Isothermal Crystallization Kinetics Research Articles

Facile Characterization of Isothermal Crystallization and Microphase Separation Kinetics of Polyamide 6 (PA6)‐Based Thermoplastic Elastomers

AbstractThe facile characterization of isothermal microphase separation kinetics in polyamide 6 (PA6)‐based thermoplastic elastomers (TPAE‐6) has long posed a challenge for the development of suitable melt spinning processes. In this study, this challenge is addressed through differential scanning calorimetry (DSC) measurements. It is assumed that the enthalpy changes of TPAE‐6 during the isothermal process are a linear superposition of enthalpy changes associated with microphase separation and crystallization of PA6 in hard phases, resembling that of TPAE‐6 without soft segments (TPAE‐6‐0). The study reveals that, as the concentration of soft segments in TPAE‐6 increases, the accelerated dynamics of phase separation become stronger than the dilution of soft segments to PA6 segments during isothermal process, resulting in an increase in the microphase separation rate of TPAE‐6. Furthermore, despite microphase separation, the overall crystallization rate of TPAE‐6 decreases with rising isothermal temperature and varies with increasing soft segment content at different temperatures. Additionally, the crystallization mode of TPAE‐6 follows two‐dimensional, three‐dimensional, or a combination of both crystal growth mechanisms, accompanied by a heterogeneous nucleation mechanism.

Distinct Crystallization Pathways of Polyoxymethylene in Methanol System

Recrystallization of polyoxymethylene (POM) in solvent is an effective post-treatment method for manufacturing a better POM product. Herein, the crystallization process of POM in methanol was investigated with the use of a series of equipment. The results reveal that POM crystallization in methanol yields two kinds of particle morphologies, including small particles with lamellar structures branching and growing in all directions and large particles resulting from melt agglomeration. The mechanism of POM crystallization in methanol with two distinct pathways was proposed, in which solution cooling crystallization of POM at higher temperature yields small particles while melt crystallization yields large particles. Furthermore, both non-isothermal and isothermal crystallization kinetics of POM were determined. The Avrami equation was employed to derive the crystallization rate constant via data fitting. The activation energy of crystallization was then obtained using the Arrhenius formula. The kinetics suggest that recrystallization of POM in methanol may dissolve and remove substances hindering raw material crystallization, achieving a faster crystallization rate for products.

Fragility and Tendency to Crystallization for Structurally Related Compounds.

The present study was designed to investigate the physical stability of three organic materials with similar chemical structures. The examined compounds revealed completely different crystallization tendencies in their supercooled liquid states and were classified into three distinct classes based on their tendency to crystallize. (S)-4-Benzyl-2-oxazolidinone easily crystallizes during cooling from the melt; (S)-4-Benzylthiazolidine-2-thione does not crystallize during cooling from the melt, but crystallizes easily during subsequent reheating above Tg; and (S)-4-Benzyloxazolidine-2-thione does not crystallize either during cooling from the melt or during reheating. Such different tendencies to crystallize are observed despite the very similar chemical structures of the compounds, which only differ in oxide or sulfur atoms in one of their rings. We also studied the isothermal crystallization kinetics of the materials that were shown to transform into a crystalline state. Molecular dynamics and thermal properties were thoroughly investigated using broadband dielectric spectroscopy, as well as conventional and temperature-modulated differential scanning calorimetry in the wide temperature range. It was found that all three glass formers have the same dynamic fragility (m = 93), calculated directly from dielectric structural relaxation times. This result verifies that dynamic fragility is not related to the tendency to crystallize. In addition, thermodynamic fragility predictions were also made using calorimetric data. It was found that the thermodynamic fragility evaluated based on the width of the glass transition, observed in the temperature dependence of heat capacity, correlates best with the tendency to crystallize.

Isothermal and nonisothermal crystallization kinetics of modified hydroxyapatite-enhanced poly(3-hydroxybutyrate-co-4-hydroxybutyrate)

Poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB) is a biodegradable material, and efforts have been devoted to enhancing its mechanical properties and biocompatibility for biomedical applications. However, there is a lack of research confirming the influence of nucleating agents on its crystallization behavior. In this study, the isothermal crystallization process was described using the Avrami model. The non-isothermal crystallization process was investigated using the Avrami-Jeziorny and Mo models. The effects of different calcium hydroxyapatite (CA-HA) contents on the nucleation activity, crystallization activation energy, and equilibrium melting point of P34HB/CA-HA composites were compared. The impact of CA-HA on the crystallization rate, nucleation rate, and crystal growth rate of the polymer matrix was discussed. The results indicate that with an increase in CA-HA content, the crystallization rate initially decreases and then increases. The minimum crystallization rate is observed at a CA-HA content of 9 wt%. Moreover, as the CA-HA content increases, nucleation activity is enhanced, suggesting that CA-HA acts as a nucleating agent, facilitating the nucleation process. When the CA-HA content exceeds 9 wt%, the increase in crystallization rate may be attributed to the further enlargement of molecular clusters formed by CA-HA, leading to a reduced dispersion of CA-HA in the polymer matrix. Furthermore, when the CA-HA content surpasses 9%, a significant decrease in crystallization activation energy is observed, indicating a reduction in the mobility of polymer chain segments.

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.

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.

Study on the Crystallization Behavior of Neodymium Rare-Earth Butadiene Rubber Blends and Its Effect on Dynamic Mechanical Properties.

Utilizing neodymium-based butadiene rubber as a baseline, this study examines the effect of eco-friendly aromatic TDAE oil, fillers, and crosslinking reactions on neodymium-based rare-earth butadiene rubber (Nd-BR) crystallization behavior. The findings suggest that TDAE oil hinders crystallization, resulting in decreased crystallization temperatures and heightened activation energies (Ea). The crystallization activation energies for 20 parts per hundreds of rubber (PHR) and 37.5 PHR oil stand at -116.8 kJ/mol and -48.1 kJ/mol, respectively, surpassing the -264.3 kJ/mol of the unadulterated rubber. Fillers act as nucleating agents, hastening crystallization, which in turn elevates crystallization temperatures and diminishes Ea. In samples containing 20 PHR and 37.5 PHR oil, the incorporation of carbon black and silica brought the Ea down to -224.9 kJ/mol and -239.1 kJ/mol, respectively. Crosslinking considerably restricts molecular motion and crystallization potential. In the examined conditions, butadiene rubber containing 37.5 PHR oil displayed no crystallization following crosslinking, albeit crystallization was discernible with filler inclusion. Simultaneously, the crystallinity level sharply declined, manifesting cold crystallization behavior. The crosslinking process elevates Ea, while the equilibrium melting point (Tm0) noticeably diminishes. For instance, the Tm0 of pure Nd-BR is approximately -0.135 °C. When blended with carbon black and silica, the Tm0 values are -3.13 °C and -5.23 °C, respectively. After vulcanization, these values decrease to -21.6 °C and -10.16 °C. Evaluating the isothermal crystallization kinetics of diverse materials via the Avrami equation revealed that both the oil and crosslinking process can bring about a decrease in n values, with the Avrami index n for various samples oscillating between 1.5 and 2.5. Assessing the dynamic mechanical attributes of different specimens reveals that Nd-BR crystallization notably curtails its glass transition, marked by a modulus shift in the transition domain and a decrement in loss factor. The modulus in the rubbery state also witnesses a substantial augmentation.

Effect of Dilution on the Crystallization Kinetics of Neodymium-Based Rare Earth Polybutadiene Rubber.

The crystallization behavior of neodymium-based rare earth polybutadiene rubber (Nd-BR) is studied in the presence of small-molecule treated distillate aromatic extract (TDAE) and high-molecular-weight polybutadiene-isoprene copolymer rubber (BIR). Pronounced inhibitory effects on the crystallization of Nd-BR are exhibited by both materials, as evidenced by reductions in the crystallization temperature (Tc), melting point (Tm), and corresponding enthalpy change. It is found that, at equal concentrations, a greater influence on the crystallization rate is exerted by TDAE oils, whereas nucleation inhibition is more potently affected by BIR. Incomplete crystallization during cooling is exhibited by Nd-BR when the TDAE oil concentration reaches 40 parts per hundreds of rubber (PHR) (31 wt.%), or BIR achieves a 60 wt.% concentration; subsequently, a noticeable cold crystallization phenomenon is observed upon heating. Insights into the isothermal crystallization kinetics are offered by the data, which reveal that the Avrami index n value for Nd-BR predominantly ranges between 2.5 and 3.0. A decrease in the n value is induced by a small amount of TDAE oil, while a noticeable decline in the n value is observed only when the BIR concentration is 60 wt.%. A correlation between the crystallization activation energy, the concentration of TDAE oil and BIR, and the crystallization temperature is established; a negative activation energy is recorded, and a decrease in the crystallization rate is noted when both concentrations are low and the crystallization temperature exceeds -50 °C. In contrast, positive activation energy and an increase in the crystallization rate are observed when the BIR concentration reaches 60%, and the crystallization temperature resides between -50 °C and -70 °C.

Isothermal crystallization kinetics of pure and surface‐modified silica/high‐density polyethylene nanocomposites

AbstractThe isothermal crystallization kinetics of high‐density polyethylene (HDPE) nanocomposites containing 0, 0.5, 0.75, and 2 wt% of pure and surface‐modified silica were evaluated at three crystallization temperatures (Tc) of 120°C, 121°C, and 122°C using differential scanning calorimetry (DSC) and applying Avrami, Tobin, and Malkin equations. According to Hoffman‐Weeks theory, the values of the equilibrium melting point () of the nanocomposites decreased with increasing nanoparticle content and were higher in the samples containing AMS nanoparticles, owing to the larger crystal. The results of all three models offered the same trend according to which the change in the crystallization temperature influenced the nucleation mechanism and the crystallization rate. It was found that a greater number of spherulites can be formed via increasing Tc from 120°C to 122°C which also decreased the crystallization rate of the nanocomposites. At the crystallization temperature of 122°C, the lowest melting temperature was recorded for the samples, attributed to the formation of more crystals with a lower thickness. Moreover, in HDPE/AMS nanocomposites, the crystallization rate was higher than that of HDPE/PSN, ascribed to the positive effect of surface modification on nanoparticles.Highlights Increased polymer/particle compatibility and isothermal crystallization. Evaluating the nucleation and crystallization using different models. The impact of isothermal crystallization temperature on crystallinity. Variation of equilibrium melting point with the nanoparticle content.

Influence of low contents of cellulose nanocrystals on the crystallization behavior of biobased Poly(propylene 2,5-furandicarboxylate)

To address the slow crystallization problem of poly(propylene 2,5-furandicarboxylate) (PPF), fully biobased PPF/cellulose nanocrystals (CNC) composites were prepared via a solution and casting method in this work at low CNC contents. The influence of CNC on the crystallization of PPF was studied in detail under various conditions, including nonisothermal and isothermal melt crystallization as well as nonisothermal and isothermal cold crystallization. The results revealed that the crystallization of PPF was enhanced under various crystallization conditions by CNC due to the heterogeneous nucleating agent role. From the isothermal crystallization kinetics study, the presence of CNC did not alter the crystallization mechanism of PPF. In addition, the thermogravimetric analysis results showed that both PPF and PPF/CNC composites displayed an excellent thermal stability. On the basis of the wide angle X-ray diffraction study, CNC did not change the crystal structure of PPF.

Tailoring the Nucleation and Crystallization Rate of Polyhydroxybutyrate by Copolymerization.

In the polyester family, the biopolymer with the greatest industrial potential could be poly(3-hydroxybutyrate) (PHB), which can be produced nowadays biologically or chemically. The scarce commercial use of PHB derives from its poor mechanical properties, which can be improved by incorporating a flexible aliphatic polyester with good mechanical performance, such as poly(ε-caprolactone) (PCL), while retaining its biodegradability. This work studies the structural, thermal, and morphological properties of block and random copolymers of PHB and PCL. The presence of a comonomer influences the thermal parameters following nonisothermal crystallization and the kinetics of isothermal crystallization. Specifically, the copolymers exhibit lower melting and crystallization temperatures and present lower overall crystallization kinetics than neat homopolymers. The nucleation rates of the PHB components are greatly enhanced in the copolymers, reducing spherulitic sizes and promoting transparency with respect to neat PHB. However, their spherulitic growth rates are depressed so much that superstructural growth becomes the dominating factor that reduces the overall crystallization kinetics of the PHB component in the copolymers. The block and random copolymers analyzed here also display important differences in the structure, morphology, and crystallization that were examined in detail. Our results show that copolymerization can tailor the thermal properties, morphology (spherulitic size), and crystallization kinetics of PHB, potentially improving the processing, optical, and mechanical properties of PHB.

Isothermal crystallization behavior of poly-ether-ether-ketone/bioactive glass composites and its correlation with scaffold warpage in laser powder bed fusion process

The preparation of poly-ether-ether-ketone/bioactive glass (PEEK/BG) composite scaffolds using laser powder bed fusion (LPBF) has enormous clinical potential. However, ensuring the desired accuracy and reproducibility of composite scaffolds during the LPBF process remains a significant challenge. Therefore, a thorough understanding of the relationship between the crystallization behaviors and the scaffold warpage during the LPBF process is crucial. To address this challenge, this study systematically investigates the isothermal crystallization kinetics of PEEK/BG composites and their relationship with scaffold warpage. The results reveal that the crystallization rates of pure PEEK and PEEK/BG composites decrease as isothermal crystallization temperature increases. Additionally, BG significantly suppresses the isothermal crystallization kinetics of PEEK, resulting in a 250% increase in the half-crystallization time (t1/2) of PEEK/25 wt% BG at 316 °C relative to pure PEEK. Extrapolating the t1/2 using the Hoffman-Lauritzen model can obtain the optimal powder bed temperature (Tb) for each powder in LPBF. Pure PEEK and PEEK/25 wt% BG Diamond scaffolds are printed at the respective inferred Tb (330 °C and 323 °C) and their warpage degrees are compared to that of the pure PEEK scaffold printed at 323 °C. The results demonstrate that raising Tb from 323 °C to 330 °C and adding 25 wt% BG are both effective methods to reduce the scaffold warpage by slowing down the crystallization kinetics of PEEK, resulting in reductions of 57.8% and 50.6% in warpage degree respectively. Furthermore, the incorporation of BG successfully tackles the challenge of simultaneously preventing warpage and secondary sintering in pure PEEK printing. Overall, this study offers a deep comprehension regarding the relationship between crystallization kinetics and scaffold warpage, which is crucial for achieving the reproducibility with desired accuracy of LPBF-printed biological scaffolds for clinical applications.

Atomic structure, thermal stability and isothermal crystallization kinetics of novel Co-based metallic glasses with excellent soft magnetic properties

In this work, Co66-xFexHf6.5B27.5 (x = 0, 10, 15, 20) metallic glasses (MGs) have been prepared by melt-spinning, and a comprehensive qualitative study including the atomic structure, thermal behavior, crystallization kinetics, and magnetic properties of the MGs is presented. The addition of Fe notably improves the thermal stability of the prepared glasses by increasing the width of the supercooled liquid region (SLR) from 26 K to 55 K. Analysis of the structure factor and the reduced-pair distribution function (PDF) reveal subtle variations in short-range ordering (SRO) and an increase of the atomic packing density of the glassy phase by 20 at% Fe addition. Notable rises in saturation polarization, Js, (from 0.21 T to 0.67 T), Curie point, Tc, (from 315 K to 530 K) and coercivity, Hc, (from 0.5 A/m to 2.5 A/m) are found after Fe alloying. The isothermal crystallization kinetics determined by the Johnson-Mehl-Avrami-Kolmogorov (JMAK) approach demonstrate that the novel Co46Fe20Hf6.5B27.5 MG exhibits a remarkably higher activation energy and a significantly longer incubation time (about 16 min) before crystallization compared to existing Fe-free (x = 0) as well as most other Fe/Co-based MGs. Slight increases in Js (up to 5%) and Tc (about 4.7%), and a remarkable drop in Hc (up to 80%) are achieved for the Co46Fe20Hf6.5B27.5 MG upon isothermal annealing for a period of 3600 s. The attractive features such as high thermal stability, low coercivity of 0.5 A/m, and higher Js (up 0.7 T) compared to many Co-based glasses, make Co46Fe20Hf6.5B27.5 MG a promising soft magnetic material for future applications in power electronics, electric machines, and fabrication of large-size glassy samples by hot consolidation of MG particles.

Modeling of the kinetics of polymorphic isothermal crystallization of poly(l-lactide) subjected to uniaxial molecular orientation

Kinetic model of polymorphic crystallization of uniaxially oriented amorphous poly(l-lactide) under isothermal conditions is formulated basing on the Hoffman-Lauritzen theory. Entire ranges of the crystallization temperatures and amorphous orientation factor are considered. The inverse transformation half-times of the amorphous phase to the individual polymorphs, between the unstable α’ and stable α polymorphs, as well as of the overall crystallization are discussed. The kinetic effects are assigned to the decrease in the amorphous phase entropy caused by deformation and orientation of the flexible chain macromolecules.The model predicts that crystallization to the stable α form is controlled by the rate of transformation of the amorphous phase to α’. Concentration of heterogeneous nuclei typical for commercial polymer is assumed and in this case the role of homogeneous nucleation in the transformation kinetics is negligible. The role of homogeneous nucleation at different hypothetical concentrations of heterogeneous nuclei is estimated vs. the Hermans amorphous orientation factor and crystallization temperature. Ranges of domination of heterogeneous and homogeneous nucleation are predicted as dependent on the heterogeneous nuclei concentration.The increase of the overall oriented crystallization rate is predicted for the entire crystallization temperature range as resulting from the increase of the amorphous-to-α′ transformation rate at increasing amorphous orientation. The model provides a view on the mechanisms for possible control of the development of α’/α composition by adjusting the crystallization time vs. orientation and temperature.

Volumetric Dilatometer Study of Thermoreversible Aging Properties in Crumb Rubber–Modified Asphalt Binders

Abstract The primary objective of this paper is to investigate the thermoreversible aging mechanism of crumb rubber–modified asphalt binders (CRMAs). In order to achieve this goal, an extended bending beam rheometer (Ex-BBR) test and volumetric dilatometer test were conducted. Additionally, isothermal crystallization kinetics (Avrami theory) and thermal stress calculation using the Hopkins and Hamming algorithm were employed to process the test data. The low-temperature properties of the asphalt specimens were characterized through calculations of creep stiffness (S), creep rate (m-value), grade loss (GL), thermal stress, and Avrami index (n). The experimental results indicate that thermoreversible aging is present in all asphalt samples during the long-term isothermal hardening process. This aging is characterized by continuous macroscopic volume shrinkage, accumulation of thermal stress, a crystallization process, and a process akin to crystallization (i.e., crumb rubber adsorbed oil at low temperatures). It was observed that CRMAs exhibit more severe thermoreversible aging and faster physical hardening rates due to their unique properties at a constant low temperature when compared with base asphalts. However, it was also observed that CRMAs can reduce the thermal stress by reducing the volumetric shrinkage coefficients and S. It is important to note that the volumetric shrinkage coefficients are not constant, which are related to the base asphalts, crumb rubber, and conditioning time. Therefore, it is not appropriate to use a single empirical constant to calculate thermal stress. Instead, multiple coefficients may need to be incorporated to account for the variability in shrinkage behavior.

Tailoring the crystallization and melting behavior of 3D protein-polymer biocomposite materials: A study of pressure-induced silk fibroin/poly(L-lactic acid) foams

Crystallization and melting behavior of 3-D composite materials is critical in the field of biopolymer materials, because the crystal structure and crystallization kinetics of the materials will affect the performance of the biocomposite materials and their fabrication process. In this study, thermal analysis combined with structural analysis such as X-ray diffraction (XRD) were used to study the melting behavior of silk fibroin/polylactic acid (SF/PLA) composite foam materials prepared under a pressure of 0–6 MPa, and the mechanism of their isothermal crystallization kinetics was discussed. The results showed that both α and α'-type crystals exist in the composite material, and their contents can be tuned by isothermal crystallization temperature. When the isothermal crystallization temperature is around 105 °C, the crystallization time is the shortest and the crystallization rate is the fastest. Besides, silk fibroin can shorten the crystallization half-life of the composite foam and improve the crystallinity of the material. However, the high isothermal temperature will facilitate the interaction between SF and PLA segments to slow down the diffusion, folding and crystallization of the PLA segments. Using Avrami analysis, it is found that the crystal growth in 3-D composites follows a non-three-dimensional truncated spherical direction. This study provides a deeper understanding of the crystallization behavior of protein-synthetic polymer biocomposite materials and offers experimental and theoretical guideline for the regulation and utilization of their structure and properties for the design of new biocomposite materials.

Separate primary crystallization of three crystalline phases in a nearly eutectic Cu58Y37Sc5 metallic glass on heating and deformation

Crystallization behavior of a Cu58Y37Sc5 metallic glassy alloy was studied on heating and on room-temperature deformation by different methods. At first, phase transformations were studied by differential scanning and isothermal calorimetries. X-ray diffractometry studies indicated simultaneous formation of the Cu2Y, CuY and CuSc crystalline phases which is the characteristic of a eutectic crystallization while the isothermal crystallization kinetics rather corresponded to primary crystallization. Moreover, transmission electron microscopy observations revealed a remarkable complexity of this crystallization process including heterogeneous nucleation on pre-existing particles.

Thermodynamically-equilibrium LCST phase diagram of PCL/SAN mixtures determined by thermal analysis: Opposing effects of hydrophilic and hydrophobic silica nanoparticles

In this work, the isothermal crystallization kinetics of PCL in PCL/SAN blend and PCL/SAN/nanosilica nanocomposite systems has been applied as a useful and sensitive variable for determining the LCST phase diagram. By eliminating the impacts of kinetic variables, the variations in the equilibrium LCST phase boundary of PCL/SAN mixtures were evaluated. The presence of hydrophobic nanoparticles shifted the equilibrium LCST phase diagram to higher temperatures as expected owing to the compatibilization effect of nanoparticles, while the hydrophilic nanoparticles shifted it to lower temperature. The preferential migration of hydrophilic nanosilica into SAN-rich phase with slower molecular dynamics caused larger viscoelastic asymmetry of polymeric phases and consequently, lower area of phase miscibility window. In contrast, the addition of hydrophobic nanosilica with better dispersion state and no preferential localization in PCL/SAN blend resulted in a shift of LCST phase diagram to higher temperatures.

Isothermal and non-isothermal crystallization kinetics of UHMWPE composites incorporating with GNP/MWCNT

Isothermal and non-isothermal crystallization kinetics of UHMWPE composites incorporating with GNP/MWCNT