Lozenge-shaped Crystals Research Articles

Application of coarse gibbsite agglomerates to formation of 2D and 3D boehmite particles by the dehydration of the hydrothermal treatment and atmospheric pressure

The coarse agglomerates of gibbsite (γ-Al(OH)3) are grateful starting materials for preparation aluminum oxides and hydroxides as boehmite and γ-Al2O3, which are extensively used as a catalysts and catalyst support for the petrochemical industry. By preparing the boehmite particles from the gibbsite and product of the heat gibbsite, we demonstrate the influence of different treatments to a morphology and particle size of the formed boehmite (γ-AlOOH). It is been established for the first time that the flaky-shaped 2D γ-AlOOH particles are formed within the coarse agglomerates producing a laminated packaging film lozenge-shaped crystals which results in a 0.1 cm3/g pore volume and 29 m2/g specific surface area. The obtained data have a high industrial importance in the area of producing materials based on the coarse boehmite agglomerates with different properties.

Phase-Separation-Induced Single-Crystal Morphology in Poly(l-lactic acid) Blended with Poly(1,4-butylene adipate) at Specific Composition

The single-crystal morphology of poly(L-lactic acid) (PLLA) in blending with poly(butylene adipate) (PBA) in PLLA/PBA blends was for the first time reported in melt crystallization. At crystallization temperature (T(c)) = 110 °C, by adding 30 wt % PBA into PLLA, the lamellae exhibit six-stalk dendrites with single-crystal packing. Phase separation and crystallization took place simultaneously at T(c) = 110 °C in PLLA/PBA (70/30) blend, leading to discrete PBA domains and continuous PLLA domains. For PLLA/PBA (70/30) blend, all PBA were rejected from the growth front of PLLA crystals, expelled, and crystallized at ambient temperature as ring-banded PBA spherulites inside the discrete domains only, resulting in a favorable environment for formation of PLLA single crystals in the continuous domain. Atomic force microscopy (AFM) observation on individual crystallites reveals that lozenge-shaped single crystals were packed with a clockwise spiral pattern, stacked in 1-3 layers, and these lozenge-shaped crystals are aligned six hexasected directions into hexastalk dendrites with occasional side branches that are also aligned at 60° to main branches. The monolamellar thickness of lozenge-shaped single crystals was measured to be about 13-34 nm, and the dimension is about 0.8-3 μm along the short axis and 1.6-5 μm along the long axis. Typically, three layers of single crystals are stacked one on another; the lozenge crystals on the bottom layer are about twice as large as those on the top layer, forming a pyramid shape in the depth direction. Formation mechanisms of single crystals in melt-crystallized PLLA/PBA blend from 700 nm film thickness are discussed in correlation with exact phase separation at 30 wt % PBA.

Preparation of single-walled carbon nanotubes-induced poly(p-oxybenzoyl) crystals

Crystallization of oligomers was applied for the preparation of single-walled carbon nanotubes (SWNTs)/poly(p-oxybenzoyl) (POB) crystals using SWNTs as a nucleating agent. Polymerization conditions were investigated to induce the crystallization of POB oligomers through SWNTs. SWNTs/POB plate-like or lozenge-shaped crystals were successfully prepared by direct polymerization of p-hydroxybenzoic acid (HBA) in a mixed solvent of DMF/Py with TsCl in the presence of functionalized SWNTs. The size of the plate-like crystals were ∼200 nm to 3 μm. The crystals consisted of some layers, ∼3 nm thick plates. Model reactions showed that esterification reactions proceed between functionalized SWNTs and HBA monomers in the polymerization system. The obtained crystals exhibited unique morphology and high crystallinity, producing a novel SWNT/POB hybrid. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1265–1277, 2008

Fabrication of Particles and Crystals of Poly(p-phenylene pyromelliteimide) and the Study on Crystal Structure

Morphologies of poly(p-phenylene pyromelliteimide) (PPPI) were investigated by using phase separation during polymerization of pyromellitic dianhydride (PMDA) and p-phenylene diamine (PPDA). Polymerizations were carried out at 330 °C for 6 h. PPDA was added to the solution of PMDA in an aromatic solvent at various temperatures after PMDA was entirely dissolved. The morphology of the precipitates was drastically changed with the temperature of PPDA addition (Tad). When Tad was 240 °C, the fine particles were formed through the formation of droplets via liquid−liquid phase separation. On the contrary, when Tad was higher than 280 °C, the mixture of lozenge-shaped crystals and starlike aggregates of needlelike crystals were formed by the crystallization of oligomers. Tad influenced the degree of imidization of oligomers, resulting in the variation in the morphology of PPPI. Crystal structure and molecular chain orientation of the lozenge-shaped crystals were also investigated by high-resolution transmission electron microscope.

Crystal Structure and Morphology of Poly(16‐hexadecalactone) Chain‐folded Lamellar Crystals

Solution-grown, chain-folded lamellar crystals of poly(16-hexadecalactone) (PHDL) were crystallized isothermally from 1-hexanol at 70 degrees C. The morphology of lozenge-shaped crystals was studied by TEM and AFM. The lamellae are ca. 10 nm thick and the chains run orthogonal to the lamellar surface with folding along (110) and (110) planes. The crystal structure of PHDL was determined by XRD and election diffraction of single crystals. The chains are in the 2(1) helix conformation close to all-trans and the structure consists of an orthorhombic unit cell with a P2(1)2(1)2(1) space group with the lattice constants a = 0.746 +/- 0.001 nm, b = 0.504 +/- 0.001 nm, and c (chain axis) = 4.116 +/- 0.003 nm. There are two chains per unit cell, which exist in an antiparallel arrangement. Molecular packing structure has been studied in detail, taking into account both diffraction data and energy calculations. The setting angles, with respect to a axis, were +/-40 degrees for the corner and center chains, respectively. By using the electron and XRD data, the best molecular packing model was refined to R-factors of 0.168 and 0.196, respectively. A brief comparison of chain-packing structure is also made with related polymer structures.

Crystal Structure and Morphology of Poly(12-dodecalactone)

Poly(12-dodecalactone) (PDDL) crystals in the form of chain-folded lamellae were prepared by isothermal crystallization from a 1-hexanol solution. The lozenge-shaped crystals with and without spiral growth have been studied by transmission electron microscopy and atomic force microscopy. Wide-angle X-ray diffraction data, obtained from PDDL lamellae sedimented to form oriented mats and annealed solvent-cast film, were supplemented with morphological and structural data from electron microscopy. PDDL crystallizes as an orthorhombic form with a P2(1)2(1)2(1) space group and lattice constants of a = 0.746 +/- 0.001 nm, b = 0.500 +/- 0.001 nm, and c (chain axis) = 3.281 +/- 0.003 nm. There are two chains per unit cell, which existed in an antiparallel arrangement. The fiber repeat distance is appropriate for an all-trans backbone conformation for the straight stems. Molecular packing of this structure has been studied in detail, taking into account both diffraction data and energy calculations. The setting angles, with respect to the a axis, were +/-43 degrees for the corner and center chains according to intensity measurements and structure factor calculations. The optimized shift along the crystallographic c axis is 0.1c (0.328 nm). A final model was obtained to yield R = 0.180 with X-ray diffraction data and R = 0.162 with electron diffraction data. A brief comparison is also made with related polymer structures.

Morphology of Poly(p-oxybenzoyl) Crystals Prepared by Direct Polycondensation of p-Hydroxybenzoic Acid with Diphenyl Chlorophosphate

We have studied the morphology of poly( p-oxybenzoyl) (POB) crystals prepared by the direct polycondensation of p-hydroxybenzoic acid (HBA) using diphenyl chlorophosphate (DPCP) in the presence of N,N-dimethylformamide. Lozenge-shaped sheaf-like POB crystals were obtained of which the longer diagonal was 16.0-16.5 μm. Favorable polymerization conditions to prepare the crystal exhibiting clear crystal characteristic were the molar ratio of DPCP to HBA of 1.5, the molar ratio of DMF to HBA of 2.6 and the polymerization concentration of 3.0%. The crystals were comprised of low molecular weight polymer of which the degree of polymerization (DPn) was 14 and possessed extremely high crystallinity. The formation mechanism of the crystals was considered by the polymerization time dependences of morphology, yield, density, DPn, crystallite size, and lattice constant as follows. When the DPn of the oligomers exceeded a critical value of about 3, they were precipitated to form the hexagonal lamellae. The lamellae grew very quickly to sheaf-like lozenge-shaped crystal through the screw dislocation with the continuous precipitation of the oligomer from the solution. Finally, further polymerization and the reorganization of polymer chains occurred in the precipitated crystals.

Evaporitic constraints on the southward drifting of the western Gondwana margin during Early Cambrian times

Lower Cambrian evaporites and carbonates are reported from nearly all the platforms of the western Gondwana margin, which comprises the Souss, Ossa–Morena, Cantabro-Iberian, Armorican and Montagne Noire–Sardinian Basins. Both lithologies were deposited in climatically restricted belts and their changing palaeogeographic distributions, according to recent biostratigraphic correlations, are used to infer the latitudinal motion of this margin. As a result, the time span involved in the Cordubian–Ovetian–Marianian interval (8–10 m.y.) requires a relative high rate of drifting, which supports the high apparent polar wander path rates (defined by palaeomagnetic data) proposed for Early Palaeozoic times. The varied and abundant relics of primary to early diagenetic evaporites (gypsum, anhydrite and halite) demonstrate that extensive evaporitic conditions were associated with carbonate and mixed platform systems in an Early Cambrian arid subtropical belt. Evaporites were originally more abundant than suggested by the reported remains because the deposits have undergone a multistep diagenesis that erased most of the former morphologies. Some petrographic criteria are proposed for recognizing silica pseudomorphs after evaporites, such as the development of ‘chicken-wire’ and enterolithic structures, and the presence of lenticular to lozenge-shaped crystals of gypsum and anhydrite relics.

Morphology and Enzymatic Degradation of Poly(l-lactic acid) Single Crystals

Lamellar single crystals of poly(l-lactic acid) (PLLA) were grown from a 0.05% solution of p-xylene at 90 °C. The hexagonal, truncated-lozenge and lozenge-shaped single crystals with spiral growth were prepared simultaneously, and these crystals were relatively stable under conditions of electron bombardment. The hexagonal and lozenge-shaped crystals gave well-resolved electron diffractograms from which the reciprocal lattice parameters a* = 0.935 nm-1, b* = 1.626 nm-1, and γ* = 90° could be determined, and these lattice parameters corresponded with those of the α structure of PLLA fibers. Accordingly, the hexagonal crystal was considered as pseudo-hexagonal symmetry, but actually with orthorhombic packing of the PLLA chains; i.e., the ratio of the a and b cell parameters is quite equal to √3. The enzymatic degradation of PLLA single crystals with a proteinase-K from the mold Tritirachium album in 50 mM Tris−HCl buffer at pH 8.5 and 37 °C was investigated by means of transmission electron microscopy, atomic force microscopy, high-performance liquid chromatography, and gel permeation chromatography. Enzymatic degradation progressed from the edges of lamellar crystals to yield a rounded shape without decreasing the molecular weights and lamellar thicknesses. It has been concluded that the single crystals were enzymatically hydrolyzed at the disordered chain-packing region of crystal edges rather than chain-folding surfaces of single crystals. As the degradation time increased, in a rare case the diamond holes were observed on the crystal surfaces of lozenge-shaped single crystals.

A comparison of oligomers and polymers in poly(aryl ketone): effect of chain folding on crystal morphology and generalizations therefrom

Single crystals were prepared from poly(phenyl ethyl ketone) (PEK) oligomers and compared with those of the corresponding polymer with respect to morphology, electron and X-ray diffraction patterns. The present comparison shows a drastic change in morphology when going from the extended chain oligomer to the folded chain polymer, the regular, lozenge-shaped crystals of the oligomer degenerating into irregular, knobbly laths for the polymer. At the same time the diffraction patterns are becoming more poorly defined, the reflections broadening and shifting to smaller angles (these effects being largest along the a direction) all indicating reduced lattice perfection. All these effects, the degeneration in the morphology and lattice order, must clearly be associated with chain folding in the polymer. The above is in sharp contrast with the behaviour of the paraffin-polyethylene system where the onset of chain folding with increasing chain length has no qualitatively noticeable effect on morphology and lattice order. We envisage the effects in PEK arising due to the more bulky and stiffer character of the chains which, while folding for kinetic reasons, cannot do so over a similarly short distance as in the paraffin-polyethylene system or other flexible polymers. The larger fold-spans then require larger volume along the fold surface exerting stresses on the underlying crystals. These stresses, being cumulative, will expand and distort the lattice and eventually set a limit to the size of the coherent structure entity in the growing crystal leading to the observed irregular, knobbly morphology. We venture to generalize this scheme to other members of main chain aromatic polymers, and beyond, to all regular polymers which crystallize slowly and with poorly defined morphologies with the difficulty in folding being the common factor. As a further step, we also invoke the degenerate morphologies of copolymers of otherwise fully flexible chains where exclusion of crystallographically incompatible comonomer units (e.g. branches) from the crystals would be expected to give rise to cumulative strain with analogous consequences.

Evidence for Distinct Sectors in Polymer Single Crystals

IT was reported earlier that long-chain polymers could form single crystals in which the molecules have a regularly folded configuration1,2. Polyethylene in particular can have a paraffin-like crystal habit consisting of thin lozenge-shaped layers with each segment of the folded molecular chain normal, or approximately normal, to the plane of these layers. It was suggested3 that the molecules might fold in the plane of the growing faces, which are of the {110} type in the purely lozenge-shaped crystals. This implies that in the four different quadrants the chains are folded along four different directions, and hence that the apparent single crystal consists in fact of four structurally distinct sectors in twin relation. So far as we know, this situation is unprecedented in crystalline substances.

The study of crystal growth with the electron microscope II. The observation of growth steps in the paraffin n -hectane

Examination of the paraffin n -hectane in the electron microscope has given evidence of two different growth mechanisms for crystals of this compound. The one corresponds to the spiral growth mechanism already observed for n -hexatriacontane (Dawson & Vand 1951), and the orthorhombic lozenge-shaped crystals of n -hectane show the typical spiral growth steps already described. The other growth mechanism gives rise to lath-shaped crystals and operates when growth takes place by the slow evaporation of a cold solution of n -hectane in xylene. The laths are invariably twinned across the diagonal of the orthorhombic cell, and growth in one direction is greatly accelerated by the occurrence of an indestructible step at the twin boundary.