Orientation Of Mineral Crystals Research Articles

Influence of chloride salt erosion on the adhesion of asphalt-aggregate interfaces considering mineral anisotropy: insights from molecular dynamics.

Asphalt, a polymer mixture composed of various hydrocarbons, is extensively utilized due to its excellent performance. To evaluate the sensitivity of asphalt concrete to chloride salt damage at the nanoscale, considering the anisotropy of aggregate mineral crystal orientation, molecular dynamic simulations were employed to model the interface interactions between asphalt and aggregate mineral components (silica and calcite) under chloride salt exposure. The wetting processes of water droplets and chloride salt droplets on different crystal surfaces of silica and calcite were analyzed. Furthermore, the adhesive energy, decohesion energy, degradation ratio, and energy ratio of the interaction model between asphalt and aggregate mineral interfaces were analyzed to reveal the variations in the interfaces between the two components. The results demonstrated that the anisotropy of the minerals significantly affects the adhesion energy of asphalt and aggregate. Moreover, the surface hydrophilicity of calcite was larger than that of silica. The interfacial adhesion energy of asphalt-calcite was larger than that of asphalt-silica under dry condition and chloride salt attack, and the interfacial adhesion energy of both asphalt and mineral decreased with the increase of chloride salt concentration. The degradation ratio and energy ratio values of asphalt and calcite were larger than those of asphalt and silica, and the anisotropy of the mineral surface affected the degradation ratio and energy ratio values. This study provides a new method and theoretical basis for further research on the damage mechanism and strengthening measures of asphalt-aggregate under chloride salt attack. To investigate the interaction between asphalt and mineral aggregates under chloride salt erosion, models of asphalt, aggregate, and asphalt/aggregate composite systems were constructed using the Amorphous Cell module in Materials Studio 2020 software. Molecular dynamic simulations of the asphalt/aggregate composite system were then conducted using the Forcite module, employing the COMPASS II force field to describe atomic and molecular interactions. Initially, considering the crystal orientation and surface configuration of the aggregate minerals, the impact of mineral anisotropy on the asphalt-aggregate interface model was analyzed. Subsequently, by simulating the contact states of nano water droplets and chloride salt droplets with different mineral surfaces, the wetting characteristics of nano water droplets on silica and calcite surfaces were determined. Lastly, considering the corrosion effect of chloride solution at different concentrations, the adhesion energy, debonding energy, degradation ratio, and energy ratio of the asphalt-aggregate interface interaction model were analyzed.

Insights from electron backscatter diffraction into the origin of fibrous calcite veins in organic-rich shale from lower Es3 to upper Es4, Jiyang Depression, China

Abstract The origin of fibrous calcite veins developed in organic-rich shales, has attracted great attentions. However the growth direction, formation temperature and stress state are still controversial. The calcite veins in organic-rich shale from lower Es3 to upper Es4 in the Jiyang Depression has been analyzed with electron backscatter diffraction technology (EBSD), which can characterize the microstructures and orientation of mineral crystals in situ. On the basis of core observation and microscopic identification of petrological characteristics, the longitudinal and horizontal profiles of calcite veins were measured by EBSD. Crystallographic information on calcite veins, obtained by pattern quality mapping, phase diagrams, grain distribution maps, Euler graphs, grain misorientations and pole figures, clarifies the origins of these veins. The results show that calcite crystals in calcite veins belong to the sharp-rhombohedral space lattice structure of the trigonal system. Calcite crystals have a preferred orientation on the longitudinal profile, while there is no obvious preferred orientation on the horizontal profile. On the longitudinal profile of calcite veins, the misorientation of calcite crystals is the cause of the interference colour and extinction difference of calcite crystals under orthogonal light. The crystal interference and extinction characteristics on both sides of middle line in calcite veins are different, indicating that the growth direction of calcite veins is syntaxial. A shallow burial environment is suggested for calcite veins initial forming by the evidence that crystal morphology of calcite in calcite veins is most in the shape of sharp-rhombohedron, and some of which have hexagonal prism shape. The average orientation difference of calcite veins on longitudinal and horizontal profiles indicates that the average orientation of calcite grains is inhomogeneous. The stress concentration of small grains is higher than that of large grains, and cracks are developed in the interior or on the border of calcite grains on the longitudinal profile, which indicates that calcite veins are formed in the stress environment of three directional extrusion circumstances.

Hierarchically ordered polymer nanofiber shish kebabs as a bone scaffold material

The ideal bone scaffold harnesses the body's ability to regenerate bone in critical size defects. A potential strategy to design the ideal bone scaffold is to mimic the natural structure of bone at the molecular level. The orientation and spatial distribution of nanocrystals in the organic matrix are two important and distinctive structural characteristics associated with natural bone. There has yet to be a synthetic system or scaffold that is able to control both the spatial distribution and orientation of the hydroxyapatite crystalline structure. To mimic the unique hybrid structure of natural bone using synthetic materials, there have been a number of reported approaches to control the mineral nanocrystal orientation on synthetic scaffolds. However, the spatial distribution of minerals is challenging to reproduce in a biomimetic manner. Herein we report using block copolymer-decorated polymer nanofibers to achieve biomineralized fibrils with precise control of both mineral crystal orientation and spatial distribution. We show that the crystallization of poly(caprolactone)-b-poly(acrylic acid) block copolymer on poly(caprolactone) nanofibers resulted in a unique shish kebab structure that significantly enhances the mechanical properties of the nanofibers, and is cytocompatible to L-929 mouse fibroblast cells. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1786-1798, 2017.

Bone mineral crystal size and organization vary across mature rat bone cortex.

The macro- and micro-features of bone can be assessed by using imaging methods. However, nano- and molecular features require more detailed characterization, such as use of e.g., vibrational spectroscopy and X-ray scattering. Nano- and molecular features also affect the mechanical competence of bone tissue. The aim of the present study was to reveal the effects of mineralization and its alterations on the mineral crystal scale, by investigating the spatial variation of molecular composition and mineral crystal structure across the cross-section of femur diaphyses in young rats, and healthy and osteoporotic mature rats (N=5). Fourier transform infrared spectroscopy and scanning small- and wide-angle X-ray scattering (SAXS/WAXS) techniques with high spatial resolution were used at identical locations over the whole cross-section. This allowed quantification of point-by-point information about the spatial distribution of mineral crystal volume. All measured parameters (crystal dimensions, degree of orientation and predominant orientation) varied across the cortex. Specifically, the crystal dimensions were lower in the central cortex than in the endosteal and periosteal regions. Mineral crystal orientation followed the cortical circumference in the periosteal and endosteal regions, but was less well-oriented in the central regions. Central cortex is formed rapidly during development through endochondral ossification. Since rats possess no osteonal remodeling, this bone remains (until old age). Significant linear correlations were observed between the dimensional and organizational parameters, e.g., between crystal length and degree of orientation (R(2)=0.83, p<0.001). Application of SAXS/WAXS provides valuable information on bone nanostructure and its constituents, effects of diseases and, prospectively, mechanical competence.

Mimicking Bone Nanostructure by Combining Block Copolymer Self-Assembly and 1D Crystal Nucleation

The orientation and spatial distribution of nanocrystals in the organic matrix are two distinctive structural characteristics associated with natural bone. Synthetic soft materials have been used to successfully control the orientation of mineral crystals. The spatial distribution of minerals in a synthetic scaffold, however, has yet to be reproduced in a biomimetic manner. Herein, we report using block copolymer-decorated polymer nanofibers to achieve biomineralized fibrils with precise control of both mineral crystal orientation and spatial distribution. Exquisite nanoscale structural control in biomimetic hybrid materials has been demonstrated.

Orientation of mineral crystals by collagen fibers during in vivo bone engineering: An X-ray diffraction imaging study

The mechanism of mineralized bone matrix deposition was investigated taking advantage of a tissue engineering approach in which bone tissue is formed when porous ceramic scaffold is loaded with bone marrow stromal cells and implanted in vivo. The aim of our study is to point out the interaction between the newly formed mineral crystals and the scaffold imposing the three-dimensional desired architecture to the growing bone. High spatial resolution Small Angle X-ray Scattering measurements obtained using synchrotron radiation and X-ray waveguide as optical element allowed a local structural study at the bone–scaffold interface. Using an original methodology for data analysis, we obtained a two-dimensional microscopic map of the mineralization degree, the collagen presence and the mineral orientation degree around the scaffold pore.

Understanding the Structure of the Mammalian Mineralised Tissues Through Their Development

AbstractMost aspects of the structure and composition of the principal mineralised tissue types [in teeth = enamel, dentine and cementum; in bone organs = woven and lamellar and extrinsic (Sharpey) fibre bone and calcified growth plate cartilage and articular calcified cartilage and calcified fibrocartilage and calcified ligament or tendon] and of the all-important junctions between them can be best understood from a knowledge of developmental mechanisms and the rules and constraints that these generate. We should consider the interface between formative cells and the organic matrices where these are secreted by an appositional mechanism; possible influences of cell movements; mineral crystal orientation and size and maturation; junctions formed by simple apposition of one tissue upon another; junctions involving a prior resorptive (partial destruction and 'etching') step; and interstitial matrix expansion, NB in cartilage.

Bone mineralization in an osteogenesis imperfecta mouse model studied by small-angle x-ray scattering.

We have studied the size and orientation of mineral crystals in cortical bone of oim/oim mice, which are known to produce only alpha 1(I) collagen homotrimers and which may serve as a model for human osteogenesis imperfecta. Long bones (femur and tibia) from young (5 wk old) oim/oim mice and from unaffected heterozygous counterparts were investigated by small-angle x-ray scattering (SAXS), which is sensitive to structures smaller than 50 nm. Mineral crystals were compared in terms of their thickness and their alignment with respect to the long bone axis. While electron microscopic tomography has recently shown the existence of large mineral blocks (with all dimensions typically exceeding 50 nm) in mineralized tendons of oim/oim mice, SAXS revealed a family of thin, possibly needle-like, crystals in cortical bone. These crystals were similar in shape to those observed previously in normal mice, but they were thinner and less well aligned in oim/oim mice relative to heterozygotes. Moreover, the crystal thickness and their alignment with the bone axis were more variable in oim/oim bone, with a close correlation (r = 0.94, P < 0.001) between the two parameters. The presence of smaller crystals with more variable alignment in corticalis of oim/oim mice may contribute to the brittleness of their bone, similar to that of human osteogenesis imperfecta.