Controlling the polymorph and morphology of CaCO3 crystals using surfactant mixtures

Inspired by mineralization in biological organisms, fabrication of higher ordered CaCO(3) crystals modified by surfactants has received much attention. In our present work, mixed surfactants of hexadecyl(trimethyl)azanium bromide and sodium dodecyl sulfate were used to mediate the nucleation and growth of CaCO(3) crystals. When the concentration of sodium dodecyl sulfate in the solution is constant (0.1 mM), the polymorph of CaCO(3) crystals changed from pure vaterite to pure aragonite with increase of the ratio of hexadecyl(trimethyl)azanium bromide to sodium dodecyl sulfate. Various morphologies of vaterite and aragonite were obtained. Based on the time-resolved experiments, we suggest that the flower-like CaCO(3) formed via aggregation of hexagon-like vaterite induced by the surfactants. More importantly, we realized that a cluster-shaped morphology of aragonite was produced through the nucleation of aragonite at the surfaces of the hexagon-like vaterite.     

Nonclassical crystallization: mesocrystals and morphology change of CaCO3 crystals in the presence of a polyelectrolyte additive

Crystallization of calcite from differently concentrated calcium chloride solutions by the CO2 gas diffusion technique in the presence of polystyrene sulfonate yields crystal superstructures with unusual morphology. From the typical calcite rhombohedra as a starting situation, the morphology can be systematically varied via rounded edges and truncated triangles to finally concavely bended lens-like superstructures. Although these "crystals" are apparently well-faceted in light microscopy, electron microscopy analysis and BET reveal that the structures are highly porous and are composed of almost perfectly 3D-aligned calcite nanocrystals scaffolded to the final, partly nicely curved superstructures. At high supersaturations, superstructures with changed symmetry indicative of dipolar interaction potentials between the building blocks are found. The present model case also gives evidence for the importance of nonclassical, mesoscopic processes in crystallization in general.     

Biological synthesis of strontium carbonate crystals using the fungus Fusarium oxysporum

The total biological synthesis of SrCO3 crystals of needlelike morphology arranged into higher order quasi-linear superstructures by challenging microorganisms such as fungi with aqueous Sr2+ ions is described. We term this procedure "total biological synthesis" since the source of carbonate ions that react with aqueous Sr2+ ions is the fungus itself. We believe that secretion of proteins during growth of the fungus Fusarium oxysporum is responsible for modulating the morphology of strontianite crystals and directing their hierarchical assembly into higher order superstructures.     

Biosynthesis of silver, gold and bimetallic nanoparticles using the filamentous fungus Neurospora crassa

The role of nonionic vesicles on the rheological behavior of Pluronic F127 is investigated above the dilute regime and below the cloud point of the nonionic surfactant. F127 is a copolymer possessing sol-gel transition by heating attributed to a phase transition from micellar to cubic. The presence of surfactant vesicles is expected to enhance the compartmentalization of a variety of drugs, independently of their affinity to the solvent. Such entrapment would be suitable for controlled release of the drugs in different applications. We address here a mixed Pluronic-nonionic surfactant system with particular emphasis to the effects of the surfactant on the rheological properties of the Pluronics, and the correlation between these properties and drug release control. The results show that the rheological properties of the mixed system are mainly governed by the behavior of the polymer alone and that the mixed system can be useful to control the percutaneous permeation of a small drug, such as Diclofenac Sodium salt.     

Efficiently stabilized spherical vaterite CaCO3 crystals by carbon nanotubes in biomimetic mineralization

Carbon nanotubes were used to induce the formation of spherical vaterite crystals and stabilize the metastable crystals in the biomimetic mineralization of CaCO3 for the first time. It was found that carboxyl-functionalized multiwalled/single-walled carbon nanotubes (MWNT-COOH/SWNT-COOH) can favor the formation of spherical vaterite crystals and stabilize the crystals. In the presence of CNT-COOH, CaCO3 vaterite crystals with diameters of ca. 1-7 microm coated and embedded with the carbon nanotubes (CNTs) were obtained in 30 min by adding Na2CO3 aqueous solution to the aqueous solution of CaCl2. The spherical vaterite crystals covered by the carboxylic CNTs can exist stably in water for a week. Carboxylic-polymer-functionalized CNTs can also facilitate the formation of spherical vaterite crystals, whereas the formed crystals completely transformed into thermodynamically stable calcite crystals in water within 10 h. "Offline" TEM observations of the mineralization process of CaCO3 in the presence of CNT-COOH or pristine CNTs revealed the stability mechanism of vaterite crystals with carboxylic CNTs. The crystals nucleate at the carboxyl groups of CNT-COOH, grow around the CNTs, and finally form spherical vaterite crystals embedded and covered by the CNTs. The strong interaction between CNT-COOH and crystals together with the strong mechanical strength of CNTs stabilizes the formed vaterite crystals and makes them difficult to dissolve in water. These findings announce that nanomaterials could strongly influence the mineralization of biomineralization matters, which may help us prepare novel biomaterials and bionanomaterials.     

Photoreactivity of crystals of a rhodium dithionite complex with ethyltetramethylcyclopentadienyl ligands: crystal surface morphology changes and degradation

A photoreactive rhodium dithionite complex [(RhCp(Et))(2)(μ-CH(2))(2)(μ-O(2)SSO(2))] (1(Et)) with Cp(Et) (η(5)-C(5)Me(4)Et) ligands was newly synthesized. Upon short-time irradiation with low intensity light, two kinds of stepwise surface morphology changes of the crystal 1(Et) were observed. Prolonged irradiation with high intensity light caused cracking and breaking down of the crystal.     

Hydration of C3a in the presence of CaCO3

The hydration of C₃A with and without CaCO₃ was studied. The techniques used were X-ray diffraction, thermogravimetry, differential thermogravimetry and calorimetry.In the presence of CaCO₃, the hydration of C₃A is accelerated. The hexagonal hydrates are formed first. They react with CaCO₃ to form calcium carboaluminate hydrate. This reaction blocks formation of the cubic hydrate. The latter appears when CaCO₃ is completely consumed.     

三元添加剂水溶液体系制备CaCO3空心球

利用原位聚合方法, 通过加入一定量的引发剂使甲基丙烯酸原位聚合, 在三嵌段共聚物(P123)、聚甲基丙烯酸(PMAA)和十二烷基硫酸钠(SDS)的三元添加剂混合溶液体系中成功地制备了CaCO3空心球. 采用扫描电子显微镜(SEM)和X射线粉末衍射(XRD)对合成样品的形貌、结构进行了表征. 结果显示, 方解石CaCO3空心球直径约0.5-2 μm. 空心球壁由直径约25-35 nm的圆形粒子组成, 壁厚约100-300 nm. 利用核鄄壳机理解释了空心球结构的形成过程.     

Production of CaCO3/hyperbranched polyglycidol hybrid films using spray-coating technique

Biomineralizing organisms employ macromolecules and cellular processing strategies in order to produce highly complex composite materials such as nacre. Bionic approaches translating this knowledge into viable technical production schemes for a large-scale production of biomimetic hybrid materials have met with limited success so far. Investigations presented here thus focus on the production of CaCO(3)/polymer hybrid coatings that can be applied to huge surface areas via reactive spray-coating. Technical requirements for simplicity and cost efficiency include a straightforward one-pot synthesis of low molecular weight hyperbranched polyglycidols (polyethers of 2,3-epoxy-1-propanol) as a simple mimic of biological macromolecules. Polymers functionalized with phosphate monoester, sulfate or carboxylate groups provide a means of controlling CaCO(3) particle density and morphology in the final coatings. We employ reactive spray-coating techniques to generate CaCO(3)/hybrid coatings among which vaterite composites can be prepared in the presence of sulfate-containing hyperbranched polyglycidol. These coatings show high stability and remained unchanged for periods longer than 9 months. By employing carboxylate-based hyperbranched polyglycidol, it is possible to deposit vaterite-calcite composites, whereas phosphate-ester-based hyperbranched polyglycidol leads to calcite composites. Nanoindentation was used to study mechanical properties, showing that coatings thus obtained are slightly harder than pure calcite.     

Photostabilization of an entomopathogenic fungus using composite clay matrices

To provide photostabilization for entomopathogenic fungi by anionic dyes, composite matrices based on clay-biopolymer combinations were prepared. In the first step, the negative surface charge of various clays (montmorillonite, attapulgite, bentonite and kaolinite) was reversed to positive by adsorption to the polycationic biopolymer chitosan. The second step involved adsorption of the toxicologically safe anionic dyes fast green (FG) and naphthol yellow S (NYS) to the clay complexes. Compared with cytotoxic photoprotectants like berberine, palmatine and acriflavine, the anionic dyes have no adverse effects up to a concentration of 1 M. In assays using various clay-chitosan-dye matrices and UV irradiation from a lamp source, it was evident that both FG and NYS provided considerable photostabilization for conidia of the entomopathogenic fungus Aschersonia spp. that served as a model biocontrol agent. Apparently, because of the light-dispersing property, bentonite and attapulgite per se provided significant photoprotection. All clay matrices containing FG provided a substantial photostabilization effect.     

Unsaturated hyperbranched polyester as a surface modifier of CaCO3 and enhanced effect on mechanical properties of HDPE/CaCO3 composites

The unsaturated hyperbranched polyester (UH20) based on Boltorn™ H20 (H20) end‐capped with methacrylate groups and carboxylic acid groups was introduced to treat calcium carbonate (CaCO₃) as a new type of surface modifier by a wet‐coating technique. The interaction between CaCO₃ and modifier was proven to be due to the ionic character by FT‐IR after the extraction with acetone. The maximum amount of tightly bonded UH20 modifier was determined to be around 9% by thermogravimetric analysis (TGA). The incorporation of CaCO₃ coated with UH20 into high‐density polyethylene (HDPE) decreased the mechanical performance of HDPE/CaCO₃ composite in comparison with CaCO₃ coated with stearic acid. In the presence of a small amount of dicumyl peroxide (DCP), a greatly improvement of the notched impact strength as well the tensile strength of HDPE/CaCO₃ coated with UH20 composite was obtained. An enhanced effect in the mechanical performance of the composite between CaCO₃ coated with UH20 and HDPE matrix in the existence of DCP was suggested. Moreover, the morphological structures of impact fracture surface of the HDPE/CaCO₃ composites were studied by scanning electron microscopy (SEM) to confirm the possible mechanism for explaining the improvement of mechanical properties of the composite. Copyright © 2005 John Wiley & Sons, Ltd.     

Induced production of cytochalasans in co-culture of marine fungus Aspergillus flavipes and actinomycete Streptomyces sp.

Secondary metabolites profiles of co-culture of Aspergillus flavipes and Streptomyces sp. that isolated from the same habitat showed an induced production of a series of cytochalasans (five aspochalasins and rosellichalasin, determined by MS and NMR analysis). These cytochalasans were found to be produced by A. flavipes in LC–MS comparison analysis, and biological activity assays revealed that they were able to cause cytotoxic effects against Streptomyces sp. within a wide range of concentrations without causing any effect to the producer A. flavipes, which favoured the producer in competition. Further induction mechanism study applying membrane-separated culture and morphology study with scanning electron microscopy (SEM) suggested that the successful induction of active secondary metabolites required microbial physical contact.     

Deformation morphology of polyester single crystals

Truncated, six-sided single crystals of a 10–16 linear polyester were grown from dilute solution in hexanol, deposited onto Mylar film, and uniaxially deformed at room temperature. For elongations below 10%, the crystals deform uniformly; however, above 20% elongation many cracks spanned by fibrils of 300 Å diameter develop approximately normal to the applied stress direction. Depending on the position of the crystal relative to the draw direction, lateral buckling pleats and cleavage cracks can also occur. Collapse of the nonplanar crystals onto the substrate with a resulting nonuniform adherence of the crystal influences the deformation. The deformation morphology is compared to that of truncated sixfold sector polyethylene crystals. Most notably, in contrast to polyethylene, {010} fold sectors do not deform differently from {110} fold sectors and phase boundaries between {110} and {010} fold sectors do not fracture easily.     

Polyethylene single crystals: Melting and morphology

Determination of important thermodynamic and physical properties of polymers has often been frustrated by the tendency of these materials to reorganize when heated. A novel technique has been developed which permits a more careful examination of the relationships existing between melting and morphology of single crystals. This has lead to the observation that high molecular weight polymers possess much narrower melting ranges than had been previously reported. By using this technique it has been possible to identify distinct transition temperatures for {100} and {110} fold sectors. DTA and DSC data have been previously reported for dried down single crystals. The applicability of this data to single crystals as they exist in suspension is questioned.