Organization Of Crystallites Research Articles

Calcite crystal orientation patterns in the bilayers of laminated shells of benthic rotaliid foraminifera

Shells of calcifying foraminifera play a major role in marine biogeochemical cycles; fossil shells form important archives for paleoenvironment reconstruction. Despite their importance in many Earth science disciplines, there is still little consensus on foraminiferal shell mineralization. Geochemical, biochemical, and physiological studies showed that foraminiferal shell formation might take place through various and diverse mineralization mechanisms.In this study, we contribute to benthic foraminiferal shell calcification through deciphering crystallite organization within the shells. We base our conclusions on results gained from electron backscattered diffraction (EBSD) measurements and describe microstructure/texture characteristics within the laminated shell walls of the benthic, symbiontic foraminifera: Ammonia tepida, Amphistegina lobifera, Amphistegina lessonii. We highlight crystallite assembly patterns obtained on differently oriented cuts and discuss crystallite sizes, morphologies, interlinkages, orientations, and co-orientation strengths.We show that: (i) crystals within benthic foraminiferal shells are mesocrystals, (ii) have dendritic-fractal morphologies and (iii) interdigitate strongly. Based on crystal size, we (iv) differentiate between the two layers that comprise the shells and demonstrate that (v) crystals in the septa have different assemblies relative to those in the shell walls. We highlight that (vi) at junctions of different shell elements the axis of crystal orientation jumps abruptly such that their assembly in EBSD maps has a bimodal distribution. We prove (vii) extensive twin-formation within foraminiferal calcite; we demonstrate (viii) the presence of two twin modes: 60°/[001] and 77°/~[6 –6 1] and visualize their distributions within the shells.In a broader perspective, we draw conclusions on processes that lead to the observed microstructure/texture patterns.

Thermal Control of Confined Crystallization within P3EHT Block Copolymer Microdomains

The local, nanoscale organization of crystallites in conjugated polymers is often critical to determining the charge transport properties of the system. Block copolymer geometries, which offer controlled nanostructures with tethering of chains at interfaces, are an ideal platform to study the local organization of conjugated polymer crystallites. The model conjugated polymer poly(3-(2′-ethyl)hexylthiophene) (P3EHT) features a depressed melting temperature relative to the widely studied poly(3-hexylthiophene) (P3HT), which allows it to robustly form microphase-separated domains that confine the subsequent P3EHT crystallites. Importantly, P3EHT crystallization in confinement is coupled to a rubbery second block via interfacial tethering, mechanical properties, and chain stretching. Here, the impact of thermal processing on the diblock copolymer structure is examined to elucidate the key driving forces controlling the final coupled diblock copolymer and crystalline structures. Surprisingly, the diblock copol...

Confined Crystallization within Cylindrical P3EHT Block Copolymer Microdomains

Confinement of crystallites within block copolymer microdomains is a promising approach to study conjugated polymer crystallization due to interfacial chain tethering and defined geometries. The nanoscale organization of crystallites is often critical to determining the charge transport properties of conjugated polymers. Here, a poly(3-(2′-ethyl)hexylthiophene)-block-poly(methyl acrylate) (P3EHT-b-PMA) system is leveraged to study the impact of confinement within cylindrical microdomains. The crystalline P3EHT permits accessible melting temperatures and robust formation of traditional microphase-separated morphologies, while the rubbery PMA allows the local deformations required to permit P3EHT crystallization. Crystallites form with chains perpendicular to the diblock interface, causing domain expansion; TEM reveals that this is accommodated in the cylindrical geometry via local deformation. Complementary SAXS/WAXS of aligned diblocks shows preferential orientation of the alkyl chain stacks down domains....

Synchrotron X-ray diffraction to understand crystallographic texture of enamel affected by Hunter syndrome

ObjectiveTo determine whether Hunter syndrome (MPS II) affects the crystallographic texture (preferred orientation) of enamel. DesignSynchrotron X-ray diffraction, being a state of the art technique, has been used to determine the enamel crystallite orientation in enamel affected by Hunter syndrome (MPS II). The incisal, lingual and cervical regions of the MPS II affected tooth were observed and compared to healthy tooth. ResultsIt was observed that there is a loss of organization of crystallites in deciduous incisal enamel affected by Hunter syndrome (MPS II) as compared to healthy deciduous enamel tissue. Generally it was observed that, in contrast to the healthy enamel, the enamel affected by MPS II possessed a lower crystallographic preferred orientation, with a more uniform spatial distribution; however, the enamel at the incisal tip was relatively unaffected. ConclusionHunter syndrome affects the enamel texture in the lingual and cervical regions of the tooth.

Second harmonic generation in germanotellurite bulk glass‐ceramics

AbstractIn this study, we have investigated the use of silver cation as nucleating agent in germanotellurite glass matrix of compositions (100−x) [70TeO2–10GeO2–10Nb2O5–10K2O]–xAg2O (x=0‐6 mol%), in order to promote bulk crystallization. Density measurements, differential scanning calorimetry, X‐ray diffraction, UV‐Vis, and Raman spectroscopies have been performed to study the crystallization process. We have observed bulk crystallization of a unique noncentrosymmetric phase, K[Nb1/3Te2/3]2O4.8, which has been investigated for its second‐order optical activity. Transparent to translucent glass‐ceramics have been successfully tailored under thermal treatment and second harmonic generation signals were recorded on the glass‐ceramic samples as a function of their synthesis procedure. It is suggested that the second‐order optical properties observed are strongly related to the organization of crystallites within phase‐separated domains.

Enamelin Directs Crystallite Organization at the Enamel-Dentine Junction

Enamel is an acellular material formed by the intricate process of amelogenesis. Disruption caused at the initial stages of development, by means of mutations in the ENAM gene encoding the enamelin protein, results in enamel hypoplasia. Little is known about the consequence of ENAM mutation on the enamel structure at a crystallographic level. The aim of this study was to characterize the structure of ENAM-mutated enamel to develop a deeper understanding of the role of enamelin protein during formation with regard to crystal organization. Synchrotron X-ray microdiffraction (SXRD) and scanning electron microscopy (SEM) have been used to measure and correlate enamel crystallography and microstructure in hypoplastic and healthy enamel. Rietveld refinement carried out on 2-dimensional diffraction patterns, collected from the Advanced Photon Source, were used to quantify changes in the preferred orientation (crystallographic texture) within the labial regions of each tooth slice and then correlated with the local microstructure. In general, healthy deciduous incisors displayed a higher degree of crystal organization across the labial surface in comparison with the hypoplastic enamel. ENAM plays the greatest functional role at the enamel-dentine junction (EDJ), as it was the region that exhibited lowest texture relative to unaffected controls. Other areas within the tooth, however, such as the cusp tip, displayed greater organization in line with healthy enamel, suggesting its effects are restricted to the early stages of enamel secretion. Observed clinically, the surface of ENAM-mutated hypoplastic enamel can appear to be normal, yet severe sub-nano and microstructural defects appear beneath the subsurface layer. Quantitative characterization of the crystallographic properties from enamel with known genotype expands the understanding of enamel formation processes and can aid better clinical diagnosis and tailor-made treatment.

Confined crystallization in lamellae forming poly(3‐(2′‐ethyl)hexylthiophene) (P3EHT) block copolymers

ABSTRACTCharge transport in poly(3‐alkylthiophene)s (P3AT)s is closely linked to the nanoscale organization of crystallites. Block copolymer morphologies provide an ideal platform to study crystallization as the chain ends are tethered at a known interface in a well‐defined geometry. The impact of soft versus hard confinement on P3EHT crystallization was studied using poly(3‐(2′‐ethyl)hexylthiophene) (P3EHT) containing diblocks with both rubbery poly(methyl acrylate) (PMA) and glassy polystyrene (PS) blocks. Here, P3EHT's lower melting point relative to the commonly studied poly(3‐hexylthiophene) (P3HT) facilitated its confined crystallization and makes it an ideal model system. While transmission electron microscopy (TEM) and small angle X‐ray scattering (SAXS) revealed well‐ordered lamellar morphologies both in the melt and post‐crystallization for both sets of diblocks, the glassy blocks inhibit confined crystallization of P3EHT relative to rubbery matrix blocks. Analysis of aligned diblocks by both SAXS and wide angle X‐ray scattering (WAXS) revealed that the P3EHT chain axis aligns perpendicular to domain interfaces, allowing preferential growth of the alkyl‐chain and π–π stacking directions parallel to lamellae. Finally, it was shown that following diblock self‐assembly in the melt, crystallite growth drives expansion of microdomains to match the P3EHT contour length. It was concluded that P3EHT chains adopted an extended conformation within confined crystallites due to the rigid nature of polythiophenes relative to flexible chain crystalline polymers. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 205–215

Testudoid and crocodiloid eggshells from the Upper Cretaceous Deccan Intertrappean Beds of Central India

Chelonian and crocodilian eggs and eggshells are relatively rare in the fossil record as compared to those of dinosaurs and avians. In India, prior to the present report, turtle eggshells have been reported from the supposed Late Cretaceous infratrappean beds of Duddukuru, Andhra Pradesh. Likewise, crocodilian eggshells were described from the intertrappean beds of Bombay whose assignment to Maastrichtian age is not based on any age diagnostic fossils. Here we report the first definitive Late Cretaceous turtle and crocodilian eggshells from the intertrappean beds of Kisalpuri, Dindori District, Madhya Pradesh (Central India). The testudoid eggshells from Kisalpuri, though broadly comparable to those of Duddukuru, particularly in radial structure, differ from each other in finer details such as external surface ornamentation and the organization of crystallites in the radial section. The crocodiloid eggshells from Central India are distinct from known fossil eggshells in having non-interlocking wedge-like crystallites and ringed craters on the basal plate groups. Keeping in view the limited fossil specimens available for the present study, the testudoid and crocodiloid eggshells from the Late Cretaceous of Central India are referred to the oofamilies Testudoolithidae and Krokolithidae, respectively.

Mapping the spatial and temporal progression of human dental enamel biomineralization using synchrotron X-ray diffraction

ObjectiveThe complex biological, physicochemical process of human dental enamel formation begins in utero and for most teeth takes several years to complete. Lost enamel tissue cannot regenerate, therefore a better understanding of the spatial and temporal progression of mineralization of this tissue is needed in order to design improved in vivo mineral growth processes for regenerative dentistry and allow the possibility to grow a synthetic whole or partial tooth. MethodHuman dental enamel samples across a range of developmental stages available through archaeological collections have been used to explore the spatial and temporal progression of enamel biomineralization. Position sensitive synchrotron X-ray diffraction was used to quantify spatial and temporal variations in crystallite organization, lattice parameters and crystallite thickness at three different stages in enamel maturation. In addition X-ray microtomography was used to study mineral content distributions. ResultsAn inverse correlation was found between the spatial variation in mineral content and the distribution of crystallite organization and thickness as a function of time during enamel maturation. Combined X-ray microtomography and synchrotron X-ray diffraction results show that as enamel matures the mineral content increases and the mineral density distribution becomes more homogeneous. Starting concurrently but proceeding at a slower rate, the enamel crystallites become more oriented and larger; and the crystallite organization becomes spatially more complex and heterogeneous. ConclusionDuring the mineralization of human dental enamel, the rate of mineral formation and mineral organization are not identical. Whilst the processes start simultaneously, full mineral content is achieved earlier, and crystallite organization is slower and continues for longer. These findings provide detailed insights into mineral development in human dental enamel which can inform synthetic biomimetic approaches for the benefit of clinical dentistry.

Disruption of enamel crystal formation quantified by synchrotron microdiffraction

ObjectivesTo understand the pathology of the ultrastructure of enamel affected by systemic disorders which disrupt enamel tissue formation in order to give insight into the precise mechanisms of matrix-mediated biomineralization in dental enamel in health and disease. MethodsTwo-dimensional synchrotron X-ray diffraction has been utilized as a sophisticated and useful technique to spatially quantify preferred orientation in mineralized healthy deciduous dental enamel, and the disrupted crystallite organization in enamel affected by a systemic disease affecting bone and dental mineralization (mucopolysaccharidosis Type IVA and Type II are used as examples). The lattice spacing of the hydroxyapatite phase, the crystallite size and aspect ratio, and the quantified preferred orientation of crystallites across whole intact tooth sections, have been determined using synchrotron microdiffraction. ResultsSignificant differences in mineral crystallite orientation distribution of affected enamel have been observed compared to healthy mineralized tissue. The gradation of enamel crystal orientation seen in healthy tissue is absent in the affected enamel, indicating a continual disruption in the crystallite alignment during mineral formation. ConclusionsThis state of the art technique has the potential to provide a unique insight into the mechanisms leading to deranged enamel formation in a wide range of disease states. Clinical relevanceCharacterising crystal orientation patterns and geometry in health and following disruption can be a powerful tool in advancing our overall understanding of mechanisms leading to the tissue phenotypes seen clinically. Findings can be used to inform the appropriate dental management of these tissues and/or to investigate the influence of therapeutic interventions or external stressors which may impact on amelogenesis.

Examination of whewellite kidney stones by scanning electron microscopy and powder neutron diffraction techniques

Kidney stones made of whewellite,i.e.calcium oxalate monohydrate, exhibit various morphological aspects. The crystalline structure of whewellite at the atomic scale was revisited through a single-crystal neutron study at room temperature using a four-circle automated diffractometer. The possible relationships between the various morphological types of whewellite stones and their structural characteristics were examined at the mesoscopic scale by the use of scanning electron microscopy and at the nanometric scale by powder neutron diffraction. All types of whewellite stones displayed a similar structure at the nanometric scale. However, significant differences were found at the mesoscopic scale. In particular, the crystallites in kidney stones resulting from a genetic hyperoxaluria exhibited a peculiar structure. There was a close relationship between stone morphology and crystallite organization at the mesoscopic level and the effectiveness of extracorporeal shockwave lithotripsy.

Ordered structure and preferred orientation of boehmite films prepared by the sol–gel method

Several boehmite films were produced using the sol–gel route. The drying process, the film structure evolution and the final texture of the samples were investigated by means of combined X-ray diffraction and weight variation. A remarkable (0 1 0) preferred orientation (about 97% of the crystallites) was found for xerogel films with thickness ranging from 1.5 to 24 μm. The ordered structure is already present in the sol state and is appeared and enhanced during drying, before gelling. This phenomenon may be attributed to the particular boehmite structure that induces special crystallite organization in the aquagel.

The ultrastructure of anorganic bovine bone and selected synthetic hyroxyapatites used as bone graft substitute materials

The objective of this study was to investigate the morphology and organization of apatite crystallites in mature mammalian bone. Anorganic bovine bone was studied in this investigation to allow for the examination of the mineral crystallites after removal of the organic phase. Field-emission low-voltage scanning electron microscopy (FE-LVSEM) was employed to obtain images at nanometer resolution without the application of a conductive coating. Transmission electron microscopy (TEM) of the samples was also performed to confirm the identification of features observed in the SEM and to allow for comparison with earlier studies of bone mineral architecture. For comparison, in order to demonstrate how the interaction of collagen and apatite results in the architecture and crystal structure of bone mineral, two synthetic hydroxyapatite materials were also analyzed: OsteoGen and OsteoGraf/LD300. FE-LVSEM revealed distinctive features of bone mineral: a fibrillar organization of crystallites, a periodic spacing of crystallites along the fibrils consistent with the banding pattern of collagen, inter-fibrillar bridging crystallites, and a plate-like habit of the crystallites. These findings supported the hypothesis, derived from the earlier TEM data of others, that the mineralization of collagen comprising osteoid proceeds by the formation of apatite crystallites within the fibers at selected periodic sites along their length. Moreover, the very presence in this anorganic material of distinct fibers comprised of the crystallites is demonstration of inter-crystallite bonding. The crystallites of the synthetic hydroxyapatite materials did not display any of these ultrastructural features.

Nanometer resolution of crystalline morphology using scanning probe microscopy

A semicrystalline segmented polyamide has been used as model system to investigate the morphology of thick and thin solvent cast films. Tapping atomic force microscopy (AFM) with height and phase detection was used to resolve the ribbon-like crystals near the surface. Methods are described for obtaining nanometer resolution of domains. Much thinner and smaller crystals were imaged in films approximately 30 nm thick due to crystallization under constrained environments. The results illustrate the danger of casting ultrathin films where the thickness is found to have a large influence on the final morphology. The results also show that details of crystallite organization in spherulites can be characterized by lower resolution phase data, and illustrate the advantages of the phase data for polymer films with long-range roughness. © 2000 Society of Chemical Industry

Nanometer resolution of crystalline morphology using scanning probe microscopy

A semicrystalline segmented polyamide has been used as model system to investigate the morphology of thick and thin solvent cast films. Tapping atomic force microscopy (AFM) with height and phase detection was used to resolve the ribbon-like crystals near the surface. Methods are described for obtaining nanometer resolution of domains. Much thinner and smaller crystals were imaged in films approximately 30 nm thick due to crystallization under constrained environments. The results illustrate the danger of casting ultrathin films where the thickness is found to have a large influence on the final morphology. The results also show that details of crystallite organization in spherulites can be characterized by lower resolution phase data, and illustrate the advantages of the phase data for polymer films with long-range roughness. © 2000 Society of Chemical Industry

Amorphous phase and interphase organization of syndiotactic polypropylene

AbstractMaterials prepared by syndiotactic polypropylene of different stereochemistry (62 ÷96% r pentads) undergo transitions in the crystal phase, which depend on the thermomechanical history. The interfaces and the amorphous phase may be affected by the crystallite organization and the stereoregularity of the material. MAS NMR techniques provided a tool for characterizing the arrangement and the mobility of the polymer chains in the inter‐crystallite region. Chemical shifts, line‐width and relaxation parameters were determined as a function of recording temperature and glass transition temperature of the material. The same parameters were followed in the presence of a plasticizer. The different degree of intimacy of the phases was established by following the diffusion of magnetization among the hydrogen atoms of the amorphous and the crystalline phase. Defective regions and boundary regions were also identified and showed a large amount of conformations in the trans arrangement; the relaxation times indicate the chains being rigid and intimately mixed with the crystalline phase.

Enamel structure and microwear: An experimental study of the response of enamel to shearing force

The anisotropic fracturing and differential wear properties of enamel microstructure represent factors that can obscure the predictive relationship between dental microwear and diet. To assess the impact of enamel structure on microwear, this in vitro experimental study examines the relative contributions to wear of three factors: 1) species differences in microstructure, 2) direction of shearing force relative to enamel prisms and crystallites, and 3) size of abrasive particles. Teeth of Lemur, Ovis, Homo, and Crocodylus, representing, respectively, the structural categories of prismatic patterns 1, 2, and 3 and nonprismatic enamel, were abraded by shearing forces (forces having a component directed parallel to abraded surfaces) and examined by scanning electron microscopy. Striation width increased with particle size for nonprismatic, but not for prismatic, specimens. Direction of shear relative to prism and crystallite orientation had a significant influence on striation width in only some prismatic enamels. The different responses of prismatic and nonprismatic enamels to abrasion reflect the influence of structure, but at the level of organization of crystallites rather than prisms per se. Such interactions explain in part the inability of striation width to discriminate among animals with different dietary habits. Heteroscedasticity and deviations from normality also may confound parametric analyses of microwear variables. Variation in crystallite orientation in prismatic enamels may contribute to optimal dental function through the property of differential wear in functionally distinct regions of teeth.

Distribution and variation in enamel structure in the oral teeth of sarcopterygians: Its significance for the evolution of a protoprismatic enamel

The property of tooth enamel to resist alteration during fossilization, is used to analyse the unique arrangements of biological crystallites amongst genera of Paleozoic sarcopterygians, with both polarized light and s.e.m. Previous concepts of crystallite organization in reptiles and mammal‐like reptiles are evaluated. Two of the Devonian sarcopterygians, are shown to exhibit a protoprismatic pattern, identical with that of a stem group therian. The patterns of crystallites, together with the arrangement of incremental lines establish that this tissue is solely an ectodermal product; monotypic enamel, in contrast to bitypic enamel with two cell products contributing to it as in enameloid or acrodin. Each genus examined has a different pattern, of significance in considering relationships amongst sarcopterygians. Recent information on ganoine and some new findings on enamel in extant lungfishes have led to the conclusion that types of monotypic enamel are present in both actinopterygians and sarcopterygia...