Metastable Crystals Research Articles

Crystallization of the polymer induced liquid mineral precursor in the constraint nanopores

The liquid mineral intermediates are very important for the formation of different biominerals in biological systems. However, the detail growth mechanisms of these amorphous phases in complicated biochemical condition, such as organic frameworks, special interfaces and compartmented cells, are still incomplete understand. To gain a better understanding of the evolution of the polymer-induced liquid mineral precursor (PILP) in the special microenvironments, the nanopores of track etch (TE) membranes have been applied. Simultaneously, several synergetic ions of Sr2+, Mg2+ and Ba2+ were introduced to tune properties (nucleation time, lifespan and flowability) of liquid mineral phases. Simultaneously, the titration experiments have also been performed to track the crystallization processes. Experiments have shown that the nanopores could effectively stabilize the metastable vaterite crystals. Under the influences of polymer, nanopores and synergetic doping ions, mono- and polycrystalline nanorods could be synthesized. Doping ions in a certain concentration rang could effectively postpone the nucleation time and prolong the lifespan of liquid mineral precursor. Our study will be helpful to understand the crystallization process of different amorphous phases in the complicated biological microenvironments.

Coupling of CFD and population balance modelling for a continuously seeded helical tubular crystallizer

A comprehensive model coupling the computational fluid dynamics with the population balance equation (CFD−PBE) for a continuous seeded mixed suspension mixed product removal (MSMPR)-helical tubular (HT) crystallizer assembly has been developed. The model accurately depicts the fluid dynamics, mass transfer, heat transfer and crystal size distribution (CSD) in the MSMPR-HT crystallizer. The crystallization system considered was to produce metastable α-form of L-glutamic acid. The PBE was discretized using a high-resolution central scheme and solved simultaneously with CFD equations in COMSOL Multiphysics® utilizing user-defined scalars. A good agreement was observed between the model and experimental data for the metastable α-form crystals of L-glutamic acid with uniform particles and a mean crystal size of 160 µm. The continuous crystallization under different stirrer speeds, saturated solution flow rates, inlet saturated solution concentrations and temperature was investigated. It was found the higher stirrer speeds, saturated solution flow rate and temperature lead to uniform distribution with smaller crystal size. Moreover, the mean crystal size becomes larger and the CSD wider when the saturated solution concentration increase.

Growth of high-quality metastable crystal of acetaminophen using solution-mediated phase transformation at low supersaturation

We improved the crystal quality of the metastable phase of a pharmaceutical compound acetaminophen (form II) using solution-mediated phase transformation (SMPT) combined with the control of supersaturation and crystal size. Form II crystals grew at low supersaturation via SMPT of the trihydrate at low temperature (10 °C). While crystal growth rate was low compared to the 20 °C condition, crystals had many defects such as solution inclusions or cracks at 20 °C, but few at 10 °C. The ratio of form II crystals with any defects was small (12%), about 1/3 that of the 20 °C condition. Since the concentration gradient on the crystal surface was relatively small at low bulk supersaturation, high-quality crystals grew uniformly. However, large crystals (>∼0.8 mm) were still defective even at low supersaturation, because concentration gradient is large on large surfaces. Using a new seed-dipping process, obtained crystals were small and uniform in size (∼0.4 mm), and the ratio of defective crystals was reduced to 6%. Powder X-ray diffraction analysis revealed that form II crystals were ∼6 times more temporally stable than in the 20 °C condition. We found that high-quality crystals of metastable phase with high temporal stability could be realized by low supersaturation and reduction of the crystal size via SMPT.

Atomic-Scale Imaging of Surface and Hydration Structures of Stable and Metastable Acetaminophen Crystals by Frequency Modulation Atomic Force Microscopy

In this paper, we have investigated hydration structures of the stable and the metastable acetaminophen crystals (Form I and Form II, respectively) by frequency modulation atomic force microscopy w...

Crystallization study of potassium sulfate-water system, metastable zone width and induction time measurements using ultrasonic, turbidity and 3D-ORM techniques

A batch cooling crystallizer was used to explore the solubility, metastable zone width (MSZW), induction time and crystallization kinetics of potassium sulphate-water as a model system. Three techniques were used: ultrasonic, turbidity and 3D-ORM probes. In the first step, the potassium sulphate solubility in water was measured over the temperature range from 15 to 35 °C by using a refractometer. In a second step, the MSZW was measured using different cooling rates for different solution concentrations by both ultrasonic and turbidity probes in order to compare between the two methods. The nucleation kinetics of the studied system was estimated based on approach the crystal growth rates were calculated from desupersaturation curve during seeded batch experiments. Finally, induction time measurements were achieved by means of a 3D-ORM and the effect of supersaturation degree and saturation temperature on measured induction time was investigated. Based on classical nucleation theory, the induction time data were used to calculate the surface tension.

Ion Coulomb crystal in a polychromatic optical superlattice

We demonstrate that the earlier suggested new all-optical method of creating long-term small (containing two or three particles) ion clusters using the rectified optical forces (RFs) can be used to create cold trapped Coulomb crystals (consisting of several tens of resonant ions). The results of the supercomputer simulations of the dynamics of a mercury ion cloud in a polychromatic optical superlattice (induced by RFs) are presented and analysed. Such a cloud (including 49 ions) in the absence of the optical field expands rapidly (during the characteristic time of the order of ) as a result of the Coulomb explosion. It is shown that the polychromatic optical field can result in the ‘quenching’ of the Coulomb explosion and crystallisation of the ion cloud: creation of a quasi-2D array of ordered and strongly coupled cold ions (with the Coulomb coupling parameter and temperature ∼10−3 K). The mean destruction time of the studied metastable crystal is of the order of 10 s. Moreover, the central core of the ion cloud can retain its crystalline configuration for a much longer time.

Continuous crystallization of α-form L-glutamic acid in an MSMPR-Tubular crystallizer system

Continuous crystallization of active pharmaceutical ingredients is of prime significance. A continuous mixed suspension mixed product removal (MSMPR)-tubular crystallizer geometry is designed and optimized to produce the metastable α-form crystals of L-glutamic acid with uniform mean size of 130 µm. The MSMPR is used to produce well-tuned seed crystals that undergo further growth in a series of tubular crystallizers. The effects of the initial supersaturation, stirring speed, nucleation temperature and residence time were optimized in the MSMPR crystallizer to tune the supply of continuous seeds by using the principal component analysis and in-situ particle tracking measurement. The continuous seeds of the desired metastable polymorphic form with specific size ranging from 5.0 to 15.0 µm and number density ranging from 500 to 1500 counts, were transferred to a series of three coiled tubular crystallizers for further growth. In addition, the cooling strategy in the tubular crystallizers was utilized to further optimize the quality of the final crystal product. The crystal size distribution (CSD) in the MSMPR-tubular crystallizer system was compared with a single MSMPR with the same residence time and found to be superior. Finally, a potential scale up strategy of the MSMPR-tubular crystallizer system was proposed for further study.

Phase Transition of Graphene-Templated Vertical Zinc Phthalocyanine Nanopillars.

We report on the graphene-assisted growth, crystallization, and phase transition of zinc phthalocyanine (ZnPc) vertically oriented single crystal nanopillars. Postcrystallization thermal annealing of the nanostructures results in a molecular packing change while maintaining the vertical orientation of the single crystals orthogonal to the underlying substrate. Grazing incidence X-ray diffraction and high-resolution TEM studies characterized this phase transition from a metastable crystal phase to the more stable β-phase commonly observed in bulk crystals. These vertical arrays of crystalline nanopillars exhibit a high-surface-to-volume ratio, which is advantageous for applications such as gas sensors. We fabricated chemiresistor sensors with ZnPc nanopillars grown on graphene and demonstrated its selectivity for ammonia vapors, and improvement in sensitivity in the β-phase crystal packing pillars due to their molecular orientation increasing the exposure of the Zn2+ ion to the ammonia analyte. This work highlights the first morphology-retentive phase transition in organic single crystal nanopillars through simple postprocessing thermal annealing. This study opens up the possibility of molecular packing control without large variations in morphology, a necessity for high-performance devices and establishing structure-property relations.

Visual observation of fuel-borne ice crystals

This study closely observed fuel-borne ice crystals and discusses their morphological characteristics. Fuel-borne ice crystals are formed naturally in jet fuel when entrained water freezes, and unfortunately, their characteristics are poorly understood. Crystals nucleating in a fluid static condition were observed at about − 38 °C. The ice crystals had various shapes that can be classified into three types: plate and spherical shapes, columnar shapes, and irregular shapes. The size of the crystals ranged from 5 to 15 microns along the prism plane and up to 30 microns along the base plane. No remarkable growth or phase change was observed after crystallization at low temperature since the number of water molecules in the jet fuel is limited. However, metastable crystals were found in the fuel, as in previous results obtained using a toluene matrix. The metastable crystals could help with the growth of hexagonal fuel-borne ice crystals. Further investigation is required for the growth rate of hexagonal ice crystals from metastable crystals.

Aggregation and collapse dynamics of skyrmions in a non-equilibrium state

Magnetic skyrmions have attracted attention because of their emergent electromagnetic properties. In particular, non-equilibrium-state skyrmions, which are protected by topology and hence can exist over a wider temperature–magnetic-field region, show promise for possible practical applications, but their dynamics remain elusive. Here, we report the observation of a magnetic-field-induced dynamical transition from the metastable hexagonal-lattice skyrmion crystal (SkX) at a zero bias-field to an amorphous state via the densely vacancy-populated SkX. With decreasing field, on the other hand, the aggregate transforms from ‘random particles’ to ‘microcrystals’ of skyrmions in a non-equilibrium state, in analogy to colloidal crystallization, and subsequently undergoes a topologically distinct phase separation between the SkX and helical/conical domains accompanied by topological defects. These observations directly demonstrate the aggregation and collapse dynamics of metastable skyrmions and may provide a route to other nontrivial topological phenomena such as the zero-magnetic-field topological Hall effect. A Lorentz transmission electron microscopy study of a thin iron germanium film reveals the aggregation dynamics of skyrmions when pushed out of equilibrium.

Superheated Melting Kinetics of Metastable Chain-Folded Polymer Crystals

The unique behavior of superheated melting kinetics of polymer crystals has been examined in terms of the metastable nature of thin polymer crystals with chain folding. The superheated melting kinetics was characterized by the heating rate dependence of the melting peak in the thermogram. By examining the behaviors of polyethylene molar mass fractions, its homologue, hexacontane, and indium, it has been experimentally confirmed that the metastability of crystals with chain folding has an essential role in the superheated melting kinetics; i.e., stable extended-chain crystals of hexacontane melts in the same way as indium without superheating, and metastable chain-folded crystals of higher molar mass polyethylene needs to overcome a larger kinetic barrier for melting.

Differences in Phase Change Processes Upon Heating Between Co and Zn-ZIF-4 Compounds

Zn and Co-ZIF-4 meta-stable compounds adopt the same topology of Zeolitic imidazolate frameworks (ZIF)-4, but differ in the metal nodes (Zn versus Co). Using calorimetric and thermogravimetric analysis, here we characterized their differences in phase change processes. Upon heating, the framework of Co-ZIF-4 meta-stable crystal undergoes the crystal-to-amorphous phase transition at 590[Formula: see text]K, which is somewhat lower than the corresponding transition previously reported in the corresponding Zn-ZIF-4. In addition, the recrystallization rate for amorphous Co-ZIF-4 is relatively higher than the corresponding one of Zn-ZIF-4. Finally, the forming Co–zni crystal begins to melt at about 824[Formula: see text]K, accompanied by quick decomposition, whereas Zn–zni undergoes complete melting which finishes at around 850[Formula: see text]K without any decomposition. Based on their differences in chemistry for Co and Zn, we elucidated the chemical origin of the discrepancies of phase transition process for Zn and Co-ZIF-4 compounds upon heating.

Improvement of metastable crystal of acetaminophen via control of crystal growth rate

We showed a relationship among the growth rate, defect generation process, and stability of the metastable phase form II crystal of acetaminophen. Appropriate control of the form II crystal growth rate via slow cooling and nanosize crystal seeding not only suppressed the defect formation but improved the crystallinity of form II. The boundary condition between the interfacial control and transport control was determined based on the relationship between the crystal growth rate and supersaturation. The nanosize crystal seeds met the conditions of interfacial control; thus, the serious defects were suppressed. Finally, better temporal stability of the form II crystal was achieved.

Kinetic Analysis of Rapeseed Oil Crystallization during Isothermal Storage

Crystallization behavior of rapeseed oil during isothermal storage was investigated by dilatometry, transmitted light intensity measurement, and differential scanning calorimetry. The volume and transmitted light intensity of the oil samples changed significantly after a certain period (induction period) during isothermal storage. In order to explain these changes, a kinetic model for the crystallization of rapeseed oil was proposed by assuming that stable crystals are formed through melt-mediated transition and metastable crystals grow via an “autocatalytic” mechanism. The crystallization process of rapeseed oil is well represented by the model, and it reasonably explains the peculiar relationship between the storage temperature and the induction period for crystallization.

Recovery of host crystals from inclusion crystals of p-tert-butylcalix[4]arene and p-tert-butylthiacalix[4]arene by the treatment with a solvent and/or supercritical CO2

Upon stirring inclusion crystals of p-tert-butylthiacalix[4]arene (2) in solvents with heating, guest compounds were efficiently desorbed to yield guest-free crystals. More specifically, upon treatment with methanol, the exchange of guest compounds with methanol in the crystals, followed by the desorption of the methanol afforded metastable host crystals 2β, whereas, upon treatment with heptane, the dissolution of the inclusion crystals and simultaneous crystallization of compound 2 afforded stable host crystals 2α. Further, a host crystal of p-tert-butylcalix[4]arene (1) was recovered by the treatment of 2:1 (host/guest) inclusion crystals of compound 1 with supercritical carbon dioxide (scCO2), and through the combination of the guest exchange of 1:1 inclusion crystals of compound 1 with hexane and scCO2 treatment of the resulting 2:1 inclusion crystals 12·hexane. Although the recovered host crystal of compound 1 contained a small amount of CO2, it could be reused for the inclusion of organic compounds.

“Freezing” of NaClO3 Metastable Crystalline State by Optical Trapping in Unsaturated Microdroplet

We reversibly controlled phase conversion between a microdroplet of a NaClO3 unsaturated aqueous solution and a metastable single crystal, which is usually a short-lived phase in spontaneous crystallization, simply by irradiating a tightly focused visible continuous-wave (CW) laser to the microdroplet. The laser irradiation allowed the metastable crystal to generate and stably grow without a polymorphic transformation. This successful metastable phase control is attributed to the combination of the advantage of optical trapping-induced nucleation that nucleation takes place from unsaturated mother solution and the advantage of microdroplet method, which suppresses additional nucleation leading to the transformation. In situ observation shows the crystal dissolves when the laser irradiation is stopped, whereas the laser irradiation stabilizes the crystal even if the size of the crystal becomes larger than that of focal spot. These observations indicate that a change in the relative magnitudes of chemical p...

Heterogeneous nucleation in Zr-Cu-Al-Ag metallic glasses triggered by quenched-in metastable crystals - A time-resolved neutron diffraction study

Crystallization of Zr-Cu-Al-Ag bulk metallic glasses containing quenched-in crystals was studied by time-resolved in-situ neutron diffraction during isothermal annealing in the supercooled liquid region. The quenched-in crystals grew slowly at the beginning, indicating good thermal stability of the Zr-Cu-Al-Ag metallic glass alloys. The neutron diffraction results demonstrated that crystallization in Zr-Cu-Al-Ag metallic glasses was triggered by quenched-in crystals, rather than traditional heterogeneous nucleation mechanisms such as atomic-level impurities, container wall or surface oxides.

Formation of Metastable Crystals from Supercooled, Supersaturated, and Supercompressed Liquids: Role of Crystal-Liquid Interfacial Free Energy

The formation mechanism of metastable crystals from metastable liquids still remains elusive, although controlling the metastability of crystals and liquids already plays a crucial role in designing new materials in physics, chemistry, biology, and materials science. This review article describes how metastable phases can be obtained by controlling temperature, concentration, and pressure. In particular, I show the role of crystal-liquid interfacial free energy in the formation of metastable crystals from metastable liquids at a given driving force. In a microscopic viewpoint, local structure similarity between the metastable crystals and liquid determines the crystal-liquid interfacial free energy, and thus the nucleation barrier for the metastable crystals. The effect of the interfacial free energy on the formation of metastable crystals from supercooled, supersaturated, and supercompressed liquids will be demonstrated with metallic liquids, aqueous solutions, and water.

Quantum time crystal by decoherence: Proposal with an incommensurate charge density wave ring

We show that time translation symmetry of a ring system with a macroscopic quantum ground state is broken by decoherence. In particular, we consider a ring-shaped incommensurate charge density wave (ICDW ring) threaded by a fluctuating magnetic flux: the Caldeira-Leggett model is used to model the fluctuating flux as a bath of harmonic oscillators. We show that the charge density expectation value of a quantized ICDW ring coupled to its environment oscillates periodically. The Hamiltonians considered in this model are time independent unlike "Floquet time crystals" considered recently. Our model forms a metastable quantum time crystal with a finite length in space and in time.

Systematic model identification and optimization-based active polymorphic control of crystallization processes

Polymorphism is an important issue in industrial crystallization, since polymorphs of the same compound can present very different properties, such as solubility, melting point or density, influencing considerably the manufacturability and bioavailability of the final product.This work proposes a model-based active polymorphic control strategy that allows obtaining large crystals of the stable polymorph at the end of a batch crystallization process, even in the case of erroneous seeding or in situ nucleation of a mixture of both the stable and metastable forms. A novel systematic experimental design was applied to estimate the kinetic parameters of dissolution, growth and secondary nucleation of the stable and metastable polymorphs of the model compound (ortho-aminobenzoic acid, OABA). Such experimental approach allows the determination of the studied kinetics without any correlation between parameters during the estimation, and without the need of off-line measurements of the crystal size distribution during the experiments.The estimated kinetic parameters were used to build a population balance model for the calculation of the optimal temperature profile needed, during a batch cooling crystallization process, for the (i) elimination of the metastable form crystals nucleated in situ or erroneously seeded and the (ii) maximisation of the size of the crystals of the stable polymorph obtained at the end of the batch process.