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Crystal Morphology (crystal + morphology)
Selected AbstractsTemplate-Directed Control of Crystal MorphologiesMACROMOLECULAR BIOSCIENCE, Issue 2 2007Fiona C. Meldrum Abstract Biominerals are characterised by unique morphologies, and it is a long-term synthetic goal to reproduce these synthetically. We here apply a range of templating routes to investigate whether a fascinating category of biominerals, the single crystals with complex forms, can be produced using simple synthetic methods. Macroporous crystals with sponge-like morphologies identical to that of sea urchin skeletal plates were produced on templating with a sponge-like polymer membrane. Similarly, patterning of individual crystal faces was achieved from the micrometer to nanometer scale through crystallisation on colloidal particle monolayers and patterned polymer thin films. These experiments demonstrate the versatility of a templating approach to producing single crystals with unique morphologies. [source] Crystal Morphology of Mesoporous Silica Thin Films Synthesized by the Spin-Coating Method Using PEO,PPO,PEO Triblock CopolymerJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2002Gyeong-Su Park Mesoporous thin films on Si substrates with thicknesses of about 460,610 nm have been synthesized by the spin-coating method using a Pluronic EO77PO29EO77 (F68), EO104PO39EO104 (F88), and EO133PO50EO133 (F108) triblock copolymer system. The triblock copolymers were preserved within the synthesized mesoporous thin films. Transmission electron microscopy (TEM) characterization of these films clearly demonstrates that long-range mesostructural ordering strongly depends on the molecular weight of the poly(ethylene oxide),poly(propylene oxide),poly(ethylene oxide) (PEO,PPO,PEO) triblock copolymer, with lower molecular weight producing higher degrees of order. Plane and cross-sectional high-resolution TEM studies coupled with X-ray diffraction (XRD) analysis also show that highly ordered F68 mesoporous silica thin film forms a cubic structure with a lattice spacing a= 6.70 nm. [source] Influence of citric acid on calcium sulfate dihydrate crystallization in aqueous mediaCRYSTAL RESEARCH AND TECHNOLOGY, Issue 2 2007S. Titiz-Sargut Abstract The crystallization of Calcium sulfate dihydrate produced by the reaction between pure Ca(OH)2 suspension and H2SO4 solution was investigated at different pH values, temperatures and citric acid concentrations. Crystal size distributions, filtration rates and zeta potentials of gypsum were determined as a function of citric acid concentrations at pH 3.5 and 65°C. The influence of citric acid on the morphology of gypsum was also investigated and discussed. The average particle size of gypsum was reached to maximum in the presence of approximately 2500 ppm citric acid concentration, where the minimum cake resistance and maximum filtration rate were obtained. In the presence of citric acid, various crystal morphologies such as tabular, plate-like, double-taper leaf-like and flower-like, etc., were obtained. The change of morphology is related to the preferential adsorption of citric acid on different crystallographic faces. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Crystallization of carbohydrate oxidase from Microdochium nivaleACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 6 2009Jarmila Du Microdochium nivale carbohydrate oxidase was produced by heterologous recombinant expression in Aspergillus oryzae, purified and crystallized. The enzyme crystallizes with varying crystal morphologies depending on the crystallization conditions. Several different crystal forms were obtained using the hanging-drop vapour-diffusion method, two of which were used for diffraction measurements. Hexagon-shaped crystals (form I) diffracted to 2.66,Å resolution, with unit-cell parameters a = b = 55.7, c = 610.4,Å and apparent space group P6222. Analysis of the data quality showed almost perfect twinning of the crystals. Attempts to solve the structure by molecular replacement did not give satisfactory results. Recently, clusters of rod-shaped crystals (form II) were grown in a solution containing PEG MME 550. These crystals belonged to the monoclinic system C2, with unit-cell parameters a = 132.9, b = 56.6, c = 86.5,Å, , = 95.7°. Data sets were collected to a resolution of 2.4,Å. The structure was solved by the molecular-replacement method. Model refinement is currently in progress. [source] The influence of supersaturation on crystal morphology , experimental and theoretical studyCRYSTAL RESEARCH AND TECHNOLOGY, Issue 9 2005Jun Jun Lu Abstract The surface docking approach of molecular modeling for prediction of crystal morphology in the presence of additives is further developed in this work. It is modified in order to take into account the influence of supersaturation on the crystal habit. With the introduction of the BCF theory and the 2-D growth mechanism in the above mentioned approach predictions have been carried out for paracetamol and caprolactam crystals, respectively. The verifications by crystals grown from solutions as simulated by the computer model give good agreements. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Guanine-Based Biogenic Photonic-Crystal Arrays in Fish and SpidersADVANCED FUNCTIONAL MATERIALS, Issue 2 2010Avital Levy-Lior Abstract Biological photonic systems composed of anhydrous guanine crystals evolved separately in several taxonomic groups. Here, two such systems found in fish and spiders, both of which make use of anhydrous guanine crystal plates to produce structural colors, are examined. Measurements of the photonic-crystal structures using cryo-SEM show that the crystal plates in both fish skin and spider integument are ,20-nm thick. The reflective unit in the fish comprises stacks of single plates alternating with ,230-nm-thick cytoplasm layers. In the spiders the plates are formed as doublet crystals, cemented by 30-nm layers of amorphous guanine, and are stacked with ,200,nm of cytoplasm between crystal doublets. They achieve light reflective properties through the control of crystal morphology and stack dimensions, reaching similar efficiencies of light reflectivity in both fish skin and spider integument. The structure of guanine plates in spiders are compared with the more common situation in which guanine occurs in the form of relatively unorganized prismatic crystals, yielding a matt white coloration. [source] Nanostructured Calcite Single Crystals with Gyroid MorphologiesADVANCED MATERIALS, Issue 38-39 2009Alexander S. Finnemore Gyroid-structured calcite crystals are grown by templating though self-assembled copolymer films. The remarkable triply periodic minimal surface is perfectly replicated on the nanometer scale, while single crystallinity is maintained. This is a wholly synthetic route to a crystal morphology found in biological systems, only on a smaller length scale. [source] Morphologies and mechanical properties of HDPE induced by small amount of high-molecular-weight polyolefin and shear stress produced by dynamic packing injection moldingJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2008Zhanchun Chen Abstract To better understand the effect of a small amount of high-molecular-weight polyethylene (HMWPE) on the mechanical properties and crystal morphology under the shear stress field, the dynamic packing injection molding (DPIM) was used to prepare the oriented pure polyethylene and its blends with 4% HMWPE. The experiment substantiated that the further improvement of tensile strength along the flow direction (MD) of high-density polyethylene (HDPE)/HMWPE samples was achieved, whereas the tensile strength along the transverse direction (TD) still substantially exceeded that of conventional molding. Tensile strength in both flow and TDs were highly enhanced, with improvements from 23 to 76 MPa in MD and from 23 to 31 MPa in TD, besides the toughness was highly improved. So, the samples of HDPE/HMWPE transformed from high strength and brittleness to high strength and toughness. The obtained samples were characterized via SEM and TEM. For HDPE/HMWPE, the lamellae of the one shish-kebab in the oriented region may be stretched into other shish-kebab structures, and one lamella enjoys two shish or even more. This unique crystal morphology could lead to no yielding and necking phenomena in the stress,strain curves of HDPE/HMWPE samples by DPIM. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Retardation of setting of plaster of Paris by organic acids: Understanding the mechanism through molecular modelingJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 12 2004Jörg-Rüdiger Hill Abstract To develop an understanding of the action of specific formulations, the growth of gypsum crystals under the influence of retardation agents (tartaric and citric acid) has been studied using molecular modeling. Surface energies of gypsum and plaster crystal faces were calculated using established protocols. The crystal morphology predicted for gypsum crystals in the absence of retardation agents is in excellent agreement with experiment. The simulations show that only in an alkaline environment is the crystal morphology of gypsum changed by retardation agents. The simulations provide a detailed description of retardation, for example, the specific mechanisms by which tartaric and citric acid retard setting of gypsum and how they differ. At high pH meso, D(,), and L(+) tartaric acid inhibit both the growth of gypsum and the dissolution of plaster while at low pH tartaric acid and citric acid will principally inhibit the growth of gypsum. The simulations provide a molecular rationalization for a range of experimental observations and a basis for the selection of alternate retardation agents. © 2004 Wiley Periodicals, Inc. J Comput Chem 25: 1438,1448, 2004 [source] Experimental determination of solid-liquid-liquid equilibrium phase diagramsAICHE JOURNAL, Issue 6 2007Sau M. Lai Abstract Liquid,liquid phase separation is undesirable in crystallization as it leads to slow crystal growth and uncontrollable crystal morphology. Therefore, it is necessary to identify the conditions under which liquid,liquid phase split occurs, so as to avoid crystallization process taking place at such conditions. In this study, an experimental approach is developed to systematically construct the solid-liquid-liquid equilibrium (SLLE) phase diagram. A four-component system is used to demonstrate the experimental technique and the overall workflow in developing an SLLE phase diagram. © 2007 American Institute of Chemical Engineers AIChE J, 2007 [source] Phenylethynyl End-Capped Fluorinated Imide Oligomer AFR-PEPA- N: Morphology and Processibility CharacteristicsMACROMOLECULAR MATERIALS & ENGINEERING, Issue 1 2007Yuntao Li Abstract Two phenylethynyl phthalic anhydride-capped imide oligomers, AFR-PEPA-2 and AFR-PEPA-8, with molecular weights of 1,601 and 4,699 g,·,mol,1, respectively, were synthesized and characterized. The AFR-PEPA- N oligomers show higher glass transition temperatures and higher thermal decomposition temperatures than phenylethynyl-terminated imide PETI-5. After curing for 1 h at 390,°C, AFR-PEPA-2 and AFR-PEPA-8 have Tgs of 370 and 358,°C, respectively. AFR-PEPA- N oligomers demonstrated lower minimum complex melt viscosities than PETI-5 due to the presence of CF3 group in the backbone structure. 1,601 g,·,mol,1 AFR-PEPA-2 imide oligomer has a complex melt viscosity of 10 Pa,·,s at 340,°C, and 4,699 g,·,mol,1 AFR-PEPA-8 imide oligomer has a complex melt viscosity of 227 Pa,·,s at 371,°C. AFR-PEPA- N film's crystal morphology was observed using polarized optical microscopy and the AFR-PEPA-8 oligomer did not show crystallinity. AFR-PEPA-2 film exhibits semicrystalline behavior and the crystallinity does not disappear until the film is cured above 375,°C. [source] Antifreeze Properties of Polyglycidol Block CopolymersMACROMOLECULAR RAPID COMMUNICATIONS, Issue 23 2007Eti Baruch Abstract In this paper, we describe a new biomimetic approach to the synthesis of block copolymers with antifreeze properties. Our approach focuses on the design of block copolymers that mimic the structure and functionality of antifreeze proteins. Hyperbranched copolymers containing poly(ethylene oxide)-polyethyleneimine blocks and polyglycidol side chains were synthesized and their antifreeze properties were studied. It is shown that these block copolymers can lower the freezing point of water up to 0.8,°C at a relatively low concentration (1 mg,·,mL,1). From DSC measurements it is proven that polyglycidol block copolymers slow down the crystallization kinetics of ice and lead to changes in the ice crystal morphology, as observed by cryo-optical microscopy. [source] High-Throughput Screening of the Influence of Thermal Treatment on the Mechanical Properties of Semicrystalline Polymers: A Case Study for iPPMACROMOLECULAR RAPID COMMUNICATIONS, Issue 1 2004Konrad Schneider Abstract Summary: High-throughput screening is a convenient tool to determine the influence of parameters, such as composition or processing conditions on certain materials' properties. In the present study, iPP was used to construct a combinatorial library made from a processing temperature gradient requiring only a minimised amount of material. Clear changes in the crystalline modification and crystal morphology of the iPP, and their impact on mechanical properties have been identified. The construction of a combinatorial library to study the effect of thermal history upon the properties of polymers. [source] The effect of shear on mechanical properties and orientation of HDPE/mica composites obtained via dynamic packing injection molding (DPIM)POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 1 2010Yufang Xiang Abstract The interfacial interaction and orientation of filler play important roles in the enhancement of mechanical performances for polymer/inorganic filler composites. Shear has been found to be a very effective way for the enhancement of interfacial interaction and orientation. In this work, we will report our recent efforts on exploring the development of microstructure of high density polyethylene (HDPE)/mica composites in the injection-molded bars obtained by so-called dynamic packing injection molding (DPIM), which imposed oscillatory shear on the melt during the solidification stage. The mechanical properties were evaluated by tensile testing and dynamic mechanical analysis (DMA), and the crystal morphology, orientation, and the dispersion of mica were characterized by scanning electron microscopy and two-dimensional wide-angle X-ray scattering. Compared with conventional injection molding, DPIM caused an obvious increase in orientation for both HDPE and mica. More importantly, better dispersion and epitaxial crystallization of HDPE was observed on the edge of the mica in the injection-molded bar. As a result, increased tensile strength and modulus were obtained, accompanied with a decrease of elongation at break. The obtained data were treated by Halpin,Tsai model, and it turned out that this model could be also used to predict the stiffness of oriented polymer/filler composites. Copyright © 2009 John Wiley & Sons, Ltd. [source] On the real crystal octahedraACTA CRYSTALLOGRAPHICA SECTION A, Issue 6 2002Yury L. Voytekhovsky A real crystal octahedron is defined as any polyhedron bounded, at least, by some of four pairs of parallel planes being in a standard crystallographic orientation with arbitrary distances between them. All the combinatorially non-equivalent shapes (30 in total) are found and characterized by 2-subordination symbols, automorphism group orders and symmetry point groups. The results are discussed with respect to the diamond crystal morphology. [source] Single-scattering properties of aggregates of platesTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 639 2009Junshik Um Abstract During the 2006 Tropical Warm Pool International Cloud Experiment (TWP-ICE) sponsored by the Atmospheric Radiation Measurement programme, the Scaled Composites Proteus aircraft executed spiral profiles and flew horizontal legs through aging anvils, fresh anvils, and cirrus of unknown origin in the vicinity of Darwin, Australia. Pristine ice crystals including both plates and bullet rosettes, their aggregates, and unclassifiable ice crystals were observed by a Cloud Particle Imager. The widths of observed plates ranged between 80 µm and 200 µm. When a fresh dissipating anvil was observed on 2 February, aggregates of plates contributed 46.2% of the total area of measured ice crystals with maximum dimensions greater than 200 µm, while it was only 7.2% and 1.0% for 27 and 29 January, respectively, when aged cirrus was sampled. Because aggregates of plates have been observed to make large contributions to projected ice crystal area near convection during TWP-ICE and other projects, their single-scattering properties that have not been previously examined are investigated here. The dependence of the scattering phase function P11, asymmetry parameter g, and single-scattering albedo ,0 on three parameters (the area ratio AR, normalized projected area An, and a newly defined aggregation index AI which varies between 0 and 1 with ice crystals with more compact shape having lower AI) defining the three-dimensional shapes of aggregates of plates were calculated using a geometric ray-tracing code at wavelengths , of 0.55, 1.38 and 2.13 µm. The scattering properties depended on the crystal morphology with, for example, the g of an aggregate of plates with a high AI of 0.818 differing by + 6.89% (+6.44%; + 4.55%) from that with a lower AI of 0.378 at , of 0.55 µm (1.38 µm; 2.13 µm), but by only + 0.29% (+0.25%; , 0.03%) from those of the component plates. The ,0 at absorbing , increased with AI, 1 , AR, and An. Adding ray distortion to the aggregates caused a decrease in forward scattering and an increase in lateral and backward scattering, decreasing g, an effect that weakened with , due to absorption. The aggregates of plates with low AI were more influenced by ray distortion compared to those with high AI. The dependence of scattering properties on crystal morphology noted here should be considered when computing bulk scattering properties of ice clouds to determine its importance for climate and remote-sensing studies. Copyright © 2009 Royal Meteorological Society [source] Crystallization and preliminary X-ray study of an N-terminal fragment of rat liver ribosomal P2 proteinACTA CRYSTALLOGRAPHICA SECTION D, Issue 4 2002David Mandelman Ribosomal P proteins have been shown to be involved in the binding of elongation factors and participate in factor-dependent GTP hydrolysis. The P proteins form the pentamer (P1/P2)2,P0 constituting the lateral flexible stalk of the 60S ribosomal subunit. The highly soluble domain (1,65) of rat liver P2 has been overexpressed in Escherichia coli as an N-terminal poly-His-tagged protein and crystallized. To reduce nucleation and improve crystal morphology and diffraction power, the crystals were grown in a gel matrix and an oil barrier was added between the reservoir and the drop to reduce the rate of vapour diffusion. This dramatically reduced the nucleation in the drops and yielded diffraction-quality crystals. Data were collected to 2.4,Å resolution at beamline ID 14-1, ESRF. The crystals belong to the orthorhombic space group P21212, with unit-cell parameters a = 37.7, b = 96.7, c = 135.0,Å. [source] Collapse temperature of solutions important for lyopreservation of living cells at ambient temperature,BIOTECHNOLOGY & BIOENGINEERING, Issue 2 2010Geer Yang Abstract In this study, the collapse temperature was determined using the freeze-drying microscopy (FDM) method for a variety of cell culture medium-based solutions (with 0.05,0.8,M trehalose) that are important for long-term stabilization of living cells in the dry state at ambient temperature (lyopreservation) by freeze-drying. Being consistent with what has been reported in the literature, the collapse temperature of binary water-trehalose solutions was found to be similar to the glass transition temperature (T,g , ,30°C) of the maximally freeze-concentrated trehalose solution (,80,wt% trehalose) during the freezing step of freeze-drying, regardless of the initial concentration of trehalose. However, the effect of the initial trehalose concentration on the collapse temperature of the cell culture medium-based trehalose solutions was identified to be much more significant, particularly when the trehalose concentration is less than 0.2,M (the collapse temperature can be as low as ,65°C). We also determined that cell density from 1 to 10,million cells/mL and ice seeding at high subzero temperatures (,4 and ,7°C) have negligible impact on the solution collapse temperature. However, ice seeding does significantly affect the ice crystal morphology formed during the freezing step and therefore the drying rate. Finally, bulking agents (mannitol) could significantly affect the collapse temperature only when trehalose concentration is low (<0.2,M). However, improving the collapse temperature by using a high concentration of trehalose might be preferred to the addition of bulking agents in the solutions for freeze-drying of living cells. We further confirmed the applicability of the collapse temperature measured with small-scale (2,µL) samples using the FDM system to freeze-drying of large-scale (1,mL) samples using scanning electron microscopy (SEM) data. Taken together, the results reported in this study should provide useful guidance to the development of optimal freeze-drying protocols for lyopreservation of living cells at ambient temperature for easy maintenance and convenient wide distribution to end users, which is important to the eventual success of modern cell-based medicine. Biotechnol. Bioeng. 2010;106: 247,259. © 2010 Wiley Periodicals, Inc. [source] Crystallization and preliminary X-ray crystallographic analysis of a highly stable mutant V107A of glutathione transferase from Anopheles dirus in complex with glutathioneACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 3 2006Jantana Wongsantichon An engineered mutant V107A of the dimeric glutathione transferase enzyme from Anopheles dirus (adgstD4-4) was cocrystallized with glutathione substrate using the hanging-drop vapour-diffusion method. The crystal diffracted to 2.47,Å resolution in space group P3221 (unit-cell parameters a = b = 49.4, c = 272.4,Å). Although the crystal morphology differed from that previously obtained for the wild-type enzyme, the crystal packing was the same. At 318,K, the engineered mutant showed an enzyme stability that was increased by about 32-fold, while possessing a similar catalytic function to the wild type. Structural determination will provide valuable understanding of the role of Val107. This residue is in the dimeric interface and appears to contribute towards enhancing the physical properties of the entire protein. [source] Gypsum Crystallization in the Presence of Cr3+ and Citric AcidCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 5 2010S. T. Sargut Abstract Reactive crystallization of calcium sulfate dihydrate (gypsum) was investigated at pH 3.5 and 65,°C in the presence of citric acid and Cr3+ ions. Concentrations of both additives varied between 0 and 4000,ppm. The combined effect of additives on crystal size distributions, filtration characteristics, and crystal morphology were investigated and discussed. It was found that the effect of citric acid on gypsum morphology was suppressed in the presence of Cr3+ ions. The change of morphology is related to the complex formation between Cr3+ ions and citric acid at high ion concentrations. [source] The Influence of Shear Stress on Crystallization in an Ultrasound LevitatorCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 10 2007S. Sacher Abstract Industrial precipitation processes often use chemical agents to influence crystal morphology and size distribution. This experimental study deals with the investigation of physical parameters including an alternative method to affect crystal growth, thus, avoiding the presence of additives as intrinsic impurities. The influence of shear stress acting on growing crystals within a droplet is investigated in an ultrasound levitator. An ultrasound levitator enables the suspension of a single droplet against gravity and the study of containerless precipitation with specific mechanical forces acting on crystals. The levitator is used as a three-phase reactor with precipitation from the gas and liquid, and as a reactor for precipitation from two different solutions. Calcium carbonate is used as a model system. The variation of temperature and the amount of applied shear stress leads to different amounts of calcium carbonate morphologies. An increase in the shear stress results in more rounded or spherical crystals. The intensity of the shear stress also influences the particle size distributions of the precipitated crystals, i.e., with increasing shear stress, particle size distributions are shifted to smaller sizes. [source] | |||||||||||||||||||||||||