Crystal Growth Modifier Research Articles

Recent advances in oriented attachment growth and synthesis of functional materials: concept, evidence, mechanism, and future

The latest advances in oriented attachment controlled morphosynthesis and crystal growth of various technically important inorganic materials have been reviewed with the focus on how to generate inorganic micro-/nanostructured materials based on the so-called oriented attachment mechanism. The overview about the basic crystallization principles nowadays falls into two types, i.e., one is the classical crystal growth mode, which is via atom-by-atom additions to an existing nucleus or dissolution of unstable phases and reprecipitation of more stable phases, and the other occurs through particle based aggregation modes involving the process of mesoscopic transformation. The systematic analysis of the particle based aggregation mechanism of oriented attachment in controllable synthesis of functional inorganic materials will be described in particular. Several fashions of attachment are undertaken in the already explored reaction systems, with nanoparticles or nanoribbons as primary building units to form 1D, 2D or 3D structures, and heterostructures. The mechanism of oriented attachment could happen in systems with addition of organic additives or without, demonstrating that organic additives are not the essential factor for this kind of growth mode, which shed new light to intensive understanding of this particular phenomenon. With organic additives, i.e., reactions in organic solvents or in aqueous solution, oriented attachment events can occur too. Current developments in oriented attachment, including the basic principles and potentials with specific examples, indubitably reinforce the understanding of detailed interaction mechanisms between inorganic nanoparticles and their subsequent high order self-assembly mechanism, which are definitely promising for rationally designing various kinds of inorganic materials with ideal hierarchy, controllable length scale, and structures in solution-based systems.

Engineering of Nanotips in ZnO Submicrorods and Patterned Arrays

Unusual nanotips have been selectively achieved in the synthesis of hexagonal-faceted ZnO submicrorods along with two types of its patterned arrays based on a mild precursor-hydrothermolysis reaction. In the synthesis, ethylenediamine (En) with two anchor atoms was introduced not only as a ligand and an alkali medium but also as a crystal-growth modifier for studying the crystal growth kinetics. It has been demonstrated that as-fabricated arrays are composed of ZnO submicrorods with exotic nanotips; the morphology of the nanotips, as well as the preferred spatial orientation and alignment of the rods, strongly depends on the adopted substrates. The growth mechanisms for the ZnO submicrorods and the patterned arrays have been discussed, respectively, on the basis of the growth model for the polar ZnO crystals.

Synthesis of Calcite with Novel Morphologies and Epitaxial Growth Calcium Bilirubinate (CaBR) on Calcite and Effects of Dipalmitoylposphatidylcholine (DPPC) Monolayer and Dextran

Controlled growth of calcium carbonate crystals with complex forms was achieved using dextran as a crystal growth modifier beneath a dipalmitoylphosphatidylcholine (DPPC) monolayer, and calcite-core-calcium bilirubinate (CaBR)-side multiple crystals were also observed owing to the epitaxial growth of CaBR crystals on calcite. During the process, interactions between the DPPC monolayer and calcium ions were studied based on the analysis of the surface pressure−molecular area isotherms. Control over the crystallization of calcite with novel morphologies, such as octahedral crystals and round calcite disks, has been observed. Remarkable morphological changes and continuous structural evolution of calcite from rhombohedral crystal to octahedral crystal to uniform round disks and polyhedrons as concentrations of dextran increased have been observed. Moreover, semirigid multiplex templates consisting of calcium carbonate crystals and DPPC monolayers were established under physiological pH conditions, and epitax...

Polar-Field-Induced Double-Layer Nanostructured ZnO and Its Strong Violet Photoluminescence

Two-dimensional double-layer micro/nanostructured ZnO disks were fabricated in large quantity by a facile solution route at 50 °C within a short reaction time using citrate as crystal growth modifiers. The disks are round-shaped and double-layer nanostructured, about 2 μm in diameter and 400 nm in thickness, which is a new member of the nanostructured ZnO family. Polar-field-induced growth is proposed for the formation of the double-layer ZnO disks. Photoluminescence measurements indicate that there is a strong violet emission in such disks, which is expected to find applications in next generation nanostructured optoelectronic devices.

Relationship between crystal growth mode, preferred orientation and magnetostriction of (Tb 0.3Dy 0.7)Fe 1.95 alloys

The relationship between crystal growth mode, preferred orientation and magnetostrictive properties of (Tb 0.3Dy 0.7)Fe 1.95 alloys was investigated at different directional solidification rates. The results showed that preferred orientation had a strong influence on the characteristics of (Tb 0.3Dy 0.7)Fe 1.95 alloys. At lower solidification rates, the sample with <110> preferred orientation showed larger low-field magnetostriction and apparent compressive stress effect. The excessive solidification rate resulted in failure of preferred orientation and a poor magnetostrictive performance. With an increase in solidification rates, the crystal growth modes changed gradually from cellular and primary dendrite morphology to developed dendritic morphology. In addition, domain configurations were observed using magnetic force microscopy, and the change of magnetostrictive properties was interpreted in terms of revealing the domain configurations.

Crystallization near Glass Transition: Transition from Diffusion-Controlled to Diffusionless Crystal Growth Studied with Seven Polymorphs

A remarkable property of certain glass-forming liquids is that a fast mode of crystal growth is activated near the glass transition temperature Tg and continues in the glassy state. This growth mode, termed GC (glass-crystal), is so fast that it is not limited by molecular diffusion in the bulk liquid. We have studied the GC mode by growing seven polymorphs from the liquid of ROY, currently the top system for the number of coexisting polymorphs of known structures. Some polymorphs did not show GC growth, while others did, with the latter having higher density and more isotropic molecular packing. The polymorphs not showing GC growth grew as compact spherulites at all temperatures; their growth rates near Tg decreased smoothly with falling temperature. The polymorphs showing GC growth changed growth morphologies with temperature, from faceted single crystals near the melting points, to fiber-like crystals near Tg, and to compact spherulites in the GC mode; in the GC mode, they grew at rates 3-4 orders of magnitude faster with activation energies 2-fold smaller than the polymorphs not showing GC growth. The GC mode had rates and activation energies similar to those of a polymorphic transformation observed near Tg. The GC mode was disrupted by the onset of the liquid's structural relaxation but could persist well above Tg (up to 1.15 Tg) in the form of fast-growing fibers. We consider various explanations for the GC mode and suggest that it is solid-state transformation enabled by local molecular motions native to the glassy state and disrupted by the liquid's structural relaxation (the alpha process).

Crystallization of Calcium Carbonate Mineral with Hierarchical Structures in DMF Solution under Control of Poly(ethylene glycol)-b-poly(l-glutamic acid): Effects of Crystallization Temperature and Polymer Concentration

CaCO3 superstructures with complex forms and hierarchical surface textures were mineralized in the presence of peptide type block copolymer poly(ethylene glycol)-b-poly(l-glutamic acid) (PEG-b-pGlu) as a crystal growth modifier in dimethyl formamide (DMF) solution. Spindle-like CaCO3 crystals with a rather smooth surface and a size of 10 µm in length and a maximum diameter of 6 µm were mineralized at 24 ± 2 °C. Unique ellipsoid-like CaCO3 particles with many similar thorns distributed on the particle surface formed when the mineralization temperature was kept at 14 ± 2 °C. Complex column-like CaCO3 superstructures comprised of many tiny rods and irregular particles were observed at 4 ± 2 °C. In addition, when the reagent concentration is varied, the morphology of CaCO3 changes from a mixture of spherical and ellipsoidal structures to a kind of complex ellipsoidal superstructure whose surface is attached by many hierarchical tubular structures, and then to a complex columnar structure, when the concentrati...

Role of Poly(vinyl alcohol) in the Crystal Growth of Ammonium Perchlorate

One of the key aspects in the development of new inorganic materials is the synthesis of particles with specific sizes and morphologies. Nowadays, water-soluble polymers as crystal-growth modifiers are gaining more importance in the field of morphogenesis of inorganic crystals. Ammonium perchlorate (AP) is an extensively used solid propellant oxidizer. Oxidizer particles with a particular morphology are a challenging requirement in the propellant field. In the present study, AP with different morphologies was synthesized by the polymer-assisted crystal-habit modification route. Poly(vinyl alcohol) and AP salt solutions were prepared and mixed in different proportions. Samples were drawn from the mixture, dried on glass slides, and analyzed by scanning electron microscopy and powder X-ray diffraction (PXRD). AP crystals with a rectangular prism and a rectangular wedge shape were obtained, and the reasons for their shapes are discussed. The PXRD patterns showed that the phase of AP obtained is the same as t...

Diffusionless Crystal Growth from Glass Has Precursor in Equilibrium Liquid

A remarkable property of certain glass-forming liquids is that a fast mode of crystal growth is suddenly activated near the glass transition temperature, Tg, and continues in the glassy state. This mode of growth, termed GC (glass-crystal), is so fast that it is not limited by molecular diffusion in the bulk liquid. We have studied the GC growth by growing multiple crystal polymorphs from the liquid of ROY, currently the top system for the number of coexisting polymorphs of known structures. We observed a new feature of GC growth that conflicts with its current description in the literature. We found that the GC mode is not truly a new growth mode suddenly appearing near Tg but one already existing in the equilibrium liquid up to approximately 1.15 Tg, in the form of fast-growing fibers. This finding is relevant to testing different explanations for GC growth and favors the view that GC growth is enabled by molecular motions that are native to the glass but still persist in the viscous liquid.

Substrate orientation-induced distinct ferromagnetic moment in Co:ZnO films

Dilute (3.8 at.%) cobalt-doped ZnO thin films are deposited on LiTaO 3 (LT) substrates with three different orientations [LT(1 1 0), LT(0 1 2) and LT(0 1 8)] by direct current reactive magnetron co-sputtering. The experimental results indicate that Co atoms with 2+ chemical valence are successfully incorporated into the ZnO host matrix on various oriented substrates, and the substrate orientations have a profound influence on the crystal growth and magnetization of Co:ZnO films. A large magnetic moment of 2.42 μ B/Co at room temperature is obtained in the film deposited on LT(0 1 2), while the corresponding values of the other films deposited on LT(1 1 0) and LT(0 1 8) are 1.21 μ B/Co and 0.65 μ B/Co, respectively. Furthermore, the crystal growth mode of Co:ZnO films on various oriented LT, the relationship between the microstructures and corresponding ferromagnetic properties are also discussed.

A Real-Time Study of Homogeneous Nucleation, Growth, and Phase Transformations in Nanodroplets of Low Molecular Weight Isotactic Polypropylene Using AFM

Nanodroplets of isotactic polypropylene (iPP) were observed using temperature-controlled AFM in order to study the polymer's crystallization behavior. The nucleation, growth, and transformation of iPP crystals on heating have been directly imaged. The strong confinement of the polymer into nanoscale droplets has allowed the controlled observation of polymer nucleation as well as access to crystal growth at exceptionally high supercooling in iPP. Different modes of crystal growth were observed depending on the film thickness, including the formation of multiple independent homogeneous nuclei within single droplets. The temperature at which the onset of nucleation was observed in individual droplets was found to be dependent on the thickness as well as the volume of the droplets. For droplets with smaller thicknesses (<5 nm), the thickness of the droplets was found to be the dominating factor influencing the nucleation temperature. This is the first real-space, real-time observation of homogeneous nucleatio...

Controlling the Morphology of Zinc Oxide Nanorods Crystallized from Aqueous Solutions: The Effect of Crystal Growth Modifiers on Aspect Ratio

The effect of growth modifiers on the morphology of zinc oxide (ZnO) nanorods crystallized from solution is characterized. During hydrolysis of zinc nitrate at pH = 7.6 and 75 °C, hexagonally prismatic ZnO crystals were grown in the presence of three growth modifiers: poly(diallyldimethylammonium chloride) (PDADMAC), sodium poly(styrene sulfonate) (PSS), and trisodium citrate. Using statistical analyses of scanning electron microscopy (SEM) images, crystal dimensions were quantified, and the median aspect ratio (ratio of prism length to width) was determined as a function of modifier concentration. In the absence of growth modifiers, the median crystal aspect ratio was 5.2. The aspect ratio was reduced to 4.7, 2.5, and 0.25 in the presence of, respectively, 67 nmol/L (nM) PDADMAC, 130 nM PSS, and 40 μmol/L (μM) citrate. These effects are explained in terms of both electrostatic and coordinative binding between growth modifier and crystal surface.

The Spectral Ice Habit Prediction System (SHIPS). Part I: Model Description and Simulation of the Vapor Deposition Process

Abstract This paper describes the Spectral Ice Habit Prediction System (SHIPS), which represents a continuous-property approach to microphysics simulation in an Eulerian cloud-resolving model (CRM). A two-moment hybrid-bin method is adopted to predict the solid hydrometeor distribution, where the distribution is divided into the mass bins with a simple mass distribution inside each bin. Each bin is characterized by a single representative ice crystal habit and the type of solid hydrometeor. These characteristics are diagnosed based on a series of particle property variables (PPVs) of solid hydrometeors that reflect the history of microphysical processes and the mixing between bins and air parcels in space. Thus, SHIPS allows solid hydrometeors to evolve characteristics and size distribution based on their movement through a cloud. SHIPS was installed into the University of Wisconsin-Nonhydrostatic Modeling System (UW-NMS) and tested for ice nucleation and vapor deposition processes. Two-dimensional idealized simulations were employed to simulate a winter orographic storm observed during the second Improvement of Microphysical Parameterization through Observational Verification Experiment (IMPROVE-2) campaign. The simulated vertical distributions of ice crystal habits showed that the dynamic advection of dendrites produces wider dendritic growth region than local atmospheric conditions suggest. SHIPS showed the sensitivities of the habit distribution in the low- and midlevel to the upper-level growth mode (T &amp;lt; −20°C) of ice crystals through the sedimentation. Comparison of the results to aircraft observations casts doubt on the role of the columnar growth mode (T &amp;lt; −20°C) traditionally thought to be dominant in the literature. The results demonstrated how the complexity of the vapor deposition growth of ice crystals, including dendrites and capped columns, in varying temperature and moisture lead to particular observed habits.

Morphological evolution of PbS crystals under the control of l-lysine at different pH values: The ionization effect of the amino acid

PbS crystals were synthesized by a simple hydrothermal process with l-lysine as the crystal growth modifier. Depending on the initial pH value of the reaction solution, the morphologies of the PbS crystals varied and the crystals with shapes of truncated nanocube, star-shaped dendrite, comb-like dendrite were obtained. The morphological evolution of the PbS crystals was explained by the different state of the ionization equilibrium of l-lysine in the solution at different pH values. The presence of differently charged l-lysine molecules would influence the crystal growth rates along different directions and result in the final morphologies of PbS crystals. It is proposed that when amino acids are used as crystal growth modifiers, besides the types of amino acids, which have been regarded to influence the crystals' growth, the ionized state of the amino acids at different pH values would play an important role in the morphological control, and this point may have been neglected before.

Mechanisms controlling primary crystallisation of Ga 20Te 80 glasses

The kinetic study of the crystallisation process of Ga 20Te 80 glass from isothermal and continuous heating calorimetric data have been performed applying a recently developed procedure. The kinetic information was complemented with X-ray diffraction measurements. With this scope, three crystallisation patterns, with three-dimensional isotropic growth have been analysed: (i) site saturation and interface controlled growth. (ii) homogeneous nucleation with interface controlled growth and (iii) homogeneous nucleation with two simultaneous modes of crystal growth (interface- and diffusion-controlled). A complex model with two simultaneous modes of three-dimensional isotropic crystal growth with decreasing homogeneous nucleation and soft impingement has been applied for modelling primary crystallisation of the Ga 20Te 80 glass. The model goes beyond the isokinetic hypothesis when coupling isothermal and continuous heating kinetic data. The apparent activation energy E a = (2.06 ± 0.03) eV/at obtained for the primary crystallisation of the phase Te is shown to correspond to an activation energy for nucleation E I = (2.85 ± 0.03) eV/at and an interface controlled activation energy for growth E u = (1.90 ± 0.03) eV/at at the crystallisation onset.

Controlled Crystallization of Tooth-Like Hydroxyapatite under Gelatin Monolayer

Based on the molecular recognition theory, an organic molecules model was designed to induce the hydroxyapatite crystallization, to build a tooth-like calcium phosphate/hydroxyapatite under a controllable way in vitro. The cross-linking of collagen on the dentin surface and gelatin was optimized by varying the molar ratio of N,N-(3-dimethylaminopropyl)- N'-ethyl-carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) at a constant EDC concentration. CaCl2 and Na3PO4-12H2O solutions were added after the crosslinking process. The whole process requires repeating the crosslinking and mineralization process for five times. The obtained composite were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) as well as energy dispersive X-ray photoelectron spectroscopy (XPS). The results showed that the dentinal tubule were blocked by neonatal hydroxyapatite layer which has a continuous structure of columns crystal with size of 10-40nm. Furthermore, there was column crystal with parallel direction inside, similar to the crystal array in the top of enamel rod. This study showed that the specific organic molecule model can be used as a potential effective crystal growth modifier.

Controlled Mineralization of Barium Carbonate Mesocrystals in a Mixed Solvent and at the Air/Solution Interface Using a Double Hydrophilic Block Copolymer as a Crystal Modifier

Mineralization and crystallization of barium carbonate mesocrystals with various shapes and complex form using double hydrophilic block copolymers (DHBCs) as crystal growth modifiers in a mixed solvent composed of N,N-dimethylformamide (DMF) and deionized water (DIW) have been systematically investigated. The effects of polymer concentration, solvent, and the volume ratio of a mixed solvent on the controlled crystallization of BaCO3 mesocrystals have been examined. Shuttle-like BaCO3 rods with different sizes and ratios of average length (L) to maximum diameter (D) can be obtained by simply altering polymer concentration in the mixed solvent. In addition, complex hierarchical shuttle-like aggregated structures can be formed at the air/solution interface that were dramatically different from the structure obtained in bulk solution. This crystallization method in a mixed solvent containing a crystal growth modifier represents a simple but versatile route to achieve unique synergic effects on manipulation of the morphology and preferential orientation growth of BaCO3 mineral both in bulk solution and at the air/solution interface, which can be extended for shape control over other minerals or inorganic−organic hybrid materials.

Poly(ethylene glycol)‐b‐phosphorylated polyglycidols as CaCO3 crystal growth modifiers. II. Macromolecular architecture versus the crystal size and shape and crystallization inhibition

AbstractIonic–nonionic dihydrophilic block copolymers with poly(ethylene glycol) as nonionic blocks and phosphorylated polyglycidol as ionic blocks of various lengths and various degrees of phosphorylation were prepared. The influence of these variables on the CaCO3 crystal structure and the inhibition of crystal growth was studied. The best results (small crystal size, low dispersity of sizes, and longest inhibition time) were observed for limited degrees of phosphorylation. A certain part of the dihydrophilic block copolymers was permanently bound to the formed particles, opening a way to the synthesis of inorganic–organic (polymer) hybrids based on these components. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 90–98, 2007

Low-molecular-weight poly-carboxylate as crystal growth modifier in biomineralization

Construction of modified inorganic mineral with controlled mineralization analogues of those produced by nature is now of current interest for understanding the mechanism of thein vivo biomineralization processes, as well as looking for fresh industrial and technological applications. Low-molecular-weight chiral poly-carboxylate ligands derived from naturally occurring L-α-amino acids have been used as model systems to study the effect of molecular properties on crystal growth modification.

Effect of Benzoic Acids on Barite and Calcite Precipitation

The effect of various benzoic acids on the precipitation of barite (BaSO4) and calcite (CaCO3) was investigated. The acids varied in the number of carboxylate groups, from dibenzoic acids (phthalic, isophthalic, and terephthalic) through to the hexabenzoic acid (mellitic acid). It was found that the stereochemistry of the dibenzoic acids was important, as was the pH of the solution (trimesic acid was used as a test case and showed that greatest inhibition was achieved with all carboxylate groups deprotonated). Interestingly, for both the calcite and barite systems, mellitic acid was found to be both a potent inhibitor and a significant crystal growth modifier. In the case of barite, the presence of mellitic acid produced nanoparticles that agglomerated. The nanoparticles were found to be ∼20 nm in size from X-ray diffraction (XRD) line width analysis and 20−50 nm from transmission electron microscopy (TEM). Humic acid was also tested and found to form bundled fibers of barium sulfate.