly of a chiral diblock copolymer, poly(styrene)- b -poly(L -lactide) (PS-PLLA), is studied. Various crystalline PS-PLLA nanostructures are obtained by controlling the crystallization temperature of PLLA (Tc,PLLA), at which crystalline helices and crystalline cylinders occur while Tc,PLLA,<,Tg,PS (the glass transition temperature of PS) and Tc,PLLA,,,Tg,PS, respectively. As evidenced by selected-area electron diffraction and two-dimensional X-ray diffraction results, the PLLA crystallites under confinement reveal a unique anisotropic character regardless of the crystallization temperature. On the basis of observed uniaxial scattering results the PLLA crystallites grown within the microdomains are identified as crystals with preferential growth directions either along the [100] or along the [110]-axes of the PLLA crystalline unit cell, at which the molecular chains and the growth direction are normal and parallel to the central axes of helices, respectively. The formation of this exclusive crystalline growth is attributed to the spatial confinement effect for crystallization. While Tc,PLLA,<,Tg,PS, owing to the directed crystallization by helical confinement, the preferential crystalline growth leads to the crystallization following a helical track with growth direction parallel to the central axes of helices through a twisting mechanism. Consequently, winding crystals with specific crystallographic orientation within the helical microdomains can be found. By contrast, while Tc,PLLA,,,Tg,PS, the preferential growth may modulate the curvature of microdomains by shifting the molecular chains to access the fast path for crystalline growth due to the increase in chain mobility. As a result, a spring-like behavior of the helical nanostructure can be driven by crystallization so as to dictate the transformation of helices, resulting in crystalline cylinders that might be applicable to the design of switchable large-strain actuators. [source]


    Fiber Field-Effect Device Via In Situ Channel Crystallization

    ADVANCED MATERIALS, Issue 37 2010
    Sylvain Danto
    The in situ crystallization of the incorporated amorphous semiconductor within the multimaterial fiber device yields a large decrease in defect density and a concomitant five-order-of-magnitude decrease in resistivity of the novel metal-insulator-crystalline semiconductor structure. Using a post-drawing crystallization process, the first tens-of-meters-long single-fiber field-effect device is demonstrated. This work opens significant opportunities for incorporating higher functionality in functional fibers and fabrics. [source]


    Induced Crystallization of Rubrene in Thin-Film Transistors

    ADVANCED MATERIALS, Issue 30 2010
    Zhefeng Li
    The poor crystallinity of rubrene in thin films is an obstacle limiting its practical applications in organic electronics. Here we report a strategy of using 6,13-pentacenequinone (PQ), an easily crystallized insulating molecule, as the template layer to induce the crystallization of rubrene in vacuum-deposited thin film transistors. This strategy relies on the bilayer steps of octadecylphosphonic acid, which play a unique role in modulating the morphology of PQ. [source]


    Polymer-Controlled Crystallization of Unique Mineral Superstructures

    ADVANCED MATERIALS, Issue 4 2010
    Shao-Feng Chen
    Abstract The origin of complex superstructures of biomaterials in biological systems and the amazing self-assembly mechanisms of their emergence have attracted a great deal of attention recently. Mimicking nature, diverse kinds of hydrophilic polymers with different functionalities and organic insoluble matrices have been designed for the morphogenesis of inorganic crystals. In this Research News, emerging new strategies for morphogenesis and controlled crystal growth of minerals, that is, selective adsorption and mesoscale transformation for highly ordered superstructures, the combination of a synthetic hydrophilic polymer with an insoluble matrix, a substrate, or the air/solution interface, and controlled crystallization in a mixed solvent are highlighted. It is shown that these new strategies can be even further extended to morphogenesis and controlled crystallization of diverse inorganic or inorganic,organic hybrid materials with structural complexity, structural specialties, and improved functionalities. [source]


    Organic Thin-Film Transistors: Controlling Nucleation and Crystallization in Solution-Processed Organic Semiconductors for Thin-Film Transistors (Adv. Mater.

    ADVANCED MATERIALS, Issue 35 2009
    35/2009)
    The grain size in solution-processed organic semiconductor thin films for TFTs can be tuned over a range of three orders of magnitude, report Yueh-Lin Loo and co-workers on p. 3605. The process involves the addition of fractional quantities of "impurities" that are capable of seeding the crystallization of the organic semiconductor, and the control thus exerted permitted studies that correlated increasing device mobility with increasing grain size. [source]


    Controlling Nucleation and Crystallization in Solution-Processed Organic Semiconductors for Thin-Film Transistors

    ADVANCED MATERIALS, Issue 35 2009
    Stephanie S. Lee
    Three orders of magnitude is the range over which the grain size (see figure) can be tuned in solution-processed organic semiconductor thin films for TFTs. Fluorinated triethylsilyl anthradithiophene (FTES-ADT) is added in fractional amounts to seed crystallization of TES-ADT. Correlation between device mobility and grain size in the active layer is described by a composite mobility model that assumes charge-carrier traps are located at grain boundaries. [source]


    Nonclassical Crystallization: Facile Synthesis and Shape Evolution of Single-Crystal Cuprous Oxide (Adv. Mater.

    ADVANCED MATERIALS, Issue 20 2009
    20/2009)
    Lian Gao and co-workers discuss on p. 2068 the synergic effect of oriented attachment and ripening mechanism with face-selective additive adsorption for the formation of various morphologies of single-crystal Cu2O. The frontispiece shows an SEM image of self-assembled microcubic Cu2O mesocrystals, clearly revealing the rarely observed combination of a nonclassical-particle-based crystallization process and subsequent classical crystallization process. [source]


    The Multiple Roles of Additives in CaCO3 Crystallization: A Quantitative Case Study

    ADVANCED MATERIALS, Issue 4 2009
    Denis Gebauer
    To date, the knowledge of the multiple roles of additives in calcium carbonate crystallization results from empirical control of crystal growth. We present a crystallization assay generating controlled supersaturation, which allows the categorization of different modes of additive action. This facilitates a novel understanding of the action of crystallization additives. [source]


    Effect of Ce, Sb, and Sn on Solarization and Crystallization of an X-Ray-Irradiated Photosensitive Glass

    INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 1 2010
    Mohamad Hassan Imanieh
    The effect of Ce, Sb, and Sn photosensitive elements, individually and in combination with each other, on solarization and crystallization of an X-ray irradiated and a nonirradiated lithium silicate-based glass were investigated. According to the results, considering the crystallization behavior of the nonirradiated glasses, they were divided into Ce-bearing and Ce-free groups, in which the former group showed a clearer solarization tendency that manifested as an appearance of an absorbance peak at 318 nm in the spectrophotometry experiment. However, the results showed that in the irradiated glasses, the presence of Sb was more important in terms of improvement in crystallization view. Antimony decreased the differential thermal analysis (DTA) crystallization peak temperature from 655C to 594C and, in combination with the two other elements, changed the surface crystallization mechanism to a bulk one. The reactions that seemed to be responsible for the above-mentioned observations were discussed by spectrophotometry, DTA, X-ray diffraction, and scanning electron microscopic methods. [source]


    Electrochemical Crystallization of Cuprous Oxide with Systematic Shape Evolution,

    ADVANCED MATERIALS, Issue 19 2004
    J. Siegfried
    The growth of Cu2O crystals that are electrochemically deposited as micrometer-size crystals with systematically varying fractions of {100} and {111} faces is reported (the Figure depicts cubic crystals). The methodical and homogeneous shape evolution is achieved by tuning the degree of preferential adsorption of sodium dodecyl sulfate on the {111} faces of growing Cu2O crystals through pH variation. Scale bar: 1,,m. [source]


    Formation of Arrayed Droplets by Soft Lithography and Two-Phase Fluid Flow, and Application in Protein Crystallization,

    ADVANCED MATERIALS, Issue 15 2004
    B. Zheng
    Abstract This paper presents an overview of our recent work on the use of soft lithography and two-phase fluid flow to form arrays of droplets. The crucial issues in the formation of stable arrays of droplets and alternating droplets of two sets of aqueous solutions include the geometry of the microchannels, the capillary number, and the water fraction of the system. Glass capillaries could be coupled to the PDMS microchannels and droplets could be transferred into glass capillaries for long-term storage. The arrays of droplets have been applied to screen the conditions for protein crystallization with microbatch and vapor diffusion techniques. [source]


    The Combination of Colloid-Controlled Heterogeneous Nucleation and Polymer-Controlled Crystallization: Facile Synthesis of Separated, Uniform High-Aspect-Ratio Single-Crystalline BaCrO4 Nanofibers

    ADVANCED MATERIALS, Issue 2 2003
    S.-H. Yu
    Uniform, separated BaCrO4 single-crystalline nanofibers with high aspect ratio (>,5000, see Figure) can be fabricated at room temperature in aqueous solution using a double hydrophilic block copolymer as structure-directing agent and introducing colloidal nucleation agents. Such fibers represent a model case for advanced polymer fillers and the exploration of quasi-1D nanostructures with interesting electrical, optical, or catalytic properties. [source]


    One-Step Synthesis of Chiral Azamacrocycles via Palladium-Catalyzed Enantioselective Amination of 1,5-Dichloroanthraquinone and 1,5-Dichloroanthracene

    ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2010
    Elena R. Ranyuk
    Abstract Asymmetric amination of 1,5-dichloroanthraquinone and 1,5-dichloroanthracene with di- and trioxadiamines catalyzed by palladium complexes with various chiral phosphine ligands gave chiral macrocycles with ee values of up to 60%. The dependence of the chemical yields and enantiomeric excess on the nature of the starting compounds and the phosphine ligands employed was demonstrated. An unexpected spontaneous resolution upon crystallization of the macrocycle comprising anthraquinone and dioxadiamine moieties was observed while in the case of the macrocycle with a trioxadiamine linker racemic monocrystals were obtained. Crystallization of the enantiomerically enriched mixtures afforded chiral macrocycles with 88,99% ee. [source]


    Crystallization and melting behavior of HDPE in HDPE/teak wood flour composites and their correlation with mechanical properties

    JOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2010
    Kamini Sewda
    Abstract The nonisothermal crystallization behavior and melting characteristics of high-density polyethylene (HDPE) in HDPE/teak wood flour (TWF) composites have been studied by differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD) methods. Composite formulations of HDPE/TWF were prepared by varying the volume fraction (,f) of TWF (filler) from 0 to 0.32. Various crystallization parameters evaluated from the DSC exotherms were used to study the nonisothermal crystallization behavior. The melting temperature (Tm) and crystallization temperature (Tp) of the composites were slightly higher than those of the neat HDPE. The enthalpy of melting and crystallization (%) decrease with increase in the filler content. Because the nonpolar polymer HDPE and polar TWF are incompatible, to enhance the phase interaction maleic anhydride grafted HDPE (HDPE-g-MAH) was used as a coupling agent. A shift in the crystallization and melting peak temperatures toward the higher temperature side and broadening of the crystallization peak (increased crystallite size distribution) were observed whereas crystallinity of HDPE declines with increase in ,f in both DSC and WAXD. Linear correlations were obtained between crystallization parameters and tensile and impact strength. 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]


    Crystallization, orientation morphology, and mechanical properties of biaxially oriented starch/polyvinyl alcohol films

    JOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008
    Jing Wang
    Abstract Biaxially oriented starch/polyvinyl alcohol (PVA) films were prepared by stretching starch/PVA blend precursor films that were fabricated by extrusion casting via a twin-screw extruder. Investigations on crystallization, orientation morphology, and mechanical properties of extrusion cast and stretched starch/PVA films were carried out by using differential scanning calorimetry, scanning electron microscope, wide angle X-ray diffraction (WAXD), and tensile testing. The fresh extrusion-cast starch/PVA films, which were almost amorphous, can crystallize spontaneously when aged at room condition. A good compatibility between starch and PVA was obtained by extrusion-casting technology. The well-developed molecular orientation, which did not occur along the machine direction during the extruding process, was observed in stretched film samples. Stretching unaged films can induce crystallization and the orientation of crystalline structures during stretching, resulting in the changes in diffraction peaks of WAXD patterns. The effect of stretch ratio and the orientation distribution in the plane of the film on mechanical properties of stretched films was studied, and the equal biaxially oriented films were found to exhibit in-plane isotropy. 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]


    Crystallization of poly(butylene terephthalate)/poly(ethylene octene) blends: Nonisothermal crystallization

    JOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008
    Jiann-Wen Huang
    Abstract Poly(ethylene octene) (POE), maleic anhydride grafted poly(ethylene octene) (mPOE), and a mixture of POE and mPOE were added to poly(butylene terephthalate) (PBT) to prepare PBT/POE (20 wt % POE), PBT/mPOE (20 wt % mPOE), and PBT/mPOE/POE (10 wt % mPOE and 10 wt % POE) blends with an extruder. The melting behavior of neat PBT and its blends nonisothermally crystallized from the melt was investigated with differential scanning calorimetry (DSC). Subsequent DSC scans exhibited two melting endotherms (TmI and TmII). TmI was attributed to the melting of the crystals grown by normal primary crystallization, and TmII was due to the melting of the more perfect crystals after reorganization during the DSC heating scan. The better dispersed second phases and higher cooling rate made the crystals that grew in normal primary crystallization less perfect and relatively prone to be organized during the DSC scan. The effects of POE and mPOE on the nonisothermal crystallization process were delineated by kinetic models. The dispersed phase hindered the crystallization; however, the well- dispersed phases of an even smaller size enhanced crystallization because of the higher nucleation density. The nucleation parameter, estimated from the modified Lauritzen,Hoffman equation, showed the same results. 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]


    Crystallization and morphology of cholesterol end-capped poly(ethylene glycol)

    JOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2007
    Yuan-Jin Qiu
    Abstract Crystallization and morphology of polyethylene glycol with molecular weight Mn = 2000 (PEG2000) capped with cholesterol at one end (CS-PEG2000) and at both ends (CS-PEG2000-CS) were investigated. It is found that the bulky cholesteryl end group can retard crystallization rate and decrease crystallinity of PEG, especially for CS-PEG2000-CS. Isothermal crystallization kinetics shows that the Avrami exponent of CS-PEG2000 decreases as crystallization temperature (Tc). The Avrami exponent of CS-PEG2000-CS increases slightly with Tc, but it is lower than that of CS-PEG2000. Compared to the perfect spherulite morphology of PEG2000, CS-PEG2000 exhibits irregular and leaf-like spherulite morphology, while only needle-like crystals are observed in CS-PEG2000-CS. The linear growth rate of CS-PEG2000 shows a stronger dependence on Tc than PEG2000. The cholesterol end group alters not only the free energy of the folding surface, but also the temperature range of crystallization regime. The small angle X-ray scattering (SAXS) results show that lamellar structures are formed in all these three samples. By comparing the long periods obtained from SAXS with the theoretically calculated values, we find that the PEG chains are extended in PEG2000 and CS-PEG2000, but they are once-folded in CS-PEG2000-CS. 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2464,2471, 2007 [source]


    Properties of High-Oleic Palm Oils Derived by Fractional Crystallization

    JOURNAL OF FOOD SCIENCE, Issue 3 2008
    M.R. Ramli
    ABSTRACT:, High-oleic palm oil (HOPO) with an oleic acid content of 59.0% and an iodine value (IV) of 78.2 was crystallized in a 200-kg De Smet crystallizer with a predetermined cooling program and appropriate agitation. The slurry was then fractionated by means of dry fractionation at 4, 8, 10, 12, and 15 C. The oil and the fractionated products were subjected to physical and chemical analyses, including fatty acid composition, triacylglycerol and diacylglycerol composition, solid fat content, cloud point, slip melting point, and cold stability test. Fractionation at 15 C resulted in the highest olein yield but with minimal oleic acid content. Due to the enhanced unsaturation of the oil, fractionation at relatively lower crystallization temperature showed a considerable effect on fatty acid composition as well as triacylglycerol and diacylglycerol composition of liquid fractions compared to higher crystallization temperature. The olein and stearin fractionated at 4 C had the best cold stability at 0 C and sharper melting profile, respectively. [source]


    Crystallization Kinetics and X-ray Diffraction of Crystals Formed in Amorphous Lactose, Trehalose, and Lactose/Trehalose Mixtures

    JOURNAL OF FOOD SCIENCE, Issue 5 2005
    Song Miao
    ABSTRACT: Effects of storage time and relative humidity on crystallization kinetics and crystal forms produced from freeze-dried amorphous lactose, trehalose, and a lactose/trehalose mixture were compared. Samples were exposed to 4 different relative water vapor pressure (RVP) (44.1%, 54.5%, 65.6%, 76.1%) environments at room temperature. Crystallization was observed from time-dependent loss of sorbed water and increasing intensities of peaks in X-ray diffraction patterns. The rate of crystallization increased with increasing storage humidity. Lactose crystallized as ,-lactose monohydrate, ,-anhydrous, and anhydrous forms of ,- and ,-lactose in molar ratios of 5:3 and 4:1 in lactose and lactose/trehalose systems. Trehalose seemed to crystallize as a mixture of trehalose dihydrate and anhydrate in trehalose and lactose/trehalose systems. The crystal forms in a mixture of lactose and trehalose did not seem to be affected by the component sugars, but crystallization of the component sugars was delayed. Time-dependent crystallization of lactose and trehalose in the lactose-trehalose mixture could be modeled using the Avrami equation. The results indicated that crystallization data are important in modeling of crystallization phenomena and predicting stability of lactose and trehalose-containing food and pharmaceutical materials. Keywords: crystallization, lactose, trehalose, crystal form, X-ray diffraction [source]