Crystallization Kinetics Research Articles

Isotope Effect-Enabled Crystal Enlargement in Metal-Organic Frameworks.

Synthesizing large metal-organic framework (MOF) single crystals has garnered significant research interest, although it is hindered by the fast nucleation kinetics that gives rise to numerous small nuclei. Given the different chemical origins inherent in various types of MOFs, the development of a general approach to enhancing their crystal sizes presents a formidable challenge. Here, we propose a simple isotopic substitution strategy to promote size growth in MOFs by inhibiting nucleation, resulting in a substantial increase in the crystal volume ranging from 1.7- to 165-fold. Impressively, the crystals prepared under optimized conditions by normal approaches can be further enlarged by the isotope effect, yielding the largest MOF single crystal (2.9 cm × 0.48 cm × 0.23 cm) among the one-pot synthesis method. Detailed in situ characterizations reveal that the isotope effect can retard crystallization kinetics, establish a higher nucleation energy barrier, and consequently generate fewer nuclei that eventually grow larger. Compared with the smaller crystals, the isotope effect-enlarged crystal shows 33% improvement in the X-ray dose rate detection limit. This work enriches the understanding of the isotope effect on regulating the crystallization process and provides inspiration for exploring potential applications of large MOF single crystals.

Non‐isothermal crystallization kinetic of recycled PET and its blends with PBT modified with epoxy‐based multifunctional chain extender

AbstractA fundamental understanding of crystallization behavior is essential for the processing of both virgin and recycled polymers. This research delves into the crystallization characteristics and non‐isothermal crystallization kinetics of recycled polyethylene terephthalate (rPET) and its blends with poly butylene terephthalate (PBT), which have been modified using epoxy‐based multifunctional chain extenders (CE). The preparation of rPET/PBT blends involved a twin‐screw extruder, with varying weight ratios and different CE concentrations. Differential scanning calorimetry was employed to perform crystallization analysis on the samples. The results underscore the profound impact of blend composition on the thermal characteristics of the system, with CE exerting only a marginal influence. The glass transition temperatures (Tg) of the two polymers were measured at 49 and 79°C. During blending, the Tg values demonstrated variations relative to the proportions but did not adhere to the Fox equation. Furthermore, PBT was found to enhance the crystallization tendencies of rPET, resulting in an increase in relative crystallinity from 11% to 36%. Notably, the crystallization rate of PBT at 0.40 min−1 exceeded that of rPET at 0.36 min−1. PBT minimally affected the crystallization rate constant of rPET‐dominant blends, while rPET significantly reduced the crystallization rate in PBT‐dominant blends.

Analyzing isothermal crystallization of poly(lactic acid)/polyol systems: Correlated DSC and simulation studies

The isothermal crystallization behavior and kinetics of poly(l-lactic acid) (PLLA) melt-blended small amounts (0.7%–1%) of polyols (D-mannitol, D-sorbitol, and xylitol) were investigated by differential scanning calorimetry (DSC), and the interaction between polyols and PLLA was clarified via multiscale theoretical simulations. The decreased peak crystallization time and full width at half peak maximum (FWHM) of polyol-modified PLLA indicates that the crystallization capability of PLLA was improved, and the process was accelerated. The crystallinity remains unchanged before and after modification at the same temperature. The Avrami exponent (n) is largely unaffected, indicating that polyols as nucleation accelerants hardly alter the nucleation and growth mechanisms of PLLA crystallization. The outputs of long-term molecular dynamics simulations were fulfilled toward large-scale periodic models for three polyol-PLLA models that involved over 20,000 atoms. Therein, the interaction energies and the derived radial distribution function (RDF) implied the hydrogen bonding occurred between polyol and PLLA. To visualize the interaction sites between the polyol and PLLA, the frontier orbital distributions of the polyols were further calculated according to density functional theory (DFT). Theoretical evidence suggests that polyols improve the crystallization capability of PLLA by hydrogen bonding between the terminal hydroxyl group and the carbonyl oxygen of PLLA.

The Effect of Powder Re-Use on the Coalescence Behaviour and Isothermal Crystallisation Kinetics of Polyamide 12 within Powder Bed Fusion.

Polymer powder bed fusion (PBF) is becoming increasingly popular for the fabrication of lightweight, high-performance parts, particularly for medical and aerospace applications. This study investigates the effect of powder re-use and material aging on the coalescence behaviour, melt flowability, and isothermal crystallisation kinetics of polyamide-12 (PA-12) powder. With increased powder re-use, a progressive reduction in melt flowability and material coalescence is observed; at 200 °C, the particle consolidation time increases from 15 s in virgin powder to 180 s in powder recovered from build 6. The observed changes in the behaviour of PA-12 were attributed to polycondensation and cross-linking; these aging phenomena also create structural defects, which hinder the rate and extent of primary crystallisation. At an isothermal crystallisation temperature of 165 °C, the crystallisation half-time increased from 12.78 min in virgin powder to 23.95 min in powder re-used across six build cycles. As a result, the commonly used Avrami model was found to be unsuitable for modelling the crystallisation behaviour of aged PA-12 powder, with the co-efficient of determination (R2) reducing from >0.995 for virgin powder to as low as 0.795 for re-used powder. On the other hand, an alternative method, the Hay model, is able to successfully track full phase transformation within re-used powder (R2 > 0.99). These results highlight the importance of selecting the most appropriate model for analysing the crystallisation kinetics of PA-12 powder re-used across multiple build cycles. This understanding is crucial for obtaining the strong mechanical properties and dimensional precision required for the fabrication of functional, end-use parts within PBF.

Preparation of Li2O–Al2O3–SiO2–B2O3（LASB）glass-ceramic with low thermal expansion coefficient from spent hydrogenation catalysts and crystallization kinetics

The recovery of spent hydrogenation catalysts occupies advantages in both alleviating environmental burden and resource shortage. Whereas, the development of conventional hydrometallurgical recovery of molybdenum (Mo) and nickel (Ni) from spent MoNi/Al2O3 catalysts has been limited by the numerous processes and the accompanying generation of waste liquids and residues. Herein, A new recycling route for the preparation of spent hydrogenation catalysts with low thermal expansion coefficients (CTE) was proposed, which has the advantages of short process, green environment and high value utilization. The Li2O–Al2O3–SiO2–B2O3 (LASB) parent glass containing Mo and Ni were obtained by melting with different contents of the spent catalysts. The thermal expansion coefficient of the glass was minimized to 6.08 × 10−6/°C at an addition of 25 wt% of the spent catalysts. Moreover, according to the crystallization peak in DTA curve, glass-ceramics were prepared by one-step crystallization heat treatment at different crystallization temperatures. The main crystalline phase of the glass-ceramic precipitated by heating at 685 °C is β-quartz (Li2Al2Si3O10), which gives the glass-ceramics the lowest coefficient of thermal expansion (0.96 × 10−6/°C) of glass-ceramic as well as the maximum density (2.45 g/cm3) and Vickers hardness (705.8 Hv). Furthermore, the activation energy (354.65 ± 17.42) kJ/mol) and Avrami index (5.39) associated with crystallization were extracted from the fitting of different theoretical model, indicating the three-dimensional crystallization of the LASB glass-ceramics. This technology provides a waste-to-material strategy for hazardous waste and a clean production route for the preparation of the functional glass-ceramics.

Review on Crystallization Strategies for Polymer Single Crystals

Polymer physics has evolved significantly over the past century, transitioning from the early recognition of the chain structure of polymers to a mature field integrating principles from statistical mechanics, thermodynamics, and condensed matter physics. As an important part of polymer physics, polymer single crystals are crucial for understanding molecular structures and behaviors, enhancing material properties, and enabling precise functionalization. They offer insights into polymer crystallization kinetics, serve as templates for nanofabrication, and have applications in electronics, sensors, and biomedical fields. However, due to the complexity of molecular chain movement, the formation of polymer single crystals is still very difficult. Over the decades, numerous researchers have dedicated themselves to unraveling the mysteries of polymer single crystals, yielding substantial findings. This paper focus on the historical evolution and advancements in polymer single crystal research, aiming to offer valuable insights and assistance to fellow researchers in this field.

Effects of Assisting Solvents on Purification Efficiency in the Layer Melt Crystallization of Glycerol.

The efficiency of layer melt crystallization for the selective separation of glycerol from a glycerol-diethylene glycol mixture containing 4 wt % of diethylene glycol was evaluated using solvent-free and solvent-aided approaches. The effect of 1-butanol and the binary solvent of 1-butanol and acetone with a total molar composition of 25 mol % on the crystal growth kinetics and the purity of the final product was studied at different undercooling degrees and crystallization yields. The melting point temperature of the mixtures was predicted by using the modified UNIFAC Dortmund model. The addition of both a single and binary solvents significantly increased the crystal growth rate and purity of the final product compared to crystallization from the solvent-free mixture. Additionally, higher crystal growth rates and product purity were observed in the binary solvent system compared to those in the single solvent system at the same degree of undercooling. The second stage of solvent-aided crystallization resulted in glycerol with a purity above 99.5 wt %, depending on the type of solvent used and the rate of crystal growth.

Kinetic analysis of the crystallization of Y2O3 and La2O3 doped Li2O-Al2O3-SiO2 glass.

Li2O-Al2O3-SiO2 (LAS) glass ceramics have a low coefficient of thermal expansion, high mechanical strength, and excellent chemical stability. With advancements in glass ceramics, researchers have explored using LAS glass ceramics with transition metal doping and rare earth doping. Most previous studies have studied the impact of rare earth element doping on crystallization primarily in the context of conventional nucleating agents present in glass. In this study, we aimed to investigate the impact of Y2O3 and La2O3 on LAS glasses in the presence of undoped nucleating agents. The crystallization mechanism of La2O3 and Y2O3 doped LAS glass ceramics was studied using differential scanning calorimetry. The crystallization kinetics of the glasses were analyzed using model-free and modeling methods. Moreover, the activation energy of crystallization and the indices of crystallization and growth of glass ceramics were calculated, and the crystalline phase and microstructure of the samples were characterized. All three fractions of the LAS glass showed consistent crystallization under different calculation methods. The glass doped with La2O3 and Y2O3 exhibited two- or three-dimensional growth during crystallization, promoting crystallization in the LAS glass. The Y3La0 sample demonstrated the most favorable crystallization effect. In the presence of an undoped nucleating agent, rare earth elements can enhance glass crystallization; this new idea can be utilized for the development of new materials.

Revisiting Dynamic Processes and Relaxation Mechanisms in a Heterocyclic Glass-Former: Direct Observation of a Transient State.

Despite decades of studies, a clear understanding of near-Tg phenomena remains challenging for glass-forming systems. This review delves into the intricate molecular dynamics of the small, heterocyclic thioether, 6-methyl-2,3-dihydro-1,4-benzodithiine (MeBzS2), with a particular focus on its near-Tg cold crystallization and relaxation mechanisms. Investigating isothermal crystallization kinetics at various temperatures reveals a significant interplay between its molecular dynamics and recrystallization from a supercooled liquid. We also identify two independent interconversion paths between energetically privileged conformers, characterized by strained transition states. We demonstrate that these spatial transformations induce substantial alterations in the dipole moment orientation and magnitude. Our investigation also extends to the complex salt PdCl2(MeBzS2), where we observe the transient conformers directly, revealing a direct relationship between their abundance and the local or macroscopic electric field. The initially energetically privileged isomers in an undisturbed system become less favored in the presence of an external electric field or ions, resulting even in an unexpected inversion of states. Consequently, we confirm the intramolecular character of secondary relaxation in MeBzS2 and its mechanism related to conformational changes within the heterocyclic ring. The research is based on the combination of broadband dielectric spectroscopy, X-ray diffraction, and quantum density functional theory calculations.

Perovskite Solar Cells with Extremely High 24.63% Efficiency through Design of Double Electron Transport Layers and Double Luminescent Converter Layers

AbstractIntroduction of fluorescent down‐conversion layer inside perovskite solar cells (PSCs) can highly improve the ultraviolet response of the devices and the light stability. However, such a device is usually confronted with the problem of inter‐diffusion with the perovskite absorber layer, which severely limits its further development. To address this problem, herein, this work employs an interfacial dual electron transport layers (ETLs) strategy, sandwiching Cd‐CsPbCl3:Mn2+ luminescent quantum dots within gap of the ETLs, which not only reduces the interface energy level offset, but also improves the nucleation and crystallization kinetics of perovskite films and prevents their diffusion to the perovskite absorber layer. As a result, the efficient synergy effect effectively elevates both the open‐circuit voltage and fill factor of the PSCs, reaching maximum values of 1.181 V and 81.14%, respectively, finally delivering progressively increased device power conversion efficiency (PCE) of 24.32% with significantly improved light stability. To further improve the ultraviolet response, this work further adopts the strategy of dual fluorescent conversion layers inside and outside the PSCs, and finally obtains PCE of 24.63%, which is the best for various luminescent conversion cells. This work opens a new door for the development of efficient and stable photoluminescence conversion PSCs.

Unique Crystallization Characteristics of Pickering High Internal Phase Emulsion Templated Porous Constructs.

To study the crystallization behavior of polymeric chains under the influence of porosity, the thermal properties of various nonporous and porous poly(ε-caprolactone) (PCL) based constructs were investigated. Porous cross-linked PCL nanocomposite constructs were fabricated utilizing in situ polymerization of CL-based surfactant-free Pickering high internal phase emulsions (HIPEs), stabilized using modified fumed silica nanoparticles (mSiNP) at a minimal concentration of 0.6 wt %. The corresponding nanocomposite constructs exhibited polyhedral pore morphology with significant pore roughness due to the presence of mSiNP. DSC thermograms of nonporous constructs illustrated diminished crystallization temperature and kinetics upon cross-linking and inclusion of mSiNP which confirmed suppressed mobility of polymer chains. Further introduction of porosity led to substantial supercooling, resulting in crystallization temperatures as low as -24 °C. Changes in the crystal structure of various nonporous and porous constructs were also studied using XRD. The crystallization behavior of porous constructs was finally evaluated using Jeziorny, Ozawa, and Mo theories under nonisothermal conditions. Significant deviation from the theoretical model, as observed in the case of porous constructs, implied a complex crystallization mechanism that eventually was not only controlled by the chain immobility due to cross-linking but also heterogeneity present in the wall thickness of the constructs. The unique melting-crystallization phenomenon observed in such constructs may further be expanded to other systems of high heat capacity for utilization as energy storage materials.

Medium-range structural order in amorphous Ge2Sb2Te5 phase change material

The crystallization rate is an important factor for the application of phase change materials as memory devices, which, thus, motivates a strong interest in the underlying crystallization processes. We analyzed the crystallization kinetics of as-deposited amorphous Ge2Sb2Te5 by differential scanning calorimetry, revealing that the thermal treatment below the crystallization onset temperature effectively enhances the crystallization rate compared to the as-deposited samples. Variable resolution fluctuation electron microscopy was carried out to characterize the corresponding amorphous structure of the as-deposited films and the differently annealed states regarding their medium-range order (MRO). As a result, relatively large MRO correlation lengths in the range of 3–4 nm were observed, whereas the MRO volume fraction doubled after longer annealing treatments, demonstrating the importance of MRO and MRO tuning for optimizing the properties of amorphous phase change materials. The increased volume fraction of the MRO seems to also favor an increased nanoindentation hardness.

Insights into the structure sustainable evolution and crystallization kinetics of amorphous Mg60Ni30La10 alloy

Nanocrystalline materials have wide potential applications due to the special properties, which can be easily prepared by nanocrystallization of the amorphous alloys. In this work, phase transformations of the melt-spun amorphous Mg60Ni30La10 alloy were characterized by in-situ XRD and TEM. The results showed that during crystallization Mg2Ni first formed from the amorphous matrix followed by LaMg3, LaMg2Ni and LaMgNi4. The phase transformation was completed rapidly, with nucleation progressing more prominently than grain growth. Nucleation and grain growth during crystallization were discussed according to Avrami index n(α) based on Kissinger equation. In addition, the classic Miedema theory was introduced to estimate the crystallization temperature and the nucleation frequency. Nucleation behaviors are closely related to the phase structures formed during the amorphous crystallization from the view of thermodynamics. This work provided a preliminary basis for controlling the evolution of amorphous/nanocrystalline structure of alloys.

Crystallization Kinetics of Hybrid Perovskite Solar Cells

AbstractMetal halide perovskites (MHPs) are considered ideal photovoltaic materials due to their variable crystal material composition and excellent photoelectric properties. However, this variability in composition leads to complex crystallization processes in the manufacturing of Metal halide perovskite (MHP) thin films, resulting in reduced crystallinity and subsequent performance loss in the final device. Thus, understanding and controlling the crystallization dynamics of perovskite materials are essential for improving the stability and performance of PSCs (Perovskite Solar Cells). To investigate the impact of crystallization characteristics on the properties of MHP films and identify corresponding modulation strategies, we primarily discuss the relevant aspects of MHP crystallization kinetics, systematically summarize theoretical methods, and outline modulation techniques for MHP crystallization, including solution engineering, additive engineering, and component engineering, which helps highlight the prospects and current challenges in perovskite crystallization kinetics

Crystallization Kinetics of Hybrid Perovskite Solar Cells.

Metal halide perovskites (MHPs) are considered ideal photovoltaic materials due to their variable crystal material composition and excellent photoelectric properties. However, this variability in composition leads to complex crystallization processes in the manufacturing of Metal halide perovskite (MHP) thin films, resulting in reduced crystallinity and subsequent performance loss in the final device. Thus, understanding and controlling the crystallization dynamics of perovskite materials are essential for improving the stability and performance of PSCs (Perovskite Solar Cells). To investigate the impact of crystallization characteristics on the properties of MHP films and identify corresponding modulation strategies, we primarily discuss the relevant aspects of MHP crystallization kinetics, systematically summarize theoretical methods, and outline modulation techniques for MHP crystallization, including solution engineering, additive engineering, and component engineering, which helps highlight the prospects and current challenges in perovskite crystallization kinetics.

Thermal stability and crystallization kinetics of Er-doped Ge–Sb–Se chalcogenide: a DSC study

Thermal stability and crystallization kinetics of Er-doped Ge–Sb–Se chalcogenide: a DSC study

Very long-time crystallization kinetics for ethylene-methacrylic acid ionomers neutralized with zinc, sodium, lithium and magnesium

Papers by our group [1] (Grady et al., 2013) and another group [2] (Paul et al. 2012) examined crystallization of random copolymers of ethylene and methacrylic acid after room temperature annealing. Similar conclusions were reached concerning the crystallization process; primary crystals were either unchanged or changed very little after annealing while secondary crystallization occurred over long time scales after annealing. The current work confirms these general conclusions for four different cations (Zn2+, Na+, Li+ and Mg2+), with the latter two not studied in either of the previous studies. Even after 6 years of annealing at room temperature, the crystallization rate is constant with logarithmic time, i.e. the material continues to crystallize. The acid copolymer does not crystallize with room temperature annealing, although secondary crystals of the acid copolymer thicken with annealing.

Crystallization kinetics and structural development of Bi2GeO5 glass-ceramics fabricated by the modified incorporation technique

This study focuses on the fabrication and crystallization kinetics of bismuth germanate (Bi2GeO5) crystals in glass ceramics. Bismuth germanate glass-ceramics were produced from a base glass containing 58.4 mol% Bi2O3, 23.4 mol% GeO2, and 18.2 mol% B2O3 using a modified incorporation technique. Differential thermal analysis was used to determine the crystallization temperature. The X-ray diffraction results showed a dominant peak corresponding to the pure Bi2GeO5 phase, which has an orthorhombic crystal structure. The local Avrami exponent (n(x)) and local crystallization activation energy (Ec(x)) were determined using a non-isothermal method with heating rates ranging from 5 to 20 °C/min. The results indicated that the crystal growth process of the glass-ceramics occurred in all three dimensions, with Avrami exponent values ranging from 1.79 to 2.5. The microstructure also revealed uniform crystallization across the surface and bulk diffusion of crystallites. The modified incorporation method successfully enhanced the crystallization of Bi2GeO5 glass-ceramics, resulting in the transition from one-dimensional needle-like crystals to the desired crystal dimensions.

Unraveling the crystallization kinetics of the Ge2Sb2Te5 phase change compound with a machine-learned interatomic potential

The phase change compound Ge2Sb2Te5 (GST225) is exploited in advanced non-volatile electronic memories and in neuromorphic devices which both rely on a fast and reversible transition between the crystalline and amorphous phases induced by Joule heating. The crystallization kinetics of GST225 is a key functional feature for the operation of these devices. We report here on the development of a machine-learned interatomic potential for GST225 that allowed us to perform large scale molecular dynamics simulations (over 10,000 atoms for over 100 ns) to uncover the details of the crystallization kinetics in a wide range of temperatures of interest for the programming of the devices. The potential is obtained by fitting with a deep neural network (NN) scheme a large quantum-mechanical database generated within density functional theory. The availability of a highly efficient and yet highly accurate NN potential opens the possibility to simulate phase change materials at the length and time scales of the real devices.

Data‐driven identification of crystallization kinetics

AbstractA novel data‐driven methodology is presented for developing mathematical models for crystallization processes. The data‐driven approach is based on the sparse identification of nonlinear dynamics (SINDy) method, which iterates between a partial least‐squares fit and a sparsity‐promoting step leading to the discovery of sparse interpretable models. The performance of the SINDy methodology is characterized for the identification of crystallization kinetics in a mixed tank operated in a continuous mode, the isothermal crystallization of lysozyme in a batch stirred tank and cooling crystallization of paracetamol. The SINDy method is robust against noise. Good agreement is obtained between the data‐driven model and the data obtained from crystallization experiments. The presented data‐driven approach can be attractive for modeling industrial crystallization processes where process analytical technology tools are available for the measurement of process variables but functional forms of kinetic expressions are unknown.