Crystallization Kinetics Research Articles

Crystallization modeling of two semi-crystalline polyamides during material extrusion additive manufacturing

In this work, a heat transfer model is developed for thermally-driven material extrusion additive manufacturing of semicrystalline polymers that considers the heat generated during crystallization by coupling crystallization kinetics with heat transfer. The materials used in this work are Technomelt PA 6910, a semicrystalline hot melt adhesive with sub-ambient glass transition temperature (Tg) and slow crystallization, and PA 6/66, a traditional semicrystalline polyamide with a higher Tg and fast crystallization. The coupled model shows that the released heat during crystallization depends on material selection, with Technomelt PA 6910 and PA 6/66’s temperatures increased by less than 1 °C and up to 6.3 °C, respectively, due to enthalpy of crystallization. Increasing the layer time decreases the layer temperature as well as the initial crystallinity. However, its effect on final crystallinity in Technomelt PA 6910 is negligible due to continued crystallization of the material after printing. Experimental validation shows good agreement for Technomelt PA 6910, but consistently underpredicts PA 6/66 crystallinity. Increasing modeled environmental temperature leads to better agreement with experimental results for PA 6/66, suggesting that higher temperatures may have been experienced. Shear-induced crystallization may also be contributing to crystallinity in this material. The results from this model highlight the importance of and interrelationships between material and processing parameter selection and can aid in achieving quality prints from semicrystalline thermoplastics.

A novel model for predicting deformation of thermoplastic composites during heat-pressing process

Carbon fiber/polyetheretherketone (CF/PEEK) thermoplastic composites are widely used in the aerospace industry due to their excellent mechanical properties and high-temperature resistance. However, the research on heat-pressing deformation and residual stress during high-temperature and high-pressure heat-pressing processes in CF/PEEK was relatively deficient. In this paper, a framework coupled with crystallization kinetics, micromechanics and thermodynamics was developed to predict the heat-pressing deformations of CF/PEEK and it was conducted by UMAT, DISP and UEXPAN subroutines. Moreover, the predictive model was verified by experiments effectively. Finally, we compared the difference in residual stress distributions between symmetric and asymmetric lay-ups and found that the melting temperature, thickness, angle and sequence of layers have a significant impact on the heat-pressing deformation. This work provided an effective tool for predicting heat-pressing deformations, which is great of significance in the manufacturing and application of CF/PEEK.

The effects of Sb/Te ratio on crystallization kinetics in Ge-rich GeSbTe phase-change materials

The effects of Sb/Te ratio on crystallization kinetics in Ge-rich GeSbTe phase-change materials

Elucidating temperature-dependent local structure change and optical properties in GeTe phase-change material

Phase-change memory emerges as a top contender for non-volatile data storage applications. We report here a systematic change in local structure and crystallization kinetics of binary GeTe thin films using temperature-dependent resistivity measurements, which offers single-stage crystallization at around 187 °C, corroborated with x-ray diffraction. Furthermore, the change in chemical bonding upon crystallization is determined through x-ray photoelectron spectroscopy core level spectra, which reveals the existence of Ge and Te components that align with the GeTe crystal structure. Also, an investigation was carried out employing a UV–Vis–NIR spectrophotometer to explore the evolution of optical bandgaps (Eg), Tauc parameter (B) representing the local disorder, and Urbach energy (Eu) of the GeTe material, as it undergoes the transition from a disordered amorphous state to a crystalline state. As crystallization progresses, a consistent shift of Eg from 0.92 to 0.70 eV corresponds to as-deposited amorphous at room temperature and crystalline at 250 °C, respectively. In addition, the reduction in Eu (from 199.87 to 141.27 meV) and a sudden increase of B around crystallization temperature is observed upon increasing temperature, indicating direct observation of enhanced medium-range order and distortion in short-range order, respectively, in GeTe thin films, revealing improved structural and optical properties. These enhancements make the GeTe material ideal for data storage applications of phase-change memory for next-generation computing technology.

Boosting Efficiency to 22.73%: Unraveling the Role of Solvent Environment in Low‐Dimensional Perovskites Through Competitive Bonding Interactions

AbstractIt is reported that the solvent environment exerts a significant influence on the property of perovskite precursor solution and resultant film, which is more pronounced in more complex low‐dimensional perovskites. Four solvent additives with varying basicity are introduced to instigate a tug‐of‐war among bonding interactions, thereby exploring the systematic effect of the solvent environment on the growth of quantum wells and the photoelectric properties of the resultant low‐dimensional perovskite films. A governing principle that diverges significantly from those previously documented for three‐dimensional perovskites is elucidated in low‐dimensional perovskites. When coordination interactions predominate in the solvent environment, the emergence of a two‐dimensional GA2PbI4 transitional phase is fostered to facilitate subsequent transformation into the desirable ACI phase, and the perovskite crystallization kinetics is retarded to improve the film quality. Hence, the highest power conversion efficiency (PCE) of 22.73% is obtained for GA(MA)nPbnI3n+1 (n = 5) based solar cells with a p‐i‐n structure. The PCE achieved in this work is a record among the reported low‐dimensional perovskite solar cells.

Cost-Effective Acetonitrile-Based Precursor Solution Mitigates Heterogeneous Nucleation for Efficient and Stable Perovskite Solar Cells.

Solution-processing is the primary method for fabricating high-efficiency perovskite solar cells (PSCs), where solvent choice critically influences film formation and quality. Although additives can optimize film formation dynamics by balancing nucleation and growth of perovskite, they can also induce heterogeneous nucleation due to competitive coordination and varying crystallization kinetics, leading to compositional heterogeneity and structural disorders. Herein, a perovskite precursor solution is developed using acetonitrile (ACN) as a weak coordination host solvent instead of the traditional N,N-dimethylformamide (DMF). The ACN-based perovskite precursor solution reduces heterogeneous nucleation typically caused by the competitive coordination effect of DMF, and cuts costs by half compared to DMF-based precursor solutions. This approach promotes a single crystallization pathway via a dimethyl sulfoxide-solvated intermediate phase to α-FAPbI3, which extends the anti-solvent operation window, and enhances the crystallinity of perovskite films, and reduces defect states. The power conversion efficiencies (PCE) of 23.62% and 20.13% is achieved for the PSC and minimodule, respectively. The PSC retains over 97% of its initial efficiency after 800h of continuous illumination under maximum power point tracking (MPPT). These findings provide valuable insights into solvent interactions in perovskite film formation and offer a cost-effective strategy for improving the device's performance and stability.

Uniform Phase Permutation of Efficient Ruddlesden-Popper Perovskite Solar Cells via Binary Spacers and Single Crystal Coordination.

2D Ruddlesden-Popper perovskites (RPPs) have attracted extensive attention in recent years due to their excellent environmental stability. However, the power conversion efficiency (PCE) of RPP solar cells is much lower than that of 3D perovskite solar cells (PSCs), mainly attributed to their poor carrier transport performance and excessive heterogeneous phases. Herein, the binary spacers (n-butylammonium, BA and benzamidine, PFA) are introduced to regulate the crystallization kinetics and n-value phase distribution to form uniform phase permutation of RPP films. The study then incorporates n = 5 BA2MA4Pb5I16 memory single crystal to achieve ultrafast stepped-type carrier transport from the low n-value phases to the high n-value phases in the high-quality (BA0.75PFA0.25)2MA4Pb5I16 films. These binary spacers and single-crystal-assisted crystallization strategies produce high-quality films, leading to fast carrier extraction and significant nonradiative recombination suppression. The resulting PSC presents a champion PCE of 21.15% with an impressive open circuit voltage (VOC) of 1.26V, which is the record high efficiency and VOC for low n-value RPP solar cells (n ≤ 5).

Unveiling the boson peaks in amorphous phase-change materials

The Boson peak is a universal phenomenon in amorphous solids. It can be observed as an anomalous contribution to the low-temperature heat capacity over the Debye model. Amorphous phase-change materials (PCMs) such as Ge-Sb-Te are a family of poor glass formers with fast crystallization kinetics, being of interest for phase-change memory applications. So far, whether Boson peaks exist in PCMs is unknown and, if they do, their relevance to PCM properties is unclear. Here, we investigate the thermodynamic properties of the pseudo-binary compositions on the tie-line between Ge15Te85and Ge15Sb85from a few Kelvins to the liquidus temperatures. Our results demonstrate the evidence of the pronounced Boson peaks in heat capacity below 10 K in the amorphous phase of all compositions. By fitting the data using the Debye model combined with a modification of the Einstein model, we can extract the characteristic parameters of the Boson peaks and attribute their origin to the excess vibrational modes of dynamic defects in the amorphous solids. We find that these parameters correlate almost linearly with the Sb-content of the alloys, despite the nonmonotonic behaviors in glass forming abilities and thermal stabilities. In a broader context, we show that the correlations of the characteristic parameters of the Boson peaks with Tg and kinetic fragility, vary according to the type of bonding. Specifically, metallic glasses and conventional covalent glasses exhibit distinct patterns of dependence, whereas PCMs manifest characteristics that lie in between. A deeper understanding of the Boson peaks in PCMs holds the promise to enable predictions of material properties at higher temperatures based on features observed in low-temperature heat capacity.

Unraveling the Formation Process of an Organic Photovoltaic Active Layer During High‐Speed Coating Via a Synergistic Concentration‐Temperature Gradient Control Strategy

AbstractThe Layer‐by‐Layer (LbL) strategy has emerged as a highly effective approach for enhancing the performance of organic photovoltaics (OPVs), notably boosting light harvesting and fill factor through spectral complementarity and morphology optimization. Crucially, the LbL processing strategy has been found to mitigate or overcome the decline in power conversion efficiency (PCE) during high‐speed blade coating. Despite these advancements, there remains a scarcity of research into the film‐formation process and the corresponding control strategies in high‐speed printing. A novel synergistic concentration‐temperature gradient control (SCTGC) strategy aimed at achieving high‐performance LbL‐type active layers at ultra‐fast coating speeds. This investigation reveals that both baseplate temperature and solution concentration exert a nonmonotonic regulatory influence on PCEs. Fine‐tuning the concentration gradient proves instrumental in balancing microfluidic competition within the wet film, thereby facilitating stable mass transport during the film formation process, and enhancing the high‐speed processability of the relevant OPV system. Additionally, the variations in crystallization kinetics under different temperatures are monitored. This work sheds light on the coating mechanism and film formation in high‐speed coating, highlighting the efficiency of the SCTGC method.

In Situ Raman Spectroscopy as a Valuable Tool for Monitoring Crystallization Kinetics in Molecular Glasses

The performance of in situ Raman microscopy (IRM) in monitoring the crystallization kinetics of amorphous drugs (griseofulvin and indomethacin) was evaluated using a comparison with the data obtained via differential scanning calorimetry (DSC). IRM was found to accurately and sensitively detect the initial stages of the crystal growth processes, including the rapid glass–crystal surface growth or recrystallization between polymorphic phases, with the reliable localized identification of the particular polymorphs being the main advantage of IRM over DSC. However, from the quantitative point of view, the reproducibility of the IRM measurements was found to be potentially significantly hindered due to inaccurate temperature recording and calibration, variability in the Raman spectra corresponding to the fully amorphous and crystalline phases, and an overly limited number of spectra possible to collect during acceptable experimental timescales because of the applied heating rates. Since theoretical simulations showed that, from the kinetics point of view, the constant density of collected data points per kinetic effect results in the smallest distortions, only the employment of the fast Raman mapping functions could advance the performance of IRM above that of calorimetric measurements.

Effect of the synergistic interaction of zinc adipate, hydrotalcite and ethylene propylene rubber on the performances of polypropylene

Polypropylene (PP) is widely used in a range of areas due to its excellent physical and chemical properties, but its low-temperature brittleness and low-impact resistance largely limits its application. Hence, this study investigated the changes in mechanical and thermal properties of isotactic polypropylene (iPP) modified by the addition of the β-nucleating agent zinc adipate (ZnAA), the inorganic rigid particle hydrotalcite (HT), and the rubber elastomer bipropylene rubber (EPR). The structure and properties of modified PP were investigated by Fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), electronic universal material testing machine, and simple-beam impact testing machine. At last, the non-isothermal crystallization kinetics of iPP was investigated by the Caze method. It was found that with the addition of EPR reached 30 wt%, the notched impact strength of iPP was 34.74 kJ/m2, which was 542.43 % higher than that of pure iPP, and more than twice as high as that of ZnAA and HT modification, and the relative crystallinity ( K β) value of the β-crystalline form reached 79.66 % when 10 wt% EPR was added to the iPP. The addition of ZnAA, HT and EPR could significantly increase the crystallisation peak temperature ( T c), shorten the half-crystallisation time ( t 1/2) and increase the crystallisation activation energy ( ΔE) of iPP.

Composition Dependence of Flow-Induced Crystallization in High-Density Polyethylene/Isotactic Polypropylene Blends.

Polyolefins, including high-density polyethylene (HDPE) and isotactic polypropylene (iPP), account for over half of the worldwide plastics market and have wide-ranging applications. Recycling of these materials is hindered due to separation difficulties as co-mingled blends of HDPE and iPP often exhibit brittle mechanical behavior because phase separated domains detach under stress due to low interfacial adhesion. Motivated to improve mechanical properties of mixed recyclates during processing, this work examines the effect of shear on the crystallization kinetics and rheological properties of HDPE-iPP blends utilizing a combination of differential scanning calorimetry (DSC), rheo-Raman spectroscopy, polarized optical microscopy, and scanning electron microscopy (SEM). In the quiescent experiments, the crystallization temperature as a function of blend composition exhibits a distinct decrease when the iPP forms the droplet phase, as expected, due to fractionated crystallization. In the presence of shear, we find elongated domains due to high capillary number. Unexpectedly, we find a compositional dependence to the flow-induced crystallization (FIC) of iPP: stronger FIC is observed in all blends compared to the pure iPP. Moreover, the flow completely counteracts the reduced crystallization arising from fractionated crystallization, indicating that the flow is able to induce nucleation in droplets to an extent such that it offsets the reduction in active nucleating agents in finite size droplets. We attribute these effects to differing microflow fields in the various morphologies as the iPP domains deform under shear.

The effect of carbon black on degradation of pipe grade black polyethylene in high concentration chlorine dioxide solutions

In this research, the impact of carbon black on the accelerated degradation of pipe grade polyethylene (PE100) exposed to high levels of chlorine dioxide (150 ppm) is examined. Tensile testing reveals a faster degradation rate in black samples compared to neat samples, indicating a detrimental effect of carbon black aggregates on the polymer's aging process. Rheological analysis shows changes in molecular weight and structure due to chemical degradation and chain scission and can be a reliable method for detecting slight changes in molecular structure. Isothermal crystallization shows a slowdown in crystallization kinetics at first, explained by gel-formation due to crosslinking which hinder the crystallization, and then an increase in the kinetics as apparently the chain scission gets dominant again. Neat samples exhibit a higher density of tie molecules, indirectly revealed by much more fibrils in crack wall observed in FESEM images, suggesting better resistance to chemical degradation while the black sample shows a much less fibrillar crack wake and becomes almost completely devoid of any fibrils at later stages of aging. The fibrils, which essentially offer a load-bearing role against the widening and growth of the crack play a key role in resistance to slow crack growth (SCG). Therefore, the higher SCG resistance is expected for neat grade compared to black samples. The study proposes a dual-layer pipe design with a UV-resistant black outer layer and an oxidation-resistant neat inner layer to prolong the lifespan of PE100 pipes by protecting against UV radiation and chemical reactions. This solution offers increased durability, lower maintenance costs, and environmental sustainability benefits.

Study of thermal behavior and crystallization kinetics of glass microspheres in the Y3Al5O12-Al2O3 system

Five types of glass microspheres with alumina and 40–80 mol.% Y3Al5O12 were prepared using solgel Pechini and flame synthesis techniques. Glass thermal behavior was analyzed using DSC/TG, XRD and SEM, and the JMAK model was applied to study crystallization kinetics and determine prevailing mechanisms. All samples, except the one with 80 mol.% YAG, had two exothermic effects in their DSC curves. The first appeared between 937 and 950 °C, while the second was observed between 958 and 1102 °C. XRD analysis of crystallized microspheres confirmed the presence of YAG and various forms of alumina phases in the samples with lower YAG/higher Al2O3 content (40 and 50 mol.%). The sample with the highest YAG content showed the strongest tendency to crystallize in the kinetics study. The value of apparent activation energy (Eapp) of this sample was 987.3 ± 13.0 kJ mol−1. For the remaining samples, the values of Eapp were higher and ranged from 1215.1 ± 10.6 to 1847.5 ± 9.3 kJ mol−1, indicating the lowest ability of these compositions to crystallization. The growth of three-dimensional (3-D) YAG crystals was predominant in glasses with the highest (80 mol.%) YAG content. One-dimensional (1-D) growth of γ-Al2O3 crystals and 3-D growth of YAG crystals was predominant in glasses with the lowest (40 mol.%) YAG content.

Use of magnetic fields to impact glass-transition and crystallization during manufacturing of ZBLAN optical fibers

ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) is the most stable glass among the Heavy Metal Fluoride (HMF) family and has a wide range of applications in medical industry, telecommunication, IR transmission, among others. But, due to crystal formation while manufacturing of ZBLAN fiber its theoretical minimum loss has not been achieved yet. Some techniques such as high cooling rate and microgravity conditions have been utilized to reduce the crystal formation but are challenging to implement during manufacturing of these fibers. Alternatively, magnetic field (MF), also a body force like gravity, is expected to influence the crystal formation mechanism and glass kinetics. In this work, ZBLAN glass is processed under magnetic fields of various intensities while simulating fiber drawing manufacturing process conditions. Then, the processed ZBLAN is analyzed using Differential Scanning Calorimetry (DSC) at varying scanning rates. Various glass kinetics parameters such as activation energy, fragility, and preferred crystallization mechanism in terms of Avrami parameter (n) have been analyzed. The glass transition temperature (Tg) increases for a given sample as scanning rate (β) increases. Samples processed under varying magnetic fields, at the same scanning rate, displayed higher glass transition temperatures. Also, when the magnetic field increases, the activation energy required for glass transition decreases, and the fragility index (m) decreases. There is also a preference for surface crystallization over volume crystallization. These results encourage application of magnetic fields for reducing crystal formation while processing ZBLAN glass.

Quantitative evaluation of the hydrogen bonding effects on the crystallization kinetics of poly(vinyl alcohol)/tea polyphenol composites

Quantitative evaluation of the hydrogen bonding effects on the crystallization kinetics of poly(vinyl alcohol)/tea polyphenol composites

Crystallization behaviour, structure, and photocatalytic properties of SiO2-B2O3-Li2O-WO3-Bi2O3 glass-ceramics containing Bi2WO6 crystals

SiO2-B2O3-Li2O-WO3-Bi2O3 system parent glass was prepared by the melt-quenching method and glass-ceramics containing the Bi2WO6 crystals were obtained by a one-step heat treatment. The crystallization kinetics of the parent glass were investigated, and the effect of the different heat-treatment regimes on the microscopic morphology and optical bandgaps of the glass-ceramics was discussed. The results show that the crystallization activation energy of the parent glass is about 300 kJ/mol and the precipitated Bi2WO6 crystals exist in a columnar structure. As obtained from the UV–Vis spectra, the glass-ceramic with a heat treatment regime of 640 °C/2 h has the smallest optical bandgap (2.45 eV). During the photocatalytic degradation of methylene blue dye, the glass-ceramic with a heat treatment regime of 640 °C/2 h shows the best catalytic degradation performance, reaching a dye degradation rate of 76 % at 120 min. The experimental results indicate that glass-ceramics containing Bi2WO6 crystals have promising applications in the field of sewage treatment.

Carbon nanotube manipulates crystallization kinetics and viscoelastic behavior of PP/EBC blends

AbstractPolypropylene (PP) offers numerous benefits to industrial applications due to its excellent processability and cost‐effectiveness. However, the widespread utilization of this commodity thermoplastic is constrained by its inherently low‐impact resistance. Herein, we suggest a ternary system with the addition of ethylene‐butene copolymer (EBC) and multiwalled carbon nanotubes (MWCNTs) to improve the overall performance of PP. We unveil the role of MWCNTs on the crystalline behavior of the PP/EBC blends when various ratios are considered. The calculated half‐time crystallization from the Avrami equation indicates that 1.5 wt% MWCNTs accelerate the crystallization of the PP/EBC blend nearly threefold. The formation of a semisolid microstructure is also reported using the rheological measurements. An upturn in complex viscosity, along with a frequency‐independent storage modulus, indicates strong interactions between MWCNTs and polymer chains. We confirm such robust interactions by employing temperature ramp sweep on the prepared nanocomposites as the decomposition temperature of the materials shifts to higher values. The dynamic mechanical analysis further interprets the role of MWCNTs as compatibilizers by bridging the gap between the glassy temperature of PP and EBC components.Highlights Theoretical prediction of the MWCNTs localization in the PP/EBC blends. Depicting the solid‐like behavior and viscosity upturn of PP/EBC/MWCNTs. Decelerating polymer chain relaxation led by nucleation role of MWCNTs. Formation of larger and more imperfect crystals upon the addition of MWCNTs. Faster crystallization kinetics in the PP/EBC/MWCNTs nanocomposites.

Crystallization Kinetics of Tacrolimus Monohydrate in an Ethanol–Water System

Nucleation and growth during the crystallization process are crucial steps that determine the crystal structure, size, morphology, and purity. A thorough understanding of these mechanisms is essential for producing crystalline products with consistent properties. This study investigates the solubility of tacrolimus (FK506) in an ethanol–water system (1:1, v/v) and examines its crystallization kinetics using batch crystallization experiments. Initially, the solubility of FK506 was measured, and classical nucleation theory was employed to analyze the induction period to determine interfacial free energy (γ) and other nucleation parameters, including the critical nucleus radius (r*), critical free energy (∆G*), and the molecular count of the critical nucleus (i*). Crystallization kinetics under seeded conditions were also measured, and the parameters of the kinetic model were analyzed to understand the effects of process states such as temperature on the crystallization process. The results suggested that increasing temperature and supersaturation promotes nucleation. The surface entropy factor (f) indicates that the tacrolimus crystal growth mechanism is a two-dimensional nucleation growth. The growth process follows the particle size-independent growth law proposed by McCabe. The estimated kinetic parameters reveal the effects of supersaturation, temperature, and suspension density on the nucleation and growth rates.

Tailoring Crystallization Kinetics in Thin Sucrose Films during Convective Drying: Impact of Temperature and Humidity on Onset, Growth, and Nucleation Rate.

Drying experiments with varying air temperature and humidity were conducted to investigate the influence of the drying process on the crystallization of thin sucrose films. For the first time, the effects of the nucleation onset, nucleation rate, and growth rate were investigated in situ and their differentiated influence on product crystallinity could be assessed. The growth rate was not influenced by air humidity but showed a strong dependence on temperature. It increased with drying temperature; however, at high temperatures, growth was inhibited when the water content falls below a critical level. Noticeable differences in nucleation behavior could be observed with regard to air humidity. Dry air led to crystallization onsets at lower levels of supersaturation, while moderately humid air retarded it. At higher temperatures, nucleation onset commenced at lower water contents but at a constant supersaturation level. The nucleation rate doubled in experiments with moderately humid air (15% RH), while an elevated drying temperature showed generally lower nucleation rates. The observed differences in the nucleation onset and rate could be explained by the film-internal concentration profile, which is strongly influenced by drying parameters. The insights therefore provide a differentiated understanding of the formation of the physical state and how it can be influenced during convective drying.