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Needle-like Crystals (needle-like + crystal)

Distribution by Scientific Domains
Polymers and Materials Science57%

Selected Abstracts

Organic Single Crystals: Azeotropic Binary Solvent Mixtures for Preparation of Organic Single Crystals (Adv. Funct.

ADVANCED FUNCTIONAL MATERIALS, Issue 22 2009
Mater.
The inside cover of this issue illustrates the solution-phase self-assembly of organic single crystals by using azeotropic binary solvent mixtures, described by X. Li et al. on page 3610, and is a snap-shot taken during the self-assembly of tri-isopropylsilylethynyl pentacene single crystals from an azeotropic binary solvent mixture of isopropanol plus toluene, on a silicon substrate. These needle-like crystals were growing with time while floating in the bulk of the solution during solvent evaporation, with bright colors showing their birefringence. [source]

Solidification of binary aqueous solution cooled from above

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 1 2010
Shigeo Kimura
Abstract Freezing and melting phenomena are important in many different fields, including crystal growth, casting, metallurgy, geophysics, and oceanography. Solidification of a multi-component solution is the one often observed in nature. In order to investigate basic features of the freezing processes of binary systems, we conducted a series of laboratory experiments in a rectangular box cooled from above using aqueous NaNO3 solution. During the freezing, the solid phase always grows into many needle-like crystals called the mushy layer. We measured the growth of the mushy layer thickness, the solid fraction, the temperature, and the concentration distributions. The average solid fraction is found to increase with time in the mushy layer. This causes a slow descent of the released solute in the mushy layer and its eventual fall into the liquid region below because of gravity. We propose a one-dimensional model to explain the horizontally-averaged mushy layer growth. In the model, the estimate of a heat flux at the mushy-liquid interface due to natural convection is found essential for a correct prediction. The proposed theory predicts well the growth of the mushy-layer and the average solid fraction, once the convective heat flux is properly given. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20278 [source]

Controlled Deposition of Highly Ordered Soluble Acene Thin Films: Effect of Morphology and Crystal Orientation on Transistor Performance

ADVANCED MATERIALS, Issue 48 2009
Christoph W. Sele
Controlling the morphology of soluble small molecule organic semiconductors is crucial for the application of such materials in electronic devices. Using a simple dip-coating process we systematically vary the film drying speed to produce a range of morphologies, including oriented needle-like crystals. Structural characterization as well as electrical transistor measurements show that intermediate drying velocities produce the most uniformly aligned films. [source]

Experimental Study of the Aging and Self-Healing of the Glass/Ceramic Sealant Used in SOFCs

INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 1 2010
Wenning N. Liu
High operating temperatures of solid oxide fuel cells (SOFCs) require that the sealant must function at a high temperature between 600°C and 900°C and in the oxidizing and reducing environments of fuel and air. This paper describes tests to investigate the temporal evolution of the volume fraction of ceramic phases, the evolution of micro-damage, and the self-healing behavior of the glass,ceramic sealant used in SOFCs. It was found that after the initial sintering process, further crystallization of the glass,ceramic sealant does not stop, but slows down and reduces the residual glass content while boosting the ceramic crystalline content. Under a long-term operating environment, distinct fibrous and needle-like crystals in the amorphous phase disappeared, and smeared/diffused phase boundaries between the glass phase and ceramic phase were observed. Meanwhile, the micro-damage was induced by the cooling down process from the operating temperature to room temperature, which can potentially degrade the mechanical properties of the glass/ceramic sealant. The glass/ceramic sealant exhibited self-healing upon reheating to the SOFC operating temperature, which can restore the mechanical performance of the glass/ceramic sealant. [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]

Two new polymorphs of di­phenyl(4-pyridyl)­methyl methacryl­ate

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 11 2004
Gerrit Gobius du Sart
The title compound (D4PyMA), C22H19NO2, exhibits polymorphism after crystallization by slow evaporation from a binary mixture of chloro­form and hexane. Long needle-like crystals have an orthorhombic structure (space group Fdd2), with one mol­ecule in the asymmetric unit, while small tablet-like crystals exhibit a monoclinic crystal structure (space group P21/n), in which two independent but chemically identical mol­ecules comprise the asymmetric unit. The bond lengths and angles are normal, while the torsion angles around the ,C,O, bond linking the di­phenyl(4-pyridyl)methyl and methacryl­ate groups show the flexibility of the mol­ecule by way of packing effects. The two polymorphs both contain weak C,H,, and C,H,O/N contacts but have different conformations. [source]

Corneal injury by wild taro

CLINICAL & EXPERIMENTAL OPHTHALMOLOGY, Issue 9 2006
Emily WH Tang MRCS
Abstract We report a case of crystalline keratopathy caused by Alocasia macrorrhiza. The diagnosis was made based on the observation of needle-like crystals in the corneal stroma following injury to that eye. The condition resolved in 3 months with the disappearance of the crystals confirmed by follow-up confocal microscopy. [source]