Unique Crystalline Morphology Research Articles

Precipitated CaCO3 with Unique Crystalline Morphology Prepared from Limestone

A carbonation method has been applied to induce the precipitation reaction of calcium carbonate powders with unique morphology. The reaction was strongly influenced by temperature, pH, CO2 gas flow rate and flow duration. Characterization of the as-prepared CaCO3 by XRD and SEM demonstrated that the vaterite phase was mostly formed at low temperature and CO2 gas flow rate. Phase transformation from vaterite to calcite phases at room temperature was initiated by the formation of calcite structure in ¼ spherical shapes and was followed by transformation to the rhombic structure. The highest growth of calcite structure, resulting in purity up to 98.6%, occurred at the CO2 gas flow rate of 5 SCFH in 36 s. Aragonite particles were produced at CO2 gas flow rate of 0.5 and 5 SCFH to yield 99.2% and 72.3% phase purities, respectively, with needle-like morphology at a higher temperature of 85oC. Furthermore, the reaction with lower CO2 gas flow rate (2 SCFH) led to the formation of aragonite with a flower-like morphology.

Degradable Polycaprolactone and Polylactide Homopolymer and Block Copolymer Brushes Prepared by Surface-Initiated Polymerization with Triazabicyclodecene and Zirconium Catalysts.

Surface-initiated ring-opening polymerization (SI-ROP) of polycaprolactone (PCL) and polylactide (PLA) polymer brushes with controlled degradation rates were prepared on oxide substrates. PCL brushes were polymerized from hydroxyl-terminated monolayers utilizing triazabicyclodecene (TBD) as the polymerization catalyst. A consistent brush thickness of 40 nm could be achieved with a reproducible unique crystalline morphology. The organocatalyzed PCL brushes were chain extended using lactide in the presence of zirconium n-butoxide to successfully grow PCL/PLA block copolymer (PCL-b-PLA) brushes with a final thickness of 55 nm. The degradation properties of "grafted from" PCL brush and the PCL-b-PLA brush were compared to "grafted to" PCL brushes, and we observed that the brush density plays a major role in degradation kinetics. Solutions of methanol/water at pH 14 were used to better solvate the brushes and increase the kinetics of degradation. This framework enables a control of degradation that allows for the precise removal of these coatings.

Unusual Fractional Crystallization Behavior of Novel Crystalline/Crystalline Polymer Blends of Poly(ethylene suberate) and Poly(ethylene oxide) with Similar Melting Points

Novel crystalline/crystalline polymer blends of biodegradable poly(ethylene suberate) (PESub) and biocompatible poly(ethylene oxide) (PEO) were prepared through a solution and casting method. The basic thermal properties, including both glass transition temperature and melting point, of both of the components are very close to each other. The two components are miscible as no obvious phase separation can be detected, forming novel miscible polymer blends of two crystalline polymers. PESub/PEO blends show two or three crystallization exotherms at different supercoolings. The complex crystallization behaviors are attributed to the occurrence of the fractional crystallization of the minor component of the blends. Depending on the blend composition, the major component of the blend crystallizes first and the minor component crystallizes later. During the crystallization of the major component, the amorphous minor component is completely included the interlamellar region of the major component or most of the amorphous minor component is expelled out of the interlamellar region while only a few is incorporated between the lamellae of the major component. In both cases, the fractional crystallization of the minor component occurs at large supercooling because of the confinement effect of the lamellae of the major component. In the present work, the fractional crystallization of PESub or PEO may occur at large supercooling when its content is low. PESub/PEO blends may be the first model that the fractional crystallization of each component occurs at large supercooling when its content is low; thus, they provide a rare system to study the unique crystalline morphology and crystallization behavior of miscible crystalline/crystalline polymer blends. Such research is very interesting and challenging for a better understanding of the crystalline morphology and crystallization behavior of crystalline polymer blends from both academic and practical viewpoints.

Synthesis, Self‐Assembly, and Properties of Homoarm and Heteroarm Star‐Shaped Inorganic–Organic Hybrid Polymers with a POSS Core

AbstractNovel homoarm and heteroarm star‐shaped inorganic–organic hybrid polymers with a polyhedral oligomeric silsesquioxane (POSS) core are prepared via click chemistry of azide POSS [POSS‐(N3)8], alkynyl poly(L‐lactide) (PLLA), and alkynyl poly(ethylene oxide) (PEO). The melting and crystallization behaviors of the polymers can be adjusted by altering the PLLA to PEO ratio. The hybrid polymers reveal unique crystalline morphology due to the influence of the star‐shaped structure and the mutual influence of PLLA and PEO. The hybrid polymers show different thermostabilities, owing to the different compositions of the polymers. The hydrophilicity can be adjusted by alternating the composition of the PLLA and PEO segments. In addition, the sizes of the polymer micelles change with the change of the ratio of PLLA and PEO arms in the hybrid polymers.magnified image

Manipulating poly(lactic acid) surface morphology by solvent-induced crystallization

Here, we report some unique crystalline morphologies of poly(lactic acid) (PLA) via organic solvent-induced crystallization. It was revealed that the surface morphology of PLA can be fine tuned by simply varying the volume ratio of a mixed solvent (acetone/ethanol). By increasing the ethanol content in the mixed solvent, we observed a morphological evolution of PLA surface from spherulite to shish–kebab and bamboo-cage-like structure. It was also interesting to find that the initial surface structure of PLA plays an important role to determine the final solvent-induced crystalline morphology. This work provides a new method for manipulating PLA crystal morphology through a simple solvent-induced crystallization.

Single crystals of mesoporous tungstenosilicate W-MCM-48 molecular sieves for the conversion of methylcyclopentane (MCP)

Highly ordered W-MCM-48 mesoporous materials containing isolated W atoms in tetrahedral framework positions were successfully synthesized following the S+I− pathway, up to a Si/W of 40. When tungsten content was increased up to a Si/W of 20, the ordered cubic structure was only partially maintained, and for a Si/W of 10 an amorphous phase was obtained. Highly isolated tetrahedral framework tungsten atoms in the W-MCM-48 with a Si/W of 40, have been identified by UV–vis band at 225nm, IR-TF band at 970cm−1 and XRD. The W 4f XPS results suggest that the tungsten atoms exist in two oxidation states, W4+ and W5+. The morphology of the samples varies as a function of tungsten content. The W-MCM-48 samples with a Si/W ratio of 40 existed as crystals with a unique crystalline morphology consisting of cubes truncated rhombic dodecahedrons belonging to the cubic Ia3d space group, while the samples with a Si/W ratio of 20 exhibited a different morphology consisting of spheres and cubes truncated by rhombic dodecahedrons. A comparison of samples with Si/W of ∞, Si/W of 40 and Si/W of 20 was performed using the conversion of MCP carried out at 450°C under H2.

Supramolecular Chemistry of Acyclic Oligopyrroles (Eur. J. Org. Chem. 32/2007)

AbstractThe cover picture shows the two representative characteristics of pyrrole, “duality” as a hydrogen‐bonding acceptor (or a metal‐coordination ligand) N and a hydrogen‐bonding donor (or an anion‐binding ligand) NH and “planarity” to form stacking assemblies, depicted by the disks of Yin and Yang. Acyclic π‐conjugated oligopyrrole derivatives, though less extensively studied so far, often potentially have even more advantages than cyclic ones. For example, the linear oligopyrroles prepared by the author form infinite and discrete coordination oligomers to give emissive spherical colloids and nanorings, hydrogen‐bonding supramolecular assemblies to afford unique crystalline morphologies, and stacking structures to yield organogels that can be controlled by anions. Details are presented in the Microreview by H. Maeda on p. 5313 ff. This picture has been provided by Mr. Takashi Hashimoto, one of the members in the author's group.

Unique crystalline structure and performance of poly(ethylene terephthalate) melt spun fibers

AbstractModification of the threadline dynamics has effected significant alternations in the structure and improvements in the properties of high‐speed melt spun poly(ethylene terephthalate) (PET) fibers. Key process parameters extant in the threadline dynamics, such as temperature, tensile stress, and deformation time, were independently controlled through proper implementation of on‐line perturbations. The placement of a liquid isothermal bath in close proximity to the spinneret in the melt spinning threadline provided tremendous increase in the spinning stress while at the same time controlled the filament temperature corresponding to development of the desired fiber structure. Characterization of the fiber structure and physical properties has been carried out using birefringence measurements, density, shrinkage, x‐ray diffraction, DSC, FTIR spectroscopy, and tensile tests. The results provided sufficient evidence to support the existence of a unique crystalline morphology that led to the significantly improved tensile properties and excellent dimensional stability of the resulting fibers. This unique crystalline morphology was typically characterized by the presence of a larger amount of extended chain segments and an enhanced molecular connectivity. ©1995 John Wiley & Sons, Inc.