Control Of Crystal Shape Research Articles

Effects of surfactants on the morphologies, structures, and electrochemical activities of WO3/Ag2O nanocomposites for supercapacitor electrodes

For energy storage, supercapacitors have been extensively developed. Among them, pseudocapacitors that use faradaic reactions of conductive polymers and transition metal oxides exhibit high electrochemical performance. In this study, WO3-based electrodes for high-performance pseudocapacitors were designed with Ag2O and various surfactants, with the aim to extend of the potential range and shape control of WO3 crystals. The WO3/Ag2O nanocomposites were prepared on a carbon cloth via chemical bath deposition with different types of surfactants: cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS), and Pluronic F-127. Both Ag and the surfactants affected the morphology of the WO3 crystals; their crystal sizes were decreased, and the crystallinity was improved. The specific capacitance of the WO3/Ag2O nanocomposite was 621 F/g at 5 mV/s, whereas that of WO3 was 397 F/g. Furthermore, the specific capacitance of the nanocomposites increased with the use of surfactants: 960 F/g for WO3/Ag2O@Pluronic F-127, 641 F/g for WO3/Ag2O@CTAB, and 846 F/g for WO3/Ag2O@SDS at 5 mV/s. WO3/Ag2O@Pluronic F-127 had superior capacitance and exhibited a charge/discharge capacitance retention rate of 135 % after 2000 cycles at 5 A/g. The symmetric electrode configuration of WO3/Ag2O@Pluronic F-127 exhibited a maximum energy density of 85 W h kg−1 and a power density of 670 W kg−1. These results highlight the significant potential of the WO3/Ag2O@Pluronic F-127 nanocomposite electrode for future energy storage devices.

Crystal Shape Control on the Repacking and Jamming of Crystal‐Rich Mushes

AbstractThe rheology of crustal mushes is a crucial parameter controlling melt segregation and magma flow. However, the relations between mush dynamics and crystal size and shape distribution remain poorly understood because of the complexity of melt‐crystal and crystal‐crystal interactions. We performed analog experiments to characterize the mechanisms that control pore space reduction associated with repacking. Three suspensions of monodisperse particles with different geometries and aspect ratios (1:1, 2:1, 4:1) in a viscous fluid were tested. Our results show that particle aspect ratios strongly control the melt extraction processes. We identify two competing mechanisms that enable melt extraction at grain scale. The first mechanism leads to continuous deformation and melt extraction and is associated with “diffuse” frictional dissipation between neighboring particles. The second is stochastic, localized, and nearly instantaneous and is associated with the development and destruction of force chains percolating through the granular assembly.

High-quality AlN growth on flat sapphire at relatively low temperature by crystal island shape control method

In this study, we found that the two-step method for heteroepitaxial AlN on sapphire has some limitations. Growing the buffer layer for a too long time will make it challenging to obtain a flat film surface. So, three-step-growth was introduced and an intermediate layer was inserted. In this step, the surface morphology of samples is controlled by NH3 flow rate and the dislocation density is further reduced. Finally, we are able to obtain high-quality AlN samples grown by metalorganic chemical vapor deposition at 1120 ℃, which is a relatively low temperature for the AlN epitaxial layers. The X-ray diffraction ω-scan full width at half maximum values for (002) and (102) reflections are 172 and 145 arcsec, respectively.

Size and Shape Control of Ice Crystals by Amphiphilic Block Copolymers and Their Implication in the Cryoprotection of Mesenchymal Stem Cells.

Precise control over the size and shape of ice crystals is a key factor to consider in designing antifreezing and cryoprotecting molecules for cryopreservation of cells. Here, we report that a poly(ethylene glycol)-poly(l-alanine) (PEG-PA) block copolymer exhibits excellent cryoprotecting properties for stem cells and antifreezing properties for water. As the molecular weight of PA increased from 500, 760, and 1750 Da (P1, P2, and P3) at the same PEG molecular weight of 5000 Da, the β-sheet content decreased and α-helix content increased. Comparing P2 (PEG-PA; 5000-760) and P4 (PEG-PA: 1000-750), β-sheets increased as the PEG block length decreased. The critical micelle concentration of the PEG-PA block copolymers was in a range of 0.5-3.0 mg/mL and was proportional to the hydrophobicity of the PEG-PA block copolymers. The P1, P2, and P3 self-assembled into spherical micelles, whereas P4 formed micelles with cylindrical morphology. The difference in the block copolymer structure affected ice recrystallization inhibition (IRI) activity and cryopreservation of cells. IRI activity was assayed via mean largest grain size (MLGS), and interactions between polymers and ice crystal surfaces were studied by dynamic ice-shaping studies. The MLGS decreased to 58 → 53 → 45 → 35 → 23% of that of PBS, as the polymer (PEG-PA 5000-500) concentration increased from 0.0 (PBS; control) → 1.0 → 5.0 → 10 → 30 → 50 mg/mL. The MLGS of PEG 5k solutions (negative control) decreased to 74 → 71 → 64 → 44 → 37% of that of PBS in the same concentration range. P3 and P4 with a longer hydrophobic PA block developed elongated ice crystals at above 30 mg/mL. The dynamic ice-shaping study exhibited that ice crystals became needle-shaped, as the hydrophobicity of the polymer increased as in P2-P4. The cell recovery in the P1 system after cryopreservation at -196 °C for 7 days was 87% of that of the dimethyl sulfoxide (DMSO) 10% system (positive control). The cell recovery was 48% for the P2 system and drastically decreased to less than 30% of that of the DMSO 10% system in the P3, P4, PEG 5k, PEG 1k, PVA 80H, and PVA 100H systems. Current studies suggest that IRI activity, round ice crystal shaping, and membrane stabilization activity of P1 cooperatively provide excellent cell recovery among the candidate systems. Recovered stem cells exhibited excellent proliferation and multilineage differentiation into osteocytes, chondrocytes, and adipocytes. To conclude, the PEG-PA (5000-500) block copolymer is suggested to be a promising antifreezing cryoprotectant for stem cells.

Optimal Control of Crystal Size and Shape in Batch Crystallization Using a Bivariate Population Balance Modeling

Abstract An optimal control framework was employed to obtain optimal supersaturation/temperature policies for controlling the crystal mass, size, and shape that meet target product specifications. It uses a bivariate population balance model that includes crystal nucleation, growth, dissolution, and disappearance. The optimal control scheme, solving a dynamic optimization problem, was applied to the batch cooling crystallization of potassium dihydrogen phosphate. The population balance model was evaluated in open-loop experiments, showing good prediction for the mean characteristic lengths and number of particles, both for the supersaturation and undersaturation zones. The deterministic optimal control simulations demonstrated the application of the control action policies to produce crystals of desired mass and average shape for different control targets.

Control of Crystal Size and Morphology of Calcium Carbonate Crystal Polymorphism

Calcium carbonate, the main component of lime, has been widely used in industry due to its stability and economy. Calcium carbonate has three types of crystalline polymorphism, calcite, aragonite and vaterite, each with different properties. Therefore, the control of crystal polymorphism is required for industrial applications. In addition, the control of crystal size and shape is similarly required for different applications. In this study, the effect of SrCO3 on the size control of fine aragonite-type calcium carbonate crystals by uniform urea precipitation and the effect of SrCO3 addition was investigated by adding solid strontium carbonate and dissolved strontium carbonate. The addition of solid strontium carbonate affected the crystal polymorphism and size of the calcium carbonate produced, depending on the properties of the solid particles and the amount of SrCO3 added. Experiments on the addition of dissolved SrCO3 showed that the supersaturation formation rate could be controlled to control the crystal polymorphism.

Undercoordinated Active Sites on 4H Gold Nanostructures for CO2 Reduction.

Electroreduction of CO2 is a promising approach toward artificial carbon recycling. The rate and product selectivity of this reaction are highly sensitive to the surface structures of electrocatalysts. We report here 4H Au nanostructures as advanced electrocatalysts for highly active and selective reduction of CO2 to CO. Au nanoribbons in the pure 4H phase, Au nanorods in the hybrid 4H/fcc phase, and those in the fcc phase are comparatively studied for the electroreduction of CO2. Both the activity and selectivity for CO production were found to exhibit the trend 4H-nanoribbons > 4H/fcc-nanorods > fcc-nanorods, with the 4H-nanoribbons achieving >90% Faradaic efficiency toward CO. Electrochemical probing and cluster expansion simulations are combined to elucidate the surface structures of these nanocrystals. The combination of crystal phase and shape control gives rise to the preferential exposure of undercoordinated sites. Further density functional theory calculations confirm the high reactivity of such undercoordinated sites.

Growth Promotion of Targeted Crystal Face by Nanoprocessing via Laser Ablation

Control of crystal shape is an indispensable step for various applications of crystalline products. However, obtaining the desired crystal shape by conventionally tuning environmental conditions (t...

Model-based analysis and quality-by-design framework for high aspect ratio crystals in crystallizer-wet mill systems using GPU acceleration enabled optimization

The simultaneous control of crystal size and shape is particularly important in pharmaceutical crystallization processes. These two quantities not only influence the dissolution rate and bioavailability of final drug products, but also contribute to the manufacturability and efficiency of downstream operations. The manipulation of crystal shape, however, is difficult since it requires decoupled growth rate control of individual crystal faces. The aim of this work is to analyze and evaluate the effectiveness of wet milling for control of bivariate size distribution of high-aspect ratio crystals during solution crystallization. Three configurations are compared: the pure batch crystallizer, the crystallizer with internal wet mill (immersion mill) and crystallizer with external wet mill. Population balance models (PBMs) are employed to describe bivariate size density function dynamics, with stirring rate dependent breakage to enable the direct optimization of wet mill operation. The generated system of hyperbolic partial differential and ordinary differential equations is solved by a fully discretized high-resolution finite volume method (HR-FVM), involving graphical processing unit (GPU) acceleration, which brings up to two orders of magnitude speed-up by compared to the serial C implementation. The simulation studies revealed that wet milling significantly extends the achievable crystal size and shape domain, but it also broadens the product size distribution. The analysis of the optimized operating profiles, which include temperature, wet mill rotation (RPM) and recirculation rate, enabled the generalization of optimal operation, which can efficiently guide a QbD approach by considerably reducing the design space without compromising the process performance.

Nanocrystals: The Preparation, Precise Control and Application Toward the Pharmaceutics and Food Industry.

Crystallization is a significant process employed to produce a wide variety of materials in pharmaceutical and food area. The control of crystal dimension, crystallinity, and shape is very important because they will affect the subsequent filtration, drying and grinding performance as well as the physical and chemical properties of the material. This review summarizes the special features of crystallization technology and the preparation methods of nanocrystals, and discusses analytical technology which is used to control crystal quality and performance. The crystallization technology applications in pharmaceutics and foods are also outlined. These illustrated examples further help us to gain a better understanding of the crystallization technology for pharmaceutics and foods.

Control of Organic Crystal Shape by Femtosecond Laser Ablation

Control of organic crystal shape is crucial for various scientific and industrial fields, while it is still very challenging even with systematic optimization of environmental parameters such as temperature and concentration. Here we report an innovative approach for spatiotemporal control of organic crystal growth by directly modifying local crystal structures via femtosecond laser ablation. We found that a crystal face that is locally ablated only with a single laser pulse shows enhanced growth without the loss of crystal quality. The underlying mechanism can be explained by the generation of energetically favorable crystal growth mode (spiral growth mode), which is a fundamental growth mode for various organic crystals. We demonstrated that various crystal shapes can be achieved by femtosecond laser ablation. The fine-tuned, spatiotemporal cue given by femtosecond laser ablation will provide a facile means to obtain organic crystals with desired shape.

Shape control of nickel crystals and catalytic hydrogenation performance of ruthenium-on-Ni crystals

Nickel crystals with various shapes were obtained via hydrothermal synthesis. The effect of temperature and surfactant on nickel morphology was studied.

Micro‐Segmented Flow Technology Applied for Synthesis and Shape Control of Lead Styphnate Micro‐Particles

AbstractIn this study, the technology of micro‐segmented flow was applied for continuous synthesis safely and shape control accurately to lead trinitroresorcinate (LTNR) particles. Besides, a micro chemical reaction and crystallization system were built. Crystal shape control technology of LTNR and micro‐segmented flow technology were first combined using the system. Additionally, the effects of the flowing rate and chemical additives on LTNR micro‐particles preparation were researched for shape control. The LTNR micro‐particles were analyzed by XRD, DSC, laser scanning confocal microscope and laser particle size analyzer. The results shows that the LTNR particles size can be controlled from 20 to 400 μm by the flow rate and the concentration of hexadecyl trimethyl ammonium bromide (CTAB), while the shape of LTNR can be controlled by the concentration of glycerol and CTAB. Besides, there is a good linear relationship between the size and the activation energy. This illustrates that the LTNR particles with smaller size are more stable and have higher heat release. This study demonstrated the power of micro‐segmented flow for generation of LTNR micro‐particles with high quality and for tuning of particle properties.

Size and Shape Control of Micron-Sized Salicylic Acid Crystals during Antisolvent Crystallization

During an antisolvent crystallization process, micron-sized crystals of salicylic acid in the particle size range 20 to 150 μm were prepared under specific sets of crystallization conditions, with a focus on drug concentration, temperature, and solvent composition. For each experiment, the size outcome was determined by a number of knock on (often competing) influencing factors, including supersaturation, mass available for deposition during crystallization, and influence of temperature and solvent composition on crystallization kinetics. A certain fraction of the crystals, especially at higher solute concentration, developed a spectacular hollow shape with an almost perfect rectangular outer cross-section. A mechanistic explanation for the formation of hollow crystals is proposed. The use of additives during crystallization introduced further control over the size and, perhaps more noticeably, over the shape of the salicylic acid crystals. The lengths of salicylic acid crystals decreased to as low as 6 μ...

Size and Shape Controlled Crystallization of Hemoglobin for Advanced Crystallography

While high-throughput screening for protein crystallization conditions have rapidly evolved in the last few decades, it is also becoming increasingly necessary for the control of crystal size and shape as increasing diversity of protein crystallographic experiments. For example, X-ray crystallography (XRC) combined with photoexcitation and/or spectrophotometry requires optically thin but well diffracting crystals. By contrast, large-volume crystals are needed for weak signal experiments, such as neutron crystallography (NC) or recently developed X-ray fluorescent holography (XFH). In this article, we present, using hemoglobin as an example protein, some techniques for obtaining the crystals of controlled size, shape, and adequate quality. Furthermore, we describe a few case studies of applications of the optimized hemoglobin crystals for implementing the above mentioned crystallographic experiments, providing some hints and tips for the further progress of advanced protein crystallography.

Application of feedback control and in situ milling to improve particle size and shape in the crystallization of a slow growing needle-like active pharmaceutical ingredient

Control of crystal size and shape is crucially important for crystallization process development in the pharmaceutical industries. In general crystals of large size and low aspect ratio are desired for improved downstream manufacturability. It can be extremely challenging to design crystallization processes that achieve these targets for active pharmaceutical ingredients (APIs) that have very slow growth kinetics and needle-like morphology. In this work, a batch cooling crystallization process for a GlaxoSmithKline patented API, which is characterized by very slow growth rate and needle morphology, was studied and improved using process analytical technology (PAT) based feedback control techniques and in situ immersion milling. Four specific approaches were investigated: Supersaturation control (SSC), direct nucleation control (DNC), sequential milling-DNC, and simultaneous milling-DNC. This is the first time that immersion wet milling is combined with feedback control in a batch crystallization process. All four approaches were found to improve crystal size and/or shape compared to simple unseeded or seeded linear cooling crystallizations. DNC provided higher quality crystals than SSC, and sequential and simultanesou milling-DNC approaches could reduce particle 2D aspect ratio without generating too much fines. In addition, an ultra-performance liquid chromatography (UPLC) system was used online as a novel PAT tool in the crystallization study.

Preliminary Mechanism of Tubular Nano-Mg(OH)2 Formation

Since the discovery of tubular nano-scale materials in 1990s, they have been considered as the ideal materials for a variety of applications due to their unique mechanical, ferromagnetic properties for spintronics, magnetic, chemical and biological properties. In our previous work, nano-tube structured magnesium hydroxide has been discovered in solution phase under the normal atmospheric pressure. The present work focus on discussing the effects of reaction concentration, temperature, reaction time, crystal shape control agent dosage on the tubular nano-Mg(OH)2 formation initially. The crystal shape control agent plays an important template role in inducing Mg(OH)2 crystal nuclei forming tubular nano-Mg(OH)2 during the synthesis process. The resulting tubular nano-Mg(OH)2 implies its potential expanded applications in many research areas like the papermaking industry, fertilizer additive, pharmacy, biomaterials and etc.

Crystal front shape control by use of an additional heater in a Czochralski sapphire single crystal growth system

The quality of sapphire single crystals used as substrates for LED production is largely influenced by two defects: dislocation density and bubbles trapped in the crystal. In particular, the dislocation density has a higher value in sapphire grown by the Czochralski (CZ) method than by other methods. In the present study, we predict a decreased value for the convexity and thermal gradient at the crystal front (CF) through the use of an additional heater in an induction-heated CZ system. In addition, we develop a solute concentration model by which the location of bubble formation in CZ growth is calculated, and the results are compared with experimental results. We further calculate the location of bubble entrapment corresponding with the use of an additional heater. We find that sapphire crystal growth with an additional heater yields a decreased thermal gradient at the CF, together with decreased CF convexity, improved energy efficiency, and improvements in terms of bubble formation location.

Modeling the atomic-scale structure, stability, and morphological transformations in the tetragonal phase of LaVO4

In this communication, a systematic study of the surface structure, including energy management during morphological transformations of tetragonal phase of LaVO4, has been carried out. For this study, we combined experimental findings and first-principles calculations to develop a Wulff construction model. Our findings can help further understand the synthetic control of crystal shape via tuning of surface chemistry.

Unraveling the Multiple Effects Originating the Increased Oxidative Photoactivity of {001}-Facet Enriched Anatase TiO2.

Crystal shape control on a series of anatase photocatalysts was achieved by varying the amount of HF employed as a capping agent in their hydrothermal synthesis. A systematic comparison between their physicochemical properties, determined by several complementary surface and bulk techniques before and after thermal treatment at 500 °C, allowed one to discern the influence of the relative amount of exposed {001} crystal facets among a series of effects simultaneously affecting their oxidative photocatalytic activity. The results of both formic acid and terephthalic acid photo-oxidation test reactions point to the primary role played by calcination in making {001} facets effectively photoactive. Annealing not only removes most of the residual fluorine capping agent from the photocatalyst surface, thus favoring substrate adsorption, but also produces morphological modifications to a crystal packing that makes accessible a larger portion of surface {001} facets due to the unpiling of platelike crystals. The photocatalyst bearing the highest amount of exposed {001} facets (60%) shows the highest photoactivity in both the direct and the (•)OH-radical-mediated photocatalytic test reaction.