Plate-like Crystals Research Articles

Colliding Ice Crystals in Turbulent Clouds

Abstract Collisions, resulting in aggregation of ice crystals in clouds, is an important step in the formation of snow aggregates. Here, we study the collision process by simulating spheroid-shaped particles settling in turbulent flows and by determining the probability of collision. We focus on platelike ice crystals (oblate ellipsoids), subject to gravity, and to the Stokes force and torque generated by the surrounding fluid. We also take into account the contributions to the drag and torque due to fluid inertia, which are essential to understand the tendency of crystals to settle with their largest dimension oriented horizontally. We determine the collision rate between identical crystals, of diameter 300 μm, with aspect ratios in the range 0.005 ≤ β ≤ 0.05, and over a range of energy dissipation per unit mass, ε, 1 ≤ ε ≤ 250 cm2 s−3. For all values of β studied, the collision rate increases with the turbulence intensity. The dependence on β is more subtle. Increasing β at low turbulence intensity () diminishes the collision rate, but increases it at higher ε ≈ 250 cm2 s−3. The observed behaviors can be understood as resulting from three main physical effects. First, the velocity gradients in a turbulent flow tend to bring particles together. In addition, differential settling plays a role at small ε when the particles are thin enough (β small), whereas the prevalence of particle inertia at higher ε leads to a strong enhancement of the collision rate.

Lidar backscatter simulation for angular scanning of cirrus clouds with quasi-horizontally oriented ice crystals.

Backscattering properties of ice crystals are numerically investigated in the case of plate-like quasi-horizontally oriented crystals of cirrus clouds. In this case, a vertically oriented lidar detects the specular reflection from the clouds while a lidar with angular scanning allows one to infer the microphysical properties like the transverse shape of the crystals. It is shown that the depolarization ratio as a function of the lidar tilt reveals a step at a lidar tilt of about 30° from the vertical. This step has been observed experimentally. Appearance of this step indicates that the transverse shapes of the plate-like crystals are regular.

Hydrothermal in situ synthesis of high-crystallinity layered double hydroxide on electrospun polyacrylonitrile non-woven membrane: Application as anion capture filter

Layered double hydroxide (LDH) crystals were grown in the presence of polyacrylonitrile (PAN) nanofibers to develop a three-dimensionally-structured hybrid filter with high anion adsorption performance. The tensile strength and chemical resistance of the PAN nanofibers manufactured by electrospinning were improved upon heat treatment at 250 °C for 60 min. The growth of LDH on PAN was conducted by hydrolysis using urea or hexamethylenetetramine (HMT), and optimum conditions for this “in situ synthesis” were investigated. As a result, LDH plate-like crystals with a lateral size of ~20 μm were obtained by hydrothermal treatment at 140 °C for 24 h using HMT. The crystals grew densely perpendicular to the surface of the PAN fibers. After converting the LDH grown on the fiber fabric to LDH contain Cl− in the interlayer, the resulting fabric was set in a filter holder and a phosphoric acid adsorption test was conducted. The results showed that the hybrid filter prepared by this in situ hydrothermal synthesis had good phosphate adsorption characteristics, and that small amounts of phosphate ions were adsorbed selectively from water containing competing sulfate ions.

Crystallization and Rheology of Mono- and Diglycerides and Their Role in Stabilization of Emulsion Droplets in Model Topical Ointments.

The crystallization behavior of commercial mono- and diglycerides (MDG) in paraffin oil is studied to develop an in-depth understanding of the polymorphic transitions useful for the physical stability of petroleum oil-based topical emulsions. Optical microscopy and differential scanning calorimetry measurements showed the formation of plate-like and spherulite crystals at high and low temperatures, in sequence, while cooling a solution of MDG dissolved in oil. High-resolution NMR and X-ray scattering demonstrate that 1-monoglycerides (mixture of 1-glyceride monostearate and 1-glyceride monopalmitate) cocrystallize to an inverse-lamellar structure (Lα polymorph) that mainly forms plate-like crystals at a higher temperature. The Lα polymorph is seen to exist up to room temperature during the cooling process. At lower temperatures, 1,3-diglycerides (mixture of 1,3-glyceryl distearate and 1,3-glyceryl dipalmitate) crystallize into β-polymorphs that form spherulites. The spherulites tend to assemble into elongated strands via aggregation, leading to the formation of a percolating network structure. The sizes of both types of crystals decrease with an increasing cooling rate, leading to a higher mechanical modulus due to the increased network connectivity of spherulites. In an emulsion, monoglycerides in the form of Lα polymorphs having plate-like crystal morphology show a higher affinity to the polar liquid/oil interface, thereby providing better interfacial stability compared to the spherulitic β-polymorphs. However, diglycerides in the form of spherulites form bulk network structures which provide network stabilization to the suspended droplets. This work demonstrates that MDG, a commercially available ingredient that combines the differential functionality of monoglycerides and diglycerides, is an effective, bifunctional, emulsifying agent for petrolatum-based topical emulsions.

Transfer printing platelike MFI crystals as seeds for the preparation of silicalite-1 membranes

High aspect ratio zeolite crystals and their seeding on support are of high desire for the fabrication of oriented zeolite membranes. Here, platelike MFI crystals, as zeolite seeds, are successfully seeded on a α-Al2O3 disk support through a transfer printing method. Firstly, platelike MFI crystals are spread on a flat substrate pre-coated with films of polyvinyl alcohol (PVA) and a fluoropolymer (4200UR) followed by coating a polymethyl methacrylate (PMMA) film. After dissolving the PVA film, the free-standing sandwich-like 4200UR-MFI-PMMA film is transferred onto the support. Then, platelike MFI crystals are successfully seeded after removing the organic species by calcination. Finally, highly (h0h)-oriented, dense and continuous silicalite-1 membranes are fabricated after a secondary growth in a zeolitic synthesis system, confirmed by XRD and SEM techniques. Binary separation of butane isomer has been performed on the silicalite-1 membranes prepared with different synthesis time, achieving a n-butane permeance and a separation factor of 2.27 × 10−7 mol m−2 s−1∙Pa−1) and 28.8 for an equimolar n-butane/i-butane mixture at 343 K, respectively.

Morphology of subsurface cracks in glass-ceramics induced by Vickers indentation observed by synchrotron X-ray multiscale tomography

The characterization of subsurface cracks induced by indentation is a challenge for understanding contact damage, impact, wear, erosion, and abrasion of brittle materials, because the crack pattern observable on the surface is only a part of the total crack system. Here we applied synchrotron X-ray multiscale tomography to observe the morphology of subsurface cracks produced by Vickers indentation in a novel CaO–Al2O3–SiO2 glass-ceramic with plate-like crystals forming a house-of-cards microstructure. It revealed a diverse type of crack systems around the semispherical microcrack zone beneath the indent, including a new mode II inclined lateral crack driven by the maximum shear stress. Tomography images provided knowledge on how the heterogeneous microstructure affected the toughening processes such as crack deflection, crack bridging, and microcracking.

Spatiotemporal control of l-phenyl-alanine crystallization in microemulsion: the role of water in mediating molecular self-assembly.

Water confined or constrained in a cellular environment can exhibit a diverse structural and dynamical role and hence will affect the self-assembly behavior of biomolecules. Herein, the role of water in the formation of l-phenyl-alanine crystals and amyloid fibrils was investigated. A microemulsion biomimetic system with controllable water pool size was employed to provide a microenvironment with different types of water, which was characterized by small-angle X-ray scattering, attenuated total reflectance-Fourier transform infrared spectroscopy and differential scanning calorimetry. In a bound water environment, only plate-like l-phenyl-alanine crystals and their aggregates were formed, all of which are anhydrous crystal form I. However, when free water dominated, amyloid fibrils were observed. Free water not only stabilizes new oligomers in the initial nucleation stage but also forms bridged hydrogen bonds to induce vertical stacking to form a fibrous structure. The conformational changes of l-phenyl-alanine in different environments were detected by NMR. Different types of water trigger different nucleation and growth pathways, providing a new perspective for understanding molecular self-assembly in nanoconfinement.

Systematic Investigation of Lanthanoid Transition Heavy Metal Acetates as Electron Staining Reagents for Protein Molecules in Biological Transmission Electron Microscopy.

Cryo-electron microscopy, widely used for high-resolution protein structure determination, does not require staining. Yet negative staining with heavy metal salts such as uranyl acetate has been in persistent demand since the 1950s due to its image contrasting capabilities at room temperature with a common electron microscope. However, uranium compounds are nuclear fuel materials and are tightly controlled worldwide. Acetates of each lanthanoid series elements except promethium are prepared at the same concentration (2%(w/v)) and used as a model on horse spleen ferritin for electron microscopic analysis to systematically evaluate their effectiveness as electron staining reagents for the protein. Analysis shows that the triacetates of samarium and europium, followed by gadolinium and erbium, and then lanthanum and neodymium could function as electron staining reagents. Thulium-triacetate precipitates thin plate-like crystals and may be used for selecting better imaging fields. Of the 14 lanthanoid-triacetates examined, about half are viable alternatives to uranyl acetate as an electron staining reagent for ferritin, and there appears an optimal range in ionic sizes for promising lanthanoids. This is the first systematic investigation of lanthanoid transition heavy metal triacetates from the viewpoint of lanthanoid contraction, using density distribution histograms of electron micrographs as an indicator for comparison with uranyl acetate.

Evaluation on physicochemical properties and stability of Thanaka bark powder for natural face powder products

Thanaka (Hesperethusa crenulata Roem.) has been traditionally applied as cosmetics in Myanmar and the northern of Thailand [1] and exhibited anti-oxidant, anti-inflammatory, anti-microbial, skin lightening, and sun protection properties [1-4]. Thanaka’s specifications for cosmetic development are sparse to be presented, although its flowability was reported [1]. Of which, the bark was more suitable than the stem for solid dosage form development [1]. Thus, this study was aimed to assess the physicochemical properties and stability of Thanaka bark powder. The yellowish light brown powder (L* = 75.63 ± 0.01, a* = 5.58 ± 0.02 and b* = 23.45 ± 0.02) (Figure 1A) with bulk and tapped densities of 0.25 ± 0.00 and 0.29 ± 0.00 g/mL, was able to absorb water and oil (17.31 ± 0.77% and 13.39 ± 0.29%). The powder was ICP-MS proved to be uncontaminated with heavy metals prohibited for cosmetics. The powder morphology was plate-like crystals with fractured as SEM observed (Figure 1B). Thermal properties examined by DSC resulted in glass transition, crystallization and melting temperatures of 66.43, 70.25 and 73.39°C, with 51.32 ± 4.13% of crystallinity by XRD. The color (ΔE ≤ 1.43 ± 0.04), morphology, thermal properties, water absorption capacity and oil absorption capacity slightly shifted following to 3-month storage under ambient temperature and 45°C.

Unusual Resistive Transitions in the Nodal-Line Semimetallic Superconductor NaAlSi

NaAlSi is a quasi-two-dimensional semimetal with superconductivity below Tc = 6.8 K and a band structure characterized by nodal lines near the Fermi level and potential topological surface states. Electrical resistivity measurements on its superconducting transitions in magnetic fields were made using plate-like single crystals. In the magnetic field-temperature phase diagram, we observed a substantial reduction in resistivity in a pre-transitional zone above the bulk superconducting regime only when the magnetic fields were perpendicular to the plane, rather than parallel to it. Significant sample (thickness) dependence, reentrant behavior, and sensitivity to electrode configurations all indicate that a portion of the crystal has an upper critical field greater than the bulk superconductivity in the pre-transitional region. This fractional superconductivity may occur on the side surface of the crystal.

Optimal condition for fabricating mechanically durable superhydrophobic titanium surface by rapid breakdown anodization: Self cleaning and bouncing characteristics

In this paper, we describe a simple, cost effective, fast, scalable and sustainable method for fabrication of mechanically durable superhydrophobic (SHP) surface of titanium by a rapid breakdown anodization (RBA) followed by molten stearic acid (MSA) chemical modification. In this new approach, the preparation time is only a minute. Instead of stearic acid- ethanol solution, molten stearic acid is the post surface modification, which made the preparation process rapid and simple. The anodized samples showed islands of TiO2 microclusters with complex hierarchical structures with nano pores uniformly distributed in the passive TiO2 matrix. Laser Raman spectroscopy (LRS) analysis revealed the TiO2 microclusters are polycrystalline in nature. The applied voltage, anodization time, immersion time and MSA bath temperature are optimized to obtain a robust mechanically durable SHP surface. FESEM images showed that both anodization and immersion parameters have significant effect on the surface morphology of microclusters. A maximum water contact angle (WCA) of 167.8° with a sliding angle of 6° was obtained for a Ti sample anodized at 50 V for 10 min after molten stearic acid immersion at 125 °C for 30 min. The prolonged anodization for 10 min promoted microcluster growth in all dimensions to form a highly hierarchical micro-nanostructure. The prepared samples showed vertical micro plate-like crystals of stearic acid on the micro clusters, which enhanced the very high WCA. The FTIR results revealed multiple bonding modes of stearic acid with TiO2 microclusters through surface hydroxyl groups. The prepared superhydrophobic samples showed excellent self-cleaning and abrasion resistance.

Constructing single-crystalline hierarchical plate-like ZSM-5 zeolites with short b-axis length for catalyzing MTO reactions

Construction of single-crystalline hierarchical plate-like ZSM-5 crystals assisted by TMG.

Mapping of Grain Orientation In Situ of 2D Perovskite Thin Films with Low-Frequency Polarized Raman Microspectroscopy

Recent developments in two-dimensional (2D) Ruddlesden–Popper perovskites have ushered in a new phase in optoelectronics through their promising physical, chemical, and optical properties. Thin films of 2D perovskites used in most optoelectronic applications contain many grains oriented either horizontally or vertically with respect to the substrate on which they grow; the orientation of such grains plays important roles, not yet fully understood, in their functionalities. Techniques to map the grain orientation in situ in 2D perovskite thin films are hence highly desirable. Here we report mapping of the grain orientation of thin films of the horizontal 2D perovskite, BA2PbI4, in which BA is butylammonium, with low-frequency polarized Raman microspectroscopy. We established a relation between the intensities of low-frequency (10–60 cm–1) polarized Raman lines of BA2PbI4 originating primarily from the PbI6 octahedra and varied orientations of a plate-like BA2PbI4 single crystal. This relation served to determine unambiguously the orientation of grains of micrometer size in a spin-coated BA2PbI4 thin film. Although this study is a case study of BA2PbI4, it opens a new window to obtain crystallographic information about 2D perovskite thin films in general and hence to understand their properties and functions.

Remineralization potential and biocompatibility of titanium dioxide-doped phosphate glasses

This study reports the remineralizing potential and biocompability of titanium dioxide doped phosphate glass (TDPG). Glass paste was prepared with polyacrylic acid and applied as a thin coat on etched dentin for different periods. Normal and etched dentin were used as controls. Remineralization potential was tested using atomic force microscopy, scanning electron microscopy coupled with energy dispersive x-ray and Raman spectroscopy. The biocompability was tested using XTT assay and human dental pulp stem cells. After 5 days of paste application, some angular or plate-like crystals were observed occluding some dentinal tubules and precipitated within intertubular dentin. After 14 days, these crystals form a thin, uniform layer, consistent with vsP–O–P, vasPO2 and vsPO peaks and has ions detected in the glass, covering the dentin surface. By 30 days, the thickness of this layer and intensity of detected peaks increased to completely obscure the underlying dentin apatite peak. By 77 days, additional glass peaks were identified. The glass extract showed comparable or significantly higher cell viability than positive control. ConclusionTDPG paste could be a suitable material for remineralization of affected dentin.

Zn2+ Substitution by Pb2+ in Alkaline-boro-aluminosilicate Glass-ceramics: Microstructural Aspects

This study exemplifies the effects of 5 wt.% Pb2+ addition replacing the same Zn2+ content on crystallization and microstructure of 10B2O3-16Al2O3-39SiO2-12MgO-12MgF2-4K2O-1Li2O-1AlPO4 (wt.%) glass-ceramic composite. Increase of linear thermal-expansion (6.93 to 7.18×10-6/K at 50-600°C) in substituting Zn2+ by Pb2+ is attributed to the field-strength of cations. Opaque crystalline glass-ceramics are derived from the transparent glasses (synthesized by single-step melt-quenching at 1500OC) by controlled heat-treatment at 1050°C and the predominant crystalline-phase was identified as fluorophlogopite mica, KMg3AlSi3O10F2. FFESEM of the ZnO containing glass-ceramics revealed that 100-200 µm sized plate-like crystals are in ‘well-packed interlocked arrangement’; which changed to ‘nanocrystalline microstructure’ combined of ‘spherical droplet like’ nanocrystals (crystal size = 10-50 nm) in attendance of PbO. Decrease in linear thermal-expansion (11.03 to 7.93 × 10-6/K at 50-700°C) due to the substitution of ZnO is ascribed to the crystallization inhibiting tendency of PbO towards boroaluminosilicate system. Thermal-expansion of ZnO containing glass-ceramic is large (> 11 × 10-6/K at 50-700 and 50-800°C) which can exhibit their enough thermal shock resistivity to be suitable for high-temperature sealing application. Copyright © 2017 VBRI Press.

Implications of unconventional setting conditions on the mechanical strength of synthetic bone grafts produced with self-hardening calcium phosphate pastes

This work presents the effects of several factors on the mechanical strength of a calcium phosphate cement (CPC) based on alpha tricalcium phosphate and correlates the results with the microstructure and percentage of conversion to hydroxyapatite. Conversion rate increased by raising the setting temperature in the studied range (4–90 °C), but the strength exhibited an increasing-decreasing trend due to changes in the morphology of hydrated crystals. Plate-like crystals were formed in the range of 22–60 °C, mechanically reinforcing the material, whereas the formation and refinement of needle-like crystals at higher setting temperature decreased the strength. Moreover, cements with dissimilar particle sizes had different optimal hydrolysis temperatures that resulted in the maximum strength. The finest powder led to higher strength at lower setting temperature due to the formation of a more compact crystal network and higher conversion. Therefore, optimization of powder particle size may allow to achieve the highest possible strength at room temperature, being beneficial for the production of the strongest pre-set CPC-based implants without the use of energy. Furthermore, the particle size can be also engineered to produce formulations that develop the highest strength at physiological temperature, with application as injectable bone grafts. The incorporation and crosslinking of gelatine further increased the mechanical strength of pre-set cements by bridging the hydroxyapatite crystals, the setting temperature showing a similar effect to that of gelatine-free cements. In contrast, moisture decreased the strength and reduced the brittleness by solvating intramolecular association between hydroxyapatite crystals and between gelatine molecules. Moreover, large cement bodies were slightly weaker than small ones, but the size effect was not statistically significant.

Impact of Radio Frequency Plasma Power on the Structure, Crystallinity, Dislocation Density, and the Energy Band Gap of ZnO Nanostructure

The aim of this study is to investigate the effect of radio frequency (RF) plasma power on the morphology, crystal structure, elemental chemical composition, and optical properties of ZnO nanostructure using a direct current magnetron sputtering technique. This study emphasized that the growth rate and surface morphology of the polycrystalline ZnO were enhanced as the radio frequency (RF) plasma power increased. This can be observed by fixing other parameters such as the growth time, substrate temperature, and chamber partial pressure. The RF plasma power alteration from 150 to 300 W can produce uniform nanograin, spheroid, and nanorods. Additionally, the RF plasma power alteration leads to the alteration in the ZnO nanorod diameter from 14 to 202 nm. It was observed that the XRD intensities are increased at higher plasma powers. This, perhaps, can be inferred from the transformation of the granular microcrystals to the needlelike or platelike large crystals, as already examined using SEM images. This also has an impact on the average crystalline size, which increased from 10 to 40 nm on increasing the RF plasma power. Moreover, the increase of the RF plasma power has an obvious impact upon the optical band-gap energy, which was accordingly decreased from 3.26 to 3.22 eV. Finally, the absorption band edge was shifted to a lower-energy region due to the quantum size effect at the nanorange.

A Novel Method for Rapid Particle Size Analysis of Ibuprofen Using Near-infrared Spectroscopy.

Particle size distribution (PSD) is often considered as critical material attribute for active pharmaceutical ingredients (APIs), and the need for regular evaluation stands as an important quality control parameter in the pharmaceutical industry. Near-infrared (NIR) spectroscopy, used routinely for API identification, was introduced as analytical tool for simultaneous determination of particle size of ibuprofen. The demonstrated potential was highlighted by the development of rapid, robust, and noninvasive method coupled with multivariate data analysis (MVA), which can be easily transferred in QC laboratories for routine analysis. Principal component analysis (PCA) and partial least squares (PLS) regression analyses were performed on a calibration set of 61 ibuprofen samples, which differed in their median particle size Dv(50). The score scatterplots revealed evident clustering of ibuprofen samples according to their particle size, as well as occurrence of a distinctive outlying group of ibuprofen samples originating from one manufacturer. Further testing by means of mid-infrared spectroscopy, X-ray powder diffraction, and particle morphology analysis pinpointed particle morphology being responsible for the observed outlying group. Consequently, PLS class modeling based on particle morphology was introduced, which delivered two separate PLS regression models: one for blade-like ibuprofen crystals and another for irregular plate-like ibuprofen crystals. The former regression model exhibited high correlation coefficients and satisfactory predictive power (R2X = 0.999, R2Y = 0.917, Q2 = 0.901), whereas the latter demonstrated lower statistical indicators (R2X = 0.99, R2Y = 0.72, Q2 = 0.55). Additionally, the study underlines the importance of particle shape evaluation and sample classification according to particle morphology similarity prior to building NIRS-based regression models for PSD determination.

The study of morphological evolution, biocorrosion resistance, and bioactivity of pulse electrochemically deposited Hydroxyapatite/ZnO composite on NiTi superelastic alloy

In this work, the effect of zinc oxide nanoparticles on hydroxyapatite deposited on NiTi superelastic alloy was studied. Various concentrations of nanoparticles (200, 400, and 800 mg/L) along with cetrimonium bromide (100 mg/L) as a dispersant agent were added to the coating electrolyte. Morphological observations showed that zinc oxide encouraged hydroxyapatite plate-like crystals to grow in longitudinal and transverse directions, turning into a bone-like structure with greater pores. XRD and FTIR indicated the favorable impact of zinc oxide on the synthesis of pure hydroxyapatite as the most stable calcium phosphate phase. Next, the corrosion evaluations revealed that zinc oxide successfully reduced the corrosion current density of composite coatings down to 1.35 nA/cm2, where pure calcium phosphate coating exhibited 19.05 nA/cm2. Topographic evaluations (AFM) proved a consistent rise in roughness parameters where the roughness average climbed from 208.3 nm for calcium phosphate coating up to 436.45 nm for the composite coating with the highest ZnO concentration. The adhesion strength of composite coatings was above 15 MPa (the critical requirement for orthopedic applications), despite calcium phosphate coating. The wettability results also differed dramatically where calcium phosphate coating exhibited 31.17°, but it dropped to 12.62° for the composite coating formed in the solution containing 400 mg/L ZnO nanoparticles. Ultimately, bioactivity analysis in simulated body fluid revealed that ZnO nanoparticles not only promoted growth but also restricted the size distribution of cauliflower-like apatite grains.

Calcium phosphate biocement using bone meal and acid urease: An eco-friendly approach for soil improvement

Biocementation technology has recently become a new soil improvement method. In majority of the biocementation processes, the formation of calcium carbonate occurs as the consequence of enzymatic urea hydrolysis, producing carbonate-ions and alkaline pH (ranging between 8.5–9.5). The problem of conventional biocementation method at alkaline conditions is the release of ammonium ions (that pollute water) and gaseous ammonia (that pollutes atmosphere). In this paper, a new biocementation method is proposed, which involves calcium phosphate precipitation driven by enzymatic hydrolysis of urea. The bone meal, one of the potential and low-cost sources of calcium phosphate, was acid-dissolved and injected into the sand altogether with urea and acid urease. Due to the enzymatic hydrolysis of urea, the pH of the reaction medium increased, hence the calcium phosphate was tended to precipitate within the pores and bind the soil particles. The content of urea was varied in biocement solution to control the increase of pH during reaction, thus the biocementation was in different pH ranges. The precipitated calcium phosphate compound was found to be brushite, but its morphology highly varied depending on the pH conditions. Molar calcium/urea ratio of 1.5 in calcium phosphate biocementation solution resulted in preferrable formation of plate-like crystals within the sand matrix and increased unconfined compressive strength up to 1.5 MPa. Meanwhile, the conventional biocementation is performed at molar calcium/urea ratio from 0.66 to 1.0. The calcium phosphate biocementation at pH changing from 3.4 to 7.5 indicated the potential decrease of ammonium ions release to environment by about 50% and the emission of toxic gaseous ammonia by approximately 90% in comparison with conventional biocementation.